THE CONODONTA G-
lesources,and
Morphology,Taxonomy,Paleoecology,
andEvolutionaryHistory of a Long-Extinct AnimalPhylum
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WALTERC.SWEEL TheOhioStateUniversity
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New York . Oxford
CLARENDON PRESS. OXFORD . 1988
PREFACE
Conodontsare common fossils.Almost anyone who dealson a regularbasiswith Paleozoicand Triassic marine rocks has probably seena few of them. Through the last 30 yedrs conodonts have come to be of exceptionalvalue in biostratigraphy, and they now have pride of place as index fossils in many parts of the geologic column. But conodonts are extinct and are unknowo to most neontologists.The sketchiness ofinformation about them in most texts on invertebrate paleontologymay result either fiom the fact that they are microfossils that haye only lately come to be important as stratigraphic tools, or from the fact that nothing quite like them exists today, so their zoologic relations axeuncertain. In this monograph, I provide a summary of information about a group with which I have worked all my adult life. Charts that name conodont-based biozones and show stratigraphic rangeofselected conodont speciesare included as Appendix B. However, I have purposely avoided a recap of conodont biostratigtaphy becauseit is constantly changing and cunent views are readily available in various other places.Instead, I focus here on the conodonts as a group of extinct animals, about which it is important to know as much as possible before assessing their distribution biostratigraphically. Of course, one takes considerablerisk in attempting such a summary, particularly of a group of animals known only from its fossil record, becausemost of what I think I know about conodontsasanimals is either conjecture or a highly personalinterpretation ofa still-irnperfect fossil record. So, with the caveal that whal followsis only one way of viewingan im-
portant group, I ofer my account of the Conodonta. For their "witting" or unwitting contributions to what I believe I know about the fascinating gtoup of extinct animals described on the following pages,I am gateful to a long list of my students and faculty colleaguesat The Ohio StateUniversity, especiallyStig M. Bergstrijm, and to members of the Pander Society, an intemational group of exceptionally goodnatured "conodontologists"that has met frequently and infomally thougl the last 20 years to share infomation about conodonts, argue conclusions,and correct the misapprehensionsof its seniormembers. Karen Tyler, faculty illustrator at The Ohio State University, drafted nea y all the figures from my very crude copy and assistedwith labeling others. Dr. Jerzy Dzik, of the Polish Acaderny of Sciences, Warszawa, provided about half the stippled drawings of conodonts that gace various figuresin Chapter 5- The anistry of tlrese two good friends is plainly evident in their work and is warmlY acknowledged. I am also grateful to Sue Shipley and David Little, of The Ohio State University, for their help in completing various parts of the manuscript and illustrations, and to Mark Klefner, who graciously cornpiled information on the ranges of Silurian conodonts and assembled the Silurian chart in Appendix B. The Department of Geology and Mineralology generously assumedmuch of the expenseof drafting and photogaphy. Columbus, Ohio February 1988
w.c.s.
CONTENTS l . Inhoduction
l.l History ofdiscovery and study 1.2 Achievements 1.3 Pending problems
2. Skeletal anatomy 2.1 2.2 2.3
2.4 2.5 2.6
J.
Composition of conodont elements Structure of skeletalelements Shapesof element crowns 2.3.1 Coniform crowns 2.3.2 Ramiform crowns 2.3.3 Rastratecrowns 2.3.4 Pectiniformcrowns Symmetry- and curvature-transitionseries Skeletalapparatuses Symmetry of elements,element pairs, and apparatuses
Whole-animal anatomy 3.1 3.2 3.3 3.4
The Scottish Carboniferousspecimens The Waukeshaspecimen Histology of demineralizedtissues Summary
4. Taxonomy 4.1 4.2
Form taxonomy Multielementtaxonomy 4.2.1 Multielementmethodology 4-3 Multielement classifications 4.4 A revised multielement classification 5. The major conodontgroups 5.1 5.2 5.3 5.4 5.5
Introduction Cavidonti and Conodonti The Proconodontida (Cavidonti) and its families (Fig. 5.1) The Belodellida and its families (Fig. 5.1) OrderProtopanderodontida, new 5.5.1 Family ProtopanderodontidaeLindstrtim, 1970 5.5.2 Family Clavohamulidae Lindstrdm, 1970 5.5.3 Family AcanthodontidaeLindstritm, 1970 5.5.4 Family DrepanoistodontidaeFihraeus and Nowlan, 1978
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6.3.3 Siluriancycles 6.3.4 Devonian and Carboniferouscycles 6.3.5 Permian and Triassic cycles 6.4 Extinction 6.5 Iterativeevolutionarypatterns 6.6 Evolutionary trends 6.6.1 Apparatuselaboration 6.6.2 Apparatusreduction 6.6.3 Elaboration of elementsin P positions 6.7 Developmentalslralegies 6.7.1 Recapitulation 6.7.2 Paedomorphosrs 6.8 Summary
7. Paleoecologyand paleobiogeography 7.1 Introduction 7.2 Mode of life, or habit, of conodonts 7.3 Ecologicmodels 1.3.1 Thedepth-stratificationmodel 1.3.2 The lateral-segegationmodel 7.4 Selectedstudiesof conodont ecology 7.4.1 Ordovician paleoecologyof Cincinnati Region 7.4.2 Mississippian paleoecology,westernUnited States 7.4.3 Paleoecologyof Pennsylvanianconodonts 7.5 Ecologicgeneralizations 7.5.1 Depth as a factor 7.5.2 Ternperutureas a factor 7.5.3 Nearshoreand ofshore faunas 7.5.4 Phyletic changesin ecologicaldistribution 7.6 Paleobiogeography 7.6.1 Late Cambrian and Ordovician paleobiogeography 7.6.2 l-ater Paleozoicand Triassic paleobiogeography
8, The phylum Conodonta 8.1 A personalbias 8.2 Summary of conodont characters 8.3 Conodonts as invertebrates 8.3.1 Arthropod and annelid connections 8.3.2 Molluscanconnections 8.3.3 Connectionswith other invertebrates 8.4 Conodonts as chordates 8.4.1 The opinions of Pander 8.4.2 Newberry, Hinde, Huxley and Myxine 8.4.3 Macfarlane and the nemertineanconnection
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1. INTRODUCTION
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With just a bit of preparation,almost any ma- opment. The literature on conodontsis now rine rock of Paleozoicor Triassicage,from al- rather large(and growingat the rate of about most anywhereon earth, will yield to the pa- 300new paperseachyear),soit will not be postient investigatoran assortmentof phosphatic sibleto exploreeveryaspectofconodontpaleomicrofossils termed conodonts. Although biology in great depth. But this book is not named and first describedin 1856,thesetiny intended as a comprehensivereview for spefossilswere paleontologiccuriositiesuntil just ciatists.It is an attempt to summarizecurrent a few yearsago.Little wasknown of their geo- knowledgeof conodontsfor the nonspecialist, graphic or stratigraphicdistribution, and they who may well have been wonderingwhy this were classifiedaccordingto a mechanicalsys- group of tiny fossilshas come to be so importem based entirely on shape. Furthermore, tant rn recent years. their relations to other, better-knownanimal groupswerehotly debated. 1.1 Historyof Discov€ryandStudy Nowadays, conodonts are mentioned in most reportson Paleozoicand Triassicbiostra- Sometimebetween1833and 1844,the Russian tigaphy, and their contribution is widely ac- paleontologistChristian Heinrich Panderdisknowtedged.Furthermore, enough has been covered tiny, lustrous, toothlike fossils in and washedresiduesof Lower Ordovician and Silearnedabouttheir anatomy,associations, patterns of developmentto make them the lurian clastic rocks from Estonia,and on the honestsubjectsofa wide variety oftruly paleo- surfaceof at least one slab of Carboniferous biologicstudies;Thirty yearsagoonly a hand- rock collectedwithin the presentcity limits of ful of paleontologistsclaimed more than a Moscow. However, these microscopicfossils passingacquaintancewith conodonts.Today, werenot illustratedor discussedin print until more than 200 personsdevotea major part of 1856,whenthey weredescribedas the remains their waking hours to the study of thesetiny of an otherwiseunknown group of Paleozoic fossils,and only a few of the world's major oil fishesthat Pander named Conodonten(concompaniesor geologicsurveysare without at odontsin English). In the yearsbetween1833and 1856,Pander least one conodontspecialist.The reasonsfor this paleontologicsuccessstory are numerous, evidently gave a lot of thought to the tiny fosbut they have to do primarily with the fact that sils he named conodonts.During part of that the conodontshave proved to be as successful time, he hadgeat troublewith his eyesandwas at solvingbiostratigraphicproblemsin the Pa- not ableto usehis microscope.However,what leozoic and Triassic as the foraminifers have he sawwhenhe wasableto studyhis specimens been in the interval from the Jurassicto the microscopicallyconvinced him that he was present. looking at the teeth and jaws of a previously In this monographI will introducethe con- unknowngroupoffishes,a groupwith no rnododonts;show how at least someof them may em analogue.Thus, in descriptionsof specibe reconstructedfrom the jumbled bags of mensin his collectionhe usedterminologyapbones by which they are commonly repre- propriate to the teeth and jaws of fishes, and sentedin the fossil record;and look at major some of that terminology survives today. Pander's1856monographnot only provided features of their long geologichistory, with an somelhingusefulabout their the first descriptions of the hard parts of a preeye to suggesting relationsto other animalsand about their pat- viously unknowngroupof animalsand a name tems of deploymentand evolutionary devel- for the group itself, but it also began debates
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INTRODUCTION J sr eral different rL< out to have rSme today agrees h :ased his conqrs.nrs bits and tra Jilferent spe! r!g:L bur for the h:.-iogists E. O. trnaal manv new presented a h.= r- .::d suggested bn-.:g:r be of cond[i< rtre srratigrrs s.rch as the he-.:rcga Shale. i rhat conl' --:.-i of priml::s ,d[ :l lhe same ,-- =E: rhe prevat :i :lese teeth I cr :ires in the bv the --::d rmly on b-E:mt:--r of zoolk ltaving Ul--a :-rib$antial f Bassler wrote ta= ir is clear :afer |!c -\meriql --:e srud] of lE:Jnrial were at l*itr:ologrsts g- 6on.on b= ll:,;. -: Studies, lllcl-:\hed b-y the i : : ll a n d 1 9 34, tirr s:.d;- of conr making hit: rcpresen-+: qosn than G l* a rc:e -oduced and deal group of r:r:: J C:.,:itnt Stud: lftir: --. . nearly G classed k- -re *e con-i
In 1941, Samuel Ellison, a student of the cur in that classification."They regardedthe evidencefor this statement,and for their fur- Missouri school,and Roy Graves,one of his ther conyiction that conodontsare polyphy- students at the Missouri School of Mines, letic, as conclusive,but they put off describing jointly reportedon a group of Pennsylvanian that evidenceuntil a later time. Unfortunately, conodont elementsthey had collected from that time never came. However, they did al- samplesof the Dimple Limestone in Texas, lude to the fact that their evid€nceof the fish which they had dissolvedin dilute aceticacid. natureofconodontsis the fact that somespec- Ellisonand Gravesdo not describethe "acetic imens are attachedto a substance". . . that ap- acid method" they used, which suggeststhat pearsbony but doesnot have the structureof they did not regardit as novel. However,they were evidently the frrst to usea laboratory proordinarybone." Bransonand Mehl also joined Pander,Ul- cedurethat, a decadelater,had becomeroutine rich and Bassler,and all previous studentsof in researchinstitutionsaround the world. The conodontsexceptHinde in usingthe shapeof significance ofthis is that prior to 1941,and for individual "teeth" as the guide to their classi about a decadeafter, most collectionsof conthey odont elements had been assembledfrom fication. That is, like their predecessors, rocks, adoptedform taxonomy. However, like Ulrich shalesand other readily disaggregated and Bassler,they thought it likety that speci and carbonaterocks were generallyignored. mens of different shapefunctioned in diferent However,as Ellison and Gravesdemonstrated ways-some as teeth and jaws, othersas body in 1941,asBransonand Mehl reportedin 1944, scales,and additional ones as denticles on and as nearly everyoneknows today, much larger collectionsof well-preservedspecimens sprnes. Between1933and 1950,the Missouri school can be isolatedreadilyfrom carbonatesby disflourishedunder the leadershipofBransonand solvingthem slowly in l0 to 15 percentacetic Mehl, and the predictionof Ulrich and Bassler or formic acid.This, in turn, meansthat, unlike that conodontsmight one day be of greatuse many other types of microfossils,conodonts stratigraphicallyencouragedother American may be collectedeasilyand relativelyinexpenstudentsto collect and describethese previ sively from both carbonateand siliciclastic the rocks. Thus their distribution in stratigaphic ously enigmaticfossils.As a consequence, literatureon conodonts-a mere200articlesin sectionsof mixed lithologic type may be deterthe late 1920s-more than tripled between mined wilh considerableprecision. 1930and 1950.It is not easyto singleout any The increasedsize of collectionsmade posof theseconributions as more important than sible by more widespreaduseof organicacids the others,but it is not diftcult to identify those encouragedmicropaleontologists interestedin that introducedsignificantnew trends. conodonts to broaden their studies through In 1934,for example,Hermann Schmidtin considerationof sectionsin which there were Germany and Harold Scott in the United no shales or mechanicallyreducible clastic Statesindependentlyreportedthe discoveryof rocks. By 1959,conodontshad beencollected clustersof morphologicaltydifferentconodont in some variety from rocks that rangein age elements on the surfacesof Carboniferous from Late Cambrian to late Triassic, and there black shale stabs. Like Hinde before them, was one report of distinctive elementsfrom Schmidt and Scott regarded these natural as- Upper Cretaceousrocks in west Africa. Fursemblagesas the more or lesscompleteappa- thermore,conodontswereknown from marine ratusesof individualconodonts-an opinion rocksin this time interval from six ofthe seyen that wasroundly criticizedby Bransonand ev- continents. The stratigraphicrange of conidently acceptedwith great reservationsby odonts had been considerably broadened other studentsof conodonts.In more recent through improvements in laboratory techyearsnatural assemblages have playedan im- niques,and geographicdistribution had been portant role in the developmentof conodont extendedand collectionsgreatly increasedin taxonomy. size.No longerwereinyestigatorssatisfiedwith
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searchingthat multielement taxonomy was lison have continued with the published biblimore desirablethan form taxonomyfor cono- ographies of the conodont literature that are donts and was also attainableeven in the ab- listed among the referencesat the end of this senceof natural assemblages to supportevery chapter. In more recent years, the bibliography diagnosedspecies.A complete multielement of conodont literature has been updated antaxonomy is still not in place, however,and nually in a supplement to The Pander Society's thereare a number of workerswho still prefer newsletter. At the end of 1987,my file included its much simpler predecessor. However,a re- the titles of more than 7000 books, articles, and vised versionof Volume W of the now-vener- papers on conodonts. able Treatise on Inwrtebrate Paleontology (Clark et al., l98l) issuedin 1981(but written 1.2 Achievements largelybefore1976)is couchedmostlyin terms of multielementtaxonomy,and a majority of The study olconodonts is very different in the current reportson conodontsat leastgive lip 1980sfrom what it was in 1950,when I began. service to this more sophisticatedmode of For example, in the last 30 years interest in classification. conodonts has again become international, For In 1967studentsof conodontsattendingan much of the time between 1926 and 1950, internationalsymposiumon the DevonianSys- study of conodonts was largely an American tem in Calgary,Alberta, were impressedwith endeavor; now there is active and increasingly the fact that data provided by conodontscon- well-informed interest in nearly every part of tributed to a very largenumber of the reports the globe. At a meeting of The Pander Society presentedand with the difficulty they experi- in 1985, the approximately 150 participants encedin keepingabreastofthe burgeoninglit- represented 31 different countries in Africa, eratureand researchinterestsof a rapidly in- Asia, Australia, Europe, and North and South creasinggroup of conodontstudents.To solve America. Study has become international theseproblems,the groupfoundedan informal again, and there is also close coordination and organization,ThePanderSociery,opento any- an unusual degree of cooperation among stuoneinterestedin conodontsand with the single dents of conodonts. These achievements, perpurposeofsharinginformationon currentcon- haps more than any others, have enabled the odont research.Subsequently, The PanderSo- rapid growth ofknowledge about conodonts in grown in membershipto more than recent decades. ciety has 250; has becomethe official working group on As noted earlier, assessmentof large, straticonodontsof the International Palaeontologi- graphically comprehensive collections on an cal Association:and has distributedan annual intemational scale has also caused a shift in newsletterthat includesreportson the research taxonomic base from the morphology of single activities of members,addressesof conodont skeletal elemenls to the composition and relaworkersand, in recentyears,current bibliog- tionships within recurrent groups of skeletal raphiesofthe conodontliterature.The Pander elements. This has resulted in a taxonomy for Societymeetsannually in North America and conodonts that, while admittedly more comat 3- to s-year intervals at various sites in plex than its predecessor,is probably closer to Europe. biologic "truth" than the form taxonomy of postof the In sortingout significantevents Pander, Ulrich and Bassler, and Branson and 1950era in the history of conodontresearch,I Mehl. Such a taxonomy is obviously a collecshould mention that students of conodonts tive effort and, like any other, will always be have been blessedmore or lessregularlywith ripe for modification and the subject for debibliographers,who have kept track of the lit- bate. Nevertheless, students ofconodonts now eratureabout conodontsand haveperiodically have the framework within which to make assembledand published lists of it. Grace biologically meaningful statements about conHolmesbeganthis servicein 1928;RobertFay odont paleoecology,biogeography, and evolucontinuedit through 1948,with a usefulcatalog lion. and that musl be regardedas an imporpublishedin 1952;and Sidneyesh and SamEl- tant achievement.
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may not apply to all conodonts,and the elongate, prominently "tailed" hagfish (or slime eel),which many hold to be the nearestliving relative of conodonts,is a largely sedentary creaturethat spendsmost ofits life in burrows in the muddy substrateof relativelydeepmarine water. Clearly, we need to addressthe mode-oflife question intensively before we delve further into headysubjectssuchas conodont ecologyor biogeography. On a more mundanelevel, but nevertheless of signalimportance,is the businessoffilling in a number of gapsin the current stratigraphic record of the Conodonta.Lower Ordovician speciesare well known in the high-latitude faunascharacteristic of Europeanlocalities,but in North America there have beenonly a few reports,and theseleavea numcomprehensive ber of important taxonomic and phylogenetic questionsunanswered.The Silurian is also a problem, particularlythe part of it above the Pterospathodus amorphognat hoidesZone.This part of the Silurian was evidently a time of with widespreadshalmajor marineregression, low-waterenvironments,evaporites,and conditions hostile to developmentof rocks from which conodontsmight be extractedeasilyand in abundance.Nevertheless, a number of very important eventsin the evolutionaryhistory of the Conodontatook placeduring the late Silurian, and we badly needwell-documentedcollectionsas the basisfor frndingout what happened. Taxonomy of Carboniferous and Permianconodontsis in lessrobusthealththan is that of earlierforms or that of most Triassic lineages.Only a few studies have addressed multielementtaxonomy of Mississippianconodontswith conviction,and a few excellentrecent studiessuggest that thereare major surprises in store for anyone who undertakes detailed studiesof Permian conodonts.I recommendthesestratigraphicstudiesstrongly. Finally, we have probablyreachedthe stage at which monographicstudiesofthe taxonomy and phylogenyof major lineagesare in order. To be sure,a numberofsuch studieshavebeen completed,and my debt to them is plainly in evidencein Chapter 5. We need still more of them, and existingcollectionswill probablybe adequateasthe basisfor many.
References Aldridge, R. J., Briggs,D. E. G., Clarkson, E. N. K., and Smith, M. P. (1986).The afrnities of conodonts-new evidence from the Carboniferous of Edinburgh, Scotland. Lethqia l9(4), 219-29t. Ash, S. R. (1961).Bibliographyand index ofconodonts, 1949-1958.Micropaleontology7, 213244. Bergstrtim,S. M., and Sweet,W. C. (1966).Conodonts from the Lexington Limestone (Middle Ordovician) of Kentucky and its lateral equivalents in Ohio and Indiana. Bull. Am. Paleont. s0(229),27t-44t. Branson,E. B., and Mehl, M. G. (1933-1934). Conodont Studies.Unlv. Missouri StudiesS.l300. Briggs,D. E. G., Clarkson,E. N. K., and Aldridge, R. J. (1983).The conodontanimal.Lethata16, 1- 14. Clark, D. L., Sweet, W. C., Bergstriim, S. M., Klapper, G., Austin, R. L., Rhodes, F. H. T., Miiller, K. 1., Ziegler, W., Lindstrtim, M., Miller, J. F., and Harris, A. G. (1981).Conodonta. I\ T rcqtise on I nvertebrate Pqleontology (ed. R. A. Robison),Pt. w, Suppl.2, wlW202. Geol. Soc. America and Univ. Kansas, 202 pp. Ellison, S. P., Jr. (1962).Annotated bibliography, and index. of conodonts. Texas Univ. Publ. 6210,128pp. (1963). Supplementto annotated bibliography, and index, of conodonts. Texqs J. Sci. 15,50-67. and Graves,R. W., Jr. (1941). I-ower -, Pennsylvanian(Dimple Limestone)conodonts of the Marathon region, Texas. Univ. Missouri School of Mines and Metallurgy Bull., Tech. ser.r4(3), l -21. Epstein, A. G., Epstein, J. B., and Harris, L. D. (1977). Conodont color alteration-An index to organic metamorphism. U. S. Geol. Surv. Prof. Paper 995, 27 pp. Fay, R. O. (1952).Catalogueof conodonts. Univ. Kansas PqleonL Contr. (Vertebrata) Aft. 3, 206 pp. Hinde, G. J. (1879). On conodontsfrom the Chazy and Cincinnati group ofthe Cambro-Silurian, and from the Hamilton and Geneseeshaledivisions ofthe Devonian in Canadaand the United Statas. QuqrL J. Geol. Soc. London
35,35r-369.
Holm€s, G. B. (1928).A biblioeraphy ofthe conodonts with descriptionsof early Mississippian species.Proc. U. S. Nqt. Mus.72, Art. 5,38 pp. Huckriede, R. (1958).Die Conodonten der Mediterranen Trias und ihr stratigraphischerWert. Palaod. Z. 32, l4l-l'75. Kohut, J. J. (1969). Determination, statistical
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2. SKELETALANATOMY
For reasonslisted towardthe end ofchapter l, it is now clear that conodonts were primarily soft-bodied animals. Their only mineralized parts formed a cephalic apparatus, at least partly of epidermal origin, that probably functioned to grasp prey and aid in the intake of food. In most, if not all, conodonts, components ofthe exoskeletalapparatuswerediscrete objectsthat becamedissociatedfrom others on death of the animal. Although collectionsat various places in the world house several hundred more or lesscompletely preservedapparatuses,discrete specimensare the ones on which most of our information about the Conodontais based. Pander diagnosed lhe Conodontenin ieffis of the physical characters of discrete specimens. However, everywherein his monograph excepton the pagebearing the diagnosis,he referred to the "teeth," "jaws," or "rernains" of conodonts and thus usedthat word both for the animals as a whole and for their hard parts. I am not aware that this dual usageof conodont has ever puzzled anyone, but tlre potential for confusionexists.In the rest of this book I will use the word conodont only for an entire individual ofthe Conodonta.The term "conodont element" (or "skeletalelement," or just plain "element") will be used for discrete components of the cephalic apparatus.
maintain that conodont elements are composed of carbonate of lime. He cited this evi denceto counter conclusionsthat the little fossils might representa group relatedto annelids or "naked mollusks," whosejaws or radular elementsare of purely organiccomposition. In 1926 P. v. Roundy reported that conodont elements". . . appearto be a phosphatic carbonateof lime." Six yearslater Staufferand Plummer asserted,without citing further evi dence, that "conodont teeth are probably chieflycalciumphosphate."Bransonand Mehl seem not to have worried much about the chemical composition of conodont elements but, in 1944, one of their doctoral students, Samuel Ellison, demonstrated from X-ray analysesthat the substanc€inyolved is a member of the apatite isomorphous group. Because ofthis, conodontelementsare relativelyheavy (2.84 to 3.10) and are less soluble in acetic, formic, and citric acids than the matrix of carbonate rocks enclosingthem. This is imporit meansthat conodont tant. ofcourse.because elements may be extracted from carbonate rocks by prolonged soaking in such acids-a capacitythat setsthem asidefrom many other fossils-and they may also be separatedfrom large acid-insoluble residues by use of healry liquids or other types of gravity separation techniques. The most definitive, and also the most recent, contribution to the subject of conodont2.1 Compositionof ConodontElements elementcompositionis a monographby PietzFrom what appear to have been rather primi- ner et al. (1968),whosestudiesled them to the tive wet-chemicalanalyses,Panderconcluded following formula for the mineral matter of that the skeletal elements of conodonts are conodontelements, composed entirely of calcium carbonale(reinCa, Naoto (POa)3.qt(COj)0.r6 Fo', (HrO)'.s5 em kohlensaurem Kalk). L few years later, however, Harley ( I 86I ) wrote that ". . .they are They interpreted the mineral to be francolite, a composedofphosphate and carbonateof lime, carbonate apatite in which the OH and CO, the former, contrary to my expectations, the ions substitute for phosphate and do not ocmore abundant constituent." Hinde (1879), cupy lattice positions as they do in hydroxylike mostothers,felt that mostof Harley'sspec- apatites.Tracesof at least 39 other chemical imens were not conodontsand continued to elementshave beenidentified in various nlaces
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thus that the Conodonta were probably not however,only the first few lamellaeoverlapped fish, as Panderand many othershave thought basally to form a very tiny basal cavity, whereaslater lamellae became progressively them to be. as the crown Elementsof the cephalicapparatusof most shorter than their predecessors conodonts were dissociatedupon death by grew larger.Basalcavitiesof crownswith feadecayof the tissuesthat held them togetherin tures like this are termed basalpils, and the retife or by digestionofthose tissuesin the gut of mainderofthe attachmentsurfaceis described basalmargin. a predator.In only a few caseshave complete as a zoneof recessive In most parts of the crowns of typical conbeenpreserved.After dissociation apparatuses most conodont elementswere moved about odont elements,lamellae are 0.2 to 1.2 pm growth with other sedimentaryparticleson the sea- thick. However,at placesof accelerated platelike floor and that agitation was apparentlysuffi- in elementsthat grewlaterallyto form cient in most casesto separatecrowns from structures,or toward the extremitiesof those basalfillings.In any eyent,most collectionsof that built elongatecomblike shapes,lamellae conodontelementsconsistentirely (or almost may be as much as 5 pm thick. As noted preentirely)ofcrowns,and we havelittle or no in- viously, each lamella of a completeelement We canseeedges formation on the internal structureor extemal surroundsall its predecessors. morphologyof the basalfillings for most spe- of lamellaealong the attachmentsurfacesof cies.I suspectthat th€ basalfillings of a great crowns-however.and outlinesof someofthem many species,perhapsthe majority, wereonly are cornmonly visible in transmitted light slightly mineralized-or not mineralized al all. within the thinner partsof many crowns.Each They aremostlyunknown asisolatedobjectsin lamellais built on a frameworkof organicmarocksthat contain lots of discretecrowns,and terial, and the tiny apatitecrystallitesthat mi they do not occur in any of the completeap- neralizethis frameworkare orientedwith their paratusesthat have been described,which prism surfacesparallel to the direction of seemto have undergonelittle, if any, physical growm. In reflectedlight crowns of conodont eledistortion subsequentto deathof the animals. Whateverthe explanation,nearly all we know mentsare shiny and translucent.They are pale aboutconodontsis derivedfrom a studyofiso- amberin color if they are from rocksthat have not beenheatedabove 80"C for any length of latedcrowns. Crownsofconodont elements,like basalfill- time; otherwisethey may rangein color from ings, are internally laminated.In morphologi- reddishyellow to brown to black if they have cally simpleforms,like the onein Fig.2.1A,in- been held for any appreciabletime at higher dividual laminaeare conicalin shape,and the temperatures.Elementsfrom some metamorentirecrown hasthe structureofa nestedstack phic rocksaregray,white, or evencrystalclear. ofpaperdrinking cups.In the conicalspecimen Evidently elements such as this have been for of Fig. 2.1A, the basalfilling is still attached. deeplyburiedand kept at hightemperatures However,ifthe two componentsofthe element such long periods of time that they have lost were separated,the surface over which they eventhe fixed carbonresponsiblefor the dark werejoined would be that of a conicalinden- colors of specimensfrom lower-temperature tation in the abapicalpart of the crown. This rocks. Thermally unaltered crowns rnay be uniindentationis termeda basalcavity,and it occupiesa part of the crown known as its b4se. formly translucentand ofthe samepaleyellowNote in Fig. 2.lA that basal edgesof succes- ish color throughout,or one may distinguish sively younger crown lamellae extend some- within them more or lessirregular, fuzzy-edged what farthertowardthe basalmaryinthan their massesthat are opaqueand of whitish appearpredecessors. Thus, the surfacealong which ance.Crownsofthe first typearesaidtobe hyacrown and basalfilling wereoriginallyattached /irq those of the latter are tened albid. Many is completelyenclosedwithin the baseof the crownshave both hyalineand albid areas,and crown. In the element depictedin Fig. 2.t8, internal distribution of the white matter thal
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VINOOONOS AHI
nl
SKELETAL ANATOMY
ta:: io leaye the r;:::-:ol ofthe tisEiil short, the -Gli''-ti masses ln F--i :nd lhe se6 :;: :-- ontogenete ...::essionsof 's-,:-?nt tn taxlz;--of rhe life E-:: ro the fact qnl-: -_:o*ns of a hs :::l -\{iddle zr :- -orm fract' - ,-r: margins. Itc '-:;: internal E:l-::-:s olfibers rr--,: !-:h distincE|[-=- :: represent :: :!\rodonts, 4 . Su:=: -ent studfrii: =: hraline mc-_-i =e butlt of t :i= ::de up of I : r-,-aled par-: *r: s-:---acesparrd :;-' re rodlike p a c k ed t::it y l. €-': : Tl l u s, alr_. erred in -:::brm COnn;,: -.: e;:. :her \!ere !-t : =-.rP distinE-,i lt|ucture. i i-- :s- or neur:= -:,'luded in
I
:s :,:, be much : tc---: :n a wide r$- 3:--ause those rr :: rhe funcbr -::-:ran basis E. :-'.i ol atten=i recogniz- --: -ee descripri IFt | :!. It!:i--- :s el\'en rn E' -_:: :tames ap-
t)
TABLE 2.1. Shapecategoriesofconodonl elemenls Major shapecategory
Primary divisions
Coniform (simple cones)
Geniculate Nongeniculale
Ramiform (bars)
Alate Teniopedate Digyrate Bipennate Dolabrate Quadriramate Multiramate
Secondarydivisions
Breviform Extensiform
Raslrate Pectinform (blades,plates, platforms)
Stellate Pastinale Carminate Angulate Segminate
plied to thosecategories in Volume W (Supplement 2) ofthe Treatiseon InvertebratePaleontoloSy (clafk et al., l98l). Pander,the first to describeconodont elements,divided his specimensinto two major categories,einfacheZahne ax.dzusammenge' setzteZahne(i. e., "simple or singleteeth" and "compound or compositeteeth"). That division is still useful,althoughit hasbeencustomary for many yearsto divide the "compoundor composite"categoryinto two or threedivisions termed Ddrs,blades,and plates (ot platforms). In the shapeclassification adopted by Treqlr'Jeauthors,Pander'ssimpleor singleteethare coniform (cote-shaped)elemenls;barlike compound or compositeteelh are ramifurm (rayshaped)element$ and blade- and plate- (or platform) like elementsare groupedtogether as pectiniform (comb-shaped)elements.Elements describedin Table 2.1 as rastratehave been regardedeither as peculiarly modified coniform elementsby someauthorsor ascompound elementsby others.They werenot specifically identified in rhe Treatise classification of shapecategoriesbut are here regardedas a separatecategoryfor descriptivepurposes.
StelLplanate Stelllscaphate Pastiniplanate Pastiniscaphate Carminiplanate Carminiscaphate Anguliplanate Anguliscaphate Segminiplanate Segminiscaphate Bisegminiscaphate Trisegminiscaphate
Coniform elementsare funher divided into two categories(geniculateand nongeniculdte) on the basis of the type of curvature.Seven major types of ramiform elementsare recognized on the basisof the number of processes and their relationshipto the cusp.Pectiniform elementsare divided into five major groupson the basis of the number and arrangementof primary processes. If pectiniformelementsdevelopplatformlikelateralextensions,they may be further describedin terms of the resulting shapeofthe attachmentsurface(planateor scaphate).Typical representatives of eachof these in Figs. 2.2, 2.3,2.4,2.5, categories are shown which information on and 2.6, also include termsusedto describefeaturesofeach ofthese elementtypes. 2.3.1 Coniformcrowns Coniform elements,which are also known in the literature as "simple cones" or just as "cones,"are basicallyof conicalshape.Pander divided elementslike this into two parts, a more or lessexpandedbase,which enclosesa subconicalbasalcavity (Ihe CavitasPulpaeof
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9I
SKELETALANATOMY f,
of cusp
Fg.n
of base
!b|
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hr
have been recognized.Names for theseshape categories arelistedin Table2.1.Typicalforms are showndiagrammaticallyin Fig. 2.3,which also includes some information on terminology. Alate ramdorm elemenlsare bilaterally symmetrical,lack an anteriorprocess,but have a posterior processand a lateral processon eachside of the cusp.In somedescriptivereports, alate ramiform elements haye been termed "trichonodelliform" or "hibbardelliform" becausethe genera Trichonodella and, Hibbardella (and several others) were origi-
l7
nally form-taxonomicconceptsbasedon alate ramiform-typespecimens. Tertiopedateramiform elementsalso have a posteriorprocessand a lateralprocesson each side of the cusp,but the lateral processes are not symmetricallydisposedwith respectto the cusp and the posterior processis commonly long and conspicuouslydenticulated. Digyrate ramiform elements are like alate elements,but they are individually asymmetrical; only rarely is the posteriorprocesswell developedand denticulate;and lateral pro-
Fig. 2.3. Ramiform crowns and their orientation. Tetus used to describeth€m include the followns: ac = anticusp;ap: antetior process;bc = basalcavity;bp = basalpit;c = cusp;d = denticle;ilp = inner laieral process; lp_= lateralprocess;olp = outer lateralproc€ss;pp = posteriorprocess;and zrm = zone ofrecessivebasalmargin. Diagramsrcdrawn from Trcatise on InvertebratePaleontology,courtesyofth€ GeologicalSocietyofAmerica;nd University of Kansas.
il
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'sluaLuala uttolraot apwotlqnru parujel eq tq8ru (pore -^ocsrp eq re^e,{us pFoqs) sosseJordlnoJ ueqt ,stuauala eJoru qll.t\ esoql s€eJeg,tl unltraD.t apuotupDnb sE pequosep er? (l?Jel?l o,{l pue ^Iet?udorddp 'Joualsod 'Jouelue) sessaJoJd .oJ?J JnoJ qlrn asoql eJ" sessecoJd fu"ruud eerql ueql^{eJ eJou qll^l uJoJnu"u EuerrJele .,{uouoxq lueurelorlJnrll pu? Kurouox?l rrrJoJ uea,{qeq uorlrsu€Jl Jo J? Jelur eql ur penedd" luql $Fo,,l\e^rldursep ur ..tutoJ -uuoporuoudoeu,, puz ..uuoJrluopouou^c,, peurJal ueeq osle e^?q s uos trl JO Sluau -efg 'sorceds luopouoc snoue^ Jo sesnlpJ?d -oe lelela{s eql ur ed^l srql Jo slueueTe ueeal
^lpnbeun VINOCONOJ EHT
8I
SKELETALANATOMY
ide skeletalapr Fecies. Eleb been rcrmed bprioniodontil+tpeared in the ]frm E\onomy rban three ic -e fu sirh four tuo larcral) Et-;dirumate F -. fce srrh more fc== be discovF"lri.amiform
tively deep basalcayity and a posterior maryin characterizedby a prominent flangelike "heel" at the posterior end and, typically, a seriesof seyeral denticles between the heel and the tip of the cusp. A few rastrate elementslack denticlesbetweenheeland cuspapexand are thus superficiallylike geniculateconiform elements.
l9
A few others(e.g.,the upper pat in Fig. 2.4) lack a "heel." 2.3.4 PectiniformUowns In 1879Hinde usedthe term "pectinateteeth" for comb-shaped conodontelementsofthe sort
Fi9.2,5, Pastinateand stellatepectiniform elements,their scaphateand planatederivatives,and terms used to describethem. (SeeFig. 2.3 for explanation of abbreviations,)Diagams redrawn from Treatise on Invertebrate Paleontology, courtesy of the Geological Society of America and University of Kansas.
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may havea narrow medial lodina) the anterior process is commonly neaththe processes groovethat is flankedlaterallyby zonesof in- adenticulateand is represented only by a conspicuousflangelikerim on the anlerior margin vertedbasalmargin of varying width. Platformlesspectiniform elements are di- of the cusp. Pastinateelementsof this type vided in Table 2.1 into five major categories, havebeentermed "dichognathiform"in some dependingprimarily on the number and ar- of the descriptiveliteraturebecausethe genus rangement of processes.Stellate pectindorm Dichognathuswas basedon such elementsin elements(Fig. 2.5) have at leastfour primary the heydayof form taxonomy. processes,of which two are anterior and posCarminate and angulate pectinifurm eleterior. One or more of these processesmay ments (Fig. 2.6) have two primary processes, which are regardedasanteriorand posteriorin branch distally to form secondaryprocesses. (Fig. 2.5) position.The categoriesdiffer only in that the Pastinate pecliniform elements which are ante- longitudinal axis of carminate elements is have three primary processes, rior, posterior,and lateral in position. In pas- straight, or essentiallyso, in lateral view, tinate componentsof the skeletalapparatuses whereasthat of angulateelementsis archedbeof some Ordovician conodonts(e.9.,Neomul- neaththe cusp.Carminateelementswerecomtioistodus, Multioistodus, Phragmodus, Plec- monly termed "spathognathodontiform"and trig. 2.7. Segminarepectiniform elements, their scaphateand planate derivative$, and terms us€d to describe them. Upper sets ofdiagrams from Treatise on lnvertebrate Paleontology, courtesy of the Geological Society of America and University of Kansas.
fr ' 5. 1.6.and Jte rcrmsused
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proccaloa brsogminiscophato
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VINOCONOJ
AHI
SKELETAL ANATOMY
It Th.se. in turn, .1 en dolabrate rliologic inter5 '-:< 6rst to recfu -..-ies. and he d. 1pes. Subserr€rt-d out, and th .iereat prac@g ihe skeletal ris :iat are repE3 I illustrate rries n Fig. 2.8, IIr .]s€q'here in series int n or seven --:on 'E ::e complete L *apes of elet..a are -ries E-1 difficult to fcncgrneric sper &enls alone. tr3 of elements
I c-E in the appah aFaents on the !r=_jopedarc eleiipr_: or dolabrale
j
U
in the symmetry-transitionseriesmay be of considerablehelp in distinguishingbetween conodontsthat belongin differenlsuprageneric stocks.Thus it is important to pay carefulattention to the correctassignmentoftransitionseriescomponentsduring the systematicstudy of any collectionof discreteelements. In a few conodontspecieswith apparatuses composedsolely of coniform elements,it has beennoted that positionsin a symmetry-transition seriesmay be occupiedby elementsthat are variable with respectto longitudinal curyature. Fahraeusand Hunter (1986) have recently termed these variable gtorrpscurvaluretransitionseriesa\d haveillustratedthosethey regard as characteristic of the apparatusesof Panderodus gracilis, Protopanderodusvqricoslatus, ajf,d Drepanoistodus sp. aff. D. suberectus. In the skeletalapparatusof Panderodusgraby Fihraeusand Hunter, ciri, asreconstructed four ofthe five componentsform a symmetrytransitionseries(Fig. 2.9).Specimensin row A ofFig. 2.9 are all bilaterallysymmetrical,alate coniformelements,but theydiffer from oneanother by slight variations in curvature;specimensin row B. whichare slightlyasymmetric versionsof the alatespecimensin row A, also exhibit some variation in curvature, as do thosein row C, which are otherwiseevenmore asymmetric versions of elementsin row B. Fihraeus and Hunter tius recognizefive curvature-transitionserieswithin a skeletalapparatusthat alsoexhibitsa three-or four-member symmetry-transitionseries. Fihraeus and Hunter evidently conclude that eachindividual of Panderodusgracilis had, a skeletalapparatusin which there were five morphologicallydistinct components,eachof which was representedby a six-membercurvature-transitionseries.Thus there must have beenat least 30 elementsin the skeletonof a complete individual. Fihraeus and Hunter regard the nature and number of such curvature-transition seriesas featuresof potential supragenericvalue in conodont taxonomy. However.they do nol seemto have given serious considerationto the possibilitythat they rnight merely be charting the breadth of morphologic variation within the particular populationsthev samDled.
A
Fig.2.9. The curvatur e-transilion seies of Panderodus gracilrs(Bransonand Mehl). Each of the five or six elements oflhe apparatusis shown to increasein curvature away fiom the planeofbilateral symmetry.Inner lateral views on lefl; outerlaleral views on dght. Redrawnfrom F6hraeusand Hunter ( 1985).
2.5
SkeletalApparatuses
We have thus far consideredthe composition, classification,and descriptiveterminologyfor discretecomponentsof the skeletalapparatuses ofconodonts.However,it hasbeenknown for at least the last 50 years that in many conodonts,perhapsin all of them, the skeletalapparatusincluded elementsof severaldifferent shapecategories.Thus, in order to compare one conodontwith anotherand to build a biologically reasonabletaxonomy for the group,
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VINOCONOJ
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for elements B nol intended of€lement$;it rnajor poslon IDverteSociety of
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ramiform elements or geniculate coniform types.Elementsin the threemajor positionsin the S seriesform a symmetry-transition series of the sort first recognized by Lindstrdm (1964).The Sapositionis occupiedby an alate coniform or ramiform element;the Sb position by a digyrate or tertiopedate element; and the Sc position by a bipennate or dolabrate rami form element. However, the nomenclaturejust mentioned (and illustrated in Fig. 2.10) provides formal identification for just the midpoint and the two extremesin the S series.In the apparatusesof many conodonts, however, there may be more than three morphologically distinct componentsof the S seriesand, to describe and locate them, it may be necessaryto invent intermediate categoriessuch as Sa-b or Sb-c.In Fig. 2.10 thereis alsoa positionin the S serieslabeled Sd, which is occupied in some reconstructed septimembrate apparatuses by quadriramate ramiform elements.It is not appropriate to use Sd as the designationfor intermediate positions in the symmetry-transition series,as some authors have recenfly done, In most skeletalapparatusesthe Sd position is not filled at all. 2,6 SymneFyof Elements,Elem€ntPsirs, and Apparatuses It takes rrery little experiencewith collections ofdiscreteconodontelementsto discoverthat, like componentsof the human skeleton,most of them corne in mirror-image pairs. The only ones that depart very obviously from this pattem are alate coniform and ramiform elements, which are themselvesbilaterally symmetrical, and a few straight pectiniform elements that are developed in the same way on both sides.Indeed, it was not until almost 1960that it becameobvious that the right and left (or dextral and sinistral) mernbersof some element pairs are not exact mirror-image replicas of one another; and the incieasingly widespreadpractice of multielement taxonomy has led to the discovery that bilateral asymmetry wasrather common in the skeletonsofat least certain groups of conodonts. Iane (1968)suggested that four major types, or classes,of symmetry could be recognized among various element pairs. These are illus-
trated diagrammaticallyin Fig. 2.1L In Lane's scheme,C/ass I symmetry is exhibited by elementsthat are themselvesbilaterallysymmetrical. For suchelements(e.g.,alateconiform or ramiform elements) no pairs can be established,and it is possiblethat they occurredsingly in skeletal apparatusesor were paied with other individually symmetrical Class I elements. C/aJs11 slrmmetry is a feature of individually asymmetricelementsthat are represented by approximately equal numbers of "rights" and "lefts" in largecollectionsof discrete specimens.As lane (1968) noted, the bulk of known typesof conodontelementsapparentlybelongin this class. ClassIII symmetry is exhibited by conodont elementpairs in which the "right" and "1eft" Fig.2.ll. Various symmetry classesexhibited by elements typica.l of (I) R hipidognathusi (Jl\ Xaniognathus; (llla) Eognat hoduii (lllb) A mory hoghalhus.
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r::Tor-lmage (or h:-
k-s:---om. S. M., k:c=:. F. H. T., I-=istrom. M., \ G ,9El ). Conrc.::a PaleontolL I \fi5cellanea), flme:,-a and Univ. rl:s-ion of conllfD- R 1986).The h:-=:al part of l4ttri:-.ruses (PanE- C-.nodonlata). ---189. Dar IE =r Conodonb ft
;e: Gatrungen C:xodontida).
r a.:,:-bed and its I ,i;:. Soc.Lonnir:s from the |' :, -le Cambroih-. ard Genesee fu = Canadaand
the United Stltes. Quafi. J. Geol.Soc. London 3 5 ,3 5 1 -3 6 8 . Lane, H. R. (1868). Symmetry in conodont element-pairs."L Paleont.42, 1258-1263. Lindstriim, M. (1964). Conodonts.Elsevier,Amsterdam,London, New York, 196pp. and Zregler, W. ( 1971) F€instrukturelle -, Untersuchungenan Conodonten. l. Die Uberfamilie Panderodontacea.Geol PaloeonL5,9-
Mikromorphologie der Cor.odor]]!e[ Paleontographica, 128, ll 5-l 52. Roundy, P. V. (1926).The micro-fauna.In, P. V. Roundy, G. H. Girty, and M. I. Goldman, Mississippian formations of San Saba County, Texas. 2. U. S. Geol. Sum. Prof. Paper 146,5-
Sr".t, W. C. (1979). Late Ordovician conodonts and biostratigraphy of thae western Midcontinent Province. Brigham Young Univ. Geol. Pan-d'er, C. H. ( 1856).Monographie der fossilen SLudies26,45-85. Fische des silurische Systemsder russisch-bal- (1981). Macromorphologyof elements tischen Gouvernemefis. Akad. lliss., St. Peand appa.atuses.Pp. W5-W20. ID Treqtiseon tersburg,9lpp. InverlebretePaleontology(ed. R. A. Robison), Pietzner,H., Vahl, J., Werner, H., and Ziegler,W. Pt. W, Suppl. 2, Conodonta. Geol. Soc. Amer(1968).Zur chemischenZusammensetzung und ica and Univ. Kansas,202 pp.
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WHOLE-ANIMALANATOMY
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G_-i:3nt aspects. :f:::s-,1!cted from E- iirrally comE
ts.:.ld specimen ir i in m (1 .6in. ) ,.0 7to 0. 08 i == lE:r-sron at one !:c,-:t apparatus r.=:::1ic lobe.On r*: _'rdged to be t =:: :reted to be f::i r. the bestlr i:!i diagnostic ak ::,r of indisr:i .r'rtenor end. hc ::-.:r- the axis L: : ilrn ct l i near ft::: :s a seriesof !bi: srop€ toward rs a-. more dise-, :d specimens EE :: :.1.( 1986),in Fe : \--like shape, E:: rhe anterior. rtt='r specimens, I a]rost to the I{: -:r'er. in that E=:sr \-'s appear di---'< as a result of k-: --eburial and ft=: and still the c$::s:r Specrmens -l - --:e V-shaped E:r 3h laken to | ::re compared (or muscle b=5 L B--: lhese inter'equivocal." d aL- i iS6) describic= rhe Scottish
Fig. 3.1. Clydagnathlls? sp. cf. C ca,rutbrmis. (A\ Cafiera-lucidadmwing of part; (B) and (C) enlargedvrews of head showing conodont assemblagein part (B) and counterpan(C).Specimenfrom "shnmp-band" in Granron Sandstones(Dinantian), Edinburgh,Scolland.Redrawn from Bflggs,Clarkson,and Aldridge (1983).
Dinantian locality, these V-shapedstructures are identified, with no further discussion,as "somites." This interpretationwas obviously quite influential in the much more subjectiye discussion ofanatomyin the 1986paper.even thoughit is in no way requiredby the evidence. Outlinesofthe anteriorend are preservedin only one of the ScottishCarboniferousspecimens(Fig.3.1).Althoughthis end is termedthe "head" by Briggset al. (1983)and Aldridge et al. (1986),thereis no evidencein it ofa brain. The term cephaliclobe may thus be more appropriate. As noted previously, the cephalic lobe of the best-preserved Scottish specimen enclosesa completeand apparentlylittle distorted conodontapparatus,which permits the
specimento be identifiedas Clydagnathus'l sp. cf. C. cavusformis. In the only Scottishspecimento preservethe cephaliclobe,right and left componentsofthe insteadof skeletalapparatusare superimposed arrayedon oppositesidesof a line of bilateral symmetry.It is thus reasonable to supposethat the cephaliclobe of this specimenis preserved in lateral aspect,that is, that the plane of the bedding approximatesthe plane of bilateral symmetry.The deepcleft at the anteriorend of the cephaliclobe may thus mark the position ofthe mouth, and the positionofthe apparatus within the cephaliclobe may indicatethe general position of a buccal cayity. If the entire specimenshownin Fig. 3.1 has beenflattened
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d =e apparatus t i ';nfonunately I o-rhrr anatomic J:!e elements in tr a basal plate, f E::sculature as! Er:r more puzig rhar might be fr :-.rrrcture comd :-ae hagfishes, r Fbst|ate for the r d- a@chment of I (onplex apparamens provide no ! r-olodont appaqrrielium or exHer elements of I eld might thus I b.'5 or whether I tt':s may have rsi. supports for Lc in a buccal
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The trunk of all four of the Scottishspeci- requirethat all segmentsofthe axial structure mensis 1.2to 1.8mm wideand preserves evi- in everyspecimenrepresentthe sameorganor denceoftwo distinctiveanatomicfeatures.The organsystem.For most ofits lengthin all ofthe most striking consistsof a seriesof V-shaped Scottish specimensthat show it clearly, the structures,which were apparentlysituatedon axial structurejoins the apicesofthe V-shaped the sidesof the animaland whoseapicespoint structuresofthe trunk. No suchrelationshipis anteriorly. In the most completelypresewed shownin the anteriormostpart of the trunk of specimen(Brigeset al., 1983;Fig. 3.1) these the best-preservedspecimen (Briggs et al., structures are rather indifferently preserved 1983;Fig. 3.1),however,and the axial structure and are confined to the posterior half of the in that specimenmay not be continuouswith, trunk. In the three more fragmentaryspeci- or represent,the sameanatomicfeature,asthe mens (Fig. 3.2) describedby Aldridge et al. discontinuouspair of axial lines in the poste(1986),the V's arebetterpreservedand may be rior half of the trunk. Aldridge er al. (1986), seento extendnearlyto the anteriorend ofthe who allowedtheir interpretationofthe Scottish trunk. The shape,serialrepetition,and lateral specimensas primitiye chordatesto restrict situationofthese V-shapedstructuresare rem- their survey of anatomic possibilities,suggest iniscentofthe myotomes(or muscleblocks)of that the double lines in the anterior parts of Branchiostoma(or "amphioxus") (Fig. 8.1) severalspecimensmight representsome parts and of other chordatessuch as the hagfish or all of a nerve chord, notochord,or dorsal Myxine (FtE.8.2). aorta.I suggest that one might alsoconsiderinBut chordalesare not the only organisms terpretingthis pair of lines as the incomplete thatmightyieldsuchV-shapedimpressions on trace of a nemertinerhynchocoel,the tubular compression.For example,nemertines(phy- cavity within which living representativesof lum Rhynchocoela)such as Nectonemertesthe curious group of invertebratesstore their (Fig. 8.1) are characterizedby a long, straight eversibleproboscis.Suchan interpretation,of intestine,which bearsnumerouspairedlateral course,would not rule out interpretingaxial diverticula that might, on flattening and lines in more posterior parts of the trunk as producepatternssimilar to those traces of a gut with numerous lateral compression, exhibitedby various parts of the severalScot- diverticula. tish Dinantian conodonts. Nemertines, of If the axial structurein the posteriorpart of course, are pseudometamericbut acoelo- the lrunk of the Scottishsflecimensis intermate invertebrates,probably derived from pretedas a gut, it appearsto have extendedto flatworms and not known to have a fossil the posterior extremity of the tail in the two record. specimensthat retain it (Figs. 3.1 and 3.2). The secondfeaturerecordedin variousways That would mean that theseanimalslackeda and with varyingfidelity in the trunk of all four postanalsegment,or true tail, featuresthat are Scottishspecimens consislsof a line. or a pair characteristicnot only of chordatesbut of inof subparallellines, more or less coincident dividuals in virtually all the deuterostome with the longitudinalaxis ofthe body and ex- phyla. On the other hand, if one assumesa tending from a point just behind the cephalic nemertinemodel, even with tonguein cheek, lobe on the anteriorto the posteriorend ofthe the problemvanishes.for in that g.roup-as in body. Aldridge er al. (1986) note rhat these most invertebrateswith a completedigestive lines might representa number of different tract-the anal end of the digestivetube is sitstructures.For example,they might be tracesof uatedat the posteriorextremity of the body. I a notochord,a nerve chord, the gut, a major agreewith Aldridgeet al. (1986)tbat anatomic longitudinal blood vessel,or a mesenteryor interpretation of the axial structuresof the septumdividing the body cavity into compart- Scottishspecimensis inconclusive;however,I ments.I agreethat a gut is the anatomicfeature suggestthat, in combination with other feamosl likely to be representedby most of the tures,thosestructuresmight well tum out to be lengthof the axial lines in most specimens.as significantin reconstructingdetailsof conoHowever,evidenceavailablethus far doesnot dont soft anatomyas the V-shapedstructures
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€'€ VINOCIONOJ AHJ
WHOLE.ANIMALANATOMY
3.3 HistologJof Demineralized Tissue
i F^ire ft=:,:'.
Formation published
19f,-,, The WauG -One-rs prelrile bmken edge atrd repretrG E E:anor part of ;fu,.v,a eriginal frte .-tphalic apilceg anes transll r::.k and with Smith, lE--rorlllat this t-esla5trafillus was qE\ls.d halyes, ds longitudinal t iobe and the &55a specimen rai ro rhe plane lEr1le. considerin the preI--'.5.:hr My was Had it trcssed to have r +ears I Carboniferous t ba..e been de|l oo compaction lFiles sery little aaatomy of lo$ E Lbar vague, lrss original seglcr aI { 1987),the pible segment lecrlr ransverse There is no indiI (ia.racreris tic of
soft-bodiedanimalswith a slender,vermiforrn body a couple of inches long that may have Fdhraeusand Fahraeus-vanRee (1987) have been either laterally compressedor dorsovenidentifiedcells,fibrousmaterial (thou8htto be trally depressed. The anterior end of the slenat leastpartly collagen),and luminaeofvarious der, elongate body is developedasa distinctceshapesin scrapsof demineralizedtissue dephalic lobe in known Silurian and Dinantian rived from the pectiniformelementsofSilurian specimens of Ozarkodina confluens. Cells of specimens and includes the apparatus of vanous types have been identified; some are mineralizedelementsby which conodontsare relatively large,with nuclei 3 to 5 pm across bestknown. The slendertrunk is divided into and long dimensionsas much as 20 pm: others serially repeated transverse structures that are smaller, contain numerous nucleoli, and occur on either side of or surround an axial structurethat may representthe gut, a notohavea stronglyeosinophiliccytoplasm. chord, a doral aorta,a longitudinalseptumor Luminae, which have the form of irregular mesentery, or somecombinationof thesestrucspherical spaces,and single and branching catures. The transversestructures,which are V nals,are relatedby Fihraeusand Fihraeus-van shaped in Carboniferous specimens(but not in Ree to the irregular frothy spaceswithin conothe Silurian one) have been comparedwith the dont elements that have been termed white myotomes (or muscle blocks) of amphioxus matter. Flbrous matter is sparselydistributed and fish and thus taken as evidence of body among cells, occurs in bundles and, for the segmentation. Those interpretations are not remost part, lacks nuclei. Some is dense,basoquired, however, and the transverse structures philic, and apparently associatedwith elonjust aswell representthe paireddigestive gatedsinuouscells.The fibrousmatterwithout might nuclei is consideredto be collagen.Fihraeus diverticulathat characterizemany acoelomate and Fihraeus-vanReeemphasizethe fact that nemertrneworms and, as such,indicate only pseudometarnerism. The posteriorend of two onty 20 to 25 percentof the tissuefragments of the flve known whole-bodied fossil conthey studied is collagen,whereascollagenacodonts is bluntly aciculate, and its margin countsfor the entirematrix ofmost othertypes bears traces of ray-supported finlike structures of mineralizedtissue.They also point out that the largenumberofcells in demineralizedcon- on oneor both sides.Linearaxial structuresexposteriormarginin bolh specimens. odont tissueindicatesthat it ". . . is not bone tend to the Ifthese represenl tracesofthe gut, the Carbonor dental tissueas we know it," becausebone iferous conodonts may not havehad a postanal ". . . is eithertotally non-cellularwith an extrasegment, or true tail. cellularmatrix largelyconsistingofcollagen. . . The five whole-bodiedfossilconodontsnow or, in cellularbone,it is dominatedby bundles known raisealmostas many questionsas they ofcollagenwith the occasional'trapped'osteoprovide answers.It is a comfort to know that cyte." They go on to statethat the demineralthe skeletal apparatusis apparentlyassociated ized conodonttissueof their study is also unwith the cephalic lobe,for most ofus had conlike that found in living inarticulate cluded from seat-of-the-pants functional analbrachiopodsor mollusks.They do not exclude ysis that this would turn out to be the case the possibilitythat primitive vertebratesmight years many before the famous Scottishspecihaveformed suchtissues,nor do they fule out mens were discovered. It is also no surprise possibility the that the tissuesthey studied that the specimens indicate an elongate, verrepresent a ".. . unique approach to biomiform shape, since that is a shape common to mineralization." mobileaquaticanimals.However,eventhough the skeletalassemblages includedin the wholebodied fossils seem to have beenonly slightly 3.4 Summary distorted by compression,they all apparently Existingevidenceon whole-animalanatomyis lack basalbodies,and it is not possibleto desparsebut may be takento confirm the conven- termine how they may have been related to tional wisdom that conodontswere prirnarilv muscularsystemsor whetherthey were com-
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VJNOCONOC EHJ-
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4. TAXONOMY
G- a-ld Kluessenf"j-rcdred biota.
4.1 FormTa-xonomy
aib,- A new exr -3e Lower Silfu- Tens. Roy. $, h-uon of the Pa ---90 in Pad L R- J, .{dridge).
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der fossilen ;le r&r russisch-bal+t .t\rd. Wiss., d t"lridge, R. J. h te lower Sid --:e apparatus I csqodonts. 9lE-{-r (ed. R. J. bssrer- 180pp.
Pander'sclassificationofconodontswasproposedlargelyas a meansof giving order to the In Chapterl, I pointedout that ChristianPansystematicdescriptionof specimensin his colder, who discoveredand named conodonts. lections.He made no attempt to give it prowrestled in his 1856 monograph with the found biologicmeaning,nor did he useit asthe choiceoftaxonomic base.He wrote (my rough basisfor discussingeyolutionarydevelopment translation): or addressingother biologic questions.Evidently the classificationwasto serveonly until We don't know what sort of teeth we have before us; wheth€r they belongto the jaws, the palale, the lips or discoveryof more completespecimensmadeit the tongue; whether each particular shape conslitutes possibleto determineif all elementsweremorsufficientbasisfor establishmenlofits own genusor spe- phologically alike in the body of a singleindi. cies; or whether different forms could have come from vidual, or if the body of the sameindividual one and the samebody. might havehadan arrayofmorphologicallydifIn the absenceof a living analogue,and un- ferentelementswithin it. able to answerthe questionshe raised about Although Harley, Smith, Hinde, and Hadfunction or anatomic position or about mor- ding contributed to conodont taxonomy bephologic monotony or yariability of elements tween 1856and 1926by describingdiscreteelein the samebody, Panderchosean admittedly ments of distinctive shapes as genera, no utilitarian classificationbasedon shapeof in- further consideration of supragenericcategodividual elements.This approachto the classi- ries seemsto havebeenmadeuntil 1926,when fication of biotic groupsis sometimestermed, Ulrich and Basslerpublishedtheir influential rather pejoratively,form taxonomy. taxonomicscheme.As you will recallfrom earTo beginwith, Panderassignedconiformele- lier discussions in this book, Ulrich and Bassler mentsin his collectionsto an informal category stated their firm conclusion that conodonts termed "simple teeth" (Einfache Zahne), and represented not only the teeth,but alsothe derramiform andpectiniformelementsto another, mal platesof extinct groupsof fishes.In additermed "compositeteeth" (Zusammengesel.ztetion, and probablyrnoresignificantly,they also Zahne). The s.impleteeth (Fig. a.1) were then concludedfrom their studiesof recent fishes further divided on the basis of crosssection, that, exceptfor the fact that they may occuras into 7 categories, which Panderdescribedand right and left mernbersofa pair, all teethin the named as genera.Finally, each of these was mouth of the supposedliving relativesof the subdividedon the basisof cuspcurvatureinto conodonts are essentially alike. Thus they groupsregardedas species.Compositeteethin wrote ". . . eachkind is characteristicof some Pander'scollectionswererepresented by 7 ob- particular genusand species."In short, they viouslydifferentmophologiccategories. among professedcompletecoDfidencethat a classifiwhich he recognized18 specieson the basisof cation basedon the shapeofdiscreteelements, featuressuch as mode of denticulation,pres- a form taxonomy,wasa true expressionofbioenceor absenceof carinae,anglebetweenpro- logic relationships. cesses,characterof platform extensions,and In their 1926 paper Ulrich and Basslerigthe like. Altogether,then, Pander recognized nored the one genus(Periodon)proposedby and named 7 generain each major category Haddingin 1913,but distributedall the others (simpleand compositeteeth)and, collectively, known at that time, and 15 new ones,among4 56 species,all basedon an analysisofshape,or supragenericcategoriesdescribed and named form. as families. Pander's"simple teeth" category
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TAXONOMY lridia) and de:sembled into 8 : tgo suborders hodontiformes) irhose elements h srborder NeuE \-rcian genera rlought to have) bas the suborEilshed for the lresented by elef irEmal strucG Eere thought Erendl' shaped r|rd ioro catego)bsrs of lhe supr tle variously i on x'hich they bn<. The three fu:dae. for ex! hsil record by rirh relatively rllich were I roirhe fish that i oi conodonts J irdiridual, dislfu a,,-mein Volat*ate PaleonP- h rlat highly rF entirely by Ddouts were asC-onodontophorI r Iamrtres. lne h Branson and iorders Neurohmes were reEsrent by Hass, ![\ze those subrc ramilies (Co,-d ldiognathotEmilies so that EL-sones recog;nred *'ith 8 in r4 in that of Ut-
I ahernative to pied as a pospractice rnto IEI
37
until 1879,when Hinde employedit for a spe- and an essentiallycomplete "natural assemcies from the Devonian of New York. In the blage" is preservedin the headof the Scottish "multielement" way of looking at things, the "conodont animal" discussedin defail in skeletalapparatusofa conodontis madeup of Chapter 3. So, since at least 1934,there has numerous parts, not necessarilyall alike in beenno good reasonto defenda form taxonmorphology.The basefor taxonornyis thus a omy for conodontsasa natural one.The pracgroup of elementsthat can be shown, or can tice persistedthrough 1962,I suspect,because reasonablybe inferred, to have occurredto- most studentsof conodontswer€ more congetherin the body of an individual conodont. cernedwith biostratigraphicapplicationsthan An apt analogy,ofcourse,is with the vertebrate with biologictaxonomy. skeleton,which consistsofnumerous morphologicallydifferentparts. Hinde (1879),the first to practicemultiele- 4.2.I Multielementmethodology ment taxonomy, based his concept of Polyg- The major difficulty with putting a general nathus dubius on an assortmentof elements schemeof multielementtaxonomy into pracpartly exposedon the surfaceof a slabof black tice for conodontshasbeenthe fact that "natshale.He took physicalproximity on the shale ural assemblages" and fused clustersare relaslab to indicate original association,although tiyely rare and are not uniformly distributed the namehe chosefor the first speciesto be di- stratigraphically,whereasthe collectionsavailagnosedin a multielementsensesuggests that ableto most systematicists arejumbled assorthe was not completelyconvincedthat all ele- ments of elementsthat may have been commentscamefrom the sameindividual. ponents of several different multielement Other, more convincing "natural assem- apparaluses.Thus, except for speciesrepreblages" of elementswere describedindepen- sentedby natural assemblages, a meansmust dently in 1934by Hermann Schmidt in Ger- be devisedfor determiningwhich elementsin many and by Harold Scottin the United States. collectionsof discretespecimenswere origiThe assemblages availableto thosepaleontol- nally associated in the sameskeletons. ogistsareall from Carboniferousrocksofabout Perhapsthe most instructive way of reconthe same age and are made up of about the structingthe skeletalapparatuses of conodonts sametypesof conodontelements.Becausethe from largecollectionsof discreteelementsis a compositionof Schmidt'sand Scott'sassem- basically empirical method. This procedure blagesis closelysimilar, and becauseeachhad wasappliedasearlyas 1958by Huckriede,who severalspecimensof sirnilar or identicalcom- noted that in his collectionsof Triassic conposition, chanceassociationwas easily ruled odontscertainforms occurredmoreor lessregout, and the assemblages were describedand ularly with certain others.From his observainterpretedas the skeletalremainsof individ- tion that certain types of ramiform elements ual conodonts.E. B. Bransonand Mehl (1936) wereregularlyassociated with one or the other and C. C. Branson(1957)attemptedto dismiss of the two most common platformedpectiniScott's specimensas coprolites,but Scott re- form elements,Huckriede proposedthat the plied (to Bransonand Mehl) that ". . . it would " Conodonten-Satz" (literally, conodont-set)of be strangeindeed to find a group of animals Gondolella navicula (the platformed pecriniwith sucha balanceddiet that the excretalma- form element)includesa pair of angulatepecterial would consisttime after time ofone pair tiniform elements(refened,thenLoOzarkodina of prioniodids, one pair of spathognaths, one tortilis), a\d ramiform elementsthat wereinpair of prioniodells,and approximatelyfour cludedin 1958in 9 form speciesassignedto 6 pairs ofhindeodells." form genera.Huckriedecomparedthe associaThere are now more than 500 "natural as- tion he recognizedempiricallywith naturalassernblages"of conodontsknown from Cam- semblagesdescribedby Schmidt (1934, 1950) brian, Devonian,and Carboniferousrocks,al- and Rhodes(1952)and evidentlynoted agreethough not all have been described and ment in at leastmajor features.He appliedsimillustrated.In addition, fused clustersof ele- ilar reasoningto a reconstructionofthe ",Salz" ments now and then appearin acid residues, of Polygnathus tethydis, with results that are
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IAXONOMY indonts did so r--ald a major bE ard of the lEries in the reH s-ith enthusi I ad voD Bitter fusring meth- iterily 6o"5hcrete elements groups that E I apparaluses of lql sp6511u1a4 rf pincal methbers. atd BergI rhai it became E to subdivide tinsial or facies tRlement spetl s.lme conclub hern een elellh apparatuses *s of the clusLFt- survey, alrihl drat these rs€ator is dealof samples C ftrms and are -er iicate rhat rergrrence of 15 ELs in l0 sam$'ould be nist h lr rhat table Dq-currence of b Ibar might be
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pairsfrom Table4.1 TABLE 4.2. Jaccardcofficientsfor element-type Type 1 l0 11 12 56 22 -_
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2 3 5 6 7 8 9 l0
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consideredto representthe skeletalapparatuses of various conodont species.Severaldifferent coefncients havebeendevelopedfor usein stating the degreeofassociationbetweentwo entities,and eachstudenthas a preferencefor one or another.Kohut (1969),for example,usedan index of affinity developed by Fager and McGowan (1963),whereasVon Bitter (1972) employedthe Jaccardcoemcient.Clustersderived from the data ofTable 4.1 are essentially the same whichever similarity coefiicient is used; so, becausethey are easierto calculate than Fagervalues,I havederivedJaccardcoefficientsfor all possiblepairs of the 15element types in that table. The Jaccardcoefncient,as usedby Von Bitter, may be given as _a J=-
a+ b + c
in which a is the number of samplesin which both the elementtypes consideredoccur, D is the numberjn which one of them is present alone,and c is the numberof samplesin which only the secondelement type occurs.Obviously,ifthe two typesofelementsdo no1occur togetherin any ofthe samplesavailableJ : 0; but if eachof the two is representedin every samplethat containseitherone of them,J = l. Ofcourse, ifJ = I for a pair of elementtypes, we must considerthe possibilitythat thoseelement types were originally parts of the same skeletalapparatus,eventhoughthey may differ greatlyin morphology. In Table4.2I givethe Jaccardcoemcientsfor
all possiblepairsofthe 15elementtypeswhose distribution is given in Table 4.1. Note that valuesof thosecoemcientsvary from a low of 0.22to a high of 1.00.What we needto do now is rearrangethe dataofTable 4.2 to revealclusters of elementtypes more closelyrelated to eachother than to other clusters.This may be done in severalways. Kohut (1969)chose,in effect, to rearrangethe similarity-coefficient matrix itself, as I have done in Table 4.3, by rnovingthe highestvaluesin eachrow and column to the diagonalmedianof the matrix. Von Bitter (1972),on the other hand, usedthe unweightedpair-groupmethodto developa dendrogramthat graphicallydisplaysthe relationship between pairs and clusters of pairs of elementtypes.I havederived the dendrogram of Fig. 4.2 from the similarity-coemcientdata of Table4.2. In both the rearrangedmatrix of Table 4.3 and the dendrogramof Frg.4.2,note rhat there are threewell-definedclustersofelementtypes. Two of theseclustersinclude six rnorphologically different typesof elements,whereasone has only three. Furtbermore,both the rearranged matrix and the dendrogram reveal the samethree clusters,which may appropriately be identified as recutent groups. In a multielement view of the conodont world recurrentgroupsare the basisfor taxonomy if their componentsalso exhibit several other important features.For example,if a recunent groupis to be interpretedasthe skeletal apparatusofa conodontspecies, onemight rea-
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41
ment or redefinition ofcertain categorieseslab-
lished in that volume. PersonalprejudicedicLjndstrdm (1970)compiledthe first classificatatesothers.Thus the classificationadoptedin tion of conodonts that recognizedrecurrent in somedetailin Chapgroups of morphologicallydifferent element this book and discussed ter 5 wilt appear,at least superficially,to be typesas the basictaxonornicunits. Conodonts quite different from that in the Treatise. Some were groupedinto 2 orders (Westergaardodibrief commentis thus in order. nida Lindstrtjm and ConodontophoridaEiFirst, I havebecomeincreasinglyskepticalas chenberg),with the latter (the "conodonts to the amnitiesand relationshipsof the tiny, proper") further divided into 8 superfarnilies phosphatizedfossilstermed protoconweakly (Distacodontacea,Panderodontacea,Chirogodonts and paraconodontsand lumped tonathacea, Prioniodinacea, Prioniodontacea, getherin the Treatiseas the order ParaconoBryantodontacea,Gondolellacea,and Polygnathacea).These major groups were defined, dontida. These superficially conodontlike forms are quite different in internal structure insofar as possible,in mullielementterms, as from the onesdescribedin Chaprer2, for which werethe familiesinto which they weredivided. Bengtson(1976)hasprovidedthe generalterm Altogether,Lindstraimwasableto assigna total Although Bengtsonhas shown "euconodont." of73 generamore or lessconfidentlyto one or how paraconodontsmight have evolyed from anotherofthe 2l familieshe recognized. protoconodonts,neitherhe nor anyoneelsehas The taxonomic schemeoutlined by Lindyet documentedthe stepsby which euconostrbm (1970)obviouslyinfluencedthe one dedonts might have developedfrom paraconovelopedby authorsofrevisedVolume W ofthe donts. Szaniawski(1982),on the other hand, Treatise on InvertebratePaleontology(Clatk et hasdemonstratedthat conicalelementsof one al., 1981),which waswritten betweenl97l and of the protoconodonts(Phakelodustenuis)arc 1976but was not publisheduntil late 1981. essentiallyidenticalin jntemal structureto the Treatise atJlhots included alt conodonts in a graspingspinesof modern anow worms such singleclassof a phylum Conodontaand folas Sagitta. Thns, Phakelodus tenuis, a protolowed Lindstrdm in assigningthe animalsI regard as "true conodonts" to one order (the conodont,may well have beenan early representativeof the phylum Chaetognathaor of Conodontophorida),which included 44 famisome now-extinctgroup closelyrelatedto the liesdistributedamong9 superfamilies. The 179 and not a conodontat all. Szageneraof "true conodonts"recognizedweredi- chaelognaths, (1987),whosecarefulhistologicstudies niawski agnosed,insofar as possible,in multielement are certainlyimportant in this regard,continterms and described in the terminological uesto hold that the proto-, para-,and euconoschemedescribedin Chapter 2 of this book, donts(i.e..the Paraconodontida and Conodonwhich was developed speciallyfot lhe Treatise. tophorida of the Treatiseclassification)form parts of a singleevolutionarylineage.He does not regardthe Conodonta(in which he would 4.4 A RevisedMultielementClassification includethe Paraconodontida) aschaetognaths, At the time ofthis writing, skeletalapparatuses despiteconsiderablehistologicsimilarities,but of speciesthat representmore than 100genera as representatives of a group that developed havebeenrecognizedfrom naturalassernblagesfrom a common ancestor.It is my conclusion, or fused clusters or have been reconstructed which is further developedin Chapter8, that from recurrentgroupsidentifiedin largecollec- the Conodonta,Paraconodonta, and Chaetogtions of discretespecimens.For the most part, nathaare similar but divergentgroups,all posthe classification adopted in the Treatise pro- sibly of phylum rank, that developed in the videsa satisfactoryframeworkwithin which to generalradiationof major structuralplansthat assessrelationshipsof the speciesso recon- characterized the Cambrian history of the structed or recognized.However, discoveries biosphere. since 1976,when the f,"eat,semanuscriptwas It would be an unjustifiedextrapolationfrom essentiallycomplete,dictate some rearrange- Phakelodusto assignall 15 generaincluded by
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YJ,NOCONOJ :IHJ
TAXONOMY h:e are the Disbi-ncation, augrber of genera lcher superfamaoval of a few l'rte Conodonta E of all other orx-a included in hctive bi- to of lparatuses raslrate eled fr-rous longituhderodontides, I erceslral stock , ppear first in I range upward prokihcation lIirh skeletalapr- or septimemhents or their hh of the P polffs major con: and content to @ of the Trea*o include in it iodontidae) astte DistacodonE gmups (Pygo*lae ). which are 3a ard Ozarkoz I have found a r &m ies of the r rhe superfamifrlellacea of the iludes some of i aurhors in the r. Prioniodinide i.mbrate apparailbrm digyrate :P positions. EleF tr'ith peglike tsi of the order x develop platl I recognize 34 ie rn r}tis order. followed drme r! Pol;gnatha: large order ineued by sexi-
43
F6hraeus,L. E. (1983). Phylum Conodonta Pander, 1856 and nomenclatural priority. ,Sl,sl. zool. 32(4), 455-459. Hadding, A. (1913). Undre dicellograptusskiffern i Skanejdmte nagra liirmed ekvivalenta bildningar.Lunds Univ. Arsskr.,Avd. 2 9(15), l-90. Harley, J. (1861).On the Ludlowbone-bed and its crustaceanremains.Q. J. Geol.Soc.London 17, 542-552. Hass,W. H. (1962).Conodonts.Pp. W3-W69. In Treatiseon InvertebrqtePqleonlology(ed. R. C. Moore). Pt. W. Geol. Soc. America and Univ. Kansas. Hinde, G. J. (1879). On conodonts from the Chazy and Cincinnati group ofthe Cambro-Silurian, and from the Hamilton and Geneseeshaledivisions ofthe Devonian in Canadaand the United States.0. ./. Geol. Soc. London 35, 351-369. Huckriede, R. (1958). Die Conodonten der mediterranen Trias uod ihr stratigaphischer Wert. Paldont. 2.32, l4l-17 5. Kohut, J. J. (1969). Determination, statistical analysis,and interpretation of recurrent conodont groups in Middle and Upper Ordovician strata of the Cincinnati Region (Ohio, Kentucky, and Indiana). J. PaleonL 43(2),392-412. Lindstrom, M. (1970).A supragenerictaxonomy References ofthe conodonts.Lelhaiq !, 42'7-445. Bergstrom,S. M., and Sweet,W. C. (1966).Con- Pander, C. H. (1856). Monographie der fossilen Fischedes silurischenSystemsder russisch-balodonts from the I-exington Limestone (Middle tischenGouvernemetts.Akad, Wiss. St.PetersOrdovician) of Kentucky and its lateral equivburg,9I pp. Bull. Am. Paleont. in and Indiana. alents Ohio Rhodes, F.H.T. (1951). A classificationof Penns0(229),21 t-441. sylvanian conodont assemblages.J. Paleont. Branson, C. C. (1957). Comment on the Moore/ 26,886-90r. Sylvester-Bradley "Parataxa PlaL" Bull. Zoo l. Schmidt. H. (1934). Conodonten-Funde in urNomencl. 15, 169. sprunglichemZusammenhang.Pqliiont. Z. 16, Branson, E. B. (1938). Stratigaphy and paleon76-85. tology ofthe Lower Mississippianof Missouri, (1950). Nachtragezur Deutung der ConoPanl. Univ. Missouri Studiesl3(3), l-208. Decheniana104, I l-19. donteL (1933). Conodont studand Mehl, M. G. -, ie^snumber l. Univ. Missouri Studies8(l), 5- Scott, H. W. (1934).The zoologicalrelationships of the conodonts.J. Paleont.8, 448-455. (1936). Geological afrnities and taxon- Smith, J. (1907).On the occurrenceofconodonts -, in the Arenig-Llandeilo formations of the omy ofconodonts, Geol, Soc.Am. Proc.Abstr. SouthernUplands ofScotland. Truns. Glasgow 1935, 436. Nqt. Hist. Soc.,n. s.7(3),235-252. pls. (1944). pp. 235-246, Conodonts, 93, -, 94. ln Index Fossilsof North America (ed..H. Stoll, N. R., Chm., Dollfus, R. Ph., Forest, J., Riley, N. D., Sabrosky,C. W., Wright, C. W., W. Shimer and R. R. Shrock). Wiley, New and Melville, R. V., Secretary(1964). IntemaYork. tional code of zoologicalnomenclatureadopted Clark, D. L., Sweet, w. C., Bergstriim, S. M., by the XV International Congressof Zoology. Klapper, G., Austin, R. L., Rhodes, F. H. T., Int. Trust Zool. Nomencl.,Londoq 176 pp. Miiller, K. J., Ziegler, W., Lindstraim, M., Miller, J. F., and Harris, A. G. (1981). Cono- Sweet, W. C. (1970). Uppermost Permian and Lower Triassicconodontsofthe Salt Rangeand d,onta. h Treatise on Invertebrcte Pqleontology Trans-Indus ranges,west Pakistan, pp. 207(ed. R. A. Robison), Pt. w, Suppl. 2. Geol. Soc. 275.h Stratigraphicboundaryproblems,PermAmerica and Univ. Kansas,202 pp. ian and Triassicof lVestPakistan (ed. B. KumEichenberg, W. (1930). Conodonten aus dem mel and C. Teichert). Univ. Kansas,Dept. GeCulm des Harzes.Paldonl. Z.12, l'77-182. ology, Spec.Publ. 4. Fager, E. W., and Mccowan, J. A,. (1963). Zooplankton speciesgroups in the North Pacific. Ulrich, E. O., and Bassler,R. S. (1926). A classification ofthe toothlike fossils,conodonts,with Science 140(3566), 453- 460.
or septimembrate apparatusesu,ith carminate and angulate pectiniform elements (or their platformed analogues)in P positions. The ozarkodinides, which appear to have been the most diverse of all the conodonts, did not appear until late in the Ordovician and persisted into only the earliest part ofthe Triassic. At present, this is the largest conodont order, with 55 genera distributed among 12 families. Chapter 5 is devoted to a description of the principal components of each of these conodont orders and to a discussion of the distnbution and geologic history of these groups. A synopsis of the classification followed here is also included as Appendix A. Apparatuses of typical speciesof many conodont generaare illustrated at appropriate places in Chapter 5, and illustrated discussionsof additional species are to be found in the Catalogue of Conodonts (Zieglel 1973, 1975, 197'1,198 1), of which four volumes have been issued to date,
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5. THEMAJORCONODONTGROUPS
shallow basalcavities,which were assembled by evolvedmembersof most ordersinto elabIn Chapter6 I look into generalfeaturesin the with orate sexi-to septimembrateapparatuses eyolutionaryhistory of the Conodonta.Before ramiform elementsin S complexly denticulate attention can profitably be paid to such airy and M positions and a varied assortmentof matters, however, some attempt must be made pectiniform elementsin the two P positions. to characterizethe major conodontgoups, ilThe stratigraphicrange of the Conodonti is lustratetheir typical members,and point out from Upper Cambrianto uppermostTriassic. tbe featuresthat provide internalunity for each Although the Cavidonti seem to have apgroupand thosethat indicatetheir relationsto peareda bit beforethe Conodonti in the Iate other major groups. Cambrian,the latter diversifiedalmost exploAs notedat the endofchapter 4, my concept sively and were clearly the dominant conof the Conodontais limited to the group disodonts throughoutthe history of the phylum. cussedcollectively as the order ConodontoThere is currently no evidencethat the Conophorida in the Treatise(clark et al., l98l). donti hs Teridontzs) are descendedfrom cavHere,bowever,that groupis elevatedgeatly in idont (e.g., Proconodontus)ancestors,which Cavtaxonomicstatusand treatedas2 classes, might suggestthat the Conodontaare polyphyidonti and Conodonti. These are further diletic. The possibility remains,of course,that vided into 7 orders:the Cavidontiinto Proconthe Cavidonti and Conodontiwerederivedinodontida and Belodellida;and the Conodonti dependentlyfrom ancestorsin the group asinto Protopanderodontida,Panderodontida, signed to the order Paraconodontidaby ZreaPrioniodontidd,Prioniodinida,and Ozarkodi/ise authors. At present,however, there are nida. reasonablestructuralgroundsfor beingskeptical aboutaffinitiesbetweenparaconodonts and 5.2 CavidontiandConodonti conodontsand, on thosegrounds,I haveomitted the Paraconodontidafrom this discussion The conodontsI assignto the classCavidonti (and from the Conodonta).Answersto all of are distinguished by thin-walled, smooththesebasicquestionsaresurelylurking in asyet surfaced elements,primarily coniform, that undiscoveredor undescribedcollectionsfrom formed unimembrateto quinquimembrateapparatuses,most of which apparently lacked Cambrian rocks. structuresin either of the P positions.Cavidonts made their debut in the Late Cambrian (Cavidonti)and (as Proconodontus)and persisted(as Belodella 5.3 The Proconodontida Its Fanilies(Fig.5.1) and.Dvorakia) into the Devonian. The Conodonti, establishedby Branson Speciesof Procozodontus(Fig. 5.2), founding (1938) as a subclassof the vertebrateclass stock of the Proconodontidaeand the oldest Piscesbut here regardedas a classof another conodonts known, built an apparently uniphylum, includesthe bulk of the Conodonta. membrate skeletal apparatus composed of This largeand important stock apparently orig- relatively large, de€ply excavated,smooth-surinated in Late Cambrian forms assignedby faced, hyaline coniform elementsthat harre Mifler (1980) ro Teridontus.Typically, these subsymmetricallyoval transversesectionsand conodonts formed longitudinally striated ele- keelson the anteriorand/or posteriormargins. ments,mostly with relatively short basesand The marginal keelsof some elementsare mi5.1 Inhoduction
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VJNOCIONOJ AHI
THE MAJORCONODONTGROUPS
Lc tanding, and ba.-r Pander, are : Enrll Cordylodr:crts (Fig. 5.2) ih qhich oneeled a.ndgeniculate k to the asymIr Lhepresumed t! :re alsodistinEuses- but the lt ercavated eleb s5on processes E dolabrateelet posteriorpror srooth curYe, tle cuspwith an le denticulated h slieletalcomE orher is a ram-
Polonodus
*E:dae. Fryxello&&iodonridae.
F ryxellodontus
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Cambrooistodus
lapetognathus
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VJNOCONOC IIHJ,
THE MAJORCONODONTGROUPS I b Lindstritm gecimen, which forographs sugrilbrm element y inegularly dislr rbrm equally ibsrrarions of a E Aom the Early na.rm Mitler's E
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riramate and tertiopedateelementsof the Pygodus apparutus form a partial symmetrytransition series,they are reasonablyassigned to S positions.The sprawlingcharacterof the other two elementsis like that associatedin other conodont specieswith P-position elements,hencethey are assignedto thosepositions.That alsosuggests, ofcourse,that the two known elementsin the apparatuses of Polonodas speciesmight atsohave beenoccupantsof P positions,although obvious elaborationof the apparatusin the evolutionofPygodasfrom Polonodusmay merelyhayemaderoom for additional positions.
coniform elements,but the entire apparatus has not yet been reconstructed.Walliserodus species(Fig. 5.3) had quinquimembrateapparatusescomposedof keeledand costateconiform elements,one a symmetricatform with anteriorand posteriorkeelsand interpretedas an occupantof the Sd position.Dvorakia (Fig. 5.3) differs from LValliseroduspintarily in that apparaluses of its two known speciesapparently lackedelementsin the Sd position.Belodella, name giver of the family (and the order) (Fig. 5.3), includesspecieswhoseskeletalapparatusesare similar to thoseof Walliserodus but are distinguishedby S elementswith finely denticulatedposteriormaryins. Speciesof Ansella(Fig. 5.3),principal genus 5.4 The BelodellidaandIts Families of the Ansellidae,built quinquimembrateskel(Fig.s.l) etal apparatuseswith a geniculateconiform In Fig. 5.I (and in the classificationoutlinedin elementin the M position and an S seriesof Appendix A), I include three closely related elongate,deeplyexcavated,surficiallysmooth groupsof conodonts(Ansellidae,Dapsilodon- rarniform elementswith adenticulateor irregtidae, and Belodellidae)in a newly established ularly serrateposterior margins.Elementsin order of the Cavidonti for which I proposethe the Sa position have three keellikecostaeand nameBelodellida.All the conodontsassernbled are triangular in cross section; Sb elements in this new order formed quadri- to quinqui- have sharpanteriorand serrateposteriormarmembrate skeletal apparatusescomposedof gins and a planoconvextransversesection;Sc typically thin-walled, smooth-surfacedconi- elementsare like thosein the Sb positionin form elementswith \'ery deep basal cavities. the apparatusesof most known speciesbut Thoseelementscommonly havedistinct ante- areofbiconvex crosssectionand,in a majority rior, posterior,and lateral keelsor costaethat of species,have no posterior denticles or developfine, needlelikeserrationor denticula- serTatlons. tion in the apparatuses of severalspecies. The apparatusof Hamarod.us(Fig. 5.3) apThe central stock of the Belodellidais the parentlyhad a geniculateconiform M element Belodellidae.Treatisearolhorsassigned,S/a1o-and a symmetry-transitionseriesthat included dus, Belodella, Coelocerodontus,and Walliser- a quadriramateelement with a few anterior odus lo this family. I add Dvorakia (Klapper and lateraldenticlesin the Sd position,and latand Barick, 1983),which was describedand erally adenticulatealate,tertiopedate,and donamed after the Trcatisewas published.The labrateelementsin the Sa,Sb,and Scpositions, better-known belodellids formed quadri- to respectively. Typical of the Hamarodus appaquinquimembrate apparatuses of slender, ratus,however,are a pair of deeplyexcavated, deeply excavated,smooth-surfaced,basically laterally compressedelements with serrated coniform elements,ornamentedby longitudi- postero-and antero-basalmargins.Evidently nal keelsand costae.The latterbearminute ser- theseelementsoccupiedP positions.Affinities rations in severalspeciesbut are undenticu- of Hamarodusarc anythingbut clear.Elements latedin others. assignedto the S positionsare surely not exThe oldestbelodellidsare includedin Slolo- actly like thosein comparablepositionsin Andus (Fi$.5.3), which Lindstr6m (1955)erected sella, which also lacks elementsin the P posifor conodontswith deeplyexcavatedconiform tions. But Ansells alsolacksfeaturesthat would elementswith threeor four asymmetricallydis- ally it very obviously with any other major posed longitudinal keels or coslae. Coelocero- group of conodonts,including the Periodontidontus (Fig. 5.3), which may not be distinct dae(Prioniodontida),whereit wasassignedin from Stolodus,includessymmetricallycostate the Treatise(Clark et al., l98l). Thus I follow
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VJNOOONOS AHJ
THE MAJORCONODONTGROUPS
tinctive pattem of chevron-shapedridges adjacent to the anterior margin. At present,BeJselodusis known only from Ordovician rocks. Dapsilodusis also representedin the Ordovician, but it is probablybest known and most in Silurian strata. typically represented 5.5 OrderProtopanderodontida,New
d
This division of the Conodontaincludesmost of the conodontsthat built uni- to multimemcomposedof longibrate skeletalapparatuses tudinally striated, laterally unfunowed coniform elements. Expresslyexcluded are the panderodontideconodonts,a goup that built apparatusesof coniform and rastrate elements with deeplateralfurrows;and the oistodontids,
JI
whoseapparatuses include pastinateconiform (or "acodontiform") elementsin an array of coniform typesthat is otherwisetypical of the Prioniodontida. With the exceptionsnoted,the Protopanderodontida is the major conodontgroup identified in the Treatiseas the superfamilyDistacodontacea,which was based on the family Distacodontidaeof Bassler(1925). Unfortunately, no one knows much about Distacodus Pander,1856,whosetypesarepresumablylost, or about the Distacodontidae,basedon it by Bassler(1925). Consequently,I suggestthat Distacodusberegarded.asa nomendubium ar.d. that it not be usedas the basisfor any supragenerictaxonomicunits. The name Protopanderodontida, although a mouthful, is taken
Fi9.5,4, The Protopanderodontidaand Panderodontida.The families Protopanderodontidae,Clavohamulidae, Acanthodontidae,and Drepanoistodontidaemake up the Protopanderodontida.The Panderodontidaconsistsof the singlefamily Panderodontidae.
z 9 o G
thca &Components Iosed by Sb, Sc, r elementmay be
P R OT OPAN i
\* r oblique orna;ior margrn. B 5.3) formed rirh nongeniculmenrs in appaFg 5.3) are gens areknown I a relationship raed bv the dis-
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THE MAJORCONODONTGROUPS
n*-ldontidae.
h
a considerable stratigraphic interval from the components of multielement Tropodus Oneotodus,its closest morphologic relative, comptus,tbe type species,as form speciesof and this suggests that ancestryand possiblyfa- Paltodus a\d. Scolopodus,which suggeststhat may be there is still uncertainty a'bout Tropodw in milial assignmentof Pseudooneotodus elsewhere. Lower Ordoviciancircles. (Fig. 5.5)built biSpeciesof Semiacontiodus representedin earliestOrSemiacontiodus, membrateapparatuses. One elementtype is bi- dovician rocks by a number of speciesprevilaterally symmetrical,anteroposteriorlycom- ously assignedto I contiodus,wasprobablyalso pressed,and has a posterior indentation or ancestralto the long-rangingEarly Ordovician costaflankedby posterolateral costae;the other stock named Glyptoconusby Kennedy(1980). elementis asymmetricand hasa costaon only The only speciesof Glyptoconus(Fig. 5.5) that one side.Sometimeearly in the Middle Ordo- has been adequatelydescribed,G. quadrapli:"ician, Semiacontiadzrgaverise to ,S/auferella callas(Bransonand Mehl, 1933),has a multi(Fig. 5.5), whose speciesformed a bi- or tri- membrateapparatusof hyaline coniform elemembrateapparatusthat differed from those ments that have only slightly expandedbases formed by Semiacontiodusspeciesin that the and slightlyrecurvedcuspsthat arequadratein basal part of the finlike lateral costaeis dis- crosssectionand bear prominent longitudinal tinctly notched. Dzik (1983) suggeststhat grooveson the lateraland posteriorfaces. Semiacontioduswas also ancestralin the MidA particularlyimportant eventin the history dle Ordovician to Scabbardella(Fig. 5.5), of the Protopanderodontidae wasdevelopment whose only known speciesformed a bimen- in the earliest Ordovician of the short-lived brate apparatus of strongly compressed ele- stocknamed Utahconusby Miller (1980).Spements, one type of which is essentiallysyrn- ctesof Utahconus(Fig. 5.5) formed a bimemmelrical and hasanlerior and posteriorcostael brate skeletalapparatusof albid elernents,one the other is asymmetricand more broadlycos- ofwhich is a primitive pastinate(or acodontitate on one sidethan the other. form) coniform element. Utahconus probably Shortly after Sezlacontiodus made its debtJt wasancestralto RossodrJ,the oldestdescribed in the very early Ordovician, it apparently memberofthe Prioniodontida.Utahconusmay spawneda stock of protopanderodontide con- alsohavebeenthe ancestorof the Acanthodonodonts characterizedby a multimembrateap- tidae,anotherof the protopanderodontide famparatusof albid, costate,and noncostateconi- ilies. ParutahconusLanding (in Fortey et al., form elements.Landing, Bames,and Stevens 1982) is similar, but its elementsmay bear (1986)haverecentlycoinedthe genericname small nodeson the baseand along the lateral Variabiloconus for the bestknown of thesecon- costa. odonls,V. basslui (Furnish,1938)(Fig. 5.5).In Fig. 5.4I suggest that Variabiloconus may have Lindstom, 1970 (Fig. 5.5),a 5.5.2 Family Clavohamulidae beenancestralto Protopanderodus long-rangingstock of Ordovician conodonts This family was establishedfor a small group with a bi- to trimembrate skeletalapparatus of bizarreprotopanderodontide conodontsthat composedof albid elementswith prominently formed unimembrate skeletalapparatusesof sharp-edgedposterior and posterolateralcos- albid elementsthat are surficially granulose, tae.In the very latestphasein the historyofthe nodose,or spinose.Speciesof Hirsutodontus Protopanderodusstock,the upper margin ofthe (Fig. 5.6) built apparatusesof Teridontus-like basewasextendedposteriorlyand cameto sup- coniform elementsthat developedspines or port a singlelargedenticle. nodesat the base.The basalpart ofcomparable Speciesof TropodusKennedy (1980) (Fig. elementsof Cldvohamulus(Fig. 5.6),however, 5.5), like those of Protopanderodus, formed spread laterally to form a hemispherical multimembrate apparalusesof deeply exca- mound with a nodoseupper surface.Elements (Fig. 5.6),on the otherhand, vated symmetricaland asymmetricalconiform of Serratognathus elements,all of which bear three to firre prom- are anteroposteriorlycompressed,bilaterally inent keellikecostae.Repetski(1982)describes symmetricalstructureswith a knifelike lower
hecrtsuatcereqc r uuoJruoc elqn E AelnJruaSuou EueJl-futouruIfs {Erqtuaurup"nb I) snpolslot0d 'pouad l?qlJo t aqt lnq 'uercr^ qodou.rsm ,{lIeD daro Jo ser3eds [? aJB 1?q1seprs ! -iI:lnJE uB qtra tou IsJuleuu^s tD,r\ suorlrsod d tqol qllr\ bruJ3 eJE^luoru slueu.r g[p eft 13q1su€ rP l:qlo eql u"ql -$ueuele ruJoJI iFeln8er ,tq pellg floqrsod rs pu? [6JPru Jouelsod 3-\?JuOJ ^lpnbA atr a ,{u?rtuosse hmb peJeprsuoc o erauaS 01peuSrss? surluelA B'S't!d
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snqteu6oluras
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VJNOqONOJ
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I nilbrm elements he- One element 4rmmetncal, and k and posterior E bur the cusp is D rie base,which Ii5 Lindstrtim es'ntdodus for elei i !-onvenientto The type k!el. may have -i..m. nrus of a species d henceis not rd this famity. F.d here to the t one another in m:lodu species, hta row of nodes beas an anterior d r}rebilaterally ilalin a speciesis notch Tle family is -srincdve -. *t
Fdhraeus
L<- Paroistodus, Ee of an impornide conodonts ! Lsad the name L-{s notedearlier Edrs is best rei thus is not suitxic categories. E apparently the trnridae, has a rirh a complete .sinctive genic'X position,and qmmencally bi B in the P posi'tr basalmargin b ilaftened, or Eacter suggests mmber of the dEstor. frg- 5.8) had a ronly described rld probably be
THE MAJOR CONODONT GROUPS
55
of recessivebasal margin at the anterobasal corner.Nongeniculateelementsthat form the symmetry-transitionseriesin the apparatusof Paroistodus speciestend to develop bases whose upper margins are drawn out posteriorly. Dzik (1983) and Stouge(1984) have bolh suggested that this processbecamedenticulatedin the youngestspeciesof the genus, P. horridus(Barnesand Poplawski,1973). 5.6 The Panderodontida
Patotsrodus Fig. 5,8, Elementsand apparatusestypical of species assignedto generaof the Drepanoistodontidae.
consideredquinqui- or evenseximembrate. An essentiallyerect, nongeniculateelement with equally concavesidesand sharp anterior and posteriormarginsoccupiesthe Sa position.Sb and Sc positionsin the transitionseriesare filled by regularlyrecurvednongeniculateconiform elements, which are flatter on one side than the other and commonlyhavebasalmargins that are diferent in conformation.M elements are geniculateconiform elements,commonly with long cuspsand much shorterbases. P positions were evidently occupiedby subsymmetricalnongeniculateconiform elements with an acutelyangularanterobasalcornerand sidesthat are almost equally convex. Certain speciesof Drepanoistodusattained an essentially cosmopolitandistribution in the Ordovician, but the genusbecameextinct at the end ofthat period. Paroistodus(Fig. 5.8) specieshad a bi- to quadrimembrateapparatus that included a symmetry-transitionseriesof laterally costate nongeniculateconiform elementsand a geniculateconiform elementin ihe M position that characterislicallydevelopsa conspicuouszone
Speciesassignedto this distinctive division of the Conodontaare distinguishedby tri- to septimembrate skeletalapparatusescomposedof longitudinallystriated,taterallyfurrowed coniform or rastrateelements.The latter are basically coniform typesbut have a few denticles alongthe posteriormargin ofthe cusp.In only a few apparatuses(e.g.,that of Plegagnathus) are denticulatedparts of any elementsdrawn out into distinct processes. In my opinion the major diagnosticfeature ofthe Panderodontidais the distinctive longitudinal fissureor furrow that is developedon one or both sidesof everyelementofthe skeletal apparatus,and I have excludedfrom the order all ofthe conodontswhoseelementslack indication of this feature. This means, of course,that my conceptofthe Panderodontida is considerablynarrowerthan that adoptedin the Treatise. In the narrow senseadoptedhere,the PanParapanderderodontidaincludesPanderodus, odus,PseudobeIodina, BeIodina,Culumbodina, Plegagnathus, Parabelodina, and Neopanderodus. Pseudopanderodus(l-anding, 1979) is excludedbecausethe ostensiblylatestCambrian coniform elementson which it wasbasedhave subsequentlybeen determinedto be representatives of Panderodus that were somehow mixed into collectionsfrom much older rocks. The oldest panderodontidespeciesknown had apparatusescomposedof furrowed coniform elements,and it appearslikely that they were ancestral to species of genera such as Pseudobelodina,Belodina, Culumbodina, and Plegagnathus,whoseskeletal apparatuseswere formed entirely of rastrate elements.Consequently,at first blush,it would seemfeasibleto assignpanderodontideconodontswith appa-
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J99
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I
arppanttusesof Para!lsed clusterofParofPodolia. From --
,4, ro Semiacond- most recently, f Parapanderodus l Tbat assignment E mination of the b in availablecoltar it is surely a lu ir sharessome lrfies of ParapanI a home for it as EE rhat Para.panrs and Poplawski, Fr q?s at least r longirudinally ar sith a broad .drher side by an *r. subsymmetrr furrow on only ltr! and an asymI s conspicuously r tb€ anterior-posldenent, which is Itpears to lack a Eradons, but it Ergitr of the mid3 ro note that that r of this element; imargin in the po7rrsible in figures Ege- and Ethingtognderodus arc t Middle Ordovi cse specresappar-
THE MAJORCONODONTGROUPS
ently containedonly two typesof slenderconiform elements, both of which exhibit a "panderodontfurrow" (or a pair of them) on the posteriorface.The basalcavity oftheseelements seemsto be somewhatdeeperthan that in elementsof P. asymmelricusblot m\ch shallowerthan cavitiesin elementsofyoungerpanderodontidconodonts. Panderodus(Fig. 5.9) made its debut a bit later in the early Middle Ordovician (Llanvirnian or Whiterockian).Accordingto Ldfgren (1978),the apparatusofthe earliestspecies,P sulcatus(Fahtaeus),had a birnembrateapparatusofslender(or "graciliform") and laterally compressed(or "compressiform") coniform elementsthat are longitudinally striated and havebasalcavitiesabout one third ofthe total elementin length.Elementsof both typesappear from Liifgren'sillustrationsto be slightly bowed,and the distinctivepanderodontfurrow is situatedon the outer, or convex,side. Later Ordovician speciesof Panderoduswere determinedfrom large collectionsof discrete elementsto have had quinquimembrateskele(Sweet,1979),and this is also tal apparatuses the casein fused clusters representingPanderodusunicostatus(Bransonand Mehl) from the Early Silurian of Podolia,which were recently describedin detailby Dzik and Drygant(1986). Although certainof the elementsin the apparatus I reconstructedin 1979are nearly bilaterally symmetrical,they are furrowed on only one side and were describedonly as "similiform." Jeppsson(1983)reportsthat there are truly symmetricalforms in his collectionsof Panderoduselementsfrom the Silurian of Gotland, and a few have also beendiscoveredby Britt Leatham, one of my students,in the large collectionson which I basedmy 1979reconstruction. Thus it is appropriateto conclude that the apparatusof fully evolved speciesof Panderodus was probably seximembrate although,as Dzik and Dryeant (1986)note, distinctionsbetweenelementsforming the S series are commonlydifficult to make. Panderodusrangedthrough the Silurian into the Devonian, but information on the species representedis sketchy.Indeed,specimensare illustratedin only a few reportson Devonian faunasand Silurian forms have receivedless than adequatetaxonomictreatment.
The youngestmembersof the Panderodontidae are late Early and Middle Devonianspecies ol Neopanderodus,which apparently had apparatuses like thoseof better-known species of Panderodusbut composedof furro\ped coniform elementswhosesidesaremarkedby longitudinal striaethat are more prominent than thoseof Panderoduselements. The oldestrastrateelementsknown are from early Middle Ordovician rocks of about the sameageas the onesfrom which the earliest Panderoduselements haye been collected. Opinions vary as to the genusrepresentedby theseelements. but I regardthemasspecimens of Belodina.Later, better-knownspeciesof ,BeIodina (Fig. 5.10)formed trimembrateapparatusescharacterizedby three differenttypes of rastrateelements,which are separatedprimarily by differences in their radii ofcurvatureand the number of denticleson the posteriormargin. One elementlacksposteriordenticlesand is formally coniform. In 1979| describeda sequenceof speciesof Belodina and noted that in younger and youngerOrdovician stratadenticulaterastrate elementsbecome more numerous and coniform ones proportionatelyless so. However, one Late Ordovician species, B. calciprominens,is known only from largeconiform rastrate elementsof the sort onceincludedin the form genusEobelodina.Although specimens assignabletoBelodiru are known from rocks of latest Ordovician age, none has yet been recoveredfrom the Silurian. Pszudobelodina(Fig. 5.10)hasa quadrimembrate skeletalapparatuscomposedof deeply excavated, laterally furrowed, posteriorly "heeled," anterolaterallycostaterastrate elements.Threeofthese elementtypesare bowed to the unfurrowedside and form a symmetrytransition series;the fourth, which may have occupiedeitherthe M or oneofthe P positions, is straight or is bowed slightly toward the furrowed side. The oldest Pseudobelodinaknown to me is an as yet undescribedspeciesfrom Middle Ordovician (Blackriveran) strata in North America.Although elementsof this unnamedspeciesareall denticulalerastrateforms and thus morphologicallysimilar to comparable elementsin the apparatusof Belodina species,thereis no coniforrnrastrate(or "eobelo-
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'pue Durpopqopnasd ro Dutpopg tufua_Euol oJourJo seoedsJo asoql ur peledrcrlu? lou el? sasnleJ"dd?JreqI .sluopouoc luopolapuzd eql lI" Jo sosnl?Jedde,tluo-etejlseJ et?roqele lsour eql outpolaqD]Dd pue snqpu8D&ald l[nq 'slueuele .uuoJruoc e13[n34uep3 lou 'aleJlseJ peTeoqelB 1?q1slUoUOduJOrqll^l lnq mpofipuod lo lEql 01 r€lrutrs ,{lp?orq snl -?JEdd?elHqr.ueurrnburnb ? pauJoJ ,?ouo(uv IIUON uJelso^t uI $[JoJ uErJr^opJO Jeddn uro{ ,{luo u^{o(Dl osp ,(01.9 .B:.i{) Dutpopq -zlrd'seuos uonrsuB4-fuleuruj,{s ? uJJoJl"ql seuo pelElnrnuop,{TeloJcsrp .el4soc eeJql pue 'ePIs pe/yrorJnJun oqt 01 pe^\oq ^lT?Jolel euo 'eprs po^\oJJnJ eql pJEltrol pe^\oq euo .slueuJ -ole eleJlspr lcuq.srp,{flec€oloqdJour a^gJo snl -"Jedd" plele{s e s€q .e3ueurv qUoN urelsa,n ur 4el1s u?rsr opro JeddIl ruo{ rE snql u^\oDl sr gclq,r\ ,(0I.S Etg) snqpu7o&al4 ^luo 'u"rcr^opJo elpprtr eql ur lerlJee qJnu l I.'ols snpotapuDd eql ulo{ peleul8uo o^eq feru qcrq,rr 'oulpopg uro{ lou pue snpoap -u0d wo$ ,([poJrp pedole^ep Durpopqopnasd leql lr {uql I ,,{JluenbesuoJ.slJor eruEs ^le{rT eql ur peluoseJdeJ eff qcrq/h ,ossatdu,toJ .B pue stsuatoluour outpopg Jo esorllpue sersods ' aurpolaqopnasd srrll Jo slueruele ueo^ueq uJoJ uJ uorl"patJolur sr eleql qJrq,{\ ur suorpelloJ uaos lou e ?q I pue ,luourele (,,r.uJoJrurp
'oEprtuopolapuedeqtJo EJouoB snouE,rol peu8rssesarcods Jo lecrd^l sesnlerBdde luaqroJo-olDrlsEx .0I.S ,i|!J
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89
THE MAJORCONODONTGROUPS
versityin shallow,tropical,or subtropicalseas. 5.7 The Pdoniodontida Dzik, 1976 Panderodusitself has a somewhatmore cosmopolitan distribution,but it seemslargelyto This major division of the Conodonta (Fig. have been replaced in higherlatitude Ordovi- 5.1l) includesconodontsin which one or both cian faunas by Drepanoistodus and, farther ofthe P positionsin the fundamentallysexi-or poleward, 14alliserodus. Specialized pandero- septimembratecephalicapparatusare occupied dontids, with rastrate-elementapparatuses, by pastinateconiform or pectiniformelements were orimarilv low-latitude forms. or their platformedequivalents.In a few spe-
Fig.5.ll. Ordovician and earliestSilurian families and generaofthe Prioniodontida.Later Silurian and Devonian reDresentatives of the order are shown in Fis. 5.17.
s
e
a t
Parubelodina to bergsand and i-ndepenies all have
apparatuses. I interpret it,
e I
l
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fl\ il\ e
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i 3
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\
of heeled,
multicostate to$ bowed tothat reptave denticles including mostof ttrey may be
s
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PERIODONTIDAE
II
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il
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the
of Culumbodishedinforlit €arlierin the America, early part (EdContemporary
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.
which must
group. panderodonts seem to have and di
il\
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',{ua3ol^qdluoJeJrpDqlel e pelsea8nss?q (tg6l) sne?lqeCpue .r?el3 lnq Suq u? sr spuuopourr u€ruo^eo pu? u?unlrs relel pup sprTlopousr u?rrnlrs-prhl ot flJeg pu? u?rcr^opJouae,{rleq dqsuouElal eql 'Je^e^roq'e"puuopouJl oql Jo uorssnJsrpful ur polou sV snuet peueuun u? lueseJdel ^[qe -qoJd pue snqnuSslqalad uro{ ,tlluepuedepur pe uap eJe,tiopnlcuoc(?g6I) uesaelopu" SJeq -pues,^rcqt,,snpou4,, upruo^ec elsl Jo serceds praaes Alqeqorder? ep[uoporuoud tsetuno^ oqJ '$[cols e^rl3urlsrpJo roqurnu e ol pllssc -u? aq 01 r?edd?pu? sacuoJJnmo uersr^opJo Je^\o'Ipelu0rrJnJop{le^\'p€eldsepr^\ peluos ^q
VINOCONOJ
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THE MAJORCONODONTCROUPS
6l
Eumented Lower 4pear to be anaive stocks.The ' probably seYeral 'r*J'that Sandbde werederived lalus and probEus. As noted in rDdae, however, ncian and Early rd tater Silurian fu alything but bs suggesteda
alstrom, 1970 rodonts with a ieletal apparatus
Protopttoniodut Fig. 5,13.
*rudae.
Oisaodus
Elements and apparatuses typical of species included in three genera ofthe Oistodontidae.
Drawings
of coniform elements,of v/hich one (P) is pastinate (or "acodontiform"), one (M) is geniculate (or "oistodontiforrn"),and the rest form a symmetry-transition(or S) series,which,when completelydifferentiated,gradesfrom an alate ("acontiodontiform") elementin the Sa position by way ofa digyrate(or "paltodontiform") laterallyunornaSb elementto a compressed, mented nongeniculate ("distacodontiform") element in the Sc position. Conodontswith such apparatuseshave been included in Rossodrs Repetskiand Ethington, 1983,Acodus Pander,1856,TripodusBradshaw,1969,Diaphorodus Kennedy, 1980, OelandodusYan Wamel, 1974, Protoprioniodus McTavish, 1973, OistodusPander, 1856, and probably JuanognathusSerpagli,1974,but it is not clear to me just how many generaare really repre(Fig. 5.12) may not have a sented.Rossod?rs fully developed symmetry-transition series, henceits two known speciesseemprimitive. (On the other hand.the "acodontiform" P elements and "paltodontiform" Sb elementsof Rossodasmay be so similar that they havenot beendistinguished).Furthermore,if the skeletal apparatusof the tlpical speciesof Juanognathus (Fig.5.12) includesa geniculateconiform element (Serpagliwas not sure about this), Juanoqnathusis probably a senior syn-
onym of Rossodzs,as noted by Repetskiand Ethington. Tripodus (Fig. 5.12) and Diaphorodus are basedon different, but probably congeneric. species;hence I regard them as synonyms. Therewill probablyalwaysbe uncertaintyasto how Acodus (or many of Pander's genera) shouldbe interpretedin a multielementsense, so I recommendthat Acodusbe consignedto the list of nomina dubia and that we go on to more important things. Oistodus,Protoprioniodus, and Oelandodus, all shown in Fig. 5.13, include specieswhose skeletalapparatusesare composedentirely of geniculateconiform elements,which neverthelessexhibit an arrayof forms closelysimilar to that in the apparatusofspeciesofRossadzsand Tripodus. ln lhe Treatise Bergstrdm expressed the opinion that furtherwork might showthese threegenerato be synonyms,and I can seeno very goodreason(asidefrom the geniculatenature of their coniform skeletalelements)to refer them to a family separatefrom Rossodzs and.Tripodw. Consequently,in the schematic classificationin Appendix A, I group all these generain the family Oistodontidae(which has priority over Juanognathidae), btt rcfer Oistodus, Protoprioniodus, and Oelandodus to a subfamilv Oistodontinae: Rossodus and Tri-
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V.JNOCONO] AHJ
l'zpodas. It is also &znae represents lhent from either bcauseit is sepa'frovician from I gpical HistiodEi describedonly q,dthough he now iulate coniform
?B2ssleL1925 t just above the 'ls debutare con*ehral apparatus r are occupied by Enate elements res: rhe M posiictrlate coniform irnally a bipenit an elongate, r pnocess;and S Eition seriesthat &re. alate, and clear that t-EDs Prioniodus PanI fnpodus, fiorn , in a somewhat rarus in which ttr out into denfr rhereis alsoa
Amo.phognathus
Fig. 5.15. Elementsand apparatusestypical ofspeciesassignedto generaofrhe Balognathidae.
greaterdegreeof morphologicditrerentiationin the S series. Prioniodus(Frg.5.14)developedphylogenetically through a successionof similar, biostratigraphicallyusefulspeciesin the Earlyand earlyMiddle Ordovician,and in rocksa couple of zones above the one in which it first appeared,spawneda new lineage,assignednow to Oepikodus(Fig.5.l4). In speciesofthe latter, the skeletal apparatus consists of Prionioduslike pectiniform elements;a geniculateconiform M element;and a symmetry-transition series of quadriramateelementslike the one in the Sd position of Prioniodus.
groups of elementsthat representa phylogenetic seriesofconodont speciesreferredto Baltoniodus(Ftg.5.l5).Species of Baltoniodus arc distinguishedfrom thoseof Prioniodusby morphologicallydifferentpastinateelementsin the two P positionsof their skeletalapparatuses. Although this is regardedas of no more than subgeneric significance by severalinvestigators, others have pointed out that Baltoniodusappeared a bit later than Prioniodus and also probablyevolveddirectly from a youngerspecies of Tripodtts and not from Prioniodus. However tbis may be, Baltoniodusis the universally acknowledgedancestorof Amorphognathus, which appearedin a somewhat later part of the Early Ordovician and ranged, Hass,1959 5.7.3 Family Balognathidqe lhrougha succession of distincivespecjes, to Beginning in Lower Ordovician rocks just the end of that period. above the onesin which Prioniodus is fitst recSpeciesof Amorphognathus(Fig. 5.15),perognizedand extendingupward into Upper Or- hapsthe best-knownand most widely distribdovician strata is a successionof recurrent uted membersof the Balognathidae(Balogna-
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snl"JEddv 'snor^qo lou aJ? sJolsecueJealc 'os ua^o :..4EJquraurlco,,flrul 1ou pu" uorlrs -od eql ur 3rgfuourp eq l(?ul snlEffdd?oql l I 'od"qs leplur?J,{d Jo sluourala (IIJoJ ^l,r\oJl"u -ru?r el?.rq?loppue 'elepedoruel'olel? leuorl -?p"r8relur,{llmrtoloqfuourJo seuesS ue puE :suoDrsodI J ur slueuele el?uuodrqJo Jred E pue etErqelop ll?d p :uorlrsod puocesaql d Jo uI sessecordpolqnrquep oAu qll^r Eueu] ^luo -sleet€uqspdo{qep?Iq:uoqrsod d ouour sosset -oJdpalencquepearql qlh{ slueluoleoleuus?d epnlcur'(Sl'S tuJ) mqpuStrlrout"g Jo sercads o,{\ls?(0861)seuJ?gpu? 'u?l^{oN'ualc?lccw pelarfuelur 'slueuIele u?ror^opJo el?.I ^qsad^le^rtcu[srplqEreJosdnoJ8lugJJnceu Jo 'e3" $[coJul ^u?Jo papJoceJ?unq luopouoc opnlrleltseqArq eql ol xapuruE eq ,(?ur'seesJeJodqns uI pelrsodep .(lqeqordare^\t?ql $[rol u"rJr^opro elE.Jrrro{ u^\oD[ sr \an]rn 'Dutuopotll8rs' teql tseJol -ur turss?duzql eJoruJo i(Frsum sr lr qtnoql l? 'uolssncsrpJequnJlueru ol u,rdou)lqEnoue llatyi ouuuopoltr8Ds rold snpoxa4uoJ Jeql 'e€prqleuSoleg -leN (2861) souJ?gpue s$perJaIN snwopo eqt ol pau8rcse ereuo8Jo serJ stueurolo lu]oJrurped '9I'S 'tld -ror\. Jo ru,{uou,tsJorues? sl'(€g6l) -edsJo cusuelJ€Jeqc ^lq?qoJd urotsEreg ,{q palcnrlsuoceJ se 'qorq^\ (gI'S '8lC) reJdnel Durluopo rSDssnue8tueuleleq eqt ot reJerosp '9I etelqurJurq perl sluopouoJ qlr.r Surl?ap lnru eq1aeprrpzuEopg leql I S 'ArC ur psl?rlsnll puE TI S 'ErCJo oeprqleuSo erar\ eA{ pe^oqeq pue urorlstreg '9961 ur 1 lEg er{t ur pepnlouros[? s 'snqtDuSoqdtoutv snqpuSosapoqy peqsllqetse e^\ ueq1,!\'urolls l"ql Eueul -8reg,(q peJedeJd uorl?cu$selc astpatJ eq! Jo osoql (uro{ JeJIplnq) elqureseJ -elael?qdecsruus?d slsrsuocsnleJ?dd"elaq rn pelllE sr tr qcrq \ qlr^l' 'snqtDuSotldtowv Jo Jo -ruourrun esottr^..'nl:ruo8ndsnpoxaldwoJ luspuecsap ? sr snueEeql ,{le{ll eJoru sr lr '(9l S 'AIeIrl SJOrrr 'el1) snqJDuSosapo?yJoJolseou?eqt sz snporu '8rC ul ue e sI snqpuSosap seguuepl (t861) sneErq-?Cqtnoqllv $qt -a{r8r II S I ^1oqsueer':l.?3q 'dno$ tuopouoc lu?Uodurr sql ,{q pe^orqc? -ot1y pue snqlouSoqdtouy drtlsuo]4el -0Josolcaql uoql 'es"c eql sr l?qt JI 'paqsqq?l uollsuuaJe.grp Jo elceuurd eql lueserdeJ -ses?.{isnuo8aqt ueq,$otp sr"e,(0Z pezq?nsr^ snrll puB eprluoporuoud Jql lle Jo sJsnleJEd e/,A euo elErquraurq oql Jo peolsur snl -de xelduroJ tsorlr eql pEq seoeds snqpuSolld Jo -rxesE seqsnqpuSo 4OUy ..'utroJ\aopopqurelt pue .,r[JoJrql"u -?J?ddeel?Jqureunrldos -sapoqYftqt pue 'elqsqsrnBunsrpur oJemqpuS -Soqd:our?,,petuJel eJ?eJnl?Jelrllueuelgrllntu -osapoqv pue snqpuSoqdnlutl sluouela Jeplo eql ur qJrq,r 'slueurele olEqd?Jsrun Jo (I uo^e illqrssodpue) ,4aouoA\ pf,utaurur,(sE ,(1pre1elq 'purlsrp ,{ ?Jr f?ql tcedsns -s?d I S snql'Ja eqlJo e^rpuEsrp$ueurelapeurJoJ -8oloqtuou perdncco era,{ suo[rsod d -l€ld oql "l lrrg 'snqpuSol4rowv Jo asotfl o^r1 oql pu€ ^qstuauele (,,uuoJr1uopoloq,, Jo) Icel elquaseJ1?ql sluauale rrrJoJrursJ epnlcul oslE alepodorUet e!?zrq eJoq uorlrsod I I oql q3rq,r l"qt seldul?seurosu rnxxo snqpuSosapoqUJo ur 1nq 'snl?Jedde snpotuo og oql uI seceld cusuep?J€qosluel'ueleel?urlsedeql're^e,{ioq J?IuIIs ur esoql 01 elqeJuduor slueluele rruoJ 'sluepnts Jno rel?I polqurass€suorloelloc -ItrrEJpopnlcur suo[rsod S eql qcrq.r ur sesnl ^q uI'stuoluele(..uuoJr1uopopque,, Jo)el"ur1sed -uedde lEtelols elerqruaurrldes'el€roq€lo p€q IeJuleuruj^s,(U?Jolellq'pelted Jo sesnl?J?dde '(snwDuSoqdnLuv Jo [u,{uou.{sJorunt e s sm.lt VINOOONOJ
AHJ
THE MAJOR CONODONT GROUPS
zll) symmetrical rm") elements.In b our students, Ets characteristic me samplesthat s rhat resemble h lack the platJthe latter.Thus lnssibly even M) u ar:rd.Rhodesoad rhat RhodesEbrate appara*ale one we rte genuswaseslea the closeregm.hus ar'd.Rhoh: 5.1I is even rhose unimemniniscaphate eleE rom) thoseof bded in the Balibstrated in Fig. nhidae the mulir Ihiipfer (Fig. d bl Bergstrdm ;mn1m of Norr( 1982).NeiE dontina is welL Er drscussion,alr rtan passinginrticb is known lu *ere probably t!- be an index to t fruna recorded hlctive typesof interpreted by G ( 1980)as two ft. 5.15), include rdendcuatedprofte pastinateelehed processes in d dolabrateand r in M positions; i:Ily intergradaI dolabraterami6ramidal shape. [ic in rhe M pofrate"; even so, rrus- Apparatus
65
stuctureis, in many respects,more like that of Prioniodus than Baltoniodus species,but the speciesmost proximate stratigraphically is an unnamed representativeof Baltoniodus(Savageand Bassett,1985;Orchard, 1980).Consequently,in Fig. 5.11,Gamachignathus (includ.ing Birl<sfeldiaOrchard, 1980)is included in the Balognathidaeand shown tentativelyas a descend.antof BaItoni odus. 5.7.4 Family lcriodellidae,new I interpretlyiodella Rhodes,1953as the stem of an important prioniodontide stock that probably also incltdes Pedavis Klapper and Philip, 197|, SannemanniaAl-R.awi,1977, and SteptotaxisUyeno and Klapper, 1980.In the Treatise all these genera were included with Icriodus and.Pelekysgnathusin the Icriodontidae,primarily on the basisof obvious sirnilarities in the Pa elementsformedby their species. Many of the other elementsof the apparatus are different.however,and the differencesare questionsasto the sumcientto raisereasonable relationship belween l%iodella and its probable derivatives and the primarily Devonian gnathus complex. Thus lcriodIcriodus-Pelelqts e//a and its kin are here set asideas a new family, the Icriodellidae,the relationshipsofwhich ICRIODELLIDAE are shownin Fig. 5.17. DISTOMODON TIDAE Basically.the icriodellidshave a quinquimembrateskeletalapparatusin which the Pa elementis pastinatein the apparatusofthe oldest speciesknown, pastiniscaphate in thoseof later forms, and stelliscaphate, with four processes,in apparatusesof the youngestspecies Fig.5.17.Silurian P oniodontida. andDeyonian known. The Pb element,in apparatuses of the Icriodella (Fig. 5.18) and Pedavis(Fig. 5.18) speciesfor which it is known, is a pyramidal ate, wilh adenticulateor faintly serrateedges. pastinateelementwith three sharp edgesthat In apparatuses of species of lcriodella (Figare adenticulateor only weakly denticulate.I 5.18)the occupantofthe Sapositionis a deeply interpret the "coronellan" elementin the ap- excavated,pyramidal alate elementwith minparuttrsof Steptotaxrsspecies(Fig. 5.18)as an utely serratedlateral processes,whereaseleoccupantof the Pb position,primarily because mentsin otherS positionsarepyramidaltertioit is related morphologicaltyto the pastinate pedateunits that are closelysimilar to the Sa coniform (or "acodinan")elementsassignedto element,but asymmetricwith respectto disthal position in apparalusesof various icrio- position of their lateral processes. S positions donts.Theapparatus ofthe only knownspecies in the apparatusesof Pedavisspecies,however, of Sannemanniais unknown, are filled by elongate,prominently costate M elementsoflcriodella, Pedavis,and prob- structuresthat apparenlly are nongeniculate a.blySteptota-xisare bipennate or even pastin- coniform elementsin the Sb and Sc oositions
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shopad Jo uo4eAUsPeq pFo,r lFseJ ftolc souo eql Jo lEcrdi(l uoueuuoJuoc o^Eq 'Jo s eql 'esecsql ur euop orea\leql JI slueuele -^\oq 'sar3odsosoqlJo sosnpJ?ddE"aqt ur slueu ed ur seuu"Frrnsol lq8re^\tsel?eJEpepJocce €13 Jeqlo (9861 Joqrsrg) st^opad Jo esoqt JAEII sluopouoJ Jo sluepnls lsorrl 'sdlqs 01 JeFrIrs eru l?ql slueruole el?qd ^TqalJeurer turssess?ul luopourol -Ecsr[a1s,(q pardncco or? -uoqpleJcrleuaSol,{qd Jo uerJnl "ll"Jlsnv esJo sesnle:sd -srp,(lJpelcoJ?suogrsodS pu? 'ni 'qdJo sluEd -rS Je^\o'I eql uro+ sercedsI?Je -ncco perunseJd1"qt lftq 'shDpadJo sercedsKq -de eg1 uI suortrsod ed sepouJo s.{or el8ursJo peu oJ osoql ol esolc fue^ ,{llmrtoloqd:our srz rrroJ aql ur sr uowFcrtuep lnq 'J?[ ^Ilu3pr^e mpowotsle ot (996I) Joqcsrg,{q poutrss?sert -rurrs eJ? ,rllasar,sad oruuouauuDs Jo stuewele -odsJosluourele?d teql palou i(p?eJlee^eqI ed ',{lJouelu€ tEq^ietxos popeuop ,{luoruruo3 'o apouJlJo esoqttllolJ luareJrpalrnb eJe l?qt (seuo pra1e1 eqt) oMt pu? selcrtuep .re srtDpadJo slnerrrolas pue 's?.1rpadJoosoql Jo olqnop e qlft\ euo lseol le 'sasseJordelEI ^\oJ uro{ ,{lq?reprsuocJeJrp stxrrotdars' Jo sluaut -nJnuJp rnoJ qll,{l sJruJruls elBqdeJsrllats ? -ole ed-uoN eepr1uopouoler+Jo snqwu8sblal sluerrlele ed qsrq&r ur sesnlerEddz ,{q peqsrnB -a7 o1peu8rsse {leur8uo oJeaserJads clls olce -uusrp or? (gt'S 'ttg) srarpad Jo serceds 's3lJ4uep -J?gc erour slr Jo ul?ilec qEnoql ue^o 'l(lrlu?J srql ol srxotofiats tfrrss€ol uorsrcep purqaq uoqs Jo ,{1or alqnop ? sJ?eq pue ssecord 's?drpad osp $ EuruosEer J?TrurrS serJads,(q rouatsod eql u?gl Jetuol l?q,$auos sr slueuJelo Jo^tu pourJoJl?ql 01J"lrurrs,(lesolcsr sorcodsu^\oDI ed Jo ssecoJdJorJelue eql 'ta^et^otf'o apouJl ,(1uoslr Jo tueurela?d aqt esn?ceqpepnlJur Jo serceds Jaqto II? uI ssecoJd Ieretq elsl sr Dluuotaauuos'sorJedsu^\ou) slr II?Jo sasnl -ncquepE loqs pu? 'salouuepJo s,{oJ elSurs " pue Jouelu? lenbeqns -EJ"ddeur suoqrsodW pue 'qd 'ed eql ot uErs qll{\ sossocoJdJouelsod esolcJoesn€J 'dsnc pprruEj,td '^qqnts ? s?q lueluele ?d el"un -sEI sluaureleueealeq ^luelrurs -eq oeprTlepouJleqt u D apouzl qlIlA pepnlxur -s?d aql 'paqucsop reJ snr]i Dnapoull Jo ser.eds s'[ slnDpad'esprluopolJclpue'eeprluopourol lseplo eqt 'tl61 'dJueH puu nooqaqs€ll 'urolls e^?q -pul'l xoJaofi o apol./4 Jo snteJedd" eqt uI -sIC 'e"p$opoucl eqt Auouls1nopelecJed 'uoucas ssol' l?lncJrc ,{ ?Duesse 1 eraua6eqt Suolu?sdrqsuonElarorteuetolfqd JlqrssodJo Jaqunu ? JlsJrpur I LI S 3ll ul Jo slueurela rrJoJruoc ele{nrrue8uou'el?lsot" 'snpoulolsr(J ,{q perdncco ,(lq?urnseJdora^\ suonrsod S (8I 'S ol ueql peuftss?s?q(986l)Joqcsrg pu?'e?pp 'fiC) sercedsstxDtotdats uI 'uonrsod ES aql uI -uopourolsrqeqlJo sebodssnou?Afq pourroJ sluelllele alErq?lop elelnJrluep,(lJouelsod lnq VINOCONOJ 3HI
THE MAJORCONODONTGROUPS
'te Distomodonrsigned them to nber of possible mg the generaI hiodellidae, Dis*b.e. Pedavis is RlcriodellidaebeEtr elementsI asriions in appara. &.nnemanniais of its only -mro that formed L :Easoningis also Irz'rol&rts to this f its more charl-r assignedto Pel=- Non-Paelexiderably from s of Pedavisarc bidella. ldements ofspeilto Distomodus Rtorhoseformed I lresumed occur are clearlydistEreric relationuodonts haye fuilarities in Pa rhis case,the lbn of Pedavis -
Rotundacodin6
Distomodus Fig. 5.19. Elemenlsand appamtusesofspecies typical ofgenera assignedto the Distomodontidae.
ftom Distomodusor some other genusof the Distomodontidae instead of from lcriodella. To my mind, the prominentlycostateelements that occupy S positions in apparatusesof Pedarls speciesareequallydifficult to derivefrom either the Icriodella ot Distomodus stock and may thus be regardedas the featuresthat distinguishPelavis.Thus, if one considersthe remaining elements(Pa, Pb, M), similarity is greatest between Pedavis and lcriodella, and that hasguidedme in assigningPelavls to the Icriodellidae. Broadheadand McComb (1983)arguefrom comparisonofthe Pa elementsof Itte Silurian Pedavisand thoseof latest Silurian-earliestDevonian Latericriodus woschmidti that the latter may have developedfrom the former by neoteny.Althoughthat is an attractiveidea,non-P elementsin the apparatusof L. woschmidti (Fig. 5.20)differ substantiallyftom thosein apparatusesof Pedawsspeciesand, in the absence of information on the ontogeneticdevelopment of the latter, it is difrcult for me to see how S elementsof the supposedpaedomorph (L- woschmidtl)might be relatedto earlierontogeneticstagesofancestorsin PedavtJ.Never-
theless,I indicate in Fig. 5.17 the possibility thal Pedavis,whosefamilial assignmentis not all that certain,might be the point of origin of Latericriodusand the lcriodontidae. 5.7.5 Family Dislomodontidqe Klapper,I9EI Conodonts assembledhere and assignedto Distomodus, Rotundacodina, and Coryssognathushaveabasrcallyquinqui- or seximembrate skeletalapparatusin which ramiformcomponentstend to haveshort,weaklydenticulateor adenticulateprocesses, and the Pa and Pb positions are occupiedby stelliscaphate and pastinate elementsor their reducedderivatives. The latter characterprovidesa link with other prioniodontideconodontsand suggests origin of the Distomodontidaein Late Ordovician balognathids such as Gamachignathusot Sagi odontinq. Thereis someditrerenceofopinion in the literatureasto the apparatuscompositionof DiJtomoduskentuckyensrBransonand Branson (Fig. 5.19),type-species ofthe stem stock,and this afects interpretationsof familial taxonomy and phylogeny. The apparatusrecon-
ffi E aarppel[ /$ol g) snpouJl 'Jet nnualo'J euJeu t 3ql roc 'sluelx D pue 'sluelxele Frruoj l€ql euo snPouJJ IO tJOrS p{e aSlppolN qlrur?J pelslnJrl I alqEu?^ leqleJ @rsod Jeqlo ur td eql uI slueu @s ,tleJeur Jo 'aE rqrlreunFul trE sluopousl IlaueJal ^lsnol^ peseq lnof e uo ne5 .{q spuno$ .snue8 peu?u rydr1 snqtDuSol plrd 01 Peu8lsse uEdde o,trl :8€6I
I :2961 'rellntl qr uI pepnlJul l9 6l pI .illraDl 919
'1rJOJOUolueSSoCOJO -JolurI snql 'Suuodruocpug I lEql ecuepr^e pel?JFnllrI?JeAes puonnqutslp Jo ,{poq8ul,{{or8pu? pquelsqns uoqs /fia^ € eq ol suerursads ur srEeddesJeqlpue pus JorreluEeql 1?fFeelJ E uo pas"q /aou sr (986I Soqcsrg 'E e) sroqlo petmo^pE sarc sr dsnc aql 'pueq Jeqlo eqt uo 'sluelxela.rz1l,1,(q poloddns pue JsdooC ^q Jo uorlorulsuoc -ouSosstto) uI 'pue ro elsod eql 1? dsnc eql -eds-ed,{teql Jo snlaedds eqt qllll 'el?gd?csururEos oJesnuet lsqlJo sar3eds -er 're^e,lroH'Woluotst(J lmrd{l e sE poloJd ,tq peuroJ slueuele Bd nq 'snqpu8sbppd -relv sl snrqnp DulpoJopunptrJI i(luo esues e luoseJdeJ slueueleasaqll?ql pelset Jo l"ep poot ? e{Er[ sluelun8J?s.uossddof Jo sorcads 'y461ur [qd:n11pue -8ns seq uossddofslodeJ snoJeunu uI '.ffiq -np DurpoJDpunJo{ petcutsuocoJ snleJedd?,srcua[4Jnl Jo slueueJJed pJgrldurs Jeddef) ^q Jo sluauodruoJpeuroJl"Iduou eq1 qcnur eql uro{ pe^uap uaeq e^?q ,{lrs?o1q3[u -u l 'e eq! l?ql llos ? Jo ssocordIeJelelpedole^ep,{Food ot esolc,fua^,(Ilm€oloqdrolu eJ?leql sluorx e rllr^\ sluelueleuuoJrurlcedel€u4s?dpoJnp -olo uuoJrrrruJpopnlcur lnq slueur ^lluar?ddE .{u? pe{Jel e^?q -er eft eseql'peqrrrsep uaeqe^eq (6I'5 AId) -ele uuoJrurl3ed peurJolqd snqpuSossttoJ Jo slueruole ed eql ol srrjsas'snpoulots!(IuI sepnlcureq qclq,ll .eup4uopoFcl ^luoeql '(6I 'S tld) (sepoqu) .flrqrp outpoiDpunlov snl?rcdd?eql l?ql setoueq Jo lcots luJls$u" s?leq lseqeqt 'uorurdofru ur usunlrs JeAuno,(Jo 'sr pu" u?rJnlrsaqlJo pue oql ol se8uerDutpoj 'ler{unC'sssn}pJedde lueJeJrpelmb osr^ueqlo ,{q pozuopeDqc '$lcols epnuopoluoud tue -Dpunpv ,{uetoeu,(q peqsllduIocce ^lqrssod suorl pedolo^epslueru o,1dl ur 's$oqdJouropesd -Jeigrp Jo eldu?xe ue eq ,(?ur ^lluapuadepur lpqt slse8itnss8uablJnt -rsod o,{rl gsogl uI sluguola Jo uorlscurTdurrs -eIe d a]{]{-Dapolrrl cqeueEol,(qd,(le^rtcedseJ'sluourele rsroJruoc -uDl O toJ (516l) JedooJ ,{q pelmo^p? ouo el?uus?d pu" al"urlsEd eldturs oJe suoqrsod arll sEqJns uollJrulsuoJJrE lEql 'otdulexJJoJ qd pue ed or{1(n osolq..l frq'snpouotslQ Jecld^l 'salouuossddof'uoDrsodd puoceseql ur luour Jo esoqtJoluecsruruerer? (6I q '49) mlqnp g -3le ol?qdecslllelse tnoqlrA\ ouo 'sI teqt '.{qd Jo snl?redd?eql ur slueuele lN pue S 'snpour -JntrJ pu? reddEIX,tq paprutsuo3eJAlpur8uo (6t61) srcuallinurl -ols?OJo Iecrd& oq ot loot snpou.toiste Jo snlEJedde oql ^OuelEdde uossddef sercedseW 'snlqnp Durpo1DpunloY sroJord (6/61) uossddof 'suos€arlere^esroC 'ssunsJluopouocu€unls qlr/t\ ol le]lseJu" se/;t.snpoutolsre 'iJot pu? 5lcolua^\aql ur AIr?elJe Suqeepsroqln? lsoru ,4qsrseqNW uo snporu -sq str uI olel^nuarcdd? 'snqpuzparaJeJ pu? suorlrsodI ol uoJq s?q -orsro -oJpDHsE pogrtueprfleurtuo esoql s? q3ns pu? s eql ur slueureleruJoJrrrr?J e\rI-snpouol sluerxela ed pauuoJ 'rfue^opu?l'I oqt ur Jelel -srcrfua^ s?q qcq,{| 'resrwA' saptotltouS1nots aIUII e euol? elll?c qcrql( 'pJlqt eqt pug snqpuSotpog luouralaDlnurJo uollsrulsuooeJ :(0zpnlepoFcl) sr1.Dpad Jo i€oloqdrour eql (9/6I) redd?I) pue Icrrreg aql uo luepued peledrcuu? l?qt stuourolo aleqd?csrTlols-ep ,{IrEelcsl 're^e,r1oq'astDatJ oql ur oepDuop "d rnq Jeqtoue:DutpotnJse pegltuepr ,(lpurEuo -ourolsrq eq7pue snpoutolsr( qloq Jo srsoutu ed& eqt Jo stueurelaed pedoJe^ep(qJu?JqIec -Ip s,rodd?D{'s rlnga 1DurpotnJsarJeds ruJoJ -rd,{teql) qsnqsrqlJo r{ruerqeuo ,l'q SldJo oqt se (/t6I) uosuergpue uosuErgfq pequcs € uours uEd ro^{ol eqt ur ..qsnq,,z se snpouolsl(I Bur -ep euo eqt qll lueureleel?qdecsrllets -ueqc srql petpcrpure^pqI pedolo^opseAee -od d puocaseql ur sepnlJurtnq ,{qdJnw pue ^q ,(Je^ popn4suoceJ eql fuolsrq ,tF?e eql roddelx ,{q eql ol srelncrued ouo -uq pra^es {rots Jo uI 'ueDJcolueA l(lJ?eeqt olur po8u?Jpue uEunl JofeIII slr ur l?lrurrs sr \a\l 'slsuatlJnlual -rSoql Jo Suruur8eqeqt 01asolJJo te lnqop slr 'O JoJ snluedde a"Jqrrrarurxese pelqurosse epeuJsnpou.totste'paqucsap lsnf s? peaar^ 'pueq roqto oqt uo '(S/6I) redooJ '(snsuDdxa 'stuJruJleJlEr.ld?Jsll snqpuSor.poxg rewl) osuDdxaLD apouotpttJ -lplsel\-Dutport7l perdnccos"1{uontsod?d sercedsuuoJ aqt se (8961)peoJxedpu€ IIoJIN ^q plole{s eql qcrq { uI snleftdd? el?Jqrueujrxes pequJsop et?unssd er?zrq oql uoll lueuele ^q e qlud serceds pue ol"rqueulnbulntt egl ur sepnlcul Jo dnoJ8? s? 'sr terlt :61'5 3rd -rsod d ur pelErlsnlllleuuEr! Jql ut snpourotste sl (tr6t) I pu? reddet) Aq petrruts '3Jd ^qtunI VJNOCONOJ AHJ
THE MAJOR CONODONT GROUPS
Er illustratedin of specieswith a l|ls in which the biodi na-like stell)igornodus made iDning of the Sib s'enlockian.In cock several lintd this by charti the lower part i bush(lhe typi of the type -!Lsanotherbuilt ic aar anticipated i (Icriodellidae); r along a little Pa elements f-d fi. as Hadrola.ein i1shisancestralto -h Jeppsson ;rcies Epical of Dlsloae apparatusof knt of thoseof 'i rtre Pa and Pb E and pastinate $. Phylogenetic r,rhese two posipedomorphosis, *t-\. RotundaE Silurian and is, rest|al stock of d
' Co4'ssognathus d- These are refuents with a trs of a sort that | from the much Endacodina duIDsson has suglsent a species of rnts formed by iiscaphate,with .ln Coryssognamd the cusp is Itcre appearsin Dbe a very short
Miiller lnd Miille\ 5.7.6 Family lcriodontidae 1957 Included in this family are Latericriodus Mtller, 19621Icriodus Branson and Mehl, 1938;two apparentlydistinct goups of species assignedto Pelekysgnathw'[homas, 1949,AntognathusLipniagov, 1978;and an as yet unnamed genus, recognized on phylogenetic groundsby Sandbergand Dreesen(1984)and basedon a groupof late Devonianspeciespreviously refened to luiodus Icriodonts are characterizedby a basically multimembrateapparatusthat includesbi-, trior merely segminiscaphate pectiniform elemenls in the Pa position.If thereare elements in other positions,they are an assortmentof rather variable coniform or only weakly denticulatedramiform elements. Weddige and Ziegler (1979) advocate divi sion of Icrioduss.l. into two groupsofspecies, Pa one that formed bi- and trisegminiscaphate Paeleelements,and onewith segminiscaphate ments.For the first goup they usedthe generic nameLatericriodus(Miiller, 1962),for the latter, Icriodus (Bransonand Mehl, 1938).I follow weddige and Ziegler in the summary that
follows but note that lcriodus in this senseis almost surely polyphyleti.c.^fhat is, I- angustus both wilh the segminiscaand,I. angustoides. phate Pa elements typical of luiodus, have beenshownby Klapper and Ziegler(1967)and Carlsand Gandl (1969)to haveevolvedat different times from different ancestors in Lateriuiodus. Serpagli (1983) has demonstrated that the apparatus of Latericriodw woschmidti, founder of the genus,is seximembrate(Fig. 5.20). A bisegminiscaphatepectiniform element occupiesthe Paposition;apastinate,lowpyramidalconiform elementthe Pb position;a more compressed pastinate coniform (or "acodiniform") elementthe M position;and a morphologically intergradational series of alale,tertiopedate,and dolabrateelementsthe Sa,Sb, and Sc positions,respectively.Klapper and Philip (1971),however.did nol recognize homologuesof the S-serieselements of .L. woschmidtiin the apparatusof Z. Iatericrescens (Fig. 5.20),which they concludedwasbi- or trimembrate.Thus,ifZ. woschmidtiandL. l^ter' icrescensdid,,indeed, form part of a single lineage,a featurein the evolution of that lineage may havebeenthe lossofS-serieselements.Al-
Fig. 5.20. Elementsand apparatusesofspeciestypical ofthe Icriodontidae
/ ! - ^/ J n
<$-<:/-{/-9,4 UV V V Latericrioclus woschmidti
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tueragp ol seneds snt4pu8st\alad Jo sdnoJa u?ruo^e(I etrl-elpplw pu? eql SuureJ ^lr?E 'de8 Jrqd€$ -ar pelseSSnse^eq sJoqlne l?Je^es -r1eJlsaqtJo esn"33g serceds-ed&eqt'snpuq) -ar d sepnlrur l?qt dnor8 ueruo^eq ote-l puz slppqatre urorJ de8 JrqdpJBrt?Jtsolq?r3erdd?u? ,{q pel€r?des eJ?sarcedsu?ruo^ec ,{lffg eseql 'suorlrsod ur uorloes ssoJc J€InJJD All"uuassa S pu? Jo slueluela uuoJruoJ el"lnJruetuou ^uu. 'suoursod n (^lqeqord) pu? qd eqt uT slueur -ele (..u?urpoc?,,ro) ruJoJruor e1?urlsed'uorlrs -od ?d eql uI slueluele eleurul8es pe/t\or-gJ8urs qlr^\ sesnter?dd? pauroJ /I g '*J ar ,.snql -ou8st4apd,, ol pou8rsse serceds u?ruo^eo pue xaput 'd @BDupoT'J) snpou)l tsrg ^VeE peeqe aW Jo IlaM, pue QtprLuq)sotl/. 7) snpou) -uajoI Jo e^rlelueserdeJ lsJg eqt Jo p?eq? trq epll.l e \xapul dJo t[JoJ eql ur) usunlrs lselel eql ur per?eddE (0Z S 8lC) snqtDu8stuppd ,, edpueJE,,u^\o sll oq ,tetu lr lnq 'cqel^qd,(lod eq lou Kern snpoltJl ^luo snqJ isluarlIalo olpqdeosrurur8es ei\-snpouJl pardncco eJ? suorusod ed sesnl?Jedde ^q esoq^\ rn serreds l?rg^es peull.eds snqnuBsbl -alad 'O861) uaseero pu? Sraqpups ot turproc -c? 'ueq,tl u€ruo^ec ele.I aql ur Je{rrql ue^e eurmoq told egJ srolsoru€ snqnu8sblapd utoJJloa'snpou)J utorJ po^Uap ueeq e^€q ,4Brx snrypuSsblapd Jo ser3eds euos lsEol te leql slse83ns1r esn?coq'asJno3Jo'Sum8ulur sr srql 'slueluele d-uou Jo € reJrurrs ? saq 'sloor JeSuno,{ lEq^leuros ^€ur peluesoJdor '?,{Zr,rJ snqwu8sllalad lEqt polou feql ..'ruro;rur -po*,, are qorq^\ Jo II? lou 'slueluela uJoJruo3 elq?u?^ ,(HArq Jo dnor8 e 'u^\oD[ szpo?.rrl lse -plo e\t'rlSDupDq 7Jo sntpr?dd? eql uI popnlJ -ul (LL6t) tured pue uoueueqC 're^e^{oH 'sluetlIala rlJoJruoc IupnuEJ^d ro elEunsEd,4un ,{Ilsou]Jo lueuruossB uE pu" sluoruola?d el?qd sflportJ -etsrunx8ss Jo pels$uoc tunsanualDl -ua1o7 Jo 1eq1e{I 'serJedssnpou)l Jo snteJed -d€ eql l"ql eeJS?sroqln" Jaqlo lsour 'snpol.tJl snue8 uroJ eqt peseq (8[6I) IqeI pu? uosu?rg qclq^\ uo sluerrJele eleqd?csrurutos oq1 Jo .tlerrluo peuuoJ (02'S '31{) srrleredde snpouiJ ue pelEco^p? (Zl6t) IouAIng q8noqllv '?teueieJnt lueJe.Up ol serceds ol/\l eql AuuErss? ^q ezru -cellqcJ" snleEdde ur secueJeJrp esaql -8o3or ol elq€leJeJd oq lq8ru lr '^le^uuulet
VJNOCONO]
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THE MAJORCONODONTGROUPS
* hasbeenlittle EI of sucha sepdberg and DreeP. inclinatus -ol centralmemd rian group, also I lor "oistodon;r ro b€ reported Ldovician. $ har-ealsoiden{c "oistodontits of one memL- onian species r hrr thought inio differentlinh elements,the lese species,are E rhree denticle timaely be dermes for these Bouckae odus rrarlable for one ls of the poorly b- posterolateral $ T-shapedout&s'. Origin and I tnown, but its : apparentlyrer hlpersalinelalfe s olked out r earliestDevotitanjte lcriodus [fti7) haveconil rhe history of r) ard Weddige Dlulionary pat4x of lciodus; [984) have rei the history of la-ol stratigraphE biofacies,and r as Devonian , prior remarks :ms in icriodont in to be solved. br that either tre elementsby
'71
Bergstrdm, which species of luiodus have customarily 5.7.7 Family Polyplacognathidae 198t been identified or the single-rowedsegminiscaphate elements taken as typical of Peleldys- I-ate in the Early Ordovician a speciesof the gnathw may have been produced indepen- Amorphoqnathusgroup (Balognathidae)was dently at different times in different lineages. apparentlythe progenitorof a stock of prionAlso, origins of the family are by no means iodontide conodonts characterizedby a recertain. duced, bimembrate apparatus of bilaterally that asymmetricalstelliplanateand pastiniplanate Klapper and Murphy (1974) suggested Icriodus sensu lato mlght have evolved from elements.Recunent groups of such elements Pelekysgnathusindex, but they found no spec- are the basis for recognizinga successionof imensthat would bridgethe gapin morphology speciesof Eoplacognathus(Fig. 5.21). These that separatesPa elements of Lateriuiodus specieshave been of considerablebiostratiwoschmidti and P. index. Nicoll (1982) re- graphicutility in rocksprimarily of earlyMidgardedRotundacodinadubius(Distomodonti- dle Ordovician age.The stock seemsto have dae) as the most likely ancestor,and Broad- died out, however, early in the late Middte headand McComb (1983)regardLatericriodus Ordovician. woschmidtias a neotenousderivative of PeDuring its early Middle Ordovicianheyday, davis. Fihraeus (1984) suggestsderivation of Eoplacognathusseemsto have giyen rise to an Pedavis from Distomodus, in which presum- important line ofspeciesthat Bergstrdm(1983) ably he included Rotundacodinadubius.I re- refers to the genusCahdbagnathus(Fig. 5.21). gard the neotenousroute suggested by Broad- The bimembrateapparafisof Cahabdgnathu\ headand McComb (1983)as unlikely because lrke thai of Eoplacognathus,is composed of a it was devisedprimarily to explain the origin of pair ofstelliplanateand a pair ofpastiniplanate the Pa elemenlsof I. woschmidlifrom thoseof pectiniform elements.Howeyer, those of the Pedavislatialatus,andit thus ignoredotherele- Cahabagnathusapparatusform mirror-image rnentsin the apparatus,which are surely not pairs, whereasthose of Eoplacognathusare biOn the otherhand, laterally asymmetrical and have more simply the samein thetwo species. there is substantialsimilanty betweennon-P ornamentedupper sides. ofR. dubiusandL elementsin the apparatuses woschmidti,as Serpagli(1983)has shown,and the remote ancestors of R. dubius certainly Fig,5.21. Elementstypical ofthe apparalusesofspebuilt scaphateelementscomparableto thoseof ciesassignedto genemofthe Polyplacognathidae. L. woschmidti.(Of course,the scaphateelements someof them built wereeven closerto those of Pedavis,which I ally to Iuiodella because of greater similarities in M and Pb elements.) While I do not claim to have specialinsight into the ancestryofthe icriodonts-or eventhe clairvoyancethat would be requiredto makea monophyleticunit out of this family-I suggest that a derivation of Latericriodus woschmidti from Rotundacodina dubius explains tlte char acters of more of the Lateriuiodus apparatus than doesa derivation from Pedavls.Pending badly needed additional information on Iate Silurian conodontfaunas,I submit that this is a more straightforwardroutethan is the oneby way of Pedavis,whoseown origins are yet to be amDlvdocumented.
ErssE osle e^eq 1Eur ue{4 'uos puSoptldy pue dd€ qcns qllt\ I lnoq€ eculs Pue 'qs '?s eql fir.q pue 'etEr^8 luedrq Jo alEJq cod al?ln8ue u" blql?u8oqcrp,, srueJeddE l31e qll.tl sluopouoc q sql uI ^lau v .tlltuD4 61 9 3ds paglueprun d e se 41'9 '3tg :.{le{qun sruees Jtz\ toJ'snpoul ern Jo lo1s9cu3 ,d e'snpotuolJd aq 'uorlsJedeJd ! rn 'leqt peuod qlo 01 lalse3ue srql Jo slequeur hoq? [e^1 $[coJ b perueuun euo npouuoJofild 'lUetllele t- Jo) eleJq?lop hnoA peueuun ur uoulsod 4 F:ls slr Jo uonrs al?lnJrueS.BpEq rrepto eqJ (ZZ S b p:lEIeJ ,(losol3 nuap al[q./t\ sno duol puE sdsnc 1 plde 'snpolslol| rJeds ezruaotel qlluJpr aft 13q1 Jo sdnoJa tueJ ' rluoN uI el"Jls lpprl{ re,!lo'I 'suorllsod q iq puE suonrs glJdrurs rq (sn2d 'Jo seDeds ,{lJee I sE.$ 'snleJedde Eu{-lsJq esoq,t\
01euor?eqleqt sessecord pedole^epfllJurlsrp eJourqlr/r\ lrq snpotJuo)Dtdld Jo sarJJdsIPJJ -^es eqlJo asoql ot ueld ur l"cquepr slueurele eulp^q .tlo8relJosuolale{sqlr/( sercedsJo uors peurol sE,r\mpouunoDld -s$cns e ,(q ^Ueuq u?rcr^oproelppq^IoqlJo u?d '(uertcorelrq^\) fra,r.eq1ro '(uelxeql)uunr^opJo ,4lJeg 1ser1:ee u?cuell]v quoN eql Jo u?d 1so1?loql uI 'luspuacsap sI (roqtreJr) r{cq^\ pue rolseJuEsr (.reqfregr) qcq,{ JeelJlou sr lr os '\snpqap J pue slsoq -l1.atq'dJo ru:o3 sqt ur) Je^e,iaoq'otuq eur?s '(/861) JenEguro{ Oep oql lnoq" l? r?edde snpoduJ pue snpoqunD -./atd'drqsuo4eleJesolJEslsottns qorq.{ 'srxpod eqt loquou e -[uopolsrotlnl 'sruljou3ouqJorcla7 l Jo Jo sntecddE lElele{soql Jo l?rrd.&stueuola .€Z.S.3H -r.U Jo t?ql aII qcnur ,fto^ flsnor^qo sr uJeu?d srqJ sauas (S) uoqrsueJl-I4euru^s pet"Ilue -JaJrp ,(lotelduoc ? r[JoJ ol lueruele uroJruo3 '(€Z S tlC) snqlDuSoqroiaT '\ao$ snpol elEI?peJrEdun ,(Iq?urnseJd e urofl?ql stueruele -stolqnwoaN-snpolluo)onldeql Jo e^4e^uep peJnpoJe eq ,{?urlI uoursodtrAIaql u! tueuele uuoJruocelEpodoruolpue el?uuedrqJo sJr?d pu? '(nD stuelueleet"lncrue8JorEd B '(qd 'Ed) u? peIcEI ,(lluoJeddesnpo$toulnw Jo senads sluauele ot?unsed J?lruns -od.{leqlJo snl€l?ddEl?lelels eql esnBcaq (ZZS sJr?do,{\l sopnlcurqcq \ ^lleJrSoloqfuour 'sluorueleuuoJ 'fuJ) snpotstoufiutoai(r peJlaJat tnq Jo ot eJeq oJ? -ruof, aurp,{q [llueuruop Jo ,{euE etErqueur sroqln? tsorlr ,{q snpo$Io\ftl4t ar ped,rj.or? uaeq e^Eq sorcadseseqJ 'selcrluepeldurrs T?Ja^es -Ixes ol -mbumb ? sr snxeld mpoIuo)Dtald eql ur seroads 3o snlzreddz I?lelels eqJ 'ru^uou^sJorunf 'stu€tllele pue'I,{ 'cS ,ropq po^{o oJ'^{or qcee B {luIEUeclsourp sr '6961 'rederNsnpouoSttJ 'qS d ^q Oql ul pepnlc 'tL6I 1arrclA UEL snporySuouJu?ql JorlrBa Jo oollE slueruelses oEprluopolsronlnI^I -ur EreueSJo sarcodsJol€crd& sesnleleddv .ZZ'S.ttd epecepp lsourl? lnq 'puno],{ snporuoudoauog ilawpl,a lo '.tq uagol.nptlll|uJ seJ?e,{eues oql ur pesodoJds?,r qcrq,|\'(ZZS '3H) (996I) sur?H pu" srrr?H Jo snpouuor -DDid esn I 'uorssn3srpsllfl uI 'snpolluoJDnld Jo 'snpotuoudoauog Jo'snpof8uDuJ ol sro\l peueJej ueeq s?r{ leql ser3eds -ns snolr?,r ^q 1u?uodur srqlJo ulels eql Jo dnort e $,{Iur?J ,961 'stttoHaop4uopolstotnl1Jtltwoi
g'l'9
'suaqrsJo u"rsr^opJo elpprw erIl uo{ sruJoJu^lou)l ,(q pa g eq ,{erII du8 er{l ^IJood 'rs]retNoq:snqpuSnDqog ar rolsacu? prtual pue ,{ ?cqdzra -od .(u? uro{J ',{ll3orqd?JEoeE -neJ$ qtoq 'psl?losrt?q^\euros,{pueunosr sns alEu?IdruDs"d -outDt' d'sluewele urJoJrurl3ed pu?ateu?ldllelsJosrredoEerur-Jourur sopnlcur at?rqueurq e ,tq pezu l?q1sntEjsdd? I"lele)ls -AoceJsr pue uErcr^oplo eJpprtr l elEl aqt ur eJur^ordlueuquocprl^lumuelllv quoN aqlJo e^nourlsrpsr'snsoruDt d 'sorcodsu^ioDllloA\ asoq^\ '(tZ S 'EtS) snqpu8uDldtlod or ^lrro IEIsacu?osl?,tlq?qojd s",r\szry'touSoJDldoT VJNO(ONOJ IIHJ
THE MAJORCONODONTGROUPS
;Eas of generainlfueDb at top of I- aid P elements.
species haye -b- most authors tiaisodus (Fig. qls of the typeanlv lacked an q be a reduced E\eomultiois-
r
rFi g . 5 . 2 3 ) ,
Esj apparatusof ! llulrioislodonti-
whosebest-knownspecieshas a bimembrate apparatus,was probablyalso derived from an early speciesof Neomultioistodus(e.9.,N. clypaas)by simplificationof elementsin the P positionsand by lossof elementsin the M and S positions. Lower Middle Ordovician (Whiterockian) strata in North America also yield two recurrent groups of dominantly hyaline elements that are identical in plan to those by which I recognize speciesof Pteracontiodus, Neomultioistodus, and.Multioistodus. but with shorter cuspsand longerprocesses, which bear numerous white denticles.Thesegroupsrecord two closely related speciesof Paraprioniodus (Fig. 5.22).The olderspecies(P. costatus)apparently had a geniculateconiform elementin the M position of its skeletalapparatus,whereasthe M position in the apparatus of the currently unnamed younger speciesis occupied by a dolaUrate(or "cyrtoniodontiform") ramiform element. Pteracontiodusrznges,in the form ofat least one unnamedspecies,into Middle Ordovician rockswell abovethosedominatedby the other membersofthis family, but apparentlywasnot ancestralto other conodonts.Dzik (1983)reported that, in a manuscriptthen (and still) in preparation,he and I might consider Pcraprioniodus, a Pteracontiodusderiyative, as the ancestor of the important Ordovician Phragmodus.Forvaious reasons,however,that now seemsunlikely, and Phragmodusis shown in Fig. 5.17 as a possibledescendantofan as yet unidentified speciesin the Tripodus compLex. 5.7.9 Family Plectodinidae, new In this new family I include prioniodontide conodontswilh a sexi-or septimembrateskeletal apparatusthat includes a pastinate (or "dichognathiform")elementin the Pa position, an angulatepectiniformelementin Pb, a dolabrateor bipennateelementin M, and alate,di g).rate,and bipennateramiform elementsin the Sa,Sb,and Scpositions,respectively. Sinceabout 1969I have assignedconodonts with such apparatusesIo Plectodina Stavffer and AphelognathusBranson,Mehl, and Branson,takenin a multielementsense.However,I havealsoassignedto thosegeneraa numberof
specieswith apparatuses in which the Pa position is occupiedby an angulatepectiniformelement (e.g.,P. tenuis,P. florida) becauseof the often repeatedobservation that, in large samples from a succession of late Middle Ordovician populations,the denticulatedlateral process of the 'dichognathiform' Pa elements rotates gradually anteriorly and ult.imately fuseswith the short, adenticulateanteriorprocessto producean elementin youngersamples that is formally angulate.As Bergstrdmand I noted in 1972,this sequenceof eventsresults in a type of apparatusthat is basicto the maJor group of dominantly post-Ordovician conodonts herein identified as the order Ozarkodinida. Becauseil is unfortunateto have a major evolutionarystep such as developmentof the Ozarkodinida buried taxonomicallywithin a genus,I suggestthat Plectodinabereservedfor specieslike P. aculeala(FiE.5.24)with pastinatePa elements,and that thosespecieswith angulate Pa elementsbe transfered to another genus, which I will identify here only as "Plectodina." The problem with Aphelognathusis just the reverse.That is, the type-speciesof Aphelognathushasan ang)latePa elementand is thus appropriatelyan ozarkodinide (instead of a prioniodontide)conodont;the two species with pastinate Pa elementsnow assignedto this genus(1. gigas,A. kimmswlckensls)will need a new genericassignment, or can be accommodated temporaily in Pleclodina. Thtts, in Fig. 5.11,I show the rangeonly of Plectodina sensu stricto. Species of " Plectodina" and. Aphelognathuswith angulate Pa elements are included in the ozarkodinidefamily Spathognathodontidae,whose content and strati graphic distribution are shown digrammatically in Fig. 5.36. PleAodina s.s. (in the form of P. acalea/orZes)almost madeit to the end of the Ordovician, and specimensrepresentinga host of variable (and largely undescribed) speciesare common in samplesfrom low- and intermediatelatitude Middle Ordovician rocks. The Plectodinidaeseemsalso to be the best home for Scyphiodus(Fie. 5.25),whoseonly known specieshas a unimembrateskeletalapparatusthat consistsof an anguliscaphate pec-
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9L
THE MAJOR CONODONT GROUPS
, end Phragmodus tlnenrs from the r-!Ls Dalota (Sweet, irns representE clearly pastina liat lateral and I dements reprebFnetic stages. Ets retain only r mark their pasir.i was apparirdontide cono(the other rtir r) ro develop a and the -trl unimembrate ..
t HasJ' 1959 crefer the genera t to the family tEssary because bm genus Cyrr specimensthat ttrugmodus cog&ble synonym t ClroniodontiD- as subfamily rirrin over the
family Phragmodontidaeeslablishedby Bergstrtimin 1981. Phragmodus (Fig. 5.24), characteristic of low-latitude Middle and I-ate Ordoyician faunas,has a distinctiye seximembrateapparatus in which the P positionsare occupiedby pastinate(or "dichognathiforrn")elements,the M position by a dolabrate(or "cyrtoniodontiform") or geniculateconiformelement,and the S positionsby the "phragmodontiform"ramiform elementsdistictive ofthe genus.The latter, which include alate, tertiopedate,and bipennatetypes,all have a terminal or subterminal cuspwith smooth sidesor with a sharp costaon one or both sidesand a long, arched, denticulatedposterior processat the crest of which is a major denticlethat may rival or exceedthe cuspin size. In 1972 Bergstrdmand I included Piragmodus and Plectodina in the family Cyrtoniodontidae and speculatedthat these genera, which dominate Middle and Late Ordovician conodontfaunasin the North AmericanMidcontinent, originated rn Pfioniodus. lt now seemsmore likely that the prioniodontideplan of the skeletalapparatusin speciesof these three generais indicative of a common, but probablynot direct,origin. Thus,in Fig. 5.1I I show Prioniodus, Phragmodus,and Plectodina as heterochronousdeiyaliyes of Tripodus. With somereservationsI alsoincludeBryantodina (Fig. 5.24) wtth Phragmodusin the Cyrtoniodontidae.Bryantodina has an array of ramiform elementsin S positions that look very much like the distinctive "phragmodontiform" elementsof Phragmodus.However,P positions are occupiedin the apparatusesof Bryantodina speciesby carminate and angulate pectiniform elementsthat are quite diferent from the pastinate P elements ol Phragmodus and cannot be shownat this time to be either ontogeneticor phylogeneticmod.ificationsof suchelements.In favor of an associationwith Phragmodus,Inote that in the apparatusofP. cognitus one of the pastinateelementsis replaced phylogenetically by an angulate pectiniform one that retains a clue to its pastinateancestryin the form ofa riblike offseton the outer faceof the cusp.No suchofset ornamentsthe outer faceof either P elementin the apparatus of Bryantodina typicalis, however; hence, if
eitherdevelopedby phylgeneticreductionofan orginally pastinate form, that reduction is not documentedby extantcollections. 5.7.I 1 Family Rhipid.ognathidae Linhtriim, 1970 ln the Treatise Bergstrom assembledBelg$roemognathus,Appalachignathus,Rhipidognathus, Carniodus, ar^dHistiodella in the Rhipidognathidae,which was assignedto the Prioniodontacea (the Prioniodontida of my taxonomy). Following publication of new information on Histiodella, which I have cited in Section5.7.1,I feelrnorecomfortableassigning that genus to the Oistodontidae.Also, Carniodus is out of place here,becausethe seximembrateskeletalapparatusofits only known specieshas a pastinateelementy/ith threedistinctly denticulatedprocesses in one P position and an alateelementwith a long, denticulated posterior processin the Sa position. Because neitherofthesecharacters is a featureofthe a[F paratusof any other rhipidognathidspecies,I feel that Carniodus should be reassigned.The only prioniodontidegroupin which Carniodus could be accommodatedis the Balognathidae, but thereis little morphologicresemblance between most of its skeletalelementsand those formed by typical balognathids.Furthermore, Siluian CarnioduJ is separatedfrom the Ordovician balognathidsby a considerablestratigraphic gap. Consequently,I follow Bischoff (1986)in assigningCarniodus1o the Pterospathodontidae(Ozarkodinida),whosenumerous Silurianspeciesbuilt apparatuses that included strikingly similar P elements. Generathat remainin the Rhipidognathidae include specieswith tri- to septimembrateskeletal apparatusesin which P position(s) are occupied by structuresthat are fomally angulate or carminatepectiniform elementsbut are allied morphologicallyto the "acodontiform" P elementsof Tripodusand olher slem pfioniodontidesthroughpossession ofa distinctrib or costaon the outer faceofthe cusp,which may be markedon the basalmargin by a conspicuous boss or lappet. In short, those elements may be regardedas very simplepastinateones, in which no sharpedgeor denticulateprocess ever deyelopedalong the anterior edgeof the
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THE MAJORCONODONTGROUPS
long posteriorprocessthat is arched,laterally compressed,and surmountedat the point of maximum geniculationby a denticle that is wider and conspicuouslylonger than the oth-
Fig, 5.27. Elementstypical of the skeletalapparatuses of speciesassignedlo th€ PeriodoDtidae.Top elements in each row Pa, followed downward by Pb, Sa, Sb, Sc, and M elements.
ilEathidae. Figl.L I 1974).Saele-
t hown part of lhr is the genus re- so it is the
? 5.u . fulstrom, 1970 (Fig. arkodina | fu Treatise to i:donlidae, reI the same famFience with, or E_cenus,but berr studies (LdfEcies of the two tt€ same Ea y d subsequently P. aculeata, i 4Daratus, with ts. one of which ftiform"; dolaments, with an i end an S series hts have short, ;rocesses and a
ers. The stratigraphic(and probably phylogenetic) predecessor of P. aculeata,P. flabellum, had geniculatecon.iform,not anteriorly denticulate dolabrateelementsin the M position, and the ramiform S elementswere apparently neither so profuselydenticulatednor so conspicuouslyarchedas those in comparablepositionsin the apparatusofP. aculeata.An even older speciesof Periodon,which has not yet in the Proteusand beennamed,is represented Eleganszonesof Jamtland(Ltifgren, 1978)by adenticulatealate elementsinterpretedas occupantsof the Sa position and by adenticulate pastinate(or acodontiform)elements.The latter, and the "tortiform" angulateelementsthat evidently replacethem in the apparatusesof youngerspecies,are the elementsthat indicate that Periodon and the Periodontidae belong in the Prioniodontida.Ofcourse,the distinctiveS elementsofP aculeataar;ldP. Srazdri,the speciesof Periodon that I know best,are also geDerally similar to thoseof Phragmodus,and this led me in the heydayofform taxonomyto sugEestlhat Periodon might be an older name for Phragmodus-I no longerhold sucha view. Speciesof Miuozarkodina, such as M. flabellum, tbe type-species,have quinqui- or seximembrate skeletalapparatusesin which the roundedanteriormargin of pastinate(?) P elements is not developedas a processand the short, anteriorlydeflectedlateralprocesscommonly bearsno more than a singledenticle.M elementsare geniculateconiform structures, and S posirionsare occupiedby alale. tertiopedate,and bipennateelementswith a long, straightposteriorprocess. According to the vielvs just summarized, Periodon ernergedftom roots in eady oistodontid populations by developmentof a highly differentiated skeletal apparatusin which processes of component elements gradually becamelongerand more conspicuouslydenticulated. As in the presurnably ancestralOistodontidae,P elementsnever differentiatedinto conspicuouslypastinatestructures,but S elements becamedistinctively archedand denti culated.In Microzarkodinadevelopmentwas apparentlysimilar. but the posteriorprocesses of S elementsare not arched,M elementsdevelop no anterior denticles, and the feature I interpret as a lateral processin P elementsremained short and bore only a singledenticle.
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lE:ltuses have rd- or reduced, hida are charblic apparatus ! and includes r digtrate eleUl slr or seven Ilrs tend to be lcrgradational E chamcteristirhire matter is i- ir elements k ro the axial , fr io diffi.rse,
fuzzy-edgedclouds that are irregularly distrib- tends downward to form a distinct anticusp uted through cusp and denticles.Speciesof a thal bearsseveraldenticleson its upper margin few early genera(Chirognathus,Curtognathus) and is thus a true anteriorprocess.It seemsunand of at least one Triassic one (Parachirog- necessaryto invent a new morphologicterm nathus)formed elementswith little white mat- for suchan element,which (if needbe) might ter and thick lamellaethat are mineralizedby be described as a quadriramate structure with apatite crystalliteswhose prism surfacesare a short,adenticulateposteriorprocess. oriented parallel to the direction of growth. Ancestors of Erraticodon (and thus the Suchelementstend to breakasif they werein- Prioniodinida)are not known, but it is surely ternally fibrous, and Bransonand Mehl used reasonableto rcgardEqaticodon as the plexus this feature to distinguish the order Neu- from which Erismodusevolvedin the shallow rodontiformes, Middle Ordovician seas of North America. It is alsoa characteristicofthe Prioniodinida Speciesof Erismodus (Fig. 5.29) differ from that there is little differencein size or basal thoseof Erualicodonprimarily in that the Pa morphology betweenthe distinctive digyrate componentsof their seximembrate apparatuses elementsassignedto the two P positions,the lack a denticulatedanterior process(but retain ramiform elementsthat occupy M positions, a bosslikeanticusp),andbipennateM elements and those that make up the morphologically lack denticleson the short posterior process conservativesymmetry-transitionseries.For (and thus have sometimesbeen describedas this reason, diferent authors have assigned "falodontiform"). The oldest speciesof .Eriscomparableelementsof variousspeciesto dif- modus with which I am acquainted are repreferent positionsin the apparatus,with the re- sentedby typically "fibrous" or "neurodonsult that homologiesare not alwaysobvious.I tiform" elements.However, the skeletalelewill attemptto be unirbrm in the followingdis- ments of later species(e.g.,E. quadridaaylus) cussion(and in the classificationin Appendix have more white matter and commonly break A), but my yiews do not alwayscoincidewith like othernonfibroustypes.This suggests to me thoseof other authors. that "fibrous" histologymay somehowbe relatedto the probablyquite unusualcondilions that obtainedin the shallow,very warm MidBransonand 5.8.1 Family Chirognathidae continentwatersin which earlyEru'smodus deMehl, 1944 veloped.Later species,suchasE. quadridactyEqaticodon, the oldest known chirognathid /as, may representforms adaptedto the more and the most ancientmemberofthe Prioniod- normal conditionsthat probablycharacterized inida distinguished thus far, appearedlate Midcontinenl seas later in the Middle Orin the Early Ordovician, when it achieveda dovician. very wide biogeographic distribulion E. patu The bizarre Chirognathus(Fig. 5.29),repreCooper(Fig. 5.29),the oldest(andbest-known) sentedin the shallow, tropical waters of the species, is distinguishedfrom otherchirognath- Nofth AmericanMidcontinentby a singlespeids primarily by featuresofthe curiouselemenl cies, is allied morphologicallyto Erismodus, I assignto the Pa position.At first glancethat from which it differsprimarily in a skeletalapelement appearsto be pastinate(or "dicho- paratuscomposedof elementswith a scarlike gnathiform"), and its associationin the same attachmentsurfaceskewedto oneface,an alate apparatuswith a Pb elementthat is an exten- Saelementwithout a posteriorprocess,and an siform digyrate(or "oulodontiform") element, M elementwith denticulatedanteriorand posand thus typically prioniodinide, might be terior processes. Cutlognathus(in which I intaken to suggestthat E. patu straddlesthe cltde Trucherognathus and Polycaulodus) is boundarybetweenthe Prioniodontidaand the alsoa Iikely derivativeof Erismodus,butitsapPrioniodinida.Closerinspection,however,re- paratus has not yet been competely reconvealsthat the distinctivePa elementof E. palu structedand, like Chirognathus,it is not likely is also basicallyan extensiformdigyrale ele- to be on the "main line" ofprioniodinide evoment, but the anterobasalpart of the cuspex- lution. Thesetwo generaare significant,how-
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v tratar) and PrionEoEed loward the
8l
ever,in beingthe primary "fibrous" conodonts platformedpectiniformelementsin P positions and thus the nucleusof Bransonand Mehl's and startedto experimentwith ontogeneticor phylogeneticreductionin the developmentor Neurodontiformes. mineralizationof elementsin various apparatus positions,the Prioniodinidaremainedcon5.8.2 Family Prioniodinidae Bqssler,1925 servativeand developmentproducedno starOulodus (Fig. 5.29), the oldest prioniodinid, tling modifrcations. seemsclearly to have evolved from Erismodus, Devonian workershave not yet dealt in deas Schijnlauband I suggested in 1975.In the tail with the Prioniodinida,but Klapper and apparatrusof O. serralrs, the type species,there Philip (1972)have demonstratedthat the apare extensiformdigyrate(or "oulodontiform") paratus of Hibbardella angulata (FiE.5.29), elementsin both positions,only minor patches type-speciesoflllbbardella, differs from that of ofwhite matterin any element,and a dolabrate Oulodus primaily in that the alate Sa element (insteadof an anteriorlydenticulatebipennate) of the former has a denticulateposteriorproelementin the M position.Thesefeatures,and cess,whereasthat of Ou/odrs hasa stubbyposscrappy evidencefrom Ordovician rocks in tenor processthat lacksdenticles.For this reanortheast Oklahoma (Amsden and Sweet, son the assemblyof elementsfrom the upper 1983)ofa possiblyslightlyolder species. sug- Middle Devonian of Manitoba that Uyeno gestthat O. seryatusmay have been somewhat (Norris, Uyenoand McCabe1982)hasrecently specialized,sinceall potentialancestorsin Er- referredto Oulodusmay representa speciesof ismodus have an extensiform digyrate (or Hibbardella, instead. "prioniodiniform") elementin the Pa position, Murphy and Matti (1982) have established and this patternis repeatedin all youngerspe- the genusErika (Fig.5.30) for a single Early ciesof Oulodus.However this rnay be, the plan Devonian species,which had a seximembrate ofthe sexi-or septimembrate apparatusof Oul- apparatuswith extensiformdigyrateelements odusis clealLyanticipatedin thoseoftnJmo- in both P positions,a breviform digyrateeledus and.Erraticodon.its ancestor.and therecan ment in the M position,and a symmetry-tranbe little doubt about closerelationship. sition seriesthat includesalate.extensiformdiOulodus qutcHy adaptedto the probably rig- gyrate,and bipennateramiform elements.The orous conditions in shallow subtidal parts of apparatusof Erika divarica, the only species late Middle Ordovician seas,in which its spe- known, is sirnilarin many waysto that ofboth cies were soon establishedas ecologrchall- Oulodus and.Htbbardella; however, the M elemarks. With enlargementof those marginal ment is not much like that formed by species zonesin the later Ordovician,Oulodusalsoin- of either genus,and the alateSa elementlacks creasedin diversity, and its evolutionaryde- a posterior processand thus difers from any velopmentis recordedin Late Ordovicianand other prioniodinideconodontwith which I am Early Silurian strataby a succession of chron- familiar. ospeciesthat is of considerableutility in Iate Accordingto Nicoll (1980),the apparatusof Ordovician biostratigraphy (Sweet, 1984). Late Devonian specresof Apatognathus (Fig. Pristognathus,representedby a single,short- 5.30)is also prioniodinide, and I include the rangingLate Ordovician species,is closelyre- genuswith the Prioniodinidaein Fig. 5.28.The lated in apparatusarchitecture to Oulodus and elementtypical of Apatognathusin form taxclearly belongs with that genus in the onomy was apparentlyan occupantof the M position. Prioniodinidae. SeveralSilurian speciesassignedeither to Sparling( l98l) has also concludedthat the Oulodusor Delotaxis(which I include in Ozl apparatusofat leastoneMiddle Devonianspeodus) cany the Prioniodinida through the Si- cies of Prioniodina (P. tortoides) (Fig. 5.29) is lurian into the Devonian but proyide evidence closely comparableto those of Oulodus and of very little changein basic plan or diversifi- Hibbardella in element tlpe and number and cation. In the Early Devonian, when sonleof in morphologicfeaturessuch as style of denthe dominant ozarkodinidesbeganto develop ticulation. Sparling'sdiscussionsuggeststhat
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potlo ueeq e^eq '8961 oql tse8itnsot procor peqsllqndeq1ur enlrt sr pu? (9161) ^qroN ^q ejeql 'eJeqdnoJ8srql o1 1ruSrsseI pue '?pIuI 'peorxsid snqnu?DpqruDT Jo serJeds ruJoJ slueuolE elu?u elqelr"^ElsePlo -poruoud eql Jo lePoru lsJeueaerITslu sntfiDu8 EuuueseJdeJ eqt eq ot suees '896I 'peolxeu snlpuSopDlx -opolx luelfuelal4Frur'p4Jn4suocoJ lsnf sv pJo sertedstuau 'I'ueqtpeuErss"(J861)p?oJxeUqclq^\ ol qorq,rroJsnue8lueurelelllnu.r suoursod qS aql ueql selr,edssnqpuSopDlx Jo -etuoc luosoJdal lEr{l sdnoJEluarlnceJ ITJJoJ e^eqol ourpouoSrT pue 'snporuoudoaN 'o apnqqlH sJsnleJedde eql ur suonrsod d pardnJJo r(lelrt ejour ere D aDpIuSoW Jo selcedsuuoJ 'D aDplruBDI4[ 'snqwuSopDlxJo sercodsuloJ s€ pezruto3eJ,(lsnor^oJdslueruelalDqt lsoE8ns s? pegrluopr ,{Fnoherd stueuolo (@tddlssrs I tnq 'sortods.tn?truSopDtxJo sasnlz:eddeeq1 -sr] I) ueuelsoqc1?q1suodel (186I)p?orxau '?purpoIUoud Jo uonJrulsuoJJJsrq ul sluauroled ezIuSoJeJ lou pp (1861)peoJxed snpoluottdoaN Jo sarr eql Jo &otsq crozoeled olq eq1 ur elor pu? u"ru?^[^suu0d -edsIIlroJsEpaguueprSuolljos eqlJo sluouele lu?lodrul ue p3,(€ld ruo+ atu?J trl{datrlElls oleJqaloppedeqs-Iord eJesnqwuSopDlx ]]ualc.t r{8noJql u?uetseqC^F?ep pJluournJop? s?q leql ptutpoluouda^tlJull -elerlFurJoslueureletN'outpouoSt7ol ^uouo eleu -slp E 'snporuoudolplJo se^n?lueserder -x?l rrrJoJur pau8rssE,4FeruJoJsluetuole ^llPe '€ 8'S uoucos uI -uedrq.{q uonrsod JS etqlpue :snltouSopEtloT prooar oslE ^eqJ ^lq?qord pezr (,{Iqeqord) pue snryDuSopolxEreueAurroJ eql peJeprsuoc eq 'eeprqleuSorlceg I[.!\ qcrq,n Jo [mrd,&stuauele etepedonrel,{q (s,peoJxol{ {prceds gql ol [eJlsaouEselcedsprurporuoud lsourl? lou 'uourdo [lu ur) pelru se^\ uo4rsod qS Jo procar lElele{seqt epnlcur ^Iulsuoc qtr^{ lpep arlt lD ap.nqqrH ol ,tlsnol^erd poJjeJet sse3 sdnor8eseql '^ mruouoxel uieqt -ord Joualsodelqncrluepe q1r/trslueurelS0lEI3 Jo pepJocersdnoJ8lualncej agl lno pallo^t ,{qperdncco sp,r snleJeddesnqtDu8 le^ s?q auo ou tnq 'oepruporuoud eql Jo ^0uerEddE soroedssnou?AluesaJdal,{lq?qordlEql slueur -oprlx luJurelJrllnu eql ur uonrsodESaql 'I€'S 8lC ur pepnloursr s/lryiouSopolx -ele uJoJrurpod pue IxroJlrueJpal?F [1u0p 'eBJElJo/qeu"A ur€luocslcol ueld Jo uorlcrulsuoJeJaAuEuISeluIuV [e^el luEJ "urorJ suoucelloJ ^leler3srp upuelseqC-aJd -gru8rs ?rusqels? l€ sdnorSlueunoeJeqlJo -drssrssrl l ^ 'l(Frq eqt roJ (eeprTlapreqqlH slueuoduroJ reqlo r{lrnddnoJ8lou op stuo(IIelo lou) puEJspJoeql roJeprurpoluoud erpJ aseql teql 1csJsql alldsep 'elu e?prurPoruorJd ^le^n?IeJ ,{Oueunuo sIqJ pos?qir\ouar? suj"u oqt tursn ,{q oseceql eq tq8ru sql l?ql ot IBcrSoI suaas e^eqI pu? 'esuesluaueleqFur ? uI sznedssnqnuSop0lx gcrq^\ uo sdnoJBluounc peledrcDu? -er oql ol suo4rppelsuuelod se(1861)p?orxel{ uorlducsep[zr,l.eDurporuoudJo serJedsJeqlo 1286I)Ilrew puer(qtuny{ urorJslueuoler{lgJo seqflels stueuele€d puE'qd 'I{ 'cS 'qS,tq Uolot po/$olloJ'lq8u uo sluaurolo pS(oeplurporuoud) puEsluouela '0€'S'3!d ol peu8rsse z{ttg puesnqrDuSotDdy sorceds Jo lEcrd,{tsosnlaEdal€
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THE MAJORCONODONTGROUPS
Sa Itio odinidae). Bftom \'lurphyand
ftiotrs to the relgn zrlrus species iendv logical to E relalively rare ler components ristically signifiEoostruction of
? i,il. *ment Kladooccupied by $ poslenorproVibbardella; the oplmon, not Ii mnrs rypical of r ard (probably) rition by bipend m form taxEls df multielebped dolabrate led as form sped I l98l) did not rEonstructionof Ls species,but I $- recognizedas ; are more likely r the apparatuses the Sb positions d them. *ment Klado,of the Prioniodmp here.There d ro suggestthe
immediate ancestryof Kladognathus, bnt spe- time regardedsuch"enantiognathiform"digyciesofthe genusappearto havebeenmembers rate elementsas occupantsof the Pb position of nearshore,shallow-waterassociationsthat in the skeletal apparatus of Ellisonia and,in also included speciesof Cavusgnathus. With thoseofa succession ofspeciesof multielement only a few exceptions,this ecologicpreference Xaniognathus and.Cypridodella. Hence, occuris also characteristicof the Prioniodinidaand rence in the Pb position of ttle ldioprioniod.us may help confirm the assignment. apparatusof elements reminiscent of these Idioprioniodus(Fig. 5.31)wasdiagnosedin a later Paleozoicand Triassic specimenspromultielement sense by Merrill and Merrill yides strongsupportfor the origin of Ellisonia (1974),and their reconstructionhas beencon- and. Xaniognathus in ldiopioniodus or a firmed in a numberof subsequent studies.Ele- closely related genus.And, becauseI regard mentsof the skeletalapparatusofthe two spe- Xaniognathusas the most generalizedcompocies known are large, mostly hyaline, and nent of the famity Gondolellidaeand E1lr'sozla include distinctive digyrate pectiniform ele- as the centralradicalofthe Ellisoniidae,strucmentsin both the P positions;dolabrateM ele- tural similarityof Pb elementsplaysan imporments (including the tlpe form speciesof Nea- tant role in my ideasconcerningthe origin of prioniodus);and a symmetry-transitionseries thoselineages. offour ramiform elementswith largecuspsand very short,sparselydenticulatedprocesses. EsLindstrdm,1970 peciallysignificantin this arrayofskelelalcom- 5.8.3 Family Bactrcgnathidae ponentsis the diglrate elementthat I assignto In the Treatise Atstin and Rhodes assernbled the Pb position. Lateral processesof this ele- the distinctive Mississippian generaBactroment tend to be quite short (althoughthey may gnathus, Doliognathus, Dollymae, Eotaphrus, be longer than those of other elementsof the Scaliognathus, and Staurognathusin a family Idioprioniodus apparatus),and they project Bactrognathidae. However,theywereunableto downwardlyand anteriorlyso as to form a dis- suggestthe relationshipofthis obviouslyintertinct V with the inflated, but undenticulated, relatedstockto any ofthe othergroupsofconbaseof the cusp.A closelysimilar type of di- odonts describedin the Treatise. gyrate element is common in collectionsof In 1985 Kad Chauff demonstrated(to my Permian and Triassic conodontsand was re- satisfaction,at least)that Bactrognathus,Dofened by Clark and Ethington (1962) to rhe liognathus,and,Staurogna.thus, the centraleleform genusEnantiognathus.I have for some mentsofthe Bactrognathidae, haveskeletalapFig. 5.31. Elements and apparatuses typical of species assigled to Kladogaathus and ldtopioniodus (pironiodinidae). Sa elementson right, followed ro left by Sb, Sc, M, and P (or pb and pa) eremenrs.
qr ilqsqord s?r\ U Jqr ur r{lr"g nrBr?dd? eq1 ur felJ qlr^{ (sJeglo EU pUE el?Uued Io Jql SEaleq/rt sp E sr sarcods rr lusurele l leql gronJrdsuoc pu? rxr ro leurs os uJ rnq 'pequJsep I Slrqrqxo oceyns \UOttdotpl eldJos gluoz lueuruloJd Dpesoduoc oq ol 3 tuauqc?lte eql $ ueql pslqnsrl hol eq ol slueur DJ .iJuaPuel oqt rcydotpJ lo selo p c6oql uro{ sals ql alEJEdessecue |Eo ilsnol^qo -sprurporuoud tsqsllq?lse ur douueue,, eseql EOJ lerFEe 9A?rI
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THE MAJORCONODONTGROUPS
liplanate and thus similar in their generalorganizationto thosedevelopedat varioustimes in unrelatedprioniodontideand ozarkodinide stocKs.
apparatus of ;i
duded that the i a groupofconC4ptotaxis that ! represented in nd While this lion- I wonderif r boking in the oftheir incepr- prioniodinide lost diversetaxd biogeographFironments. EpIoropes seemto srccessfully, if Ghore habitats. asr sdmespecies an sucha stock. ddirional signifhioniodinida ber corectly, they lb.tform rnaking m15. As in other platformed elec- Doliognathus, 7 in the curious t modificationof aions.It may not slite their origin lrres. theseplatcame to be stel-
85
tina(FiE 5.33),ktown thus far only from a distinctive Pb elementfrom the I-eonardianHess Limestoneof Texas.Later Permiancollections, describedin detail by Wardlaw and Collinson (1986)and Croft (1978),includethe complete array of elements,which indicatesth^t Swee5.8.4 Family EllisoniidaeClark,1972 lin a had a seximembrateapparatuslike that of The first representatives ofthe Ellisoniidae,in- Ellisoniabuthad,an elementin the Pb position terpretedby von Bitter and Merrill (1983)as that is reminiscentoflhe triradiateextensiform two speciesof Ellisonia, appearedin the Ato- digyrate element of Ordovician Erraticodon, kan (Pennsylvanian).The youngest species the earliestprioniodinideknown.That element known are of Late Triassic(mid-Carnian)age, has one long and one rather short lateral proand the type-species(-E lrlaJsicd) is Early cessand a stubby posteriorprocessthat bears Triassic.In architectureof their skeletalappa- only one or two denticles. ratuses,speciesof Ellisonia (Fig. 5.33)are simSpeciesof Merrillina (Fig. 5.33), another ilar to speciesof ldioprioniodus,from which Permianellisoniid,developedskeletalapparatheyalmostcertainlydeveloped.The apparatus tusesthat were closelysimilar in their conforis a sexi- or septimembratecomplex, with mation to thqseof Sweetinaspeciesbuthad exmorphologically conservative alate, digyrate, tensiform digyrate Pb elementsthat lack a and bipennateramiform elementsin the S and postenor process. In successiyelyyounger M positions,an extensiformdigyrateelement Permianpopulations,the short lateralprocess in the Pa position and, in the Pb position, of Pb componentsbecomeseven shorter,and another digyrate element, with processesre- in the youngestPermian collectionsI have flected sharply downward and anteriorly. I seen,the short processis largelyvestigial.Spehaveearliercommentedon the significanceof cies of both Sweetina ard, Merrillma were eyr these "enantiognathiform" digyrate elements dently restrictedto the Permianand were apin establishing relationships within the parentlybestadaptedto very shallow,agttated, probably hypersalinewater. Commonly, their Prioniodinida. Obviously only minor morphologic ditrer- largeelementsarethe dominant (or only) comencesseparatethe apparat.uses of Ellisonia spe- ponents of collections in which they occur; ciesfrom thoseofpartly contemporaneous spe- however,thoseelementsalso tend to be fragcies of Idioprionioda.r.Such featuresinclude mentary,soreconstructionofapparatuses is difthe tendency for processesof Ellisonia ele- ficult and only a few speciesare known in ments to be longer and more profuselyden- detail. ticulated than those of Idioprioniodus and.for In the Early Triassic(Scythian)E/llsoziawas the attachmentsurfacesof E/ftsonraelements joined (or replaced)in shallow-waterenvironto be composedof smallbasalpits borderedby mentsby speciesof Furnishius,Hadrodontina, prominent zonesof recessivebasalmargin.In and Pachycladina(all illustratedin Fig. 5.33), some IdioprionioduJ elements the attachment which formed seximembrate apparatuses surfaceexhibits featuressimilar to thosejust whosecomponentelementsare distinguished described,but in nonethat I have seenare pits by wide zones of recessivebasalmargin and so small or recessive-margin zones so broad whosealate Sa elementslack a posteriorproand conspicuous.It might also be noted that cess. Pa elements are extensiform digyrate the M elementin apparatuses of ldioprioniodus structuresin apparatusesof speciesof both speciesis a distinctive dolabrate structure, Furnishius and Hadrodontina, blot extensiform whereasthe one in Ellisonia apparatsesis bi- Pb elementsdevelopan additionalrow ofdenpennateand readily confused(by me, among ticles on the anterior face. In Pb elementsof others)with elementscommon in Sb positions Hadrodontinathe supplementalrow joins the in the apparatuses ofother species. main denticlerow at both ends.In comparable Early in the Permian a speciesof Ellisonia elementsof Furrrishiusthe supplementalrow wasprobablythe ancestorofa speciesof Swee- joins at only one end and additional denticles
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VJNOCONOJ:lHl
98
THE MAJORCONODONTGROUPS
Fig. 5.34. Iareral and undersideviews of a Pa element of Gladigo ndoIella (Ellisoniidae).
ThaynesFormation of Utah, and one ofthose collections also contains a number of platformed pectiniform elementsthat are gradational in morphologywith the unplatformedPa elementsof.E. triassica,and.are also identical in form with the elementson which Huckriede (1958) based Polygnathustethydis,the typespeciesof Gladigondolella Mnller (1962) (Fig. 5.34).Paull (1983)noted the samefeaturesin her large Triassic collections and describedthe Lower Triassicspecimensasrepresentatives of G. meeki. A distinctiye featureof gladigondolellidPa elementsis the fact thal narrow platform brims completelysurroundboth anterior and posterior processes, hencethe elementsare formally anguliplanate.Comparable elements of the gondolellids, which also occur in Triassic rocks,are segminiplanateand thus are readily separatedfrom those of Gladigondolella.
I
9
5.8.5 Family Gondolellidae Lin^ftam, 1970 The late Paleozoicand Triassicconodontsassembled by Treatise afihorc in the families Gondolellidae and Xaniognathidae form an obviouslyinterrelatedstockthat is bestconsidered as a singlefamily. The name Gondolellidae,coinedby Lindstriim in 1970,is the oldest one available for the combined family. Gondolellid conodonts formed a basically seximembrateskeletal apparatusdistinguished primarily by angulatePa elements,breviform digyrate Pb and M elements (the former "enantiognathiform"), and a slrnmetry-transition series that includes alate Sa elements with a
Es rhe Sa element I ross indicate that
lndcles in either i- E. triassica, is tkrions I made Lo*er Triassic I
long.profuselydenticulated posreriorprocess; extensiformdigyrateSb elements;and bipennateScelements,commonlywith long,delicate anterior and posteriorprocesses. In the apparatusesof generalizedgondolellids,the postenor processof Pa elementstends to be short and fragile. whereasthe anterior processis stout and is commonly surroundedat midheight by a well-developedmidlateral rib. In gondolellids,however,the posterior specialized processof Pa elementsdisappearsand the segminate structuresthat result may also develop platform segmentsthat are confined to the sidesor joined aroundthe posteriorend ofthe cuspto form a continuousbrim. For many yearsit has been my contention that when gondolellid conodonts developed segminateor segminiplanate elementsin the Pa positionthey alsoceasedmineralizationofelements in other positionsin the apparatus.Accordingto this view, the Gondolellidaewould include specieswith both unimembrate and seximembrateapparatuses. This interpretation ofgondolellid organizationis basedon my observation that collections made from rocks within the range of the Gondolellidaecommonly conlain either the segminatePa elements or an assortmentof ramiform and pectiniform elementsfrom which it is possibleto assemblea completeseximembrateapparatus. Only rarely do collectionsinclude a balanced assortment of platformed and ramiform elements. For a number of gondolellidspecies,particularly Triassiconesreferredto Neospathodus, Platyvillosus, Epigondolella, Mosherella, and Misikella (seeFig. 5.35),I believemy original idea holds. That is, those speciesformed unimembrateapparatuses-or at leastonly those elementsin the Pa positionsweremineralized. However,evidencefrom a coupleofnatural assemblages [one almost certainly coprolitic (Rieber,1980)lindicatesthat othergondolellid specieswith segminateor segminiplanatePa elementsmay have had complete seximembrate apparatuses.Fot example,Pseudofurnishias (Fig. 5.35)and at leastsomespeciesof Gar?dolella (Fig. 5.35) and,Neogondolella(Fig. 5.35) appearto have had apparatusescomposedof segminiplanateelementsin Pa positions and ramiform elementslike those tvoical of Xan-
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THE MAJORCONODONTGROUPS
?s.udolutnishtus
be [n rheapparatuses Sb.5c.M, Pb,andPa E badmultimembrate L rom thosein the
l egminate or segrcloped from time re sp€cializedspeled only by substigminiplanate) ele:!'r-ative angulate h orhers, developdniplanate Pa eleEcompanied either n ofthe apparatus d€ments in M and
Origin of the Gondolellidaeis obscure.Ap- dle Ordovicianage;the youngestare from earparatusesof Xaniognathusspecies,the most liest TriassicstEta. generalizedgondolellids, are very close in Except for a few generatransferred from the structure to those characteristicof Ellisonia Prioniodontida,my conceptof the Ozarkodispecies,and it is likely that both stocks ap- nida is essentiallythat of the superfamilyPopeared at about the same time in Atokan lygnathaceair the Treatiseclassification.In (Pennsylvanian)seas. I have already com- Fig. 5.36 (and in Appendix A) I divide the mented on the likelihood that Ellisonia devel- Ozarkodinida into 12 families. Treatise auoped from the prioniodlnid ldiognathodus, and, thors recognizedonly 6. the gondolellidsmay havehad a similar ances- The cenlral family in the taxonomicscheme try. This suggestionreceiyes some support of Fig. 5.36, the Spathognathodontidae, infrom the fact that PennsylvanianXaniognathus cludesan assortmentof ozarkodinidegenera arld Gondolella characterizea relatiyely deep- that is superficially quite heterogeneous. It waterbiofaciesthat overlapsone in which ldi- could be made much lessso by includingEogoprioniodus is also very cornmon. Ellisonia nathoduswith the Polygnarhidae;by erecting and its kin, of course,are especiallycommon separatefamilies for the compactbut distincin rocks that represent very shallow-water tive stocksnow represenled,by Ancyrodella, by environments. Amydrotaxis ar.d Ancyrodelloid.es,and by PoMy views on relationshipsbetweenmajor lygnathoideq and,by further revision of Bispageneraof the Gondolellidaeare summarized thodus and,reassrgnmentof the resulting parts. diagrammaticallyin Fig. 5.28,and apparatuses In effect,that lype of raxonomictrimmingwas characteristicof typical gondolellidspeciesare begunin the Treatiseby crealingseparatefamillustratedin Fig.5.35. 11 is my suspicion,llies for Kockelella and,Ancoradella and. for however,that formation of segminate(or seg- Pterospathodusand.its kirr. miniplanate) elements in Pa positions (and I have resistedthe temptation to erect the commonly concurTentapparatus reduction) severalnew generaand familiesjust suggested happenedrepeatedlyin the history ofthe Gon- on the groundsthat sucha task is bestunderdolellidae,perhapsasan expressionofiterative takenby someonefar morefamiliar than I with adaptationby successive membersof the Xan- all the speciesinvolved. On the other hand, I iognathus-Cypridodella stock to similar envi- have not hesitatedto referAlternognathusand. ronmentalconditions.If that werethe pattern, Siphonodel la to the famity Elictognathidae, bethe taxonomysummarizedin Fig. 5.28is vastly causespeciesofboth arewell setofffrom those oversimplified,ofcourse,althoughit is difrcult retainedin the Spathognathodontidae and auto imaginea defensiblealternative. thors who havecontributedmost to unraveling the evolutionary history of the two generic stocksagreethat.despiteresemblance in some morphologicparticulars,this stock originated 5.9 The Ozarkodinida Dzik, 1976 in the Spathognathodontidae independentlyof The basic skeletalapparatusof ozarkodinide the Polygnathidaeand at a much later time in conodontsis sexi-to septimembrate, with P po- the Devonian. Those authors may not, howsitions occupied by carminate and angulate ever, be too happy about my choice of pectiniform elementsor their platformedana- Elictognathidae. logues.In ozarkodinideconodontswith fully I have also divided the Idiognathodontidae developedappantuses,elementsin S and M of lhe Treatiseclassificationinto Gnathodonpositions are commonly generalizedin mor- tidae and Idiognarhodontidae, becausesuch a phology and, from published descriptionsat division recognizes a naturaland highly signifleast,are much the samefrom one speciesto icant interval in the mid-Carboniferous history the next. Pa elements,on the other hand,r/ary of both groups.The Palmatolepidaeis newly greatlyand haveprovidedthe principal means establishedfor a phyletic lineagepreviously of taxonomic differentiation.The oldest ozar- submergedin the Polygnathidae,and the Dikodinideconodontsarefrom rocksoflate Mid- plognathodus-Sweetognathuslinea$e is re-
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! 6
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batidae Hqss, 1959 nls are a Yariable, d.rp. as befits their )zarkodinida. The
sexi-or septimembrate skeletalapparatusis basically simple, with bladelike carminate and angulatepectiniform elementsin both P posi tions;a dolabrateor bipennateM element;and an undistinguishedsymmetry-transitionseries that includes alate, diglrate, and bipennate elements in the Sa, Sb, and Sc positions, respectively. The alate Sa elementsof most of the earliest spathognathodontids(e.9., "Plectodina," posterior Aphelognathus) lack a well-developed process,and breviform digyrateelementsoccupy the Sb position.A few, however,haveSa elementswith long,profuselydenticulatedposterior processes and at leastonespecieshad developed extensiform digyrate Sb elements by early in Cincinnatian(I-ateOrdovician)time. The Spathognathodontidaeare recordedfirst near the baseof the Nonh American upper Mohawkian (i.e., the Rocklandian) by conodontswith severaldistinctive types of apparatus. One, typified by the specimensBergstriim and I (1966)referredto "Bryantodina" abrupta (bat probably referable now to Yaoxianognathusabruprrs),has a simplecarminate Pa element,an angulatePb element,a dolabrate(or "cyrtoniodontiform") M element,and a symmetry-transitionserieswith a bipennate Sc element, an extensiform digyrate Sb element,and an alateSaelementwith a long,denticulated posterior process.Bergstriim and I ( 1966)referredthe ramiform assemblyto a species we named Plectodina? posterocoslatatI transferred it to "Bryantodina" abrupta in t979. A secondtype ofearly spathognathodontid is represented by the LexingtonLimestonespecimens from Kentucky and Ohio that Bergstrtim and I (1966)made the typesof Bryantodina2 stauferi. '[he apparatus of B-? stauferi includes only slightly arched, angulatePa elements,conspicuouslyarchedPb elements,and an alate Sa elementthat lacks a denticulated posterior process.Other componentsof the skeletalapparatusof B.?stauferi haye yel to be identified. 8.2 stauferi ranges into only the early part of the Late Ordovician (Cincinnatian), but a specieswith morphologicallysimilar P elements, "Ctmognathus" pseudofissilis of Lindstrdm (1959), may have continued this line into evenyoungerpartsofthe Ordovician. The third and by far the most common type
9l
of early spathognathodontid is representedby speciesthat have been included in Aphelognathus and. ln Plectodina.The type-speciesof Plectodina,however, hasa pastinateand not an angulateor carminatepectiniform elementin the Pa position and is thus a typical prioniodontide. The type-speciesof Aphelognathus, and all other specesofthe genusexceptMiddle Ordovician A. kimmswickensisand.A. gigas, has a pair of typically spathognathodontidP elements.Thus, in this volume I will assign species such as Pleclodina tenuis, P. florida, and P. bullhillensis to "Plectodina," for their P elementsare angulateand carminatepectiniform elements,not the pastinateand angulale structurestypical of Plectodinas. s. Similarly, Aphelognathus gigas and A. kimmswickensis will have to be included for now in "Aphelognathus,"in recognitionof the prioniodontide structureoftheir Pa elements. " Plectodina"(Fig. 5.37)evolved from P/eclodina, it the late Middle Ordovician, an event documentedin greatdetailin sequentialcollections from the L€xington Limestone of the Cincinnati Region.Aphelognathus(Fig. 5.31), which wasalsocommonin the late Middle Ordovician,cameto be evenmore widespreadin marginalpartsofthe lowlatitude seasthat covered North America in the Late Ordovician. The youngesl "Pleclodind" speciesare evidently the Earty Silurian "P." hassiand "P." oldhamensis,which have beenreferred in most studiesto Ozarkndinabut evidently represent "Plectodina," becausetheir skeletal apparatusesseemto hayeincludedbreviform digyrate (or "zygognathiform")Sb elements,insteadof the extensiformdigyrate(or "plectospathodontiform") Sb elementstypical of Ozarkodina. The three typesof spathognathodontid conodonts describedthus far from Ordovician rocksdiffer from one anotherin severalparticulars and probablyrepresentdiferent lines of development.That therewere also other lines is indicatedby discoverya few yearsagoofdistinctive but as yet undescribedforms with extensiform digyrate Sb elements in early Late Ordovician rocks in both Kentucky and Oklahoma and by the sporadicoccurrencein late Ordovician strata in Europe of more or less typical representativesof Ozarkodina (e.g., Ozarkodinan. sp. of Bergstriim),whoseP, M, and Sc elementshave been known for more
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THE MAJOR CONODONT GROUPS
dorinellinaMiller and Miiller, 1957(Fig. 5.38), which Uyeno (in Norris, Uyeno, and McCabe, 1982)has shownto be closelysimilar in apparatus construction to Mehlina Youngquist,
'aa :rosl widespread l. x- \1. Pb, and Pa
Ers, dolabrate or r Eansition series I ror "plectosparor "hindeodelSbard Sc posiISa element of t hnculated poste*r Devonian and Fcies with triraL position to Par-
,as O:arkodinaad .lL andPaelements. hasa welld€vel-E.:
91
(Fig.5.398,5.39C,and 5.39D);in the EarlyDevonian of Ozarkodinaseffi (Fig. 5.39G), the shortliyed speciesfrom which Lane and Ormiston (1979)derive both Eognathodus(Fig. (Fig.s.a0). 19as 5.39H) and Polygnathus(Fig. 5.39I) of the Unfortunately,the completeapparatusesof Polygnathidae;and in the late Middle Devospecies nian, when Ozarkodinasemialternans(Wirth) only a handful of spathognathodontid havebeenworked out, so it is not alwayspos- spawned" Polygnathus" latilossdtusWirlh and. sible to decide if Ozarkodina or Mehlina or the Palmatolepidae. Evidently,as Bransonand Pandorinellinais the appropriategenericas- Meht noted long ago,the notoriouslyunstable signmentfor many Devonian and early Car- basal cavity of spathognathodontidPa €leboniferous forms or which generic stock is mentsexpandedand migratedtowardthe posinvolved at various evolutionary junctures. terior end for the last time in the early MissisSandbergand Ziegler (1979) have somewhat sippian.Speciesproducedin that episodeand simplified the problem by restricting Pandoi- their successors herein the famare assembled nellina Io those spathognathodontidswhosePa ilies Anchignathodontidae,Sweetognathidae, elementsare morphologicallycloseto thoseof Cavusgnathidae, and Mestognathidae. Carminate P. inslla (Stautrer),the type-species. In a secondtype ofdevelopment,sidesofPa Pa elementsofthe latter havea high finlike an- elementsexpandedat or near midlength to terior processthat exhibitsa slightrightlateral form lobulate lappets on one or bolh sides offsetat itsjunctionwith the posteriorprocess. above the central part of the basal cayity. Not which is built of much shorterdenticles. uncommonly,the upper sidesof theselateral Althoughtherearecertainlywell-markeddif- extensionsgrew longer phylogeneticallyand ferencesin other elementsof the spathognath- cameto supportone to seyeralnodelikedentiodontid apparatus,dividing the family into cles,commonlyarrangedin singlerows.Pa elesubordinatetaxonomicgroupsand tracingde- ments modified in this way characterizeearly (Fig. 5.39F) in the velopmental history has been accomplished stagesof Pterospathodus primarily throughstudiesof Pa elements.This early Silurian; Amydrotaxis and. Ancyrodelstructureexhibitsgreatplasticity,as I attempt Ioides (Fig. 5.39E, 5.39P,and 5.39Q) in the to showdiagammaticallyin Fig. 5.39. early Devonian; and Ancyrodella(Fig. 5.39K, In typical representativesof Ozarkodinq and 5.39L)much later in the Devonian. Each (Fig. 5.394'),the basalcavity of Pa elementsis oflhesemodifrcationepisodesrepresents a geoa groovelikeindentationalong the lower mar- logicallyshort excursionby spathognathodongin that expandslaterally to form a cuplike tid ozarkodinidesinto the never-neverland of structure at about midlength of the element platform building in the Pa position.Although and tapers toward the processextremities. Trealrseaulhorsidentifiedthe platform-buildFrom time to time in the long history of the ing excursionthat Ied to Ptercspathodusand its Ozarkodina-Mehlina-Pandorinellina plexus, allies as a stock worthy of recognitionat the however,and possiblyalso in the still-obscure family level, the otherswere not so identified Early Silurianhistory of "Plectodina"and spe- and I will not tamperwith this situation. cies derived frorn Aphelognathrrs,the laterally In speciesof Silurian Polygnathoidesand expandedportion of the basalcavity cameto mid-Devonian Torlodus, Pa elements were occupya longerand longersegmentof the un- modified in yet a third way. That is, riblike dersideof the posteriorprocess.Elementslike thickeningsof the sidesof basicallycarminate this (e.g.,Fig. 5.39.Gand 5.39H)have a ladle- spathognathodontidelementsdevelopedinto with the unmodified smooth-surfacedbrim- or shelflikeplatforms or scooplikeappearance, anteriorprocessservingas handleand the pos- alonga segmentof the element,commonlythe teriorly widenedbasalcavity as scoop.An ex- posterior process(e.g., Totlodus, Figs. 5.39J ercisein basal-cavitymodificationlike this ap- and 5.41),or around the entire element.The parently precededdevelopmentin the early latter type ofdeyelopmentcharacterizes the bi(Ftg.5.40),which Silurian of Kockelellaand the Kockelellidae zarreSilurianPalygnathoides
ffi
ed,$ qgnoJ e '^lleurC Jo s,{roJlall?Jedqns'elqnopJolueudola^ep I?n -grpou lueurale-ed 3o 'seqrlr?J A{ouJo sed^l epPlu Suroq -p€€ ur reJrptnq ( D6E 9'AIJ.)*as'O ro (v6€'S 'eIJ) oiDulput outpo4lDzo leqlre Jo osoql Jo peetsul aeprluopoqlzuEoql?ds aql ur paul?l ol J?lrurs suollsJnEguo3 ,{1l^Ec-l?s?qe/r?q -er ele qloq ecueq:aleqa,{u" o}.,3ull ul€llr,, sarcedseserllJo slueuele ?d (It'g puE 'O6E S eql uo ueeq e^eq ol sJeedde sapnqlDu8tlod 'N6€ g 'I 16gS 'sBr{) se^rl?Auep snoJolrrnu )ou snpouoJ JJqlIeu 'soJnlJnrs Jo sod^l J^ll sr pue snpolltDdslarJo sor3eds snoleJluoq -cuuslp.qqtq splo uoD?culPour luelllolo-Ed -rpC pu€ ueruo^e(Irelel pus (It'S pu" H6E S 3o adfl srql qSnoqtlv snlH?dde plluopoqleuSo 'sErJ) snpolltouSog uEtuo^e(I ,tFPg Jo serJ -ql?ds 'e^nrulud paapur ',{l"uIPJo ,fie^ e^?q " s?q (€86I) uossddal plal3{s sezuelceJ"qtuoqec ot peurrrralep -edsur sosnl"Jedde ^llu$er
'sapo aporlbuV ld\' (d)'.snp (N) :su.uoJe^qE^losuoJ'.t po|FDdslg\lN)'eae:utl D apoJtJul (1'J'OIl 4\todslg p.cte^pE (O\ :sn1.flou3ots.ttpoqY (3) :spl olelco{ (l)'.s!m@lP!(u1l' sipoybji)'.nqiou&i1o41i1:snpoqbdbx (u):outpo4rDz)(D\:srlpotllodsoQtd sn6r:e"1ftj113; '1g1:i"tpdinio 6^ne"lxuoJ 1yf siaeeuq ruengrp Jo lecrddtslueuroloruroJol pocnporderer$ eq1uisrueusiet43osJpriiqrqcrq,riursre,risioue,'r.eq1e1e4sn11o1urE-€elc'6€'s'8ttr aeplruopoireit-ioqieis
x JILL pelerNnllr tfi./FJo sosnt?Jed '0t'S '8If rrr[l
Euatuele ?d Jo lqqs: 'slueureTe | '^lr r ^fienlue^a eql Jo uorsuEd ttt' 1q6t'9 puE ,,aqt pue 0 al L eql ur slueur tqt .iSoloqtuoru ror .ilr^ec ps"q E€rul'eldtuexo ql uI 'passnJslp o suort?sgrpoul ISql UOrle^OU pe{J?ru r^Js p Jo ^q ftotsrH o pue e?p4uop qquapl sdnoJB rzq srqlJo suon PuoJas Jeuoqs E qrre uo poJep hqeurs ? surJoJ I ol lueuela eql iEurud eql ',t\or qt uo salslluep VJNOCONOS
t6
IIHJ
THE MAJORCONODONTGROUPS
denticleson the upper surface.One denticle row, the primary one,extendsfrom one end of the elementto the other.At the anterior end it forms a single-rowed"blade," which is bordered on either its right or left side by the shorter secondaryrow. Numerous modifications ofthis basicpatternleadto ozarkodinide groupsidentified here as the farniliesGnathodontidae and Cavusgnathidae. History of the Spathognathodontidae was marked by severalintervals of accelerated innovation that were expressedprimarily in modificationsof Pa elementsalong lines just discussed. In the late Llandovery(Silurian),for example,migrationofthe expandedpart of the basal cavity toward the posterior end initiated morphologythat cameto be typical of Pa elements in the apparatusesof speciesof KockeIella and,the Kockelellidae(Fig. 5.39B,5.39C, and 5.39D).At aboutthe sametime, lateralexpansionofthe centralportion ofthe basalcavity, eventually to form denticulated platform elements,establishedthe pattern characteristic of Pa elementsin apparatusesof speciesof
(Fig. 5.39F) and other memPterospalhodus bers of the short-lived Pterospathodontidae. The Early Devonian included two closely spacedepisodesof innovation in the spathognathodontid stock. In the first, shortly after the beginning of the Devonian, Pandorinellina (Fig. 5.38)separatedfrom contemporaryOzarkodina populations (Fig. 5.38) by developing Sa elementswith a denticulatedposteriorprocessand distinctively finned Pa elements.At about the sametime, iniiation of Amydrotaxis (Fig. 5.40) andAncyrodelloides (Fig. 5.40)was heraldedby rapid, lobulate expansionof the centralpartsofbasal cavitiesin Pa elementsin segmentsof widespreadpopulationsof Oz4rkodina remscheidezsrJ. In the secondEarly Devonian episode,posteriorwideningofthe basal cavity in Pa elementsofsom€whatlater populations ofthe sameOzarkodinastockled to O. selrt(Fie. 5.39G)then, promptly, to early representatives of Eognathodus, with doublerowedPa elements(Figs.5.39Hand 5.41),and Polygnathus, with triple-rowed Pa elements (Fig. 5.39I). Although Klapper and Johnson
Fig. 5.40. Elements and appamtuses of sp€ciestypical of genera of the Spathognathodontidae. The complete aFF palatrrsesof AmydrcIaxis, Polygnathoides, and Mehlina ate shown, but only the P elements of Ancyrodelloides ite illustrated. The M and S elementsofthe latter are no1 known.
Rq Fo€trathodontidae ;@r (C), (D) various a6hui (J) Tortodus; )l\atr'cEd B$palho-
lFratuses in speGnothodus (Figs. Eronian and Carfrhodus and its r 5.39M, 5.39N, G of thesespecies Iions similar to J inclinata (Fig. )bur difer in gradtbparallel rows of
Ancy.ode
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4
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-uersseI3 ureJJo uousenb eql eq ueql plno^r ueruo^e(Ielrl luelodulr ornJouo4?rllul spJo eql Jo seltedsJoJ -cal (qloq rn ,(lsnoeuerodufetuoaro) oltul Dull ereql 'qcusJq..snPogl?dslq,, DulpolttDzoteqllz pspeou aq p[no,t\ eueu cuaueS raqlouY '.tnp lauHopuod ro luuDulauuDs oqlodsrg ur pouEleJ eq pFoc lL{IuO 'sOrCOdsJo suonslndodur uo$etgrpou lueuele-?d Jo e u?Iuo^eCIelppq I lseleleql uI -ed,{l eqt 'snQ$oJrlnurds 8r sepnlcul qcuelq aposrdeJeuq 'eepqteuEflod eqt',{IlueJ eql esn?cog'seurllueJ3,ulp7eslllq .,sn1?elncE,, -"r.s 8r uro{ padoleAePeaeeu\ snpoql0dsry er41 luejeurp ?Jo ruels .w se pue oulpoTrDzo uJo+ Jo seqJuErq.,snloarJo '9,, pve .;npolllDdslq lueurdola^epluopuedJPurue se snqtouSilod '8r,, pu? trJ ur'pu? a"plluopoql?uSoqteds (tr6l) ,{lreolc unsnY eql almpur '9€'9 leql ^\oqs uElal I 'uoseel 'EJoqpues're1fler2iq pezueuruns serpnls'sr eqr ur (It's 'Eq) snpoqlDuSog leql ,$e8ms puoqlpp" annbeJ plnot\ .srtpoqt renEl aql nl srulpu8ltlod Jo uoqelp"l Pele -rdsrg'eeprluopoqleu8oqledse\l Jo DuUqaI,4{ -qur l"ql euo e\l 'aDauandsnLlPuSIIod Pue 01peuErssesJeJz.i,.r. ',snpoqlodslgJo sruJoJuels 'uoq?lndod lEllsecu?.{lpesoddts2rI1'snlDPS SurauH-Auoloql eq ol peJeplsuoc,!\ou eJ?puB ?Jo esoqluoo/qeqASoloqfuotrluI puoqsu8Jt (slueueleeS et?I?snou?rul pue) sluaruelePd sluouele {cel qclq l 'e)ls?lv ruo{ suollcel "d po^\oJ-olSurs e^Eqqary ',ssuaqoln'g pue slllq 1oc Jreqlur spualElu poloddns lou sI luo^e ^q (616I) uorsruuo pu? -rl,s'gJr ue^g'[(t86I){crq3s1nc puESreqpues u? qons l?rtrltno lurod :(tl6l) uusnv pue 'tueqpues 'reIezrz ''e'el euv-I 'snporltDuSog Jo suowFdod,{llee u.Io{ suodeJa^rleluoron?ur snueSeql uI pepnlsur mqwuS/qod Jo uoll? uep persotilns (St6l) JJe slueurJlJ Ed pe,rol-JlqnoP pu? -JlE -urs qloq qlr^\ sorcsdsasn"Jeq'Je^e,t\oq'0epl1 -uopoql"utoqtEdseql ur (I?'S 'erl) snpo|lDd -,r/8rsnoJeJruoqrPJ,{F?g-uauo^eq ul?loJ I 'V xlpuoddv uI Pu? 9€'9 '8ICuI ecrl -J?rd lEql ,{lolloJ I pue 'oeprqlEuasn^uJeql Jo se^rlelueseJdoJrelel q1l& pedno$ t iqell ^luourlloJ :.r2 snqwuSoptl) puz snqlDuSo$od e Jo ol?Jedes -tllrs 'o?prqlsuSolcllgoql "{lIu?J su?ds" (V xpueddv uI pu?) 9t'S 8ICur u^\oqs .Je D apouoqdls pue sn\wuSouD V eauzH 'snoreJruoqJB]lsolueJ Jql ul eJuEuodul crqdeJErleJls l?e$ Jo sr tl)rqn.l.'Dapouoqds 01 'u?ruo^ecllselq ero ur 'pel 1?q1eeeoulleql pelewur snqlDuSouatlv pluz'eEprl{}"u3oleer\s pu? eeprluopoqleu9eql Jo Jolsecueeql '(It 9 'a1g)snpoqtDdslgot esu oABB(Of S atd) Dull -LpW snwouSDptt) pue snqpuSotlDd Jo selo -edssnouE^'retellrqe'puE(ltS AIu)snqfiu sezrutoceteuo qcrq^\ -SlqdoJSJo sorcads ^ll?eaqlJo Jotlaa8ursnJuoc ,tq suuoJpaaoJ-alqnop e or pal (8€'S 'AIJ,)Dul auuopuodJo tuolsq ueluo^o(I el?'I eql ur seEeNI?re.\os1€suon"ln -dodur stueruelopdJo suort?cgPou ',(UeuIC 'oeprluopoqleu8oql?ds eql ur osl? 1r spnlcurI 'u?rus"Jceql Jo Pu3 eql l?eu enssrlnoqqrnpe4dxee^eq01srEaddP lPql at?a -ur[ cueueSouour'altuls ? ur popnJcur,(Fpeor sr esoreleql lcols eqt osnEceq'pu"(0t S tIC) sapolppo.thuv Jo tueurdole^ep ol pel leql eq1 sIFJer eposldasrql euo usruo^e( ^lleg ',{llecrSolorldrol l lcors (It'S 'Brl) o apor{ruv VjNO(IONOJ
AH]
THE MAJORCONODONTGROUPS
Iorphologicalty, J Devonian one Anatodelbides d that aroseis mogeneric lin:d sithout issue I include it also fuenrs in popr l:te Devonian B 5.i8) led to a >rosed forms by rirs of ScaphigEr- vanousspefrtathus. Mehfuvrhodus (Ftg. lhdonddae and Sulus initiated !I Devonian,to ln. sratigraphic Carboniferous. fuionodella are Edir \) asparts lnarhidae. Simfitgnathus arc f rEpresentatrves frlloe that pracBlsrtomferous -r.{. Fhogllalhodonrs sirh both sinI elemenls are Eirarive reports | ,{usdn (1974); l[ Evenif 8. stcrrr single-rowed lde Sa elements) :ft long-ranging ac reassignedto fuatidae, BispaEI surgery.That l4ler, Sandberg, lare that th€ "8. t r" branchesof Eed from .8. s/ar |le "aculeatus" E4lnJ, the type-red in Bispathorould be needed r- branch.There f familial assign-
me']tfor Bispathodusand the new genus.Since spathognathodontid species such as Ozarku the situation with Early Deyonian Eognatho- dina abrupta(Aldridge, 1972)beganto widen dus (Fig. 5.41)seemsalmost preciselyparallel, toward the posterior and also to expand it seemsto me that thebestsolutionis to assign conspicuously to the sides, giving rise to carbroadly conceivedand unrevisedBispathodus miniscaphateelementswith a relatively long, [and its obvious later Carboniferous deriva- even-crested anteriorprocessand a rathershort tive, Rhachistognathus(FE 5.41)1,to the postenor processsurmountedby small dentiSpathognathodontidae. clesthat declinein sizetoward the processtip. Finally, Bispathodusstabilis, with conserva- Near the end of the Llandovery, continued tive, single-rowedPa elements,wasapparently modification resultedin Pa elementswith an the stock from which speciesassignedto Psea- even shorterposteriorprocessand a large,aldopolygnathus(Fig. 5.al) developedat leasr mostposteriorbasalcavity whosebasalmargin twice, oncein the late Devonianand a second hasan almostcircularprofilein superiorview time in the early Carboniferous.The complete (Fig. 5.398).Pa elementsofthis sort characterapparatusof Pseudopolygnathas has yet to be ize the apparatus of Kockelella ranuliformis described,but Pa elementsof primitive species (Walliser),which alsoincludesangulatePb and in both the Devonian and Carboniferousiter- bipennate (but neverthelesspick-shaped)M ations of the genuscombine open, Bispatho- elements and a symmetry-transitionseries daslike basalcavitieswith at leastrudiments composed of bipennate Sc, asymmetrically of three (not 2) denticlerows.Later speciesin alateSb, and symmetricallyalateSa elements, both lineagesaredistinguishedby carminiplan- the latter lacking a denticulated posterior ate Pa elements,with a largebasalpit that is process. surroundedby a zone of recessivebasalmarSubsequentdevelopment of the Kockelella gin. In this respect,Pa elementsof Pseudopol- lineageinvolved litlle apparentmodificationof ygnalhusarehomeomorphicwith thoseofPo- elementsin the M or S positionsbut substanIygnathus,znd,the two heterochronouslineages tial changein those in the Pa position. That now includedin the genusv/ill probablymerit changeis markedfirst by developmentofshort sepamtegenericand familial identity sometime processes on one or both sidesofthe cusp,with in the future.At present,it seemsbestto retain no conspicuousmodification in profile of the Pseudopolynathusand," Pseudopolygnathus"in basalmargin. The basalcavity of Pa elements the Spathognathodontidae with the ancestral in samplesfrom slightlyyoungerpopulationsis BispathodusstabiI is stock. laterally restricledbeneal.ha posleriorprocess that is somewharlonger than in specimens from older populations;and, in the Pa ele5.9.2 Family Kockelellidae Kkpper, 1981 ments of the youngest speciesof Kockelella Toward the middle of the Llandoyery (early (Fig. 5.aD, lateral processes lengthenand also Silurian),the basalcavity of Pa elementsin a bifurcate,and the basalcavity beneaththem is Fig. 5.42. Elementsand the apparatustypical ofa speciesof(ockele/1a, typical genusofthe Kockelellidae.
FrEdde lelele)s [[nJ ueeq EJ aqJ Eifod ^ral u -9! utDf , 69
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',{ueE 'seuoceqslueuIaled ur ,(luellrulscr8oloqfuour pue'(9L61 'reddEIXpu? Icur"g :Z16I 'llocrN -oluo ur e8els potue^p" ,{lqEqoJd e 1? leql pue pEorxad'3'e) ecueuncJo-oo uo ?teppeqsl puE-slueuJle Ed ur uoneuuoJ uttJBut qnd ,{q pouuguoJ lou sl snpaw -l?seqJo sloJluoc eql uI Urqs roulut e ^Iuo ^lFoo^rnbeun -Ddsotatd S pue I I eq ol pesoddns e^Io^ur plnoar ssuaT1aoF DnapDnJuV Jo sluourela suerurcedspu? slueluols qd puz ed crlsou Jo pcrdih esoql olul slllqDlro^ o aPl)ox -a?rp uee,{$equo4ercosseeql 're^eaoH 'selc Jo cllsuepEr"qc slueruola 3d eql Jo uon -edsDulpoqozo ,fuHoduatuoc Jo sasntHedd? -"ruJoJsueJleslexeq'DllaplJox IJro+ pe^lo^e eql ur seJnFruls olqeJ?durooueql eJolu serrods D apDloruv teql [pelou o^eq (9161) red snpou.toisreJo sesnt?Jeddeeql uI asoql elqures -d?I)I pu? {olr?g sel slsa8EnsAIuI?lec sluoul JsolJ3t.1tlnq 'slsua4zdold -er (Eb'g 'Arg,)snpolltDdsoDtd senedsu^{ou{ -JlJ Bd ur Jo ^luelrturs eql Jo Ir/t\oDl sI elou tuqloN eerql oql Jo o^\l Jo sesnl?J"dd"oql uI suortrs 'U Jo snl"Jedde -od S pu" I I perdnccoo^"q or (916I) redd?DJ 'alEu"ld{lets or? slueruale ?d eseqt 'uoqs uI ul3l"ru J?s?qo^rsseceJJo auoz peoJq P pus {crueg ,{q tq8noqf slueurole 'eJns 0q oI 'asrtDatJ eql ur petEJo^p?s? 'f,Iurey eprluopor pepunolns sI qtlq,rr' '1rddsn3qns? ol peJnp -eJsr Ir^Dc les?qeql 'sJleql 'xeldruoceJour -uoud u?unlrs lou 'sluopouot opruIpolJ"zo ^q " Jo lcols ? s€ e?p4uopoqledsoreld eql pJeEeJ sr acEyns lueurqcql? oql lnq 'JosITl?A\s41g I,{q asuesluetuelall -D!to^ ofiap\)ox Jo seuo elEqdecsqlalsaql Jo I '(2861)utel{ pue ^qtunl (Ot'S 'AIC)sapn apo ) esoqt ol JElrurrs.{Jasol3eJ?Jesrlp,/!\s,suqJaold lnru ? ur paqursep saptor11ou? DnapD.toiuvJo sluauale ed 'eulnno uI -uf'Jo sercedsJo osorll pue ns111e16 'olBqdsJsltlels,(UBruoJ eJ" -oqdtoluD snpoqtodsotaq Jo slueurelo qd pue $ 1nq 3^oqe zd uea^uaq ,{tu?l[urs eql Jo qfuers oql uO stuelllale qcns 'alstl8lp ^llcuqslp reEuol ou q uIEJeu uo{J pea\er^ sz JBIncJIc ps"q aquo olgoJdeql l?qt os 'pepulser requru tltutDf ll6J zadooJavpuuopotllodsonid
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86
IIHJ
THE MAJORCONODONTCROUPS
I
lntidae.
k
Cooper,)977
riq between Pa Hus amorphodspecies of lnfred in a mula Uatti (1982),I E a 5asto cko f r Silurian prion,.i the Treatise. t$ Barrick and b d V and Sp o Iro of the three ls (Fig. 5.43) re= of Distomodus .!fructures in the O::nrkodina sper between diagand specimens ats of Pterospantrrmed by pub:g.- Rexroad and per. 1976),and rments becomes,
for me, a more compellingreasonfor reclassi- earliest speciesknown by carminiplanatePa fication ofthe family. elements,angulatePb elements,dolabrate(or The Pa position in the apparatusof Pteros- bipennate)M elements,and an S serieswith bipathodus speciesvtasoccupiedby stelli- or pas- pennateSc, extensiformdigyrateSb, and alate tiniscaphatepectiniformelementswith simple Sa elements, the latter with a denticulate or bifurcate lateral processes that may be ad- posterior process. Pa elements formed by enticulateor may beardenticleson oneor both early speciesof the stem Eenus,Polygnathw sides.It seemsobviousthat suchstructuresde- (Fig. 5.a4) (e.9.,P. pireneae,P. dehiscens,P. veloped from Ozarkodina-Like carminateele- gronbergi), are carminiscaphate; however, in mentsthroughgraduallateralexpansionofone slightlyyoungerspecies(e.g.,P. lalicostatus,P. or both sidesat midlength(Fig. 5.39F),just as inversus)the undersideof Pa elementsis planPa elementsof Amydrotaxis (FrE.5.40) andAn- ate, a condition that was attainedby develop(Fi!.5.40) arethoughtto havede- ment of a wide zoneof recessivebasalmargin cyrodelloides velopedin the Early Devonian. The Pb posi- at progressivelyearlier ontogeneticstagesand tion in the apparatusof the type-speciesof consequentrestriction of the inilially broad Pterospalhoduswas occupied by a distinctive basalcavity to a pit in forms representing later angulateelement,which bearsat midheight a stagesofeither growthor phylogeny.The pit is stout lateral rib or ridge that projectsout and commonly elongate,situatedat elementmiddownwardlyon the outer side to form a chev- length,and enclosedwithin a keellikeridgethat ron-shaped lateral lappet. An element of projectsbelow the lower surface,is narrowly almost preciselythe sameconformationoccu- groovedon its under edge,extendsthe compied the Pb position in the apparatusesof pletelength of the element,and represents(as various speciesof Early Devoniat Ancyro- doesthe pit it encloses)the under edgeof the delloides. element prior to the stage at which the basal The stelliscaphate Pa elementsof Astropen- margin beganto recede. tagnathus(Fig. 5.a3),Aulacognathus,and ApIn Pa elementsof a few species(e.g.,Polysidognathus(Fig. 5.a3)are only slightly differ- gnathusspicatus) thereis no discemible keel in ent in plan from those of Pterospathodus,and, the immediatevicinity of the pit, which is surall three genera were included vith Pterospa- roundedinsteadby a flat areaof varyingwidth thodusin the Treatise concepl of the Pterospa- that mimics a structuretermed a pseudokeel. thodontidae.However,if elementssuchas the Suchstructuresare common to the undersides onesWalliser(1964)refened to the form spe- of Pa elementsof Siphonodellaspeciesand ciesAmbalodus galerus and Pygoduslyra werc may,in mostcases,be usedto distinguishthose also components of the Apsidognathlrs appara- structuresfrom comparablePa elementsofPotus, as has been suggested by severalauthors, Iygnathw species. then all bets are ofl at least for Apsidognathus. Soon after the character of Polygnathus beUnfortunately,I have no other idea about re- came establishedin populationsof Early Delations or alternative classification of Apsido- vonian conodonts d escended, from Ozarkodina gnathusand corrlinueto showit in Fig. 5.36as selfi l-ane and,Ormiston ( I 979),three main lina member of the Pterospathodontidae. Car- eageswere founded. Theseare identified in Fig. niodus,as rcconstracted by Bischof(1986)and 5.45 as the linga{ormis, robusticostatus,and others,is also assignedto the Fterospathodon- costatusslocks.The natureofthese stocksand tidae and not to the prioniodontide family their many branchesand the subsequent Early Rhipidognathidae as was done in the Zreatise. and Middle Devonian history of their compoThe apparatusof the type speciesis illustrated nent specieshave been explored in some detail in Fig. 5.43. by Weddige (1977) and Weddige and Ziegler (1979),who drew Fig. 5.45and madethe interpretationsthat I summarizein the following 5.9.4 Family PolygnathidaeBassler,1925 paragraphs. The few polygnathid ozarkodinides that have The three rnain stocksrecognizedwithin Pobeen fully reconstructedhave a seximembrate lygnathus by Weddige and, Ziegler are distinskeletal apparatus characterizedin all but the guishedin the fossil record by the outline and
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001
THE MAJOR CONODONT GROUPS
end ofthe element.Thus the Pa elementsofP cooperi are transitional in rnorphology between those typical ofthe linguiformis and Ihe robuslicoslatus stocks. In the early Middle Devonian,Polygnathus cooperi apparentlygaverise to forms with subsymmetricalPa elementsthat lack a posterior "tongue" and are distinguishedby a carinathat extendsto the posteriortip. In speciesof the zieglerianusbranch(Fig. 5.45.1, 5.45.2,5.45.3, and 5.45.41),platform segments ofPa elements becomereducedin widlh and the carina iuts
r01
out beyondthem for slight to considerabte distancesposteriorly.Pa elementsofthe morphologically conservative robusticostatus brarrch (Fig. 5.45.33),on the other hand, are symmetrical, retain both platform segments,and differ from those of ances1ralP- cooperi only in lacking any traceofa posterior"tongue." Symmetrical Pa elementsof the trigonicus branch (Fig. 5.45.16,5.45.18,5.45.36,and 5.45.37)are blunt, robust,and havewide adcarinaltroughs that extendfar to the posterior. Pa elementstypical of the Polygnathuscos-
Fig. 5.45. Lower and Middle Devonian lineages it Polygnathus- Speciesrepresented by the el€ments figured are identified in the text. Modified, with additions, from Weddige(1977)and Weddigeand Ziegler(1979).
b lr&i
Pelmatolepis
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*phodontd l-lrDgnathus and of Polylophr> F
!s DoE assigned lrl5 are pastlmI of a laterally I e carila on the ! loEer one and trctive row of a a $ell-develE keels on the threelaerally Hanate Pa eler.lar in outline fulnrulolepis reabger-us ManE (rntral node E and differ in Eration. They rtiniplanate eleia prioniodon(,ahabagnathus, {r related. ConF\er. that the rs of considerteletal architecNlble to relate t ro episodically listory or sur-
21
*midtognathus, Erated in Fig. 5.14), together mmmonly been
Fig.5.4?, Elementstypical ofmajor speciesofthe Palmatolepidae.Modified, with additions and omissions,from Helms and Ziegler, in Clark et al. (1981). (l) "Polygnathuf' lalilossalusWirth, (2) "Polygnathus" limitaris, (3) " Polygnathus" cristat s,(4\ Schmidlognalhus wittekindti,(5) Klapperina disparilis;(6) K. dispatalvea,(7) Mesotatis asymmelncusi(E\ Palmalolepistrunsilans,(9')P. p nclata; (10) P. proversa,(ll) P. hassii(12\ P. nicornis,(13) P. subtecla;(14) P. gigas;(15) P. lmguifurmis; (16) P. t ahgulaisi (17) P. pe obataperlobata;(18) P. uepida; (19\ P. termini; (20, 23) P. pe obata schindewolj; (21) P. perlobata moximai (22) P. perlobata helmsi; (24) P. pe obata postera, (25) P. pe obata sigmoideai (26\ P. rugosa ampla; (27\ P. pe obata grossi; (28,29) P. minuta minuta; (30) P. minulo schleizia;(31) P. grac is gacilis;(32) P. gtucilis gohioclymehiae,(33\ P. grucilis ma ca; (34) P. quadruntinodosa nllexoidea; (35\ P. quadrantinodosa iaflexa; (36, 31\ P- marginifera; (38\ P. ntgosa tachyteru; (39) P. rugosarugosa:(40) P. quadrantinodosalobata;(4l)P. subpe obata:(42)P. ten ipunctata;(43)P. gtabraprima,(44) P. klappen: (45\ P. glabra acutai (46\ P. glabra lepta; (4'7) P. glabra pectinalat and (48\ P. glabru distorta.
103
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t0r
THE MAJORCONODONTGROUPS
Erses of species Fina hzve not ibed nor have nl specieswith E rclationshipof d ro the betterS Palmatolepis tarures of their r duparilis (Fig. JI-6r. and.K. disdose. and carh bladesand a ir of midlength Each the postete under side, hel- is a distinct I$inctly to one rtasal pit seems fupperina from ruhus cristatus I bsal pit tends im morphologSnatolepis(Fig. ronll have no rr5 built by spe. 5--11.4)have a r-like basal pit llh of the platI On the other rrlin iplanatePa pc-rarru" Wirth lrc be the anceshrared near the ioped platform. rdantly reprerl from many lied intensively * for the high'[per Devonian P. | 971)and varE publications. 4- of Palmatolelosn schemati;ed largely from m preparedfor $' Helms and I and Zieg.ler(in r number of dis-
105
tinct branches,most Out not all) of which are rugosa.P. rugosa ampla (sketch 26) is thought shown schematicallyin Fig. 5.47.Initial Fras- to be a derivative of the P. (Palmatolepis) nian radiationis represented in Fig. 5.47by Pa stock,which is whereit is placedin Fig. 5.47. elementsofthe groupofspeciesnumbered8 to However,Sandbergand Ziegler(1973)postu15.This speciesgroup is identifiedby someau- late development of P. rugosa trachttera thors as the subgenusManlicolepis. Note that (sketch 38) and P. rugosa rzgosa (sketch 39) Pa elements of theseearly speciesof Palmato- from a speciesin the Conditolepis stock that is lepishave a prominent lobe on the outer side; relatedto the one u/ith Pa elementslike those a straightor only slightlysinuouscarina;an un- shown in sketches36 and 37. If the phylogedistinguishedcentral node; a downwardlyde- netic arrangementof thesethree subspecies is flectedposteriortip; and no parapetalong the as shownin Fig. 5.47(and we may alwayshave inner margin. to guessabout that), some nomenclaturaladThe severalFamennianlineagesrecognized justmentswill obviouslyhaveto be made.The vtithin Palmatoleprs diverge from P. triangu- more important lesson,however,is that gross laris (Fig.5.47.16),whosePa elementsare re- morphologyofsingle elementsmay not always latedin rnanymorphologicparticularsto those be the best guide to relationship.All of these of the Frasnian"manticolepids"but differ in "subspecies"are said to be connectedthrough havinga moredistinctlysinuouscarina:a more morphologically intermediate Pa elements conspicuouscentralnode;and a platform that with other membersof the lineagesto which is flexed upward (instead of downward) they are assignedinFiE 5.4'1. posteriorly. Species in the Palmatolepis branch repreSketchesI 7 and 20 to 27 in Fig. 5.47 are Pa sentedby sketches28 to 33 in Fig. 5.47 are elementsof a group of species(or subspecies) characterizedby small, narrow Pa elementsin that includes lhe type of Palmatolepis, P. per- which the smooth-surfaced platformwithdraws Iobata.Pa elementsofspeciesin this groupare phylogenetically from the anteriorend and belargeand conspicuouslysinuous;have narrow comeswidest and best developedposteriorof outer laterallobesthat generallybeara distinct the centralnode.Anterior of the centralnode, secondarycarina;and developa low, ridgelike the main axis ofthe elementis developedas a parapeton the inner sideanteriorto the central conspicuousblade.A more important characnode. ter of this stock, which was referred to the The Palmatolepislineagethat begins with subgewsDeflectoleprs by Miiller (1956),may species42 in Fig. 5.47 is distinguishedby Pa be the discovery by van den Boogaardand elementswith long, mostly smooth platforms Kuhry (1979)that Pb elementsare not "noththat lack an outer laterallobebut beara serrate ognathellan"but are archedpastinateforms of or ridgelikeparapeton the inner side,anterior a type that hasbeenreferredin form taxonomy of the centralnode.Speciesin this lineageare to severalspeciesof Tripodellus Sannemann.It inluded by many authors in the subgenus is difficult to seehow thesestructurescan be Panderolepis. homologizedwith the "nothognathellan"Pb van den Boogaardand Kuhry (1979) refer elements of speciesin other Palmatolepis linmost of the Palmatolepisspeciesin the stock eages,so it may tum out that this group will thar beginswith skerch 35 (Fig. 5.47) to the ultimately merit separate generic distinction. subgenusConditolepis.Pa elementsof most When (and i0 that day comes,the venerable speciesin this group lack an outer laterallobe, name TripodellusSannemann,1955 (not Dehaveovateto quadrateplatformswith a carina flectolepis M.ijller, 1956)will be available. that is weakly developed posterior of a large Conventional wisdom has it (e.8., Ziegler central node; and a sharp-edgedparapet that and Lane, 1987)that Polygnathuslatifossatus rims the inner margin to a point well posterior Wirth (Fig. 5.47.1),progenitorofthe Palmatoofthe centralnode. lepidae, developed from speciesof the PolygPa elementsdepicted.insketches26, 38, and nathus varcus stock (the far righthand branch 39 in Fig. 5.4'7have been taken to represent in Fig. 5.45).Speciesin that stockbuilt carmi three chronologicsubspeciesof Palmatolepis niplanate Pa elements with long, subquadrate
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90r
THE MAJORCONODONTCROUPS
Tgnathuslattfu* b Poh,gnathus, rnerable genus Itassary to reas15.17.2), P. uishr specieswith f are supposed ELJ. As a temribiiatus might rlrus and the irii. which has '$l- esymmetriI have not foly routeshere,or : rsed the rubric trrmal assignwell be de$t of the speDnsructed and -les
bsin and d ro this family td Polygnathus, r the attachment l- -\ moreor less dia-n groove, oc,.hn its position I b1 a broad flat fr may have a I of its lengh, or msiderably less dthe pit. 7 is complicated, . 5.48):the genus That is, Siphonbnognathus by :lhat namecould rue it had been cE.in 1944Branhtirute name.$ldle (1934) had boper (1939)the thus znd. Dinohblv parts of the della. Althou$t g,Falcodus,Elicfunodella to be d s-ork 1o prove
107
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Fig. 5.48. Elements typical of m\ltielement Siphonodella (Elictognathidae).
it. When (and if) that happens,Falcodus will and that they might not yet haye appearedin clearlybe the oldestvalid namefor the typical populationsof S. praesulcatd,the earliestand genus of the family Elictognathtdae, and EIic- least Siphonodellalike speciesof the genus,or tognathw, Dinodus, ard Siphonodella will be even in early populationsof S. sulcata.Those junior synonyms.The family name Elictog- earlyrepresentatives may haveevolvedPa elenathidaewill stand.however.becauseit is the ments with the essentialcharactersof Siphonoldestone proposedfor any ofthe genera(syn- odella,bnt they might have retainedthe genonymsor not) now includedin it. eralizedPb, M, and S-serieselementsof their Although a greatdeal of attention has been ancestors.In short, evolution of Siphonodella paid to the morphologyofelictognathidPa ele- may not have affectedall componentsof the ments,there is no publishedreconstructionof skeletalapparalus equallyor at the sametime, the complete skeletal apparatusfor any of the and there is no reasonto assumea priori that 20 speciesnow includedin the family. No one, non-Pa elements were morphologically the 10my knowledge,hasventuredevena guessas samein the apparatuses ofeveryspecies. to compositionofthe apparatusof any species With the exception of Siphonodellapraesulof Alternognathus(Fig. 5.49.1to 5.49.3),but cata Sandberg,all known Late Devonian repSandberget al. (1978)speculatedthat the Pb resentalivesof the Elictognathidaebelong in position was occupiedin the apparatusof at Alternognathus, which was created by Ziegler least some speciesof Siphonodella by anguli- and Sandberg(1984)for speciespreviouslyreplanateelementsofthe sortcommonlyreferred fened with question to Polygnathusor in1oEliclognathustthat the M position included cluded in Scaphignathus, whosespecieshave elementsthat havebeendescribedin form tax- Pa elementsthat are closely similar in moronomy as Falcodus angulus; and that various phologybut wereprobablyderived from Panform speciesof Dinodus occnpredpositions in dorinellina,not from Mehlina. the S series.As Sandbergand his colleagues The oldestknown speciesof Alternognathus, noted, however, no specimensof Dinodus, A. pseudostrigosus (Dreesenand Dusar) (Fig. Elictognathus, or Falcodus angulus have been 5.49.1), formed carrniniplanatePa elements reported from rocks with elements of ^trplron- with a narrow,asymmetricallydevelopedplatodellapraesulcata(Fig. 5.49.a)or from collec- form that bears only a few nodes marginal to tionswith earlyrepresentatives of ,Srphonodellathe sigmoidally curved carina, and with a narsulcata(Fig. 5.49.5).Theseobservationswere row, flat undersurfacethat has an elongate taken to mean either that S. praesulcata and, basalpit but no very distinctkeel.Youngerspethe earliestrepresentatives of ,S.sulcalawould ciesof Altemognathus(Fig. 5.49.2and 5.49.3) have to be removed from Siphonodellaon are characterized by Pa elements with more groundsof apparatusincompatibility, or that elaboratelydeyelopedplatforms,which havea the occurrenceof Dinodus, Eliclognathus, and. median carina that is separatedby a slight Falcodus angulus with the Pa elements typical depression from the anterior blade and rnarof alI other speciesof Siphonodellais a rcs,rlrof ginal rows ofnodes or short transverseridges. "similarity of niches." I suggestthat there is Although there is currently a substantial also the possibility that the really distinctive stratigraphicgap betweenthe youngestknown features of Siphonodella developed gradually specimensof Ahernognathusand the oldest
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the simplestand presumablymost generalized memberofthat genus,and not from oneofthe probablymore specialized, youngerspecies. As indicatedin Fig. 5.49,Siphonodellapraesulcata was succeededearly in the Carboniferous by ,t sulcata(Fi9.5.49.5),which was evidently the progenitor of highly variable ,S. duplicata(FiE.5.49.6,5.49.9, and5.49.13). Following an interval of substantialyariation,the duplicata zones,featurescharacteristicof Pa elementsin various segmentsof the S. duplicala populationsstabilized,and youngerpopulationswith thosecharactersarerecognizedas independentspecies,most of which rangedto the end of the KinderhookianEpoch.
'Sionodella from ft | -il -1. rcgularis; t tgt S- duphcata, qudruplicata; )S 'rc:cha-
rd the only one i,d€velopednartat are carminItal stages but r6es. which exIsrcrior to the n of S. praesulI carina that is ndose marginal Ss- Zieglerand '. S. praesulcata lEeudoslrigosus,
109
that appearedearly in the Mississippian(Fig. 5.50.5),anterior endsof cup segmentsare directly opposedon oppositesidesof the blade. In Pa elementsof two somewhatyoungerMississippianspecies(Fig. 5.50.6and 5.50.7),howjoin sides ever, anterior endsof cup segments of the blade at slightly different points. This conditionheraldsonethat is commonto the Pa elementsof all speciesof Gnathodus,but it is combined in Pa elementsof Protognathodus praedelicatus(Fig. 5.50.6)and P. cordiformis (Fig. 5.50.7)with featuresof surfaceornamentation that are more like the Pa patterns of older speciesof Protognathodus than those of somewhatyoungerspeciesof Gnathodus. Shortly after Protognathodus praedelicatus (Fig. 5.50.6)appearedin Early Mississippian new 5.9.7 Famib Gnathodontidae, seas,it was joined by geographicallywideConodontsassembledhere (Fig. 5.36) devel- spreadpopulationsof conodontswith similar oped late in the Devonian frorn Bispalhodus but substantially more elaborate Pa elements. rrdbil,1 (Spathognathodontidae).They are Theseconodonts,which representthe first specharacterizedby a basically seximembrateskel- ciesof Gnathodus,differ from P. praedelicatus, etal apparatusin which Pa elementsare car- their presumedancestor,in a numberof ways. miniscaphate,and Scelementsare alate,with a First, Pa elementsare conspicuously asymmetdenticulated posterior process.The sides of ric. The anteriorend ofthe cup on the concave gnathodontidPa elementsflare laterallyposte- (or "inner") side of the element invariably rior to midlength,and their uppersurfacesrnay joins the btadeat a point well anterior of the be smooth or ornamentedby a few scattered point at which the anterior end of the cup on nodes or by longitudinal or radial rows of the conyex (or "outer") side meetsthe blade. nodes. Little attention has been paid to the Furthermore,nodeson the uppersurfaceofthe complete skeletalapparatus,so taxonomy of inner cup segmentcommonly join to form a gnathodontidconodontsis basedalmost en- distinctive ridge- or comblike parapet, vthich tirely on featuresof Pa elements. may be short and weakly definedor long and The oldestgnathodontids,from rocksof lat- prominent. In Pa elementsof most speciesof est Famennian(Devonian)age,are referredto Gnalhodus,the outer cup is more broadly exProtognathodus(Fig. 5.50.2to 5.50.6),whose pandedthan the inner one; it may be essenspeciesformed carmlniscaphatePa elements tially smooth,may bear inegularly distributed with attachmentsurfacesin broadly expanded nodes,or may have longitudinally,radially,or basal cavities (or "cups") that occupied the concentricallyarrangedrows of nodesor low posteriorhalfofthe under surface.Pa elements ridges. In the highly variablepopulationsof Gnalrof the three late Devonian speciesof Prolognathodus difer primarily in the manner in odus that spread with the initial explosive which the upper surfaceofthe posteriorcup is burst, Lane, Sandberg,and Ziegler(1980)recornamented;one species(Fig. 5.50.2)formed ognized three rnajor groups. The group that Pa elementswith smooth-surfaced cups;Pa ele- centerson G. delicatus(Fig. 5.50.8),and also ments of another(Fig. 5.50.4)bearshort rows includesG. cuneiformis(Fig. 5.50.1l),is charof nodeson either side of a subcentralcarina; acterized by Pa elements with a long, well-deand homologouselementsof a third species fined parapet.The groups4pified by G. lypicus (Fig. 5.50.3)havea node or two on either side (Fig. 5.50.9) and G. punctatus(Fig. 5.50.10) of the carina. In Pa elementsof theseLate De- have Pa elenents with short parapets.The latvonian soecies-and in those of a fourth one ter groups are distinguished by the fact that
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ht is also clearly Ets fiom the two nples of G. typ5-50.12. r-d(1980),who are llilogenetic inter. 5-50.recognized andre;. 5-50.14) is formedPa eler of rhe two early , a long, well-deinendy widened
denticlesin the posteriorsegmentofthe carina. on reLaneand his colleagues did not speculate lations between G. bilineatus and earlier species of Gnathodus.However, since simplification in the morphologyofPa elementsappears to have beenthe hallmark of evolutionarydevelopment in the three major groupsof early Mississippianspecies,it seemsunlikely that G. bilineatus, with its highly complex Pa elements, is very closelyrelatedto either the lypicusot punctatus grcups, eventhough posteriorly widened denticles are characteristic of the latter. Thus, if thereis a relationshipbelvteenG. bilineatus and any group of early Mississippian gnathodontids,one might be postulatedwith the delicatus Eroup,which specializedin building Pa elementswith long parapetsand might also have taken up denticlewidening in midMississippiantimes. Belka (1985) deives Gnathodusbilineatus from his species,G. praebilineatus, which is said to be "... a perfect horneomorph of Gnathodus delicatus." Although this would seem to vindicate my "guess" that the G. bilineatus slock had its origrns in the delicatus group,I shouldalsonote that BelkachoosesG. semiglaber(Fig. 5.50.13),a member of the punctatusgroup,asthe likely ancestor,and not a speciesofthe /elicatus grcup.This would require reversalof morphologictrendsin the G. punclatus group rccognizedby Lane, Sandberg, and Zie{er (1980)by requiring that posterior denticlesofthe carinarevertto simplicity in G. praebilineatus(only to becomecomplexagain in G. bilineatusitself),and that the parapetbecome longer,despitea tendencyin the puncta,rJ group for the parapetto begin short and become shorter! Gnathodusgirtyi (Fig. 5.50.15),which appearedat aboutthe sametime as G. bilineatus, might be a somewhatsimplifiedmemberof the same group. However, Belka (1985) has recently describeda new species,G. awtini, which is said to have Pa elementstransitional in morphology betweet lhose of G. texanus,an end memberof thepunctatusErorrp,and G.gir/yi. Derivation of G. girtyi from G. austini, however,would require that a short parapet, with a high anterior node,becomelongerand more uniform in heiglt; and that the posteriorly wideneddenticlesof G. texanus,G. aus-
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,infs presumedprogenitor,be abandonedin favor of a sirnpler arrangement.I opt at this stagefor a scenario that requires fewer reversals in trend-that is, for a relationship to tJIe delicatus grotp (and, perhaps, G. bilineatus), which has a long parapetand posteriorlysimple denticles. 5.9.8 Lochrieqand Vogelgnathus referred Two additionalMississippianlineages, tentativelyto the Spathognathodontidae in Fig. 5.36,merit discussionhere,separatefrom the Gnathodontidae.One lineageis formedby the several speciesof Lochriea (also known as Paragnathodw)(Fig. 5.51), the other by the two known speciesof VogelgnathusNotby and Rexroad(Fig. 5.51).Speciesof both Lochriea and Vogelgnathus are represented by bedding-planeassemblages, hence there are few mysteriesabout skeletalanatomy. There are substantialquestions,however,about their relationshipsto other conodonts. Lochriea commutatrs (Bransonand Mehl) hasa seximembrateskelelalapparatusin which the Pa posilionwas occupiedby carminiscaphateelementsthat are closelysimilar to those of Protognathodusmeischneri(Fig. 5.50.2)in that the cup is smoothon its upper surface.Indeed,it would be easyto confusePa elements ofthe two specieswhich, however,differ in relative height of carinaand basalcavity and in the fact that denticlesof the carina tend to widen laterallyand developa distinctive cancellatepatternrn L. commulatus.L. cracoviensisBelka,the oldestknown speciesof Lochriea, is distinguishedby Pa elementswith cups of more elliptical outline and laterallyexpanded, surficiallycancellatedenticleson both anterior blade and posterior carina.Other speciesof Lochriea,like other speciesof Protognathodus, developedPa elementswhose cups are variously ornamentedby nodesand ridges. Lochriea uacovienJri appears stratigraphicallyin the biozonejustabovethe onein which Protognathodus cordifurmis is last recorded andjust belowthe onein which Z. commutatus and Gnathodusbilineatus(Fig. 5.50.14)make their debut.It is easyto postulatea relationship betweenZ. cracoviensisall:dL. commutatus, but difficult to relate either sDecieslo Para-
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THE MAJORCONODONTCROUPS
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rix processand dose laterally qr are smooth s of Vogelgnar of late Missistlrcir phylogeil Norby and tottr name and t that the Pa futhodus pass tages that are *ments of ZoIs might be an tved through tklus stabilis, r other gnatho: been considrceding discus5t an attactrYe a rhat Lochriea Leage separate a and Gnathoriable to create r- I recommend : until the relaI relaled genera E[ considered, ls in the same Fesent the hisEd by so many : made out yery
Fibodonridae).
A Fig. 5.52. Upper views ofPa elements typical ofvarious genera ofthe ldiognathodontidae. (A) Declnognathodus; (B) Idiognathoides; (C) Neognathodusi (D) Idiognathodusi and (D Strcptognathodus.
5.9.9 Family ldiognathodontidae Harris qnd Hollingsworth,1933 Idiognalhodontidconodontsare distinguished by carminiscaphatePa elementswhoseupper surfacestlT,icatly bear three longitudinal rows of nodesor denticles.One of theserows, the carina, is a posteriorcontinuation of thefree blade, which is assignedan anterior position and may account for more than half the total length of the element.Conceptually,at least, the other denticle rows are maryinal to the carina; in fact, the carinacurveslaterallyat varying distancesposteriorto the end of the blade to join one ofthe marginalrows or is replaced across much of the platform by a median groove or trough, so that many idiognathodontid Pa elementsappearto have only two denticle rows. The complete skeletal apparatus is known for only a few of the speciesnow includedin the Idiognathodontidae. In thosespecies, the apparatus is seximembrate, includes
an alateSa elementwith a denticulatedposterior process,and is in other respectsclosely similar in compositionto that of the presumably ancestralGnathodontidae. Declinognathodusnoduliferus(Fig. 5.52.\), the oldest knowr idiognathodontid,is drstinguished by carminiscaphatePa elementsin which the carina curves laterally to join the outer marginal denticle row a short distance posterior of the end of the blade. In Pa elementsofspeciesof Idiognathoides(Fig. 5.528), which appea6 shortly afler Declinognathodus, the posterior end of the blade curves abruplly to one sideandjoins the outer maryinaldenticle rorv wihout forming even a short carina. Furthermore,Pa elem€ntsof some speciesof Idiognathoides exhibit ClassIII symmetry; that is, sinistral and dextral specimensdiffer in morphologic detail, but not in overall pattern. Early speciesof Neognathodw(Fig. 5.52C) built subsymmetrical Pa elements in which a well-developed carina extends nearly to the
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THE MAJOR CONODONT GROUPS
d photographic E tbat represent a elongatecup is ro the poste:en subparallel an of course, JStreptognathord to that genus Rl) larger spechs'erse ridges d lobaleareas r rt€ platform's I h.gesl Pa elets illustratedby l!85). the carina rt of the platEard by transI atrtrolaterally ndose marginal hents are the lnathodus spemll Straka,and lar cryptically, tErs to have r to ldiognathtmsylvanian." t dominated by th those domifr the Pennsylplicated underr€s€ntsa maJor Eronomy, m*-art) Slreptondzs. as stratirdicate, and if z.SlreptognathE)- as ontogeatically in Fig. n and Permian rldiognathodus caicshiftsofjuders into adult iritial ancestor, r€ and more diI earlyPermian f,!' through the Fosis affected drs. If such an ned in the detrtant group of
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are of Early Mississippian (Kinderhookian) ageithe youngeslare ofearliest Triassicage. The rootstockofthe Anchignathodontidae is formed by a successionof Carboniferous, Permian, and earliestTriassic speciesherein assigned collectively (and probably quite loosely) to Hindeodas.Only a few ofthese specieshavebeendiagnosedand describedin fully modern, multielement terms, so future work may well establishthat severaldifferent lineagesare involved.In line with the practicein many other families, each of those lineages would merit recognitionas a genus,and there are namesalreadyavailablefor most of them! The oldestanchignathodontidknown to me, Hindeoduscrassidmtalus(Bransonand Mehl) (Fig. 5.5a),representsa group of Early MissisFig. 5,53. Ontogenetic sequencein Pa elements of sippian (Kinderhookian)speciesin which carIdrognathodus- Smallest specimens have morphologic miniscaphatePa elementshave a cup-shaped fea]]'Jfesof Slrcptoghalhodus. D.'aw,n froni photographs basalcavity beneaththeir posteriorhalf and a in van den Boogaardand Bless(19E5). finlike anterior blade that consistsof three or four denticlesthat decline in length and deconodonts,I suspectit involved severallin- creasein width posteriorly. These elements eages,u/hich may have been affectedto differ- wereoriginallydiagnosedin form taxonomyas ent degreesand at diferent times. Sorting this various speciesof Spathodusor Spathognathoout will requirecarefulbiometricstudiesofcol- dus, and it is not possible at present to deterlections from rock sequencesthat represent mine if they representone or dozensof species long-continuedstability of depositionalcondi- in a multielementsense.In any event, Pa eletions. I doubt that it rvill be worked out in the ments of this type are regularlyassociatedin cyclicdepositsby which the Carboniferousand collections from Kinderhookian strata with Lower Permianare represented in much ofthe bowedangulatepectiniformelementsthat have world, despitethe fact that collectionsfrom relativelyshortsubequalanteriorand posterior and have been identified previously such rocks are commonlyrich in specimens processes that represent the Strepognathodus-Idiognath- asspeciesofSzbDryanrolrffBransonand Mehl, 1934. Such elementsqualifu morphologically odzJplexus. and fraternallyas Pb componentsof speciesin the H. crassidentatusgJrou'p. Maybe, after this 5.9.l0 FamilyAnchignathodontidae Clark, group has been revised and its taxonomy 1972 brought up to date, Subbryantodus will t.urn Ozarkodinideconodontsincludedin this fam- out to be the oldestavailablegenericnamefor ily have a basicallyseximembrateskeletalap- rt. paratusthat includescarminiscaphatePa eleCudotaxis piceslingl Chauff, based on maments, angulate Pb elements with relatively terial from somewhatyounger,middle Mississhortprocesses, and alateSaelementsthat lack sippianrocks,alsoseemsto be a memberofthe any trace of a posterior process.At presentone crassidentatusgroup, and I seeno way to disanchignathodontidspeciesis assignedto letitinguishit genericallyfrom otherspeciesin this ota-,cis,which is peculiar in that its apparatus plexus. appearsto havelackedelementsin the P posiHindeodus scitulus (Hinde) (Fig. 5.54) reptions, and all the othersare included in Ilin- resentsa secondcomponentof the Mississipdeodus, wbich is probably interpreted far too pian species-grouphere referred loosely to broadly. The oldest anchignathodontidsknown Hindeodus. H. scitulus has a distinctive car-
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h- and Aethotaxis ts. P elementsof
audus. Pa ele,idcztatusgrotp tnds in cuplike le unit and like rmarion of the . tte most diagz of Hindeodus [s ertensiform te Sb position b" One lateral rbeb€ntsharply t distance from mmonly devel'oflong, needleq./as group ape \tississippian
1r7
(Meramecian)age,and the lineageclearly ex- includesancestorsof Homoiranognathus, the tends through the remainder of the Carbonif- lesswell-known Permian Rabeignathusand,Irerous, the Permian, and into the lowermost anognalhus,and the Early Tiassjc IsarcicellaTriassic.Initially, in 1970,I interpretedPa ele- In the Treatise, Clark and I included all these ments of the youngestspecieskrown, H. typi- genera (except Homoiranognathus) with Hincdlrj (Sweet),as componentsof the unimem- deodusand,Aethotaxts in the Anchignathodonbrate apparatusof Anchignathodustypicalis, 1idae.However, information published since whereasoccupantsof the Pb, M, and S posi- the Treatise manuscript was prepared makes tronswereregardedascomponentsofthe mul- me uncomfortablewith lhat assignment.Thus, timembrate apparatus of Ellisonia teicherti I now treat Diplognathodusand its kin as an Sweet.Later (Sweet,1973)it becameobvious independentgroup with familial status. The that Anchignathodus typicalis and, Ellisonia family Sweetognathidae was established(as leicherti werc names for different parts of the Sweetognathinae)for this group by Ritter apparatusofthe samespecies, which ultimately (1986) who, however, included it within the (Sweet,1976;Sweet,in Ziegler,ed,.,1977)was family Anchignathodontidae. shown to be closely similar in skeletalarchitecIn terms of the morphologyof their pa eleture to other species of Hindeodus as inter- ments, speciesof Diplognathodus(Fig. 5.55) preted in a multielementsense.Before all of are in many respectshomeomorphic replaysof this had beensortedout, however,Cl ark(19'12\ the simpler speciesof Late Devonian-Early had baseda family-groupnameonlnchignath- Mississippian Prolognathodusand.mid- to late odas(superfamilyAnchignathodontacea), and MississippianLochriea. The pa elementsin this must prevail for the family under consid- question(Fig. 5.55)are carminiscaphate struceration despite the fact that Anchignathodus tures with a cup that expandswidely to the has been considereda junior subjectivesyn- sidesand extendsto the posteriortip. Upper onyrnof Hindeodussinceat least 1977! surfaces of the cup are characteristically The skeletal apparatus of Hindeodus cristu- smooth, but rare specimensin a large sample /ff (Youngquistand Miller), the Mississippian may havea nodeor denticleor two. Esoeciallv type-species, is now well known,asarethoseof distinctive of lhe Pa elementsof DiplignathoLate Permian H. julfensis (Sweet) and Late dzs, however,is division of the med.iandentiPermian-EarliestTriassic1L lypicalis (SweeI). cle row into a high anteior free blade and, posFor the most part, howeyer, Pennsylvanian terior of it and abovethe cup, a lower carina and Permianspecieshave beenneglected,and that may consistofa few denticlesbut is more their skeletalapparatuses are largelyunknown. typically fused to a smooth idge ot spatula, In fact,a majority ofauthors.whodealwith late which has a subquadrate lateral profile and Paleozoicand early Triassicconodont faunas drops off steeplyto the posterior end of the recognizeonly one speciesin this long interval, cup.Diplognalhoduswas said to have a multiH. minutus (Ellison) which, despitesubstantial membrateapparatusat the time it was estabdifferencesin morphology of its various skele- lishedby Kozur and Merrill (in Kozur, 1975), tal elements,is evenregardedasthe seniorsyn- but no illustrationswereprovided.It is signifionym of FL typicalis, whosetypesare from the cant to note, howeyer, that a hibbardelliform Lower Triassic.The timited materialavailable (i.e., alate)elementwith a long posteriorproto me suggests, however,that critical analysis cesswaslisted as a component. of larger collectionsthat span greater stratiIn the same year that Kozur and Merrill graphic intervals will result in recognitionof (1975)establishedDiplognathodus,perlmutter many species.But that is a job for the future. rnterpreted an aggregation of elements that form a recurrent group in severalsamplesfrom the Lower Permian of Kansasas the skeletal 5.9.11 Family Sweetognathidqe Ritter, 1986 apparatusof D. expansus.Perlmutter'sreconThe group of Carboniferous and Permian spe- struction,which includesan alate Sa element cies refened to Diplognathodus, Sweetogna- with a long posteriorprocess,follows the plan thus, and.Neostreplognathodusnakes up a dis- mentronedvaguely by Kozur and Merrill in tinctive and probably related stock that also their genericdiagnosis.However,perlmutter's
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'snpoqtDuSotdal$oaN esoql e)IIl qJnu xTqeqord ore lnq pequcsep uoeq lo pa,rolloJ tou e^eq flquuSopa^S pue snpoqtouSoldle Jo slueuole qS Uel 01 sluou.rele?d pue .qd .W ,cS ,qS 'lq8u uo slueuole eS oeprqleuSoFe^{S eqt Jo aeueS ol pou8rssEsolcedsJo sesnleledds puE stuetllala ^q.gg g .3![
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THE MAJORCONODONTGROUPS
l&menrs ig',trrs
on right, have not
ln diferencesin ItEir skeletalapI Diplognathodus fueb-' related as Hr Pa elements Mus expansus, r(1975),is taken Es of otherspers profitableto !d io 1977-that E closely related t to Hindeodus. lis suggestionis b oldest named tphanus, is sepe of L. commu!trt to the entire d interpreied to nillion years of xt of this inforr. b-vnoting that l9E2) have illuselements from l eastern Canada
I l9
that appear to represent Diplogndthodus and are from a stratigraphicinterval that is well within the rangeof Lochriea and.Vogelgnathus. Close sirnilarity in morphology between Pa elementsof DrplognathodusexpansusPerlmutter (1975) Sweetognathus merrilli Kozur ^nd. that the Sweetognathus (1975) suggests slock developedfrom diplognathodontanancestors in the Early Permian. Speciesof Sweetognathus (Fig. 5.55),like thoseof Diplognathodus,had, a quinqui- to seximembrateskeletalapparatusin Babeignethus which alateelementsin the Sa position havea long, denticulatedposteriorprocessand structures in the Pa position are carminiscaphate elementswith a relativelyshort anterior blade Fig. 5.56. Pa elementstypical of speciesassignedto that continuesposteriorly acrossthe broadly Rabeighat hus and I sarcicella (Sweetognathidae). expandedbasalcup as a carinathat is basically an adenticulateridge, but may be replacedby a singlerow oflow broad nodesor supplemented yet completelyconvincedthat this pattern(or laterallyby a pair of subparallelrows of such that of Pa elernentsof Rabeignathus) merrts nodes. A characteristic feature of the Pa ele- recognitionat the genericlevel. ments formed by speciesof Sweetognathusis Sweetognathuswlritei (Rhodes, 1963) was development of a pustulosepattern on the also the apparentancestor,in the Early Permupper surfaceof posterior nodes.Such a pat- tan, of NeostreptoqnathodusClark (1972) (Figtern was also developedon Pa elementsby 5.55), a stock of stratigraphicallyimportant speciesof Lochriea, which may suggesta rela- sweetognathidspecieswith Pa elementschartionship. Evolutionary development of the aclerizedby subparallelrows of nodes sepaSweetognathuslineagehas recently beentraced rated by a well-marked median groove or chanby Ritter(1986). nel. It is also of interestto note that nodesin Ritter (1986)has demonstratedthat species the posterior rows of Pa elementsof Neostrepol RabeignathusKozur (1978)(Fig. 5.56)have tognathodusspeciesseemnot to have the disa quinqui- to seximembrateskeletalapparatus, tinctively pustulosesurfacethat is characterissimilar to that of Sweetognathus.The Iwo tic of comparablenodes in the Pa elements known speciesofRabeignathusare recognized, formed by speciesof Sweetognathus,Homoirhowever, by their distinctive Pa elements, anognathus,Rabeignathus, and Lochriea- T||re which are like the double-rowed carminisca- significance of these features is diftcult to asphate elementsof someSweetognathzsspecies sesswith information presentlyavaitable.It is but differ in having one or two additional sub- possible,of course,that Neostreptognathodus parallel rows of somewhat rnore irregularly representsa stockdevelopedde novofron Dipustulosenodes latenlly. Rabeignathus,which plognathodus, whose stratigaphically disconalmost certainly developed frcm Sweetogna- tinuousrecordextendsalmostto the end ofthe thus, has a r/ery short range in the Early Permian. Permian. The Late Permian Pa elementsfor which Homoiranognathus wasestablishedby Ritter Kozur, Mostler, and Rahimi-Yazd (1976)es(1986) for a singleEarly Permian species(1L tablished Iranognathus arc, in many respects, huecoensis)known only from carminiscaphate homeomorphic replays of those on which Pa elementson whoseupper surfacean aden- Ritter (1986) basedHomoiranognathus.Evoticulate,pustulosemedian ridge is flankedlat- lutionary patternsin Permian stocksare curerally by two to four subparallel rows of pus- rentty diftcult to reconstructbecausecollectulose nodes. Elementsof H. huecoensisare tions from criticat intervals and facieshave yet surelydistinctive in appearance, but I am not to be madeor describedin detail. However,it
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THE MAJORCONODONTCROUPS
liss III symmetry; E of a pair may be r e\ en thoughthe i end ofthe same H membersof a rlle of denticula4ftarures. ; Cloghergnathus, frognathus (all ild Pa elementsin lerior end of the ldiare between its . Patrognathus apI a-ndrangesinto iia-Upper Crenr of this group ap, some two zones ld are either conch- into the next lis disjunct strati lbe very difficult to f tbe four genera. ghergnathw differ o\' in the profile lce blade,whereas ra'nticlesin Pa elel ma)' be replaced Ess of nodesthat I featuresare cerI the Pa elements b samegenus,but l:nce on the geb its debut in the tha, Patrognathus rtbe Lower Missis:nulata Zone, inr lhat built Pa eler end of the blade fix end of the row h of the doublehis is also the case Eears in the late mft4s and continMississippian,and *Yed in the latest mugh the Pennsylf the Permian. oany singlefeature mbination of feaIte Pa elernentsof
t2l
ClogheEnathus
Adetogntthus
Clydagnathus Fig. 5,57. Elementsand apparatusestypical ofspeciesofthe Cal.usgnathidae.
Clydagnathus, Cavusgtathus, and AdaognalruJ. Apparatusesof Cavusgnathus speciesapparently exhibit Class IIIa symmetry in that right and left Pa elements are distinguished solely by being bowed in different directions. Right and left Pa elemelrtsof Adetognathus,on the other hand,are morphologicallysomewhat differentand thus exhibit ClassIIIb symmetry. In addition, Pa elementsformed by speciesof Adetognathushal/e essentiallyno fixed blade, whereasin comparablePa elementsof Cavusgnathus srycies as rnuch as half the length of the blade may be incorporatedinto the marginal platform row with which the blade is confluent. I would ascribemy consistentinability to separatespecimensrepresentingspeciesof CavusgnathusandAdetognathusto rny lack of ex-
periencewith thesegenerawere it not for the fact that specialistson Carboniferousconodonts appear to have problems lhat arc aI leastasgreatasmine! In any event,elementsof cavusgnathidconodontsare common in rocks that recordmarginalmarineenvironmentsthat werecharacterized by shallowwaterofvariable salinity, and they are useful as guides to such environments. Ancestorsof caYusgnathidconodontshave beenidentifiedby Sandbergand Ziegler(1979) in Late Devonian populationsof spathognathodontid ozarkodinidesreferredto Pandorinellina insita (Stauffer).In thosepopulations,Pa elements (Fig. 5.38) are dominantly singlerowed,carminatepectiniformstructureswith a prominentfinlike bladethat is deflectedto the rightat its posteriorend. However.minor seg-
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'€pluIpolJ?zo eql Jo seE?eulltueJe.grpsnorr? uI peldop" ,{lepl,|alueludole^ep Jo uJe Bd eql ^lreelc s?/i\ 1r tErll p"J eql loJ ld$xe Euruonueur quo.4 aq lou plno,,A,{trJrqrssod srqJ sJotseju? puruouuopuedpetuouncopunro poullueprun pedole^op(mqlnu8n te, s? rrIolJ {1e,r4ere1r -Ll8ol) pte'snlqou8tutDrtdD)'srullDuSoiapv -mqnuSsn^D) 'snqpuSoqdDJ ''a 0 spqleua -sn^EcJe13leql 13q1lno pe[u oq lou uec 1ros J4"l eqlJo sa^4 'Je^e^\or{'slJols prql?u8sn^?J -Elueserdar$rg eqt uro{ snqpu8DptlJ pue sdEC qcueJq snqtDuSo.tlod aleJedos,(lluoJJnc ere'sntlpuS snqpuSopq) et+Jo std.olrcnu\ttd.o} -otapv 'ratel 'pu9.snl ou8sn oJ leql pue '^lr -urE orp qtu?Jq snqpuSolpd eqt vrorJ etJrrl Jo usrddrssrssrl l-pllu ur pedole op snqpuStu -tnudDJ pue'srulpu8nq8ol)'snq JouSoqdoJ l"ql ssonE1q3[u ouo urroyeld eql Jo eprs ssopoueql glr^\ snonunuoc lqEu eql uo sr ePsJq eql^\oJ sluauJaleEd Jsoq^r ur 'sr?{,| -DuBDpqJ ol Jo 's,r\oJpurS:eur o,lrr1slr uee/(l -oq [uJoJl"ld eqt surof teqt opqq ? qt[^{ '.snryl -DuSottDdot Jaqtreesu ue^6 o^"q ot tq8noql eJe eseql Jo sluEU?A 'epelq eql 01 Jouel -sodselcuuope{rlapouJos^1orelqnoppodola^ suoq?Fdod au?s eqt Jo stuour -ap ^llusJedd?
VJNOCONOJ
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[t986). That study [en1. and distriYdtognathus speb collections were Drxsfucting comE onl) the Pa eleh qere mineralimed them. drzs species are *rucures with a merior V-shaped dtransversely ned by adcarinal , srbmedial carina fu of the platform. iro fiee and fixed Fal length,is conts margin of the flte oppositemarirdvely denticuBitter. Sandberg, Rmjer taxonomic irui Pa elements in keel,which enrior of midlength '6e pit by narrow rgln (termed an lr. Sandbergand ficb may include s!-e. is developed b carina and parl of f{estognathus roryhology of the ladorm maryin; a Ent ofthe anterior of the secondary lt ofbroader and sal margrn mard posteriorto the I rEpresent early Aognathusspecies b Pa elementsof E scaphateunder =sive basalmarhct that the latter lronouncedin its y. suggesBto von I (1986)thatMes&gnathus (family
t23
Cavusgnathidae), whosescaphatePa elements havea double-rowedplatforrnand a bladethat joins the right maryinalrow. Pa elementsof Mestognathusare homeomorphic with those of Scaphignathus(Fig. 5.41),which is thought to have evolvedin the Late Devonianfrom Pandorinellinainsita (Fig. 5.38;- as did Clydagnathus,the proximale ar\cestorof Mestognallrus.Short of a thorough restudy and revision of Pandorinellina, the Cavusgnathidae (including Clydagnathus), and, Fig. 5,59, Elements typical of sp€ciesincluded in the Meslognathus,however, I seeno way ofaccom- Coleodontidae. modating these remarkable homeornorphs (and their common ancestors)in the samesupragenenccategory.Thus, somewhatanomalously, I suppose,| rctain Scaphignathusit the is difficult, if not impossible,to diagnosepropSpathognathodontidae, whereas its younger erly becausethe type-species of Coleodus,its homeomorph, Mestognathus,is accommo- typegenus.is basedon fragmentary specimens datedin a separate family, the Mestognathidae. that make comprehensiyemorphologicinterPossiblythe bestway to insuretaxonomicsym- pretationimpossible.In general,howeyer,spemetry would be to establish a separatefamily cies in this taxonomically isolated group also for Scaphignathus,which would raise the formedrelativelylargeelementsthat havehyapossibilility,of course,of a separatefamily for line, fibrouscrowns,which (in the caseof,S/ereachconodontgenus! eoconusandMixoconuJ)consistofrobust conMestognathusis interpretedas a denizenof iform elements or chains of such elements harsh, nearshoremarine environmentschar- weakly (in the caseof Archeognathus)or stoutly acterizedby high saliniry and probably land- connected(in Coleodusand.Neocoleodus)with ward of the shallow,inshoreenvironmentin- their neighbors at the base. Undersidesof habited by its progenitor,Clydagnathus-von crowns are flat, broadly convex,or longitudiBitter, Sandberg,and Orchard(1986)speculate nally grooved,and in numerousspecimensof that restriction to such an extreme envron- Archeognathusand,Coleodzscrowns surmount ment may help explain the rarity of Mesto- a prominent basalstructurethat consistsofan gnathus and.the fact that it may have mineral- elongatebar that exhibitsa conspicuousdownized only the Pa element$ of its skeletal ward projectionand apparentlylacksa cavity apparatus. or excavation.No basal structureshave been observedwith elementsof .S/ereoconus, Mixoconusor Neocoleodus. Barskov,Moskalenko,and Starostina(1982) 5,10 OrderUnknown illustrate numerous bonelike featuresin the Bransonand 5.10.1 Family Coleodontidae basalstructureof Siberianspecimensreferred Mehl, 1944 to Coleodus,bntK)apper and Bergstrdm(1984) This family is retained for ColeodusBranson were unable to identifi, comparablefeaturesin and Mehl, 1933,Archeognathus Cullison,1938, the basal structure of Archeognathus.Altho]j;gh andNeocoleodus Bransonand Mehl. 1933.and the crownsof elementsassignable to speciesof possibly related forms such as Stereoconus the Coleodontidaeclearly exhibit the intemal Branson and Mehl, 1933, a.nd Mixoconus structure of conodonts, the basal structures Sweet, 1955.Elementsof speciesassignedto have no counterparts elsewherein the Conothesegeneraare shownin Fig. 5.59. donla. No relationshipto olher groups is In connection with their thorough recent apparent. The Coleodontidae,if a natural study of Archeognathus,Klapper and Berg- unit, might representa separateclass of the stritm (1984)point out that the Coleodontidae Conodonta.
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THE MAJORCONODONTGROUPS furdse Acad. We54, rt. B- (1979).Sta: Palmatolepis apdoDlophorids) at d specific level. 1r5 from the Fort Horician), Mararc- {3(5), ll374h1.- and paleonFatr of Missouri. r IJ{3). r-208. - C- | 1947).Lower lEk\'. J. Paleont. ; G. ( 1933).Condodts from the rado: Bainbridge Do City (Lower jr-llissouri StudG no. 3: ConShaleof Missouri. l? l -159. rlJs lcriodus ard I J. Pateont. 12, 233-246 i\ Index E \I . Shimer and 'aL ft. R. (1983).Paea frmily Icriodonlifiw. Fossilsand *t'oniar. Icriodus nl. et Palaeo . 6, fuatigraphie und es der dstlichen ial ){. Jb. Geol. rr. D. G. (1977). conodonts from 51,'772-796'ar. [tte multielement trs. Doliognathus .- 59\2), 299-309. ria.n crisis and its coDodont taxont7-158. Clark, D. l 2). Suwey of r North America. gudies 9(2), 102teqstrom, S. M., Rhodes,F. H. T., , Lindstriim, M., G- (1981).Cono-
dolta- In Treatise on inyertebrate paleontology Pt. W, Suppl. 2 (ed. R. A. Robison). ceol. Soc. America and Univ. Kansas,202 pp. Cooper, B. J. (1975). Multietement conodonts from the Brassfield Limestone (Silurian) of southern Ohio. "/. Paleont. 49,984-1008. (19'77\.Toward a familial classif,cationof Silurian conodonts.l. Paleont.5f , 105?-1071. Cooper, C. L. (1939). Conodonts from a Bushberg-Hannibal horizon in Oklahoma. "l PaIeont. 13, 379-422. Croft, J. S. (1978).Upper Permian conodontsand other microfossilsfrom the Pinery and Lamar Limestone members of the Bel[ Canyon Formation and from the Rustler Formation, west Texas. Unpubl. M. Sc. Thesis,The Ohio State University, Columbus, 176 pp. Drygant, D. M. (1974).ProstyeKonodonty Silura i nizoy Devona Volyno-Podolya (Simple conodonts ofthe Silurian and lowermost Devonian of the Volyn-Podolian arca). Paleont. Sb. Lvov Univ. GlO, 64-70. Dzrk, J- (1976\. Remarks on the evolution of Ordovician conodonts. Acta Palaeont. Polonica
2r,395-455.
(1983).RelationshipsbetweenOrdoyician Baltic and North American Midcontinent conodont faunas.f'offils and Strata 15, 59-85. Dzik, J., and Drygant, D. M. (1986). The apparatus ofpanderodontid conodonts.Ielrara 19, -
r33-141.
Ethington, R. L., and Brand, U. (1981).Oneotodus simptex (Fumish) and the genus Oneotodus (Conodonta)."/. Pqleont. 55, 239-24'1. Ethington, R. L., and Clark, D. L. (1982). Lower and Middle Ordovician conodonts from the Ibex area, western Millard County, Utah. Brigha.m Young Univ. Geol. Studies 28(2\, t160. Fahraeus,L. E. (1984).A critical look at the Treatise family-group classificationof Conodonta: An exercisein eclecticism. Lethaia 17. 293305. Fahraeus,L. E., and Nowlan, G. S. (1978). Franconian (Late Cambrian) to early Champlainian (Middle Ordovician) conodonts ftom the Cow Head Group, westen Newfoundland.. J. Paleont.72, 444-47L Fortey, R. A., I-anding, E., and Skevington, D. (1982). Cambrian-Ordovician boundary sections in the Cow Head Group, western Newfoundland. Pp. 95-129 in The CambrianOrdovician boundary: Sections, fossil distributions,and correlatioflJ(ed. M. G. Bassettand W. T. Dean). Nat. Mus. Wales,Geol. Ser. 3, 27 pp. Furnish, W. M. (1938).Conodontsftom the Prairie du Chien (I-ower Ordovician) beds of the Upper Mississippi yalley. J. Paleont. 12,318340.
Gagiev, M. H. (1979). [Conodonts from the Devonian/Carboniferousboundary depositsof the Omolon Massifl. Guidebook, Tour 9, Biostratigraphy and fauna of Devonian-Carboniferous boundary deposits. l4th Pacifrc ScienceCongress,Khabarovsk,USSR, August 1979,Suppl. 2, 104 pp. (In Russian,\ryithEnglish diagnoses ofnew generaand species.) Harris, R. W. (1964). Subgeneraof the conodont ge\!s Multioistodus in Simpson-Burgen (Ordovician Arbuckle) conodontsf.om Oklahoma. Okla. Geol.Notes 24. 108-lI8Harris, R. W., and Harris, B. (1965). Some Wesr Spring Creek (Ordovician Arbuckle) conodonts from Oklahoma. Okla. Geol. Notes 25, 34-4'1Harris, R. W., and Hollingsworth, R. V. (1933). New Pennsylvanian conodonts from Oklahoma. Am. "L Scl., ser. 5,25(t47), t93-2O4. Hass,W. H. (1959).Conodontsfrom the Chappel Limestone of Texas. U. S. Geol. Sury. Proll Paper 2941,365-40Q. Helrns, J. (1961).Die " nodocostata-Gruppe"der Gattung Polygnathus.Geologiet0, 6'14-'71t. Huckriede, R. (1958).Die Conodonten der Mediterranen Trias und ihr stratigraphischerWert. PalAofi. 2.32. L4l-175. Huddle, J. W. (1934). Conodonts from the New Albany shale of Indiana. Bull. Am. Paleont. 2r(72), 136 pp. Jeppsson,L. (1974) lL9'151.Aspectsof Lare Silurian conodonts,Frssils and Strata 6,19 pp. (1983). Silurian conodont faunas from Gotland,.Fossilsand Stratq 15, l2I-144. Kennedy,D. J. (1980).A restudyofconodonts described by BRANSON & MEHL, 1933, from the JemersonCily Formation, t-ower Ordovician, Missouri. Geol. et Palaeont.14,45-76. Klapper, G., and Barrick, J. E. (1983).Middle Devonian (Eifelian) conodontsfrom the Spillville Formation in northern Iowa and southernMi[rrcsota.J. Pq.leont.57(6), 1212-1243. Klapper, G., and Bergstrom,S. M. (1984). The enigmatic Middle Ordovician fossil Archaeognathus arrdits relationsto conodontsand vertebrates.I Paleont. 58,949-9'16. Klapper, G., and Johnson,D. B. (1975).Sequence in conodont ge rs Polygnathusin Lower Devonian at Lone Mountain. Nevada. Geol.et Palaeont.9,65-83. Klapper, G., and I-ane, H. R. (1985). Upper Devonian (Frasnian) conodonts of the Polygna/ltis biofacies, N.W.T., Canada. J. Paleont. s9(4),904-951. Klapper, G., and Murphy, M. A. (1975).SilurianI-ower Devonian conodont sequencein the Roberts Mountains Formation of central Nevad,a.Univ. Calif. Publ. ceol. Sci. ttl, t-62. Klapper, G., and Philip, c. M. (197D.Devonian conodont apparatusesand their vicarious skeletal elements.Ietra ia 4,429-452.
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THE MAJORCONODONTGROUPS r and Llanvirnian rcrthern Sweden. L r C, R. (1982).Rer fuovician-Early d Group, Clarksrt Sci. 19, 14'74I
:S- ald Bames,C. j a new multielele latest Ordovit- Geol. Surv. Cant!s!). phylogeny, r ot the conodont -{rbuckle Moun-ff- l410-1433. aaafumarion (Lower -donbgat. EltL Geol. et Pa. U- ( 1974).Pennlnts- IIa: The dinidu' Geol. et fua of the Notch trrician), House
ar.i-139.
lrrsions of some 'frovician conoievolution. U/riy. 4.1pp. lb der Conodonr Der ons. l. Die Stnckenb. Naturho Einteilung der
z x. 109-n7.
lf, ( 1957). Early bce) conodonts 3r- 1069-I 108. I ( | 9E2l,ower Dec-kindlei Zones), t to Pvblications, ED€nt genus,{pdria-o of The Canh {lcheringa 4, Eposition of the &anson & Mehl of the Canning ,-]IR J. Austrul.
B_(1e68) F9691.
rkontology of the Creek Member of brian) in southLKentucky. 1/dirts of Nora Fm.,
Toko Range,Glenormiston, pp. l2-15. In Hill, phylogeny of post-Early Permian crisis br'sseftD., Playford, G. and Woods, I.'1., eds.,Ordowhitei Zone corodonts with comments on Late vician and Silurian Fossils of Queensland. Paleozoicdiversity. Geol. et Palaeont.20, 139QueenslandPalaeont.Soc.(Brisbane). 165. Norby, R. D., and Rexroad,C. B. (1985). Vogelg- Sandberg,C. A., and Dreesen,R. (1984).I-ate Denalhus, a r'ew Mississippian conodont genus. vonian icriodontid biofaciesmodels and alterIndiana Geol. Sur,. OccasionalPaper 50,l-14. nate shallow-water conodont zonation. Geol Norris, A. W., Uyeno, T. T., and Mccabe, H. R. Soc.Am. Spec.Paper 196,143-178(1982). Devonian rocks of the Lake WinniDe- Sandberg,C. A., and Gutschick,R. C. (1984).Disgosis-LakeManiroba oulcrop beh, Maniroba. tribution, microfauna, and source-rock potenGeol. Surv.CanadaMem.392, 280 pp. (Also istial of MississippianDelle PhosphaticMember sued as Manitoba Mineral Resources Div., of Woodman Formation and equivalents,Utah Dept. Energy and Mines, Publ.77l.l and adjacentstates.Pp. 135-178.In HydrocarOrchard.M. J. (1980).Upper Ordovicianconobon source rocks ofthe greater Rocky Mountain donts from England and Wales. Geol. et Paregion(ed,.J. Woodward, F. F. Meissner,andJ. Iaeont. 14.9-44. L. Clalton), Rocky Mountain Assoc. GeoloPander, C. H. (1856). Monographie der fossilen gists,Denver. Fischedes silurischenSystemsder russisch-bal- Sandberg,C. A., and Ziegler, W. (1973). RefrnetischenGouvernemetts.Akad. Wiss. St.Petersment of standard Upper Devonian conodont burg,9L pp. zonation based on sections in Nevada and West Paull, R. K. (1983). Dennirion and strarigraphic Germany. Geol. et Palaeont.7,9'7-122significanceof the Lower Triassic (Smithian) (1979).Taxonomy and biofaciesofimporconodonr Gladigondolella meeki n. sp. in the tant conodonts of Late Devonian styri4ctrrvesternUnited States.J. Paleont.59(l), 188Zone. Unired Shtes and Germany. Geo!.et Pat9 2 . laeont. 13,173-212. Perlmutter, B. (19?5).Conodontsfrom the upper- Sandberg,C. A., Zle9l,e\ W., IJuteritz, K., and most WabaunseeGroup (Pennsylvanian)and Brill, S. M. (1978). Phylogeny,speciarionand the Admire and Council Grove groups (PermzonaIi,on of Siphonodella (Conodontz, I)pper ian) in Kansas.Geol.et Palaeont.9,95-l15. Devonian and I-ower Carboniferous). Newsl. Puchkov, V. N., Klapper, G., and Mashkova, T. Stratigr. T, 102-120. V. (1981).Natural assemblages of Palmatolepis Sannemann, D. (1955). OberdevonischeConofrom the Upper Devonian of the northern donten (toII"). Senckenbergiana Lethaea 36, Urals. Actq PalaeonL Polonica 26(3-4\, 281123-156. 298. Satterfield,I. R. (1971).Conodontsand stratigraRepetski, J. E. (1982). Conodonts from El Paso phy of the Girardeau Limestone (Ordovician) Group (Lower Ordovician) of westemmost ofsoutheast Missouri and southwestIllinois. "/. Texas arrd southern New Mexico. New Mexico Paleont. 45,265-273. Bur. Mines Min. Res Mem. 40, l2l pp. Savage,N. M., and Bassett,M. G. (1985). CaraRepetski,J. E., and Ethington, R. L. (1983) Rosdoc-Ashgill conodont faunas from Wales and sodus manitouensis(Conodonta), a new Early the Welsh Borderland. Palaeont. 28Gl- 679Ordovician index fossll.J. Paleont. 57(2),2897 t3. 301. Serpagli,E. (1974).Lower Ordovician conodonts Rexroad, C. B. ( l98l). Conodonts from the Vifrom Precordilleran Argentina (Prowince of San enna Limestone Member of the Branchyille han)- Boll. Soc. Paleont. Ital. 6, t7-98. Formation (Chesterian) in southern Indiana. (1983). The conodont apparatus of Indiana Geol. Surv. Occasional Paper 34, l-16. Icriodus woschmidti z,ie9ler Fossilsq,nd Strata Rexroad, C. B., and Nicoll, R. S. (1972). Cono15, 155-161. donts from the Estill Shale(Silurian, Kentucky Sparling,D. R. (1981).Middle Devonian conoand Ohio) and their bearing on multielement dont apparatuseswith seventypes ofelements. taxonomy. GeoL et PqlaeonLSBl, 57-74. J- Paleont.55, 295-306. Rhodes,F. H. T. (1953).Some British Lorver Pa- Stouge,S. S. (1984).Conodontsofthe Middle Orlaeozoic conodont faunas, Philos. Trans. Roy. dovician Table Head Formation, western NewSoc. London Ser. B. 237,261-334 foundland. Fossils and Strata 16, 145 pp. (1963).Conodontsfrom the topmost Ten- Sweet, W. C. (1970). Uppermost Permian and sleepSandstoneofthe easternBig Hom MounI-ower Triassic conodonts ofthe Salt Range and tains, Wyoming. "/. Paleont. 37, 401-408. Trans-Indus ranges,West Pakistan, pp. 207Rieber, H. (1980). Ein Conodonten-clusteraus 275- In Stratigraphic Boundary problems: der Grenzbitumenzone (Mittlere Trias) des Permian and Triassic of West Pakistan (ed,-BMonte San Gioryio (Kt. Tessin/Schweiz).lzr. Kummel and C. Teichert), [Jniv. Kansas Dept. Naturhist. Mus. Wien 83, 265-214. Geol. Spec. Publ. 4. Ritter, S. M. (1986). Taxonomic revision and (1976). Skeletalanatomy of the Late pa-
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6. EVOLUTIONARY PATTERNS
Fnten der Eifelknchbarten Fat Lahaea 5t,
6.1 Introduction
1979)-Evolutionb mnodont genCteol-et Palaeont. rg des hiiheren ! im Gebiet des ) mit Hilfe von hnt. Abh. 127, Devonian conofr.le (?) of Iowa. ! und Phylgenie I und ihre stati2x- I-andesamtes Eh-\' of the EuLlt Symposium Fd w. C. Sweet, z -lmerica Mem. f conodonts. E lhandlung 3, lJohnson, J. G. ivision ofthe yarts?Upper DevoJn€Iicz. Geol. et ll9E7). Cycles in Fonian to midb, Palaeobiology idge). .Ellis Hort (19E4). Palma.r IEfl of standard lion. Geol. Soc. L d -\ustin, R. L. shodus Etoup Devonian and c, Pelaeont. 8,
data basesthat are the enq' of their peerswho studylargerfossils.This is duepartly,I believe, As noted in ChaptersI and 2, conodontsoccur to the caution automaticallyprovided by very abundantlyin most typesof marine sedimen- largepopulationsamplesfrom stratigraphically tary rock; they are widely drstributed geograph- well-controlledsequenc$.In somepartsofthe ically; and, as a group,they have a long strati- geologiccolumn, densespacingof large samgraphic range. Consequently, conodonts are ples provides an almost continuousrecord of exceptionallyuseful as providers of biostrati the developmentof populationsthat can be graphic information to geologistsinterested in seento have had and to have rnaintained very a broad spectrumofproblems, and thoseofus great internal complexity for appreciableinterwho study conodontshave expendedmost of vals of time. Not uncornmonly,it is difficult or our efort in supplying biostratigraphic service irnpossibleto expresswhat we know about to the geologiccommunity. We have had little such populations within a generally accepted time left over in which to addressthe more es- systematic framework that yr'as designed to otericaspectsofwhat might be consideredtruly handle a rigidly typological taxonomy. And paleobiologictopics. this, of course,has resultedin hiding a good On the plus side, however,our serviceori- deal of very useful information in categories entationhasresultedin the assemblyofan ob- namedand treatedas speciesor generain acjective, if widely dispersed,data base,which is cord with principlesestablishedand rigorously several orders of magnitude larger than that maintainedby Ihe InternationalRulesofZooavailablefor any other group of Paleozoicor logical Nomenclature. Triassic "macrofossils" and is also one that But studentsof conodontshave had addimay be viewed within a biostratigraphic frame- tional excusesfor caution.That is, the subjects work currentlycapableof resolvingthe 300-my oftheir studyrepresenta groupof animalsthat history ofthe Conodontainto 152divisions.In evidently does not occur in the living bioaddition, of course,we now have a fairly clear sphere.This means,of course,that thereis litidea that recurrentgroupsof morphologically tle unequivocalanatomic information availadifferent element types are more suitable than ble for conodonts and that biologicalty individual elementsas the basis for species- meaningfulsystematicand ecologicconcepts level taxonomy;and, as I havetried to showin must be generatedquite indirectly Chapter5, speciesmay now be assembled into Now, however, there are in place at least the supraspecific categoriesthat provide consider- broadoutlinesofa defensibletaxonomy,and it ableinsight into the patternsofconodont el/o- is probably time to take up the biologically lution. At present,our organizedcollections (and philosophically)challengingtask of evoprovide little information as to the modesor lutionary interpretation.To this end, I assemprocesses by which evolutionarydevelopment ble in this chapter some observationson the was effected,but pattemsmay ultimately sug- evolutionary patternsI recognizein the 300gestprocessesthat may also be testedagainst my historyofthe conodonts,and commentson the objectiYeevidence. a few examplesthat seemto suggestprocessas Micropaleontologists,as Lipps (1981) has well. Perhapsrny observationsand comments emphasized,are not noted for generating,test- will proye sufficiently outrageousto stimulate ing, or evaluatingfundamentalpaleobiologic more penetratingstudiesofevolutionary mode hypotheses, despitetheir accessto finely tuned and process.I hope so.
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+ht also have r and post-Misbnra. Logs conr series-by-series Fnera also show r of diversity cyFpiled recently rsit-v of Ordovi:cies on a zoneiin this chapter b evolutionary Isent three logs rs{evel diversity cmire late Camhte Conodonta. il. 6.2,and 6.3, t fuctuations in b, which Clark k ofevolution. Lof 4 first-order
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cyclesin conodont diversity and also delineate about 20 second-ordercyclesthat supportthe conceptadvancedby Zieglerand Lane (1987). The logs,ofcourse,extendthat conceptto both earlier and later intervals of time than Ziegler and Lane considered. In the tabulationsdepictedin Figs. 6.1, 6.2, and 6.3 I have includedonly the 1446species
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Fig. 6.3. Speciesdiversitylog (uppcr solid line) and log oforigination-extinction ratios (Iower dashedline) for 48 Permian and Triassic zones. Stippled segments of origination-€xtinction logs indicate times when more species evolved than becameextinct; asterisksindicate times ofsignificant extinction separatilgdiversily cyclesidentifred with Roman numemls XIV to XX.
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tst diYersityin h- in the interrt€ Ibexian and E whiterockian i diwersity to a rtre early Mot- corresponds in Dost u.idespread rdepositedin the America (Sloss, rlme Middle Orftersity of conryrdly to a Late bllowed (with a in at the Ordor generaldecline rian hto the earildle Ordovician : correspondsin r during which Tippecanoe SeBlionh America rth America,an iau rhrough the od by formation c KaskaskiaSe|Fig. 6.2 that inalnost symmetly Devonian and rsiqv maximum ! nme. tia Sequencein fNorth America r and lesswideEara which colrgressive-regresmed Absaroka. I outlines of the roka cycle are rr-Mississippian qtich show a l5rlranian and a , decline in the i to interpret the Ite cratonic cy{- record major
eustaticepisodes,and first-ordersegmentsof the species-diversity logs in Figs.6.1, 6.2, and 6.3.The simplest,I believe,is to postulatea direct relationship betweendiversity of conodont speciesand the expansion(and subsequentreduction) of suitable habitats recorded by rocks of the transgressive-regressive sequences.
eage,which foundedthe Paraconodontida and, in the very early Ordovician, launched the Prioniodontida. Early diversification of the Cavidonti wasalso accomplishedearly in Cycle I. The Proconodontidasurelyreachedthe acme of their evolutionary developmentthen, and only Polonodus and,Pygodus are known from rocksdepositedduring later Ordoviciancycles. The Belodellida,which I interpret as descen6.3 Second-OrderCycles dants ofthe Proconodontusstock, appearedat Superimposed on the first-order cycles re- the climax ofdiversity in CycleI but werenot cordedin the logs of Figs.6.1, 6.2, and 6.3 is conspicuouscomponentsof Ordovician conthe record of 20 second-ordercycles,eachwith odont faunasuntil the interval of CycleII. the generalcharactersofthe onesrecognizedby The 40 conodontgeneraand 227speciesthat Ziegler all.d,Lane (1987)in the Devonian and are largelyconfinedin their known rangeto the Early Carboniferous.By and large, each of interval ofcycle I representtwo groups.Oneis thesecyclesbeginswith an interval oflow spe- made up of mostly shortJived experimental ciesdiversityin which the ratio of speciesorig- stockssuch as the Clavohamulidaeand Corinationsto speciesextinctions(the "evolution- dylodontidae, which appeared briefly during ary index") is below1.0,followedby an interval the initial radiation of cavidont and conodont of higher diversity-that is immediately pre- lineagesbut were apparently not ancestral to cededby an innoyative episodesignaledby a anything else; whereasthe other, typified, for spurt in the evolutionary index. Cyclesare ter- exarnple, by Rossodus, Tripodus, and, Prionminaledby moreor lessabruptdropsin species lodzs, includesgenerathat foundedor are indiversity which, for the most part, seemto be termediate parts of evolutionary lineagesthat, the expectableconsequences ofa declinein the in modified form, assumegreaterimportance evolutionary index in immediately preceding in later cycles.Theselalter lineageswere evizones. dently subjectedto more or less continual As is clearfrom the logsin Figs.6.1,6.2, and, pruning during the prolonged regressivephase 6.3, whose horizontal scaleis approximately that characterizedthe waning stagesin North proportionalto the length of time represented America of the Saukcratoniccycle,so thereis by the intervals shou,n, second-order cycles no evidenceof their catastrophicor massexwere of greatly different durations and hence tinction at the end of CycleI. seemunlikely to have beenthe resultsof any Note that by early in the Ordovrcranconregularlycyclic mechanism.As the following odonts werecommon not only in the tropical remarkswill show,thesecyclesare complexin- to subtropical waters of North America, Austemally,and it may be difficult to find a general tralia, Siberia,and probablypartsofChina, but explanationfor them. also in seasat much higher latitudes,such as those that overspreadEurope, western Australia, and western South America. Although 6.3.1 CyclesI andII there were remarkable parallels in the evoluIn the latestCambrian,Ordovician,and Silu- tionary developmentof low- and highlatitude rian history ofthe Conodonta,I recognizefive Ordovician faunas, already evident in the insecond-orderevolutionary cycles. These are terval of Cycle I, there was limited exchange identified by Roman nurnerals I to V in Fig. betweentheir chamcteristicfaunas.Very pos6.1. sibly the existencethrough the Ordovician of Cycle I, which began in the Late Cambrian well-developedconodonl faunas from the with the appearanceof the first conodontsin equatoralmost to the pole contributedto the the shallow low-latitudeseasof North Amer- exceptionallyhigh diversity ofthose faunas. ica, Australia,and China,is largelya recordof Cycle II is related, at least in North America the rapid diversification of the Teridontus lin- whereit is best known, to a short-livedtrans-
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VINOCONOJ AHI
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.As indicatedin Fcies to be the hida which dir ard dominates Llcle III is genfnction and is mbined effects hg of the world rr glaciation.Of Esentedby speEs only 7 suregocks were all Qunas in low he of the lin(or colder* ainued into the
y of the Conod-order cycles, Flonged interbrery, followed :Easintroduced btionary-index Fenlock Epoch. drh diversificarilies IcriodelliI rle ozarkodiltidae, PlectoIdae. The patmtrnue in later rhich are charhtionary bursts Foduced iteraIte icriodellid, [' from succesB.
e are sparseand tler Cycle V is b introducedby nionary vigor, rde of innovarDse from the i/es from the Co4ssognathus m-ery in diverdectinedalmost ime.
135
lygnathusestablishedin earlier phasesof the cycle,and diversity droppedto 2l in the midAs noted in Section 6.2, Ziegler and I-ane Givetian low-diversity interval that initiated (1987) have recently recognizedsix second- Cycle VIII. A bit later in the Givetian (late order cycles in the evolutionary development Middle Devonian), iterative developmentof of Devonian and Early Carboniferouscono- "Polygnathus" latifossatus from the spathodonts.Theseare identifiedin Fig. 6.2 as Cycles gnathodontid stock led rapidly to establishVI to XI. ment of Mesotaxis, Schmidtognathus,KlapperCycle VI began with a short interval in the ina alnd,ultimately, Palmatolepis,which I have late Silurian and earliest Devonian during set asidein Chapter 5 as the new family Patwhich the diversity of conodont species matolepidae.Speciesof these genera,which droppedto a low of 6. This critical interval in were apparently adapted to the increasingly the history ofthe Conodontawasterminatedin widespreadopen marine enyironmentsof the mid-Lochkoviantime by an innovative burst, late Middle Devonian, together with new effectedby vigorous speciation within Ozarko- forms developedfrom surviving membersof dina and iterctive deyelopmentfrom the spath- Ihe Polygnathus stock and short-liyed species ognathodontid, icriodellid, and/or distom- of Ancyrodella that also evolved iteratively odontid stocksofa flood ofspeciesassignedto from spathognathodontid ancestors, accounted Amydrotaxis, Ancyrodella, Pedavis, Pelel
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bthodontidae), b Spathognathnar-r/ eYents, u. tt the Polygmisian high-di It more than 50 fted at a hUh im by developf earl;-'speciesof r prioniodinide lnl short-lived ',futtrognathus, Staurognathus). fr rhe conspict the evolutionte Visean and rfosippian) segcorresponds in bse of Sloss's t- The end of imus declinein Ie primarily to ination in la1e ryhodus, PseuEl stocksas the lch they were tea- However, G a-ndincrease Erzed by much rtle salinity and q)porrumty to ih and priond and thereby rr1 in specieslbdiversity in,lbgelgnathus, erolved from tte innovative iat a\d. VogelI this cycle,but lrir ed through hanian. pecies-leveldiion of Cycle XI ment of Cayusdinction in the dus. Lochriea, os-el.er,during dnian) interval C!'cleXII, pop-
137
ulations of idiognathodontid conodonts de- also provide in Fig. 6.3 a zone-by-zone log of scendedfrom highly variableGnathodusgirtyi the ratio of origination to extinction of conogradually segregated into discreteand some- dont species.That log may be used (with the what lessvariablestocksidentifiedas Decllno- customarycaveats)as a crude index to temgnathodus, Idiognathoides, Neognathodus, poral oscillationsin eyolutionaryvigor. Idiognathodus,and'streptognarhodus. RadiaAlthough at least lg5 conodontsfeciesorigtion ofthesestockskept the evolutionaryindex inatedin the permian-Triassicinterval,speciis above the maintenancelevel of 1.0 through diversity hoveredaround l0 at any one time, mostofthe Morrowanand promoteda slowre- dropping to a low of 5 in the earliestTriassic coveryin species-level diversity,which peaked but reboundingrapidly in the sameinterval to in the succeeding Atokan epochwith addition a post-Mississippia nhigh of 22. of the first representatives of Diplognathodus Fig. 6.3 also ouflines four second-ordercyand the Gondolellidaeand gradual phyletic cles in the permian and another four in the evolutionofthe/ry'eognathodusltneage. Triassic. Extinction of Neognathodus and probably The earliest of the Permian cycles,Cycle alsoof Rhachistognathusin tl|'elate Desmoine- XIV in Fig. 6.3,followeda long interval in the sian (Pennsylvanian)markedthe end of Cycle late Pennsylvanianand Asselianwhenthe evoXII, which is also shownin Fig. 6.2 to be ter- lutionary index was consistentlybelow1.0and minated by a rapid declinein species-level di- was provoked by the appearancein the Sakversity. Continuedgradualphyletic speciation marian of an early speciesof Neogondolella(N. in the I di ognathodus-St rept ognathodus lineage, bisselli), the first speciesof Sweetognathus(5. togetherwith the appeaftnce of Aethotaxis, EI- merrilli), and a distinctive speciesof DrploIisonia, and new speciesof Gondolella, Diplo- gnathodus (D- sakmariensis). N. bisselli is gnathodus, and Hindeodus, signaleda brief in- thought to have evolved ftom N. praebisselli, terval of innovation in the eady part of the which precedesit stratigraphically.However, mid-PennsylvanianMissourianEpochand the thesetwo speciesare separatedby much ofthe somewhatlater peak in species-level diversity Pennsylvanianfrom N. clarki, the earliest spethat marked culmination of Cycle XIII. Note cies with elementsmorphologicallyassignable in Figs. 6.2 and 6.3 that in the latter half of to Neogondolella.For this reason,I suspectthat CycleXIII the evolutionaryindex was contin- the N. praebisselli-N.bissellilineageis an inuouslybelow1.0and that speciesleveldiversity dependent Permian development from the declinedgraduallyto 15in the Virgilian and to long-ranging Xaniogna.thus-Cypridodellastock l0 in the succeeding Assel.ian Stageofthe Early which, as I speculatedin Section 5.8.5, was Permian. Although speciesof Hindeodus, Di- probably the progenitor of several Gondolella plognathodus, Streptognathodus, Idiognatho- lineagesin the Pennsylvanianand earliest dus, Adetognathus, Gondolella, and.E llisonia Permianand the ancestor,aswell.ofnumerous survivedthroughmuch or all ofthis long inter- additional lineagesof Neogondolella, Neospaval ofsorely restrictedevolutionaryvigor, only thodus, and, Epigondolella later on in the the Hindeodus, Diplognathodus, gondolellid, Triassic. and Ellisonia lineagessurvived Clark's (1972) SecondaryCycle XV follows the early ArtinEarly Permian crisis to provide the basis for skianextinction of the typically Carboniferous secondarycyclesin later Permianand Triassic genera Streptognathodus, I diognathodus, and seas. Adetognathus. Following a brief interval of slightly lowered diversity, a short innovative burst resulted in the appearanceof the earliest 6.3.5 Permianand Triassiccycles speciesof .ly'eostrep tognathodus,Sweetina, and Fig. 6.3 is a zone-by-zonesummary of con- Merrillina. Neostreptognathodus apparently odont speciesdiversity through the Permian representsa modification of the Diplogndthoand Triassicperiods,which togetherrepresent dus-Sweetognalhus stock, whereasI have inter78 million yearsof geologictime. As in sum- preted,Sweetinaand.Merrillina jn Chapter 5 as mary logs for earlier parts of the Paleozoic,I successive stagesin a prioniodinidelineagethat
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EVOLUTIONARY PATTERNS
d almoslincesE of secondary b to -Anisiandenia and perhaps Ents elsewhere l Chirodella and l_r very tiny eleim (or part o0 I Xaniognathustine, several the type, M frg dr debut. It is rdr ed from ScyhEd iteratively 'Hella stock. I rily- becauseno i assembling a Enstates morrn Scythian and ts a high-divertd to developEXaniognathusige commonly t perhaps better rdla. which was ) b!- Kiril BuduI preceded the ; XD( was reina development 1udolurnishiustde andthe last 1 beganin Kart of Pseudofurinella group of fdiversity epi! siFaled by itlaest Karnian I of Epigondok- a replay of d rle only stock e Triassic.
Dd phyletic exrc evolutionary Ioq'ewer, Clark
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Fig. 6.4. Survivorship curves(left figure)for cohortsofconodont genera(e.g.,all generaoriginaling in Ordovician) and curve oflongevity ofconodont generaofall ages(on right). Redrawn from Clark (1983).
(1983,1987)hasrecentlyfocusedparticularattention on events in the late Paleozoicand eady Mesozoichistory ofthe phylum that precededits extinctionat the end of the Triassic. In his 1983study Clark presenteda seriesof survivorship curves (Fig. 6.4) for Cambrian through Triassic cohorts of conodont genera and a summary curve for all conodont genera listed in the Treatise(Clark el al., t98l). Clark noted that thesecurves indicate that the ayeragesurvival of systemiccohorts was 109 my and that meansurvival ofconodontgenerawas about 30 my. Thus, as Clark pointed out, an observerin the late Paleozoicwith accessto the samerecordswould not have foreseenthe endTriassic extinction of the phylum but would probably have predicted surviyal into at least the Jurassic and possibly into the Early Cretaceous. The record indicates that the Conodonta did not survive into the Jurassic or Cretaceous, however, but that the phylum becameextinct in the latest Triassic. Conodonts were not the only groupto becomeextinctor to suffermajor declinesin diyersity at this time. Indeed,Sepkoski and Raup (1986),summarizingthe opinions ofothers,note that "the I-ateTriassiccontains one ofthe five largestmassextinctionsof
the Phanerozoicmarine record." The data they present, however, like those for conodonts shown graphicallyin Fig. 6.5, show generally high extinction intensities throughout the Late Triassic,with a maximum in the latestNorian (or Rhaetic).This suggests to me, as it apparently did to Clark (1983),that the end-Triassic extinctionofconodontsmay havebeenthe cumulative result of severalfactors.not of a single catastrophiceventthat terminatedthe phylum "well beforeits time." Farly in the Permian,at the endofsecondary CycleXIII, a majority ofthe typically Carboniferous stocks disappeared,following a long late Pennsylvanian and early Permian interval during which species-level diversity plummetedand the evolutionaryindex was consistenfly below the maintenancelevel. Permian recoyery was surely not spectacular.It primarily involved a coupleofbursts of speciationby the gondolellid stem group, one eachby lhe EIIisonia and.the Diplognathodusstocks,but very little action on the part of Hindeodus, which merely "showed the flag" through most of the Permian.Note in Fig. 6.5, however,that, despite these fitful attempts to restock Permian environmentswith new and vigorously successfulconodont stocks,extinction intensity
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groupsof conodonts,particularlythe Ozarko- gin iterative deyelopmentfrom basic lineages dinida and Prioniodinida.A similar patternis is also an attractive explanation.Plectodina apparent,however,in at leastsegmentsof the and.Phragmodus,for example, appearde novo Panderodontidaand Prioniodontida, and it in the early Middle Ordovician, and their spemay be generalin the Conodontaasa whole. cies forrned skeletal apparatusesthat are, in a As shown diagrammaticallyin Fig. 5.36, nurnberof ways,closelysimilar to thosebuilt which summarizesmy viewson the phylogeny by severalspeciesin the Multioistodontidae of the Ozarkodinida,elaborationof the sides (e.g.,Paraprionioduscostotus\.Becausethe latand surfacesofPa-elementcrownswascarried ter precedePhragmodus and,Pleclodina slratiout repetitively in spathognathodontid popu- graphically,they havebeenconsidered(by me, lationsat severalwidely spacedintervalsin the among olhers) as attractiye candidatesfor Silurian and Deyonian.As a consequence, ap- ancestors. However, multioistodontid eleparatusesofthe speciesthat developedin each mentsare mostly hyaline,and thereis little to ofthese iterativeburstsare closelysimilar. For recommendthem in other morphologicparticexample, Ancyrodelloides of the early Devo- ulars as hallmarks of the ancestorsof either nian has Pa and Pb elementsthat are very sim- Phragmodusor Plectodina. I now suspectthat ilar to those of early Silurian Pterospathodus those two lineagesdevelopedindependently, and also essentiallyidenticalin morphologyto and at slightlydiferent times,from generalized those of later Devonian Ancyrodella. The spe- prioniodontide ancestors in Tripodus (Oixocies of early Siltian Kockelella experimented dontidae).Although one may distinguishreadwith elaborationof Pa elementsin much the ily betweenrnany of the elementsin apparasamemanneras did early DevonianEognath- tuses of Phragmodus and, Plectodina, others odus, pitnitive representatives of somewhat (includingcertainPa elements)are closelysimyounger Polygnathus, and, a number of later ilar. Thus homeomorphymay not be as great Devonian and early Carboniferousspeciesas- as between Ancyrodelloides and,Ancyrodella, signedto Scaphignathus(Spathognathodonti- but it is nevenheless substantial. dae)and the Cavusgnathidae. And iterativedeI suspectthat iteration alsocharacterized Sivelopment of the Protognathodus-Gnalhodus,lurian developmentofthe prioniodontidefamDiplognathodus, Lochriea, and,Rhachistogna- ily Distomodontidae,but this may be very dif/lius lineages from B ispathodus (Spathognath- ficult to establishobjectively,and there are odontidae)producedsuch a welter of species surely other possibilities,as indicated in Secwith morphologicallysimilar Pa elementsthat tion 5.7.5.Ifthe basicapparatuspatternofthe phylogeniesare notoriouslydiffi- distomodontsincludedunplatformedpastinate supraspecific cult to reconstruct or defend. elementsin the P positions,then iterative deIn Section5.6I havealsonotedmy suspicion velopmentmay have beenresponsiblefor in! that Parabelodina denticulata, a panderodon- tiation of stockssuch as thoserepresentedby tide specieswith well-developed rastrate ele- Icriodina, Hadrognathus and, ultimately, even ments in its skeletalapparatus(and thus simi- some or all of the icriodonts.Chattertonand lar to speciesof Belodina and,Pseudobelodina), Peny (1977)seemalso to have suggested that evolved directly from a conlemporaryspecies iteration might have been the active pattern in of Panderodus(P.bergstroem), not from some icriodont evolution when they wrote that earlier speciesof Belodina or Pseudobelodina. Other evidence,mostly unpublished,suggests speciesthat could be or have beenassignedto the genus that Panderodusitselfincludes a number oflin- Pelekysgnathus, as it is broadly conceived, may have eages,eachprobablydeservingof independent been derived from other genera during four diferent generic(or even familial) designationand rep- evolutionary events(origin of"P." inder in the Late Silurian, origin of I hadnagyi in the Lochkovian, origin resenting chronologically distinct iterations of of lsteptotaxis'l Iumishi group in the Eady Devonian stocks characterized by skeletal elements of and.oigin of "P." comn r/rrs in the late Devonian. closelysimilar morphology. Within the Prioniodontida rhere are quite a The recent suggestionby Sandbergand Dreenumber of"cryptogenic" stocksfor whoseori- sen(1984)that a groupof LateDevonianspe-
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143
6.6.2 Apparatusreduction
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... im rtrrough Triasmany post-Sigroups.Also, nic from those a.lions. -rent
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145
specieswith platformedpectiniform elements tial ecologic controls in the materials they in the Pa position.The Prioniodinidadelayed study. developmentof platformed P elementsuntil The large, stmtigraphicallywell-controlled the Mississippian,when the curious, short- collectionsayailableto studentsof conodonts lived Bactrognathidaeinvented thern. Later, should also be well suited to studiesof develhowever, in the Pennsylvanian(and increas- opmental, or evolutionary, strategy.Because ingly in the Permianand Triassic),prioniodi- well-madecollectionscommonly include elenide stocks came to be characterizedby plat- ments that representvarious stagesin the onformed pectiniform elements in the Pa togenetichistoryofthe speciesthat contributed position. to thosecollections,it shouldbe possibleto reIn the absenceof firm information as to the late ontogenetictiming ofthe morphologicfeafunctionofelementsin any positionin the con- tures recorded to developmenlal strategiesin odont apparatusit is diftcult to relateevolu- the lineagesthat formed them. And, if collectionary elaborationofP elementsto specificen- tions are carefullyrelatedto the petrologicand vironmental or behavioral factors. However, other biologic properties of the rocks from from the fact that such elaborationcharacter- which they vvereobtained,it should also be ized someor all of the lineagesin nearlyevery possible,in time, to determinethe natureand major stockat onetime or anotherin their his- extent of any relationship betweendeyeloptory, it may be concluded that platform elabo- mental strategy and environmental paration was surely of positive adaptive sig- rameters. nificance. Althoughinformation on the ontogeneticdeNicoll (1987),who suggests tllat the skeletal velopment of various skeletal elementshas elementsofconodontsmay havebeeninternal been provided by various authors,I am not supports for ciliated tissue in the food-gather- awarethat anyonehas yet documentedstages ing systemof generallymicrophagousanimals, in the ontogenyof a conodont speciesfrorn concludesthat P elementswere opposedand studiesthat involve all elementsof the skelelal operatedin sucha fashionasto roll, bruise,and apparatus.Consequently,in the following seccrushparticulatematter caughtbetweenthem. tions I summarizepertinentinformation from Phylogeneticelaborationof P elementsmight a few recentstudiesofPa elementsthat sugg€st thus have beenrelatedto changeswith time in that developmental strategies may have difsize,shape,and bruise-or cmshabilityof food fered greatly from one group of conodonts to particles.If P elementsfunctionedas teeth,as the next. We can only guessat the extent to Jeppsson(1979, 1980)and othersconclude,a which additional strategiesmay be suggested similar relationshipmight alsobe postulated. by future studies of complete apparatuses.
I P positions t ard developirus lineagesa boration of peciions. In a maritions in even , were occupied ments; in only dae. Polyplacorments formed ian. platformed rdl-v in P posiE Spathognath.nd Icriodelli later in the locks included
6.7 DevelopmentalStsategies
6.7.1 Recapitulqtion
Gould (1977)hasprovidedsignalserviceto the biologic community by emphasizingnot only that "parallels between ontogeny and phylogeny are produced by heterochrony" but also that theremay be a continuumofrelationships between ecologic factors and the life-history patterns that may result from alterations in the timing by which various somatic and beharrioral features develop. In short, Gould expandedon Van Valen's(1973)somewhatearlier observation that eyolution might well be the control of development by ecology.Paleobiologists are thus encouragedto seek informatioD on developmentalpattemsand poten-
Heterochrony involves "changesin the relative time ofappearanceand rate ofdeyelopment for characters already present in ancestors" (Gould, 1977)and may be effectedeirherby accelerationor retardation.Ifa characterthat appearsin the adult stageofan ancestorappears at a youngerstagein developmentofa descendant, accelerationis the processinvolved and classicalrecapitulationthe result. Ii on the other hand, a character that appears in the youngstageofan ancestorappearsin, or is retainedinto, the adult stagesofa descendant, retardation is the processand paedomorphosis the result.
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9br
EVOLUTIONARY PATTERNS
E fPrioniodonir (Prioniodonl:ted by paeDren!, of the ar While steps |P Postulateare ttive evidence, I Inmary anengts of Pedavis sbfiantial difG ln other api Section5.7.6, a. Icriodus may m Pelekysgnadubius, -dina distantly re4Elities are conbern involved. lat the Pa elespeciesof Epr:rain juvenile Er ontogenetic d this paedoh-v. In a more El more extenI has substantiirr at least two r relatedvein, I ebeeninvolved dh from Pseut of Misikella fulel Ia or those il ancestorsin
d of the Conlhat of a classirhich therewas loration of the dablishment of the subsequent i:al fluctuations des-level diverMer eustatic t a one-for-one ts conserYatlve @es of repeatrgh iterative,or
repetitive, development of generally shortlived lineages that were strongly homeomorphic with their predecessorsin featuresof their skeletalapparatuses. From the l-atePennsylvanian on, however, speciesJeveldiversity was low, and populationsappearto have been at or below the maintenancelevel for long periods of time. With only a brief interruption in the Early Triassic, extinction intensity increasedfrom the Early Permian to the end of the Triassic,when the phylum wasreducedto a few species,probably representedby populations of small sizeand provincial distribution. Although studiesof generic-levelsurvivorship would not have led Permian observersto predict the extinction of conodontsbefore some time in the Jurassic,the phylum did not survive the Triassic.Reasonsfor extinction are not at all clearbut may haveincludednot only thosebuilt into the long post-Iate Pennsylvanian decline,but also a dollop of bad luck in the Late Triassic when surviving basinal populationsmay havebeenunableto adaptto conditions producedby a worldwide drop in sea leYel.
References Bergstritm, S. M. (1983). Biogeography,evolutionary relationships, and biostratigraphic significance of Ordovician platform conodonts. Fossilsand Strata 15, 35-58. Broadhead,T. W. and McComb, R. (1983). Paedomorphosis in the conodont family lcriodontidae and the evolutiolJ of lcriodus. Fossilsand Strq.ta15, 149-154. Chattenon, B. D. 8., and Perry, D. G. (1977). Lochkovian trilobites and conodonts from northwestern Canada. I Paleont. 51, 7'72796. Clark, D. L. (1983). Extinction of conodonts."/. Paleont.:57, 652-661. (1987).Conodonts:The final fifty million years. Pp. 165-114 Palaeobiology of Conodonts (ed. R. J. Aldridge). Ellis Horwood, Chichester,180 pp. Clark, D. L., Sweet, W. C., Bergstriim, S. M., Klapper, G., Austin, R. L., Rhodes, F. H. T., Miiller, K. 1., Zieg)er, W., Lirdstrijm, M., Miller, J. F., and Harris, A. G. (19E1).Conodonta. In Treotise on Invertebrate Paleontolof? (ed. R. A. Robison). Pt. W, Suppl. 2. Geol. Soc. America and Univ. Kansas,202 pp.
t47
Gould, S. J. (1977).Ontogenyand Phylogeny-The BelkDap Press of Harvard Univ. Press,Cambridgeand tondon, 501pp. Jeppsson,L. (19'19).Conodont element function. Lethqia 12, 153-l'll. (1980). Function of the conodont elernents. Lahaia 13, 228. Johnson,J. G., Klapper, G., and Sandberg,C. A. (1985).Devonian eustalic fluctuationsin Eurameica. Bull. Geol.Soc.Am.96,567-587. Lipps. J. ( l98l ). What. if anlthing. is micropaleo\toloqy? Paleobiol. 7(2\, 167-199. Merrill, G. K., and Powell, R. J. (1980). Paleobiology of juvenile (nepionic?)conodontsfrom the Drum Limestone(Pennsylvanian,Missourian-Kansas City area) and its bearing on apparatus ontogeny. J. Pqleont. 54, 1059L0'74. Mosher, L. C. (1970). New conodont speciesas Triassic guide fossils.J. Paleont. 44,'137-742. Nicoll, R. S. (1987).Form and function ofthe Pa element in the conodont animal. Po. 78-90 in Palaeobiologyof Conodonts (ed. R. J-.Aldridge). Ellis Horwood, Chichester,180 pp. Orchard, M. J. (1983). Epigondolella popllations and their phylogenyand zonation in the Upper Triassic.Fossl/sand Strata 15, l'77-192. Sandberg,C. A., and Dreesen,R. (1984).Late Devonian icriodontid biofacies models and alternate shallow-water conodont zonation. Geol Soc.Am. Spec.Paper 196, 143-178. Sepkoski,J. J., Jr., and Raup, D. M. (1986). Periodicity in marine extinction events.Pp. 3-36 in Dynamics of Extinction (ed. D. K. Ellion). Wiley, New York, 294 pp. Sloss,L. L. (1963). Sequencesin the uatonic interior of Nonh Ameica. Bull. Geol. Soc. Am. 74(2),93-t14. Sweet, W. C. (1970). Uppermost Permian and Lower Triassicconodontsofth€ Salt Ranseand Trans-lndus ranges.west Pakjstan. Ppi 207275 h Stratigrephic boundary problems, Permian and Triassic of llest Pakislqn (ed. B. K.ummel and C. Teichert). Univ. Kansas, Dept. Geol., Spec.Publ. 4. (1985).Conodonts:Thosefascinatinglittle whatzits."L Paleont. 59(3),485-494. Vail, P. R., Mitchum, R. M., Jr., and Thompson, S. III (1977). Seismic stratigraphy and global changesof sea level, pt. 4: Global cycles of relative changesofsea level. Pp. 83-95 in,Sedmic Stratigraphy-Applications to Hydrccarbon Exploration (ed..C. E. Payton). Am. Assoc. Petrol. Geol.. Mem. 26. Van Valen, L. (1973). Festschrift. Science 180, 488. Walliser, O. H. (1983). Geologic processesand g.lobalevents. Terra Cognita 4,l'l-20. (1984).Pleadingfor a natural D/C-Boundary. Pp. 241-246 it The Devonian-Carbonifer-
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7. PALEOECOLOGYANDPALEOBIOGEOGRAPHY
7.1 Introduction
understood as a preamble to the following discussion.Obviously,until we have satisfiedour curiosity and reachedsome agreementas to thesematters,conodontswill be lessusefulin reconstructingconditions in past depositional environmentsthan are featuresof the rocks formed in thoseenvironmentsin interpreting the conodonts.Thus I approacha discussionof conodontecologycautiously,urith initial emphasis on featureson which there is general agreement.
For many yearsaftertheir discoveryit wasgenerally held that conodontswere cosmopolilan in their occurrence within the marine realm and that most specieswould turn out to be worldwide in their distribution. However. as more and nore information was assembled, it gadually became clear that conodont species behavedlike the speciesof most otheranimals. That is, there were lateral limits to their geographicdistributionand decided,ifbroad, ecologic factors that determined where they lived within Paleozoic and Triassic seas. Further?.2 Modeof Life. or Habil of Conodonts more, in 1958 Huckriede suggestedthat the developmentof Triassic conodontsfollowed It is common knowledge that elements repredifferent courses in various biogeographic sentingthe same or closely similar conodont provinces,and in 1959Sweet,Turco, Wamer, species may be collected from sedimentary and Wilkie concluded that the distribution of rocks that representa wide variety of deposi conodontsin rocksoflate Ordovicianageout- tional environments.In addition, many conlined two distinct faunal provinces. odont specieshave beenshownto have had a Neither the ecologynor the biogeographyof very broad geographicdistribution, and a few conodontscould be studiedin a very meaning- may have beencosmopolitan.Thosefacts,toful way, of course,until a biologicallysound gether with the elongate, wormlike body and taxonomy had been developedand fleshedout distinctively finned tail of the few complete systematically.Nevertheless,the repeateddis- specimensknown, support the generallyheld covery between 1926 and 1966 that conodonts conclusionthat the animalswereprobablynekare exceptionally useful biostratigaphically tic in habit and that the distribution of most stimulated the assembly of comprehensive, speciesmay have beenlargelyindependentof geographicallywidespread collections through conditionson the bottom. Suchan interpretathe known range of the group. Thus, with the tion seemsto be supported most strongly by developmentof the multielementtaxonomy I the common occurrenceof conodonts in cerhaveoutlinedin Chapter5, much of the infor- tain typesof black shalesthat yield fossilsonly mation neededfor both paleoecologicand pa- ofpelagic organismsbecausethey accumulated leobiogeogaphic interpretation of conodont under anoxic bottom conditions that inhibited faunashasfallen into place. developmentofa benthicfauna. Becauseconodonts are extinct and have no Conodonts occur in rocks with corals,brachvery closeanalogsin the living biosphere,fea- iopods,echinoderms,and cephalopods, whose tures of their biologic associationsand lithic living representativesare all marine, but they occurrencesmust be usedto reconstructtheir havenot beenreportedasautochthonouscomhabits, habitats and ecologicpreferences.Infor- ponents of rocks known to have accumulated mation derived in such indirect waysis always in nonrnarineenvironments.Thus,asat leasta subject to debate, revision, and periodic rein- first approximation, conodonts may be interterpretation, of course,and this must be firmly pretedas pelagic,probablynektic,marine ani149
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PALEOECOLOGY AND PALEOBIOGEOGRAPHY
bn from various rd fiom different med Pa elements ts the elements ir the skeletalapbat this disjunct, badsto the comn over-represenm late Paleozoic skeletal apparamt speciesmay Aom one ontotbat such differ: from a pelagic retic stagesto a rin later ones. b some or all of E mode of life, it d study to deterries represented cttobenthic nibmore at home in ove the deposirYe had diferent r itr their life histbs€rvation that, le water column tauon, rn a neariphering the life qreciesbecomes hl it is a game lattention to the of conodontsto sitional basinas I arrangement of mts.
heses,have been rlbution of condc marine rocks. bl, outlined in tan with the ase pelagic and attion for puzzling iistribution. The brnes and FihI, attempts to exiF of conodonts lateral distribu-
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Fig.7.1. Schematicexplanationofthe depth-stratificationmodel ofseddon and Sweet(1971).Diagram showstwo species;one indicated by crossesis uniformly distributed in a surficialwater stratum; the other, indicated by filled stratum. Elementsofboth sp€cieswould accumulatelogetheron ellipses,is uniformly distributed in a deepe!-wa1er the seafloor,butbetweenA andB thoseofthe "cross" specieswould dominate,whereasbetweenB and C the reverse would be tlue. Redr-awn,with omissions,from Seddonand Sweet(1971).
tion in sedimentaryrocks.To Bamesand Fahbioraeus,the existenceof laterallysegregated facies was taken to indicate that most conodontswerebenthicor nektobenthicorganisms, whereasSeddonand Sweetfound that laterally segregatedbiofacies (which are real) required a special explanation if conodonts were pelagic. Although the two models seem very different-and they certainly began with very diferent premises-neither has been generally acceptedor rejected.They both bear summarydiscussionbeforewe go on to more concretematters. 7.3.1 The depth-strattficationmodel Seddonand Sweet(1971)pointed out that the Ordovician and Devonian conodonts they were studying in eastem North America and Australia, respectively, characterized distinct, laterally segregatedbiofacies instead of being more or less uniform in their lateral distribution, as one might expect the remains of truly pelagicorganismsto be. To explainlateralsegregation of conodontsin the benthic record, Seddon and Sv,/eetproposed that, in their lifetimes, different conodonts inhabited diferent levels in the sea,in the manner of living chaetognaths.A schematicillustration ofthe depthstratificationmodel is given in Fig. 7.l.
Figure 7.1 considersjust two pelagic conodont species,one representedby crosses,the other by filled ellipses.The crossspeciesis assumed to have been widely and uniformly distributed in a stratum nearerto the surfacethan the ellipse species,which was also uniformly distributed, but was confined in its lifetime to a deeper-u,aterlayer. As individuals of eachof thesespeciesdied,their heavy,phosphaticskeletal remains would haye settled to the bottom. We would expect to find fossil representatives of the crossspecieseverywhereon the bottom. However, skeletalelementsof the ellipsespecies would accumulateonly seawardof the level at which the top of its depth zone "dragged bottom." Consequently,there might have been a tract of the bottom to the left of point A in Fig. 7.1 on which no specimensof the ellipsespeciescameto restand in which the fossil record was exclusively of the cross species. On the other hand, the ellipsespecies,a relativelyrare componentof colleclionsmade from tlre rocksthat accumulatedbeneathpoint A, would pradually increase in abundance relative to the cross sp€ciesin samplestaken fron rocks that were formed at greater and geater depth. At point B in Fig. 7.1, for example, the two speciesmight be representedby approximately equal numbers of specimensl farther to the right, at point C, specim€nsof the
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Fcies wereinterrrized by a very csseDtiallithofadal apparatuses Its. The lateralnhesis has been n of the simplicm of the distribra4 deposits.As rgh- as Klapper rn- the laterally t car in no way : or nektobenthic t disfibution are lals were nektoI of the vagrant lhculr to explain distribution of m occurrenceof rt shales,which rr anoxicbottom beeD hostile to tinglJ compelling ; to abandonthe t conodontswere cnthicand to use m the mode-ofEcords with the
rt Ecology c generalizations I conodonts as a :ilcludes a numrich it tnay evensrch principles. nake generalizaX-- I sumrnarize nine if the conEst any common
of Cincinnati abundant in the tEr OrdoYician lncinnati Region ia (Fig. 7.2). The
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Fig. 7,2, Situation ofthe Cincinnati Region in the Middle and I-ate Ordovician. The Cincinnati RegioDis th€ tristatetract in the centerofthe map. In general,it was part ofa broad carbonateshelfto which terngenousmaterial was introduced from the southeast and that was bordered on the norlhwest by the distal extremity of a narow, deep sag(white) that permitted connectionwilh cold, phosphate-richwatersto the south. Approximale positions of l0'and 20'S paleolatitudesindicated by heavy lines; Iight arrows suggestprevailing-wind direction; hea\rier arrows in sag suggestwind-driven circulation pattem permitting upwelling of phosphate-rich water in Cincinnati Region.Adapted from Crcssman(1973).
speciesrepresentedare quite well known taxonomically, and their stratigraphic and geographic distribution has been worked out in considerabledetail. Somewhatlessdetailedinformation is availableon the petrologyof Ordovician rocks in the Cincinnati Region,and questionsaboutthe thereare someunanswered environments in which they accumulated. Nevertheless, enoughis known to supportgeneralizationsabout at least some of the factors that may have controlled distribution of the conodontsin the warm, low-latitudeseasthat covered this area in the Middle and Late Ordovician. The Middle and Upper Ordovicianrocksof the Cincinnati Region accumulatedon a cra-
tonic platform that was situated a few to as many as 20 degreessouth of the Ordovician equator. Lithofacies are various mixtures of shalederived from orogenicsourcesfar to the east and highly fossiliferouscarbonaterocks generatedon the spot, primarily from skeletal matter furnished by echinoderms, brachiopods, and bryozoans and reworked and fragmented in some environmentsby wave- or storm-generated currents.Fossilsin mostofthe carbonaterocks haye been transported,but probably not too far frorn their living sites. The conceptually straightforward deposi tional frameworkofthe CincinnatiRegionwas complicatedby differential uplift and subsidenceof segmentsof the platform along pre-
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PALEOECOLOGY AND PALEOBIOGEOGRAPHY
t ddepositional enEeristic conodonts, d below.
ryesent Phrag'r few are assign' dozen species E shallow end of Eel,! glauconitic hite, with ripr the upper part, bial corals.The rr deposit that tl shallowly subr ma-v have en! on the Drakes fumed in water fflatfleld, 1968). lla-kes are quite a least half the erable to RhipEeas the other Hognathus and. r rn rhe Drakes, &ost any speHorician of the p here and there rllemes marked ler and Drakes nops of facies, f the conodonts
155
they contain but are mapped as differently dominated.by Phragmodusundatu4 have only named formations or membersbecausethey minor nurnbersof elementsassignable to Oulare composedof carbonatesand shalesin dif- odus or Aphelognathus,and,never yield speciferentproportionsor because they developpar- mens of Rhipidognathus- ln Clays Ferry and ticularly conspicuousinternal structures. Fairview strata, on the other hand.,PhragmoIn the late Middle Ordovician, before the ar- dus, Plectodina, Oulodus, and,Aphelognathus rival in the Cincinnati Region of much terri- are almost equally represenled,specimensare genousdetritusfrom the southeast,phosphatic characteristically larger, and total collections limestonesassigned to the Grier Memberofthe are smaller. Furthermore,Rhipidognathusis kxington Limestonewerethe chief depositin represenledby an occasionalspecimenin samoxygenated, well-lit watersomewhat,to consid- ples from the Clays Ferry (but not from the erably,shallowerthan that in which the Logana Fairview). Member was deposited.Cressman(1973)esti The CallowayCreek facies,entirely of Late matesthal the Grier accumulatedin water less Ordovician age, accumulated in probably than l5 m deep, but the range may have been somewhatdeeper-water settingsthan the mudmuch greaterthan this for at the basethe Grier flat environmentsin which the Drakes Forgrades both laterally and vertically into the mation was deposited,and in quieter-water deeper-,quieter-water l-ogana and, at the top environmentsthan thosein which the conspicinto the Brannon or Tanglewoodmembers, uously cross-beddedTanglewoodMember of which formed in very shallow, more highly ag- the Lexington Limestone was deposited. In itated water. Furthermore, the lower Grier both the Calloway Creek and Tanglewood, shows a dominance by Phragmodusundatus Oulodus and.Aphelognathusare the dominant nearly equal to that of the I-ogana, whereas conodonts; Plectodina is common, and PhragPlectodina dominates in the upper Grier. The modus is reducedto about 25 percentof the high phosphatic content of the Grier, a matter fauna.Specimensof Rhipidognathusmay conof specialinterestto Bourbon whiskeydirtill- stitute as much as 5 percent of the collection ers, suggeststhat water above Grier deposi- from someunits. The Grant Lakeand Ashtock tional sites was supplied by upwelling with formations were deposited,in Late Ordovician more phosphatethan could be abstractedby time, at various sites slightly seaward of the plants.This addsto the suspicionthal at least Drakes flats; the Grant Lake representswavesome of the carbonaterocks now included in agitatedshell-heapshoals,betweenand among the Grier were depositedbelow 15 m depth, which various faciesof the Ashlock (or rnemperhapsnot too far aboye the compensation bersofthe Grant Lake)weredepositedin sheldepth. tered lagoons. Grant Lake conodonts are Late in the Middle Ordovician considerable mostly referable to Plectodina, Oulodus, and. quantitiesof silt and clay spreadinto the Cin- Aphelognathus, but specimensof Rhipidognacinnati Region from the southeast.Much of thus arc also common and, locally, may make this bypassedor was washed through bathy- up as much as 10percentofa collection.Rl,rpmetric highs to settle in thick beds in topo- idognathus may be as important in samples graphically lower portions of the seafloor (the from the Ashlockas in samplesfrom the very elongate,southwestward-opening sagshownin shallow-waterDrakes, but the proportion of Fig. 7.2). Thus the broad regioncharacterized Plectodinais comrnonly greater.Otherwise,the in the Middle Ordovicianby carbonatesofthe two formationsresembleone anotherlithologGrier Member was partitioned in later Ordo- ically and faunally. vician times into deeper-waterareasin which It shouldalso be noted that the Loganaand the very shalyKope and lessshalyPoint Pleas- Grier membersof the Lexington Limestone, ant formations accumulated, and somewhat and the Late Ordovician Kope Formation, shallowerareasin which the much less shaly grade laterally into dark, fissile shales comClays Ferry and (later on) Faiwiew formations monly loggedby drillers as the "Utica," but is weredeposited. nowhere exposedat the surface in the CincinThe Kope and Point Pleasantfaciesareboth nati Region. We have retrieved only a few con-
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PALEOECOLOGYAND PALEOBIOGEOGRAPHY
Eton Limestone) dow the oxygenbt .lmorphognai ttre cool water I irself. qFclmens repre'k maximumin Epreted as the rimati Region. rine1on, thought rr accumulated qnh. exiibits the 'P. undatusof all E in Fig. 7.3, I Fl inhabitantof r the colderbotE- of the more tidal-flat areas fddle and Late fugnathus, Ould the ozarkodirens of collec4ion lithofacies, r importance in rl shallownearincreasein relaf closelyrelated 73 | show PlecladLJ (an almost ter). as inhabit My of water, Modus progesa onshoredirecr norcd, wascerrt in tidal-flat ti Regrbn.I show re is no compelI data ofthe sort irn rocks of the r profound conEn water depth rolled distribuE west(north in Eti Region, spenively moreimblomitic Upper Whus a d Oulbrodontide conmon in stratain
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Fig, 7.4. Location ofthe DeseretBasin and adjacentfeaturesofthe Mississippianof the westemUnited States. Redrawnand simplified from Sandbergand Gutschick (1984).
northern Wyoming thought to have accumulated at sites marginal to those in which evaporites formed in the Williston Basin (Sweet, t979). These featuresin the distribution of thoseconodontssquarewith the onesdeduced from the record in the Cincinnati Region but ofer little more as to the actual ecologic controls.
western 7.4.2 Mississippianpaleoecology, UnitedStates Sandbergand Gutschick(1979, 1984)provide accountsofthe distributionofconodontsin the Mississippianrocksof westemUtah and adjacent Neyada that are rich in detail and of exceptionalvaluein building up a generalpicture The rocks in quesof conodont paleoecology. tion weredepositedon and alongthe westedge of the broad carbonate platform of the conti-
nental interior, and in the Deseret Starved Basin, which was separatedfrom the Antler Flysch Trough on the west by a narrow submarine rise, or sill. The generalarrangementin the Deseret Basin and adjacent platform areas of Mississippianrocksof the Anchoralis-Iatus Zone is shown in Fig. 7.4. From the distribution of conodonts in the several lithofacies shown in Fig. 7.5, Sandbergand Gutschick (1984) have also inferred the habitat of conodont speciesthat represent the genera indicated in that figure. Dark brown to black mudstones,phosphorites, and phosphaticshalesare the deepestwater depositsrecognizedin the Mississippian transect summarized diagrammatically in Fig. 7.5. Sandbergand Gutschick(1984)conclude that thesedark-coloredrocks formed in cold, oxygendeficientmarine water at teast300 m deep along the axis of the DeseretStarved Basin.
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The deep-waterdepositsintertongue east- the reconstructedforeslope,including its preward with thicker accumulationsof dolomi- sumably dysaerobic,deep-watertoe. The abtized biosparitethat include encriniteswhose senceof BaclrognarrrJsspecimensin axial detextures proclaim their formation as debris posits of the DeseretBasin, coupledwith its flows. Theserocks, thought to have accumu- occurrencein samplesfrom both poorly and lated on the foreslopeof the broad cratonic well-oxygenated slopeenvironments,suggested platformjust eastofthe DeseretBasin,proba- to Sandberg and Gutschick (1984) r}|lat Bacbly weredepositedin the murky but well-aer- trognathuswasa swimmer,but that it confined atedwaterof the aphoticzonelthe encrinites, its swimming to the aeratedwater just basinof course, are built of material that moved ward of the slope floor. In other words, Bacdown the slope from the shelf edgeor from trognathus, like its close relatives, Scaliognasiteshigheron the slopeitself. thus and.Doliognalhus,was mesopelagic,but Eastof the platform margin, rocks of the An- its habitat may have huggedthe bottom aboye choralis-LatusZone arc thick-bedded,light- the oxygen-minimumzone. colored, bioclastic limestonesthat are replaced Gnathodus and Pseudopolygnathusare also farther eastward by more thinly bedded lime- represented by specimensfrom upperand midstones.These,in turn, gmdelaterally into do- dle slope deposits, but by very few from rocks lomites. Sandbergand Gutschick infer that the that representslopeenvironmentsinterpreted latter rocks should merge even farther to the to havebeenbelowthe oxygen-minimurnlevel. eastwith sandydolomites,perhapswith anhy- Because of the latter fact,it seemsunlikely that drite or other evaporites.Thosefacieshave not individuals of either genusever strayedmuch yet beensampled,however.In general,all these abovethe bottom or out into water abovethe facies representdeposition in the relatively deepestparts of the basin. In short, speciesof shallow-waterenvironmentsof the carbonate Gnathodus and. Pseudopolygnathusmay well platform. All those environments were cer- have been nektobenthic,with habitats that tainly within the euphoticzone. "bottomed out" basinwardagainstthe oxygenRepresentatives of Bispathodus utahmsis minimum layer. Sandbergand Gutschick, 1984, and PolygnaEotaphrus is confined to rocks that formed Ihus communisBransonand Mebl, 1934,have high on the slopeand in adjacentparts ofthe beenrecoveredfrom all but the mostnearshore shelf edge; Hindeodus is commonly reprefacies.This near-ubiquityof occurrencesug- sentedin strata depositedon the outer shelf; geststhat both specieswerepelagicand inhab- Pandorinellina appears to have characterized ited the euryhaline environmentsof the eu- the inner shelf, in environmentsaboye wave photic zone. basefand.Mestognathus,a closerelative ofboth Scaliognathus and Doliognathus, curiously Pandorinellina and the cavusgnathids, may specializedand biostratigraphically very useful well have beenadaptedto hlT,ersalinelagoonal prioniodinidesof the family Bactrognathidae, environmentsalong the innermost margin of are representedin the deepest-waterdepositsof the platform. Thereis little in the reporteddisthe DeseretBasin as well as in the much shal- tribution of conodontsassignableto any of lower-waterstrata of the foreslope(Fig. 7.5). these generathat proyides a definitive answer Such a distribution logically suggeststhat indi to their mode oflife. Their absencein slopeor viduals of these generawere also pelagic, but deep-basin depositssuggests theymay not have liyed at greater depths than did Bispathodus been petagic, in the manner of Bispathodus utahmsis andPolygnathuscommunis. In shor1 and Polygnathus. Possibly they were also speciesof thesetwo generawere probably me- nektobenthic. sopelagic.Their depth zone may well have It is always risky to generalizefiom obserbeen defined by the well-oxygenatedbut still vations made in limited areas,no matter how rnurky conditions of the dys- and aphotic sophisticated the studiesor convincingthe conzones. cfusions. However, it may be noled, that PanBactrognathus,a distinctive prioniodinide, is dorinellina is the acknowledgedancestorof the representedin sarnplestaken from all parts of Cavusgnathidae and. that Cavusgnathus(and,
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PALEOECOLOGYAND PAIEOBIOGEOGRAPHY
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in Merrill and n governed the rbdon of these are outlined r- in comprehenr|s by Heckel =mann (1975), E misleadingto lrtemEnt on all y of Pennsylvadearly basicdifmatters.Not all r occasionalstrirent would suglion of informaqrorts proYides r and habitats of Fobably also of E midcontinental in a chain of rere situated in b equator.This
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areawas borderedon the north and northeast middle limestoneis followed by a meter or so by the relativelystablecratonicinterior and on of abundantly fossiliferousgray-brownshale, what were then the south and northwest sides which is typically (but not invariably) introby active rangesoffolded or fault-block moun- ducedby (or includes)a distinctivecomponent tains. The southernmargin and the southeast- offissile black,phosphaticshale.In this "coreem end of the foreland-basinchain received shale" interval, conodont diversity may drop great quantities of terigenous detritus from off, but frequency of occurrencecommonly streamsdraining the Appalachianand Oua- reachesa rnaximum and preservationis genchita-Marathonfoldbelts. This spreadout to erallyoptimum. Representatives of Gondolella form a complex of laterally shifting alluvial are almostcompletelyrestrictedin their occurplains and coalescingdeltaic systems,which rence in Kansasand Iowa to the core-shaleinwereonly occasionally(andthen briefly)trans- terval, and specimensof the prionidinide 1d,gressedby offshore marine environments. Far- oprioniodusare more numerousin this facies ther westand north, the basinchain was more than in any of the othersin the Kansas-Iowa persistentlyoccupiedby the sea,sedimentsare cyclothem. offiner grain,and the recordofconodontsand In the basatpart of the "upper limestone," other groups of fossils is more nearly con- which succeeds the coreshaleofa Kansas-Iowa tinuous. cyclothem,maximum conodontdiversityis reIn parts ofthe foreland-basinchain that were establishedand specirnensof the Idiognathomost persistently occupied by the sea, the dus-Streplognathodusplexus continue to domPennsylvanianrock record is made up of a inate in frequency.Adetognathus,represented successionof cyclothems. These are repeated by few, if any, specimensin the lower part of setsof distinctive rock types,which record a upperJimestoneintervals, tlpically becomes number of transgressive-regressive cycles that more abundantlyrepresentedupward in those are comrnonly regarded as the results of eu- intervals and may regain a dominance in the static rise and fall of sealevel. Heckel and Bae- uppermostpart that carriesover into the lower, semann(1975)and Swade(1985)have related marine part of the superjacentoutside-shale the distributionand frequencyofconodontsto unit. the lithic componentsofa numberofthe PennAs indicatedin Fig. 7.7, the typical Kansassylvaniancyclothemsin Iowa and Kansas,with Iowa Pennsylvaniancyclothem is viewed by the generalresultssummarizedin Fig. 7.7. mostgeologists as the recordofa transgressiveNote in Fig. 7.7 that sandy"outside shales" regressiveevent. Thus, from the relationship at the baseofa typical Kansas-Iowacyclothem betweenconodontsand the lithofacies that repinitially recorddepositionin nonmarineenvi- resenl vanous stagesin thal transgressive-reronmentsbut, in their upper parts, pick up a gressivehistory,it shouldbe possibleto reconfew fossilsthat indicateshallow,nearshorema- struct a general ecologic model. Such a model rine environments.The first conodontsto ap- hasbeendevelopedby Heckeland Baesemann pear in theserocks representAdetognathusarLd, (1975)and Swade(1985)and is showndiaEllisonia, but others referable to Hindeodus, gammatically in Fig. 7.8. Aethotaxis, and. the ldiognat hodus-Strepto- Heckel(1977)concludesthat the phosphatic gnalhodusplexusfollow shortly. In the "mid- black shalecomponentof the core-shaleinterdle limestone,"just abovethe "outside shale" val accumulatedin anoxic bottom water bein a typical cyclothem, the inyertebrate fauna neath a thermoclineand thus representsthe becomesmore diverseand is much betterrep- deepest-waterenvironment recordedby any of rcsented..Adetognathus may continue to be a the lithofacies in a cyclothem of Kansas-Iowa prominent memberofthe conodontfauna,but type. From this conclusionit followsthat condiversity commonly is greaterthan in shaty odonts commonly representedin core black rocksbelowanddominancebeginsto be shared shaleswerenot only pelagicbut werealso segwith conodonts of lhe ldiopathodus-Strepto- regatedin depth zones in life. That is, Gozgnathodus plexus. dolella, Idioprioniodus, Neognathodus, and In the typical Kansas-Iowacyclothem,the various members of the ldiognathodus-Strep-
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PALEOECOLOGY AND PALEOBIOGEOGRAPHY
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dense,oxygen-poorwater of the thermocline, to which Gondolella was best adapted and in which ldioprioniodus also thrived. As Heckel (1977) noted, that water may also haye been rich in settling organic matter, phosphate,and heavy metals,and thesemay also haveplayed a part in defining Gondolella's depth-zone habitat. Adetognathusand.Ellisonia were certairLlyat the otherend ofthe ecologicspectrumin Pennsylvanian seas.The common occurrenceof specimensof Adetognathus,for example, in rocks that representobviously nearshoreor marginal marine environments(like the outside shaleof FiE 7.'l), in dolomitic stratathat intertonguewith evaporitesequences, and also (in greatlydiminished abundance)as componentsof higher-diversityconodontfaunasthat include forms associatedmore commonly with normal marine conditions suggeststhat ldetognathus$tasearyhalineand adaptedto life in well-oxygenated nearshore waters that were susceptibleto wide variationsin salinity.Mer-
163
rill recognized ihe Adetognathus biofacies in 1962and, in subsequent reports(Merill, 1968; von Bitter, 1972),it hasbeensuggested that ratios between specimensof Adetognathus and, Idiognathodus or Streptognathodas, which dominate environmentsmore offshore,might provide a quantitative senseof distancefrom shoreand a measureof relativesalinity. Environments intermediate between the shallow, well-oxygenatednearshore waters with highly variable salinity and the much deeper,colder,more dysaerobicwatersof the thermoclineseemto have supportedthe most diverseconodontbiotasin the Pennsylvanian. Throughoulthe Pennsylvanian, dominantconodonts in these intermediate environments were members of the ldiognathodus-Streptognathodusplexus,and rocks that accumulated in them have been assignedto a ubiquitoi]s I di ognathodus-Strept ognathodus biofacies (Merrill and von Bitter, 1984).But theseintermediate environmentswere also the ones in which the closely related anchignathodontids
Fig. 7.8. Hypothetical c.oss sectionsofPennsylvanian seaat maximum extent in the U.S. Midcontinent. Upper diagram relates sedimentary facies to inferred quasi-estr.rarinecirculation pattem; lower diagram shows inferred living distribution of conodontsas reconstructedfrom tieir occurrencesand frequenciesin various sedimentarv facies.Redrawn and slightly modified from Swade(1985). prevartrng w rnd
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PALEOECOLOGYAND PALEOBIOGEOGRAPHY
nd commonly conglomerates r maryinal enr black shales : rnterpretedas rposits. Heckel lansgression of rigenousinflux r['trt have proNronment unbr- so that the er-e foundered @uent deepb offshore,an['fine-grained I|c matter setrded by superble directlyon rb situations Ie explanation r insistingthat r inrerpretedin
ized in Section rencesas to the t can be made Jationship beEtary rocks in :- *'as irnplied r and lateralrd by Seddon and Fihraeus re also learn Ering distribu;dures of both hion that the t have yaried nhic. On the i is rarely posrnical, or biotsolled the disr example,that lhids were, for lftalrs of shalHts that were zted temperalinit_v, but it is icron of those
165
harsh environments controlled the distribu- Idioprioniodus and, Gond.olellain Pennsylvations obserYed. nian cyclothemsin Kansasand Iowa suggests that speciesof those generawere confinedin life to a relatively deep part of the water col7.5.1 Depthasafactor umn and also that their depth zone may haye Many of us who have written about conodont been defined by the cold, dense dysaerobic paleoecology havediscussed the distributionof water ofthe thermoclinethoughtto be responvariousspeciesin termsofwater depth,not be- siblefor anoxicconditionson the bottom. Uncausedepth pel Je is a significant ecologic fac- fortunately,from studyofthe skeletalelements tor, but becausea senseof at least relative of cold-waterOrdovician and Pennsylvanian depth may be derivedfrom the textures,struc- species,I havebeenunableto isolatemorphotures, and other fossils in the sedimentary logic featuresby which other cold-waterforms rocks from which our conodont collections might be identified. havebeenmade.Althoughdepthitself may not have exerteda primary influenceon conodont distribution, factors such as temperature, light 7.5.3 Nearshoreand ofshorefaunas penetration,lieht intensity, turbidity, energy, All threeof the modelssummarizedin section salinity,and water densityfluctuatedirectly or '1.4relatethe distribution of conodontsto oninverselywith depth,and oneor a combination shore-offshoretransectsreconstructedfrom the ofthese may haveexertedthe direct control on distribution and nature of the sedimentarydistribution. I suspect,for example,that tem- rock record.In all threemodelsthereis reasonperature,not depth, was the important factor ably clear distinction between an offshore governingdistribution of speciesof Amorphu group of speciesthat may be relatedto stable gnathus and, related balognathids.That is, temperatures,"normal" marine salinities,and those speciesare representedin highlatitude limited turbidity; and anothergroup that apOrdovician rocks that formed in cool, rela- parentlythrived in nearshoreenvironmenls tively shallow water, whereas at lowlatitude characterized presumably by harsher, more sitestheir remainsare largelyrestrictedto the varied environmentalconditionssuchas great depositsof deeperwaters in which tempera- fluctuationsin temperature,salinity, and turtures may have been comparableto those bidity. It is ofinterestthat conodontstypical of nearerthe surfaceat high latitudes. the offshoreand nearshoreendsofthe environmental spectrumin all three models have a numberof featuresin common. 7.5.2 Temperatureas afactor In all threeofthe situationsdescribedin SecDiferences in temperature were probably re- tion 7.4,speciescharacteristicof nearshoreensponsiblefor development,in the Ordovician, vironmentsbuilt apparatuses of relativelylarge ofdistinctive conodontfaunasin the high- and elements, with a reduced nurnber of discrete low-latitudemarine realms.This conclusionis denticlesof circular crosssectionand little, if suggestedby the fact that rare invasions into any. white matter.I alsohavethe impression higher latitudes of speciescharacteristicof low thal elemenlsof nearshorespeciesare more latitudes were accompanied by accumulation variable in morphologicdetail than those of of vaughnitic carbonate rocks that indicate offshore species,and their apparatusesare concurrent invasions of warmer than usual more variable in composition. Furthermore, water.Also, as noted in Section7.5.1,the few note that Ordovicianand Triassicrocksrepretypically highlatitude speciesthat migrated senting nearshore environments have profrom time to time in the Ordovician into the duced all of the "fibrous" elementson which low-latituderealm becameestablishedtherein Bransonand Mehl (1944)basedtheir concept deeper-waterenvironments that were probably of the suborderNeurodontiformes.Finally, it similar thermally to the high-latitudeonesin is clear that at any time speciesdiversity was which the species weremostwidely distributed. considerablylower in nearshorethan in ofAs notedin Section7.4.3,the distribution of shoreenvironmentsand, becauseit is my ex-
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VJNOOONOJ :IHI
991
PALEOECOIOGYAND PALEOBIOGEOGRAPHY
ied denticles ner. Their dehdovician, apt apparatuses res" Developinilar history. i:s are repreI and the eleershore featte primitive ,dina," clearly mr-rronments. F ous to use r elsewherein iks to the enE OrdoYician rlusion from Etioned that, I paleoecology rI To be sure, --<)r eYenthe I a generalaffie. shallowei'en at this teep in mind hioniodinida ue explorers mid-Pennsyld nearshore Ere frrmly esed Ellisoni-
r I notedthat rs of Triassic rctively, had hde that dur:n history the rts may have ) s.rggestions, ilerable skepE Eell-estabfrough it has = h their hismmopolitan 4rh) is cural circlesbe-
causeofthe light it may shedon the positionof major crustalplatesin the past.For this reason, a number of defailedstudiesof conodontpaleobiogeographyhave been published in the lastfew years.Most ofthesehayebeenbrought up to datefairly recently(€.9.,Clark,ed., 1984), so I provide only a brief summaryhere. 7.6.1 Late Cambrianand Ordoyicqn paleobiogeography
t67
ley Province in the late Ordovician of the wann-water realm. tateral differencesin contemporaneousconodontfaunasalso permitted recognition of British, Baltoscandic, and Mediterranean provinces in the cold-water marine realm, in which conodonts may have lived in subpolarseaswell above 60 degreessouth of the equator. I-ate in the Ordovician, as noted in Section 6.3.2,conodontspeciesdiversity declineddramatically, and this seemsto have led, by the end ofthat period,to virtual eliminationofthe fauna characteristic of the cold-water realm. Stocksthat survivedinto the Silurian (i.e..the Icriodellidae, Prioniodinidae, Spathognathodontidae, and Panderodontidae)are either onesthat werewell establishedin low- to midlatitudeseasofthe Ordovicianor aresurviving relatives(e.g.,Distomodontidae)of onesthat were.
Miller (1984) notes that both classesof conodonts appear to have originated in the Late Cambrian in warm, low- to midlatitude seas. By earliestOrdovician time, however,representativesof both groups had spread into higherJatitude seas,and Cordylodus (a cavidont) had becomeessentiallycosmopolitan.A pair of major eustaticeventsin this Late Cambrian-earliest Ordovician interval are thought to hal/e been influential in directing the development of the Conodontaso that, by late in and Triassic the Tremadocian, very different faunas had 7.6.2 LaterPaleozoic paleobiogeography evolvedin low- and higherlatitudeseas. The faunaldifferentiationoutlinedby Miller Reported Silurian conodont faunasare surpriscontinued through the Ordovician, when the ingly cosmopolitan. However.46new species manne realm was clearly divided into two are described from the Lower and Middle Simajor biogeogaphic units (Sweetand Berg- lurian of New South Walesin a recentreport strijm, 1974,1984).I now preferto regardthese by Bischof(1986),which may suggestthat Silmajor units as warn- and cold-water realrns, urian cosmopolitanismmay be partly a result althoughthey were originally describedas the of faulty knowledge of Silurian conodont North Atlantic and North American Midcon- faunas.It is alsoofinterestto notethat Silurian tinent provinces.Descendantsof the pioneer conodonts have been collected largely from lineageof the Conodonti,the Teridontusstock, rocks thought to have been depositedequatorfigured prominently in faunas of both the ward ofthe 40th parallels(Charpentier,1984). warm- and cold-water realms and, as BergKlapperand Johnson(1980),whosecomprestrdm and I pointed out in 1974,there was a hensive review is authoritative, confirm that not-surprising parallelism in development. conodontsappearto have beenrestrictedin the Only a few cosmopolitan species existed, Early and Middle Devonian to more or less mostly representativesof Drepanoistodus and, tropical areas.Early in the Devonian, endePanderodus,but also including the cavidonts mism was relatiyely high, but later in the peDapsilodus, Walliserodus,ar:.dAnsella. riod, with increased rnarine transgression of By the Late Ordovician,and possiblybefore, cratonic areas, endernism decreasedand the distributionofconodontshad cometo defrnea nurnberof cosmopolitanspeciesincreased.Alnumber of biogeographicprovinces in the though Klapper and Johnsonnoted that most warm- and cold-water realms. For example, a conodont genera were uniformly distributed, combinationofR- and Q-modeclusteranalysis they loggeda number of differences,at the speof data from 26 sites in North Arnerica (Sweet ciesleyel,betweenthe conodontfaunasofvarand Bergstrdm, 1984) permitted discrimina- ious epeiric seasof the Early and Middle Detion of an equator-straddling Red River Prov- vonian.It wastheir choicenot to formalizethe ince and a soinewhat higherJaiirde Ohio Val- endemicunits asproyincesbecause sucha pro-
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PALEOECOLOGY AND PALEOBIOGEOGRAPHY lion and one of r as a feature in f an1-'age. Sublrd a Tethyan tDgaea, a Gerilce in central Pro\-ince on the :aner's (1984) I endemism did that Middle Ecupied by inmt faunas. Be! Triassic have E specieslevel, ilentifications) t role in supprincialism or bm. Until there B roday on the E I doubt that Eraphic distri-
E (1975).Provpoposed nektoDdontophorids. d Middle Silulm New South t Senckenberg E (1978).Late aian history of c, central KenI Soc.Am. Bull. i. (1934).Coneuti Studies 8, E-246 h Index . W. Shimer and L odo[ts through nodoot provinr 196, lL-32. rt biofaciesand Aemoir 196, Ltrarigraphy and ' the Lexington rtral Kentucky. t68. r-59. [-v and paleoe| (Cincinnatian)
169
in Indiana, Ohio, and Kentucky. Geol. Soc. Devonian and Mississippian rocks along the America Spec.Paper 95, l-34. Wasatch Front and Cordilleran hingeline. Heckel, P. H. (19'1'7).Origin of phosphaticblack Brigham Young Univ. Geol. Studies 26: tO7_ shale facies in Pennsylvanian cyclothems of 133. mid-continent North America. Am. Assoc.pe- (1984). Distribution, microfauna, and trol. Geol.Bull. 6l(7), 1045-1068. source-rock potential of Mississippian De[e (1980). Paleogeographyof eustatic model Phosphatic Member of Woodman Formation for deposition of mid-continent Upper pennsylvanian cyclothems. Pp.l97-215 in Paleozoic paleogeography of the west-central united States(ed. T. D. Fouch and E. R. Magathan). Rocky Mountain Sec.. Soc. Econ. Paleont. Mineral. Heckel, P. H., and Baesemann,J. F. (1975). Enton Group (Ordovician) in New york, southern vironmental interpretation of conodont distriOntario and Quebea.N. Y. State Mus. Sci. Seru. bution in Upper Pennsylyanian (Missourian) Bull. 405, l-1O5. megacyclothemsin easternKarlsas.Am. Assoc. Petrol. Geol. Bull. 59, 486-509. Huckriede, R. (1958). Die Conodonten der Medirerranen Trias und ihr stratigraphischerWert. PaLiont.Z. 32, l4l-175. Klapper, G., and Johnson, J. G. (1980). Endemism and dispersalofDevonian conodonts.I Paleont. 54, 400-455. Geol.Survey,Tech.Information Ser. 14, l-:-l. Kozur, H. (1976). Paleoecologyof Triassic con- Sweet, W. C. (1979.).Conodonts and conodonr odonts and its b€aring on multielement taxonbiostratigraphy of post-Tyrone Ordovician omy. Geol.Assoc.CanadaSpec.Paper 15,313rocks of the Cincinnati Region. U. S Geol. 324. Sum.Prof,.Paper t066-G, ct--G26. Merrill, G. K. (1968). Allegheny (Pennsylvanian) (1979). Late Ordovician conodonts and conodonts. Unpubl. Ph.D. thesis, Louisiana biostrati$aphy of the western Midcontinent StateUniv., Baton Rouge, 184 pp. Proince. Brigham YounR t-lniv. Geol. Studies Merrill, G. K., and Martin, M. D. (1976). Envi 26,45-85. ronmental control of conodont distribution in Sweet,W. C., and Bergstriim, S. M. (1974). prothe Bond and Matoon formations (Pennsylvavinciatism exhibited by Ordovician conodont nian, Missourian), northern lllinois. Geol faulnas.Soc. Econ. Paleont. Mineral. Spec.publ. Assoc.Canada Spec.Paper 15,243-27L 2r, 189-202. Merrill, G. K., and von Bitter, P. H. (1984).Facies (1984). Conodont provinces and biofacies and frequencies among Pennsylvanian conof the I-ate Ordovician. Geol. Soc. Am. Spec. odonts; Apparatuses and abundances. Geo,/. Paper I 96, 69-87 . Soc.Am. Spec.Paper 196,251-261. Sweet,W. C., Turco, C. A., Warner, E., Jr., and Miller, J. F. (1984).Cambrian and earliestOrdoWilkie, L. C. (1959).The American Upper Orvrcran conodont evolution, biofacies,and prodovician Standard.I. Eden conodontsftom the vincialism. Geol.Soc.Am. Spec.Paper 196,43Cincinnati Region of Ohio and Kentucky. "/. 68. Paleont. 33, 1029-1068. Nicoll, R. S. (1976). The effect of Late Carbonif- yon Bitter, P. H. (1972). Environmental control erous-Early Permian glaciation on the distriofconodont distributon in the ShawneeGroup bution of conodonts in Australia. Geol. Assoc. (Upper Pennsylvanian) of eastern Kansai. Canada Spec.Paper 15,273-278. Pojeta, J., Ir. (1979). The Ordovician paleontology of Kentucky and nearby states-Introduction. U. ^S.Geol. Surv. Prof. Paper 1066, AlA.48. Rhodes,F. H. T. (1952).A classificationofpennsylvanian conodont assemblages.J. Paleont.
26,886-901. Sandberg,C. A., and Gutschick,R. c. (1979). graphischeBedeutung.Abh. Hess.Landesamtes Guide to conodont biostratigraphyof Upper Bod.enforsch. 3t, 1-l 66.
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bt evidencein Fosition ofthe ndonts is prod assemblages r on the shape dized elements r4000speciesis I discretespecib€ rest is really tretation. rScottish specIghtly different t leasttwo difrions in which lreserved as a rith overlying csecompressed mains of elonl-bodied organo 1.8mm wide. qreted as a ced- bilobed,and iDaturalassemlt are oriented r to that of the site end, interI more or less rs to i blunfly d setsofshort, inpressionsinurrounding the Gterior part of l secrmen may ttenorly openracterize what of ar least the nens.Although riately cautious hrcs with the ruscleblocks of kh. Aldridgeet
111
al. (1986)describethesefeaturesas "somites" nonmarine. The first true conodonts are from without further justification and this evidently Upper Cambrian rocks, the last from strata of figured prominently in their ultimate determi- latest Triassic age. Conodontshave been renation that the affinitiesof the conodontsare coveredfrom virtually all types ofsedimentary with the chordates. rocks. and records of conspecificspecimens Also indicated with varying degreesof fidel- frorn rocks representingmany diferent depoity on all four Scottishspecimensis a pair of sitional envionmentsare common. Especially subparallellongitudinal lines, which extend significant(to me, at least)is the fact that most from a point (in one specimen)not far behind conodont generaare representedsomewherein the cephaliclobe to a point near the posterior the world in black shale deposits, which comend of the tail. Aldridge et al. (1986)point out monly lack remainsof benthic organismsbut that theselines might represent". . . a septum in many placesinclude well-preservedspecidividing the body somites longitudinally, a mensof pelagicones. mesentery separatingcompartments of the body cavity, a major longitudinalblood vessel, as Ilvertebrates a stiffeningrod or notochord,a nerve chord, 8,3 Conodonts the gut." They note that the gut is the one of In the 130yearssincetheir first formal recogthese structuresmost likely to be preserved; nition, the conodontshave beenreferredat one however,they alsonote that ifthe pairs oflon- time or anotherand with variousdegreesofsegitudinal lines do representthe outlinesof the nousnessto most ofthe major phyla of invergut, the fact that they extendalmostto the pos- tebrateanimals.The hypotheses represented by terior end ofthe tail in two specimenssuggests many ofthesereferralsareeasilydismissed,but that the animal lackeda postanalsegment,or someothersare not so readily discountedand true tail. should at least be mentioned in this ooinion As noted in Chapter 2, the intemal structure polt. of conodont elementsindicatesthey are composed of two parts, crown and base, which must have been completelyenvelopedby (or 8.3.1 ArthropodandAnnelidconnections embeddedin) secretorytissue at least during EvenbeforePander'soriginaldiagnosisofcontimesof growh. Apatite crystallitesin lamellae odontswaspublishedin 1856,Murchison,Barof crowns are oriented with their prism sur- rande, and Carpenter had registeredthe opinfacesparallel to the direction of growth. Bases ion that the tiny fossils were the tip-ends of are less densely mineralized, and the frame- some parts of tlre trilobite carapace,and thus work of organic material may be thicker. In a were arthropod, not chordate, fragments.And, few specimens, the basalportion may includea not long after Pander'smonographappeared, plug of bonelike material v/ithin which Bar- Owen (1860) suggested that conodontsmight skov, Moskalenko,and Starostina(1982)have be analogouswith the ". . . spines,hooklets, or identified structuresinterpreted as osteoblasts. denticles,of nakedrnolluscsor Annelids." Among the other charactersthat havo been Although no one seemsto have followedup consideredin speculations on the biologicaffin- on the interpretationof conodontelementsas ities ofconodonts,I shouldalso mention their parts ofa trilobite carapace,two authors (Hargeographic and stratigraphic distribution and ley, 186l; Simpson,in Newberry, 1875) sugthe cosmopolitanoccurrenceof many species gestedthat conodontelementsmight b€ crusin rocks representing a wide variety of sedi- tacean remains. These suggestionshave not mentary facies.Conodonts are common indig- proved particularly appealing, largely, I susenousfossilsin rocksthat containthe remains pect, becausethe variety of elementtypes of of animals such as brachiopodsand echino- most natural assemblages is not duplicatedin derms,which are exclusivelyrnarineat present the array of spines that rim crustacean and apparently always have been. They have carapaces. been found only as reworked or redeposited Owen'ssuggestionthat conodontsmight be specimensin rocks that might be interpreted as a group of the Annelida received seriousatten-
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csed the possinight represent lalso raisedthe E Edular teeth I srggestionhas blogists, but it rberry, 1875), 5). all of whom rs morphologic rents of living irm conodont 3 the argument be the radular : most types of Dlogic counterf living gastronot found in mdanl gastro: conodont eleE the radular rts are entirely t radular teeth in sl mmetrical $ow considerr conodont eleft et at., l98l) lrt punch,sugEt most living Fologically to d henceare untoup to which Edif (1986)haye rodonts might lrn-t featuresof rcimens invite f caudofoYeate rh a comparihm that living oe size as the hts: that in some AplacoIinro two syrnI grooveofliv:nral suture of itions reministtish conodont I ttrechevron-
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shapedimpressions,which are such strikine and mollusks, which have already been disfeaturesof the Scortishspecimens. mighrcorl cussed,these include the lophophorata (or respondeither to the dorso-ventralmusclese- tentacutala) and such disparate groups of ries of the Solenogastres or to the chewonlike wormlike animals as various aschelminthes, arrangementof dermal spiculesthal character- gnathostomulids,and chaetognaths.In fact, izesthe dorsalsideofother aplacophoranmol- about the only major invertebrate phyla that lusks. Accordingto Tiltier and Cuif, features have not beensuggested as the parentalgroup interpreted as fin rays in the tail region of two for the conodonts are the Archaeocyathida Scottishspecimensmight alsobe duplicatedin (which were largely or entirely extinct before certarnprochaetodermatids by very long sp! conodontsappeared),and the porifera, Bryculesin the posteriorregion. ozoa,Echinodermata,and Hemichordata. Tillier and Cuif further suggestthat the ceLindstriim (1973) and Conway-Morris phalicapparatusofthe Scottishconodontsmay (1976) have either directly or indirectly sugbe analogousin arrangementand errenrn mrn- gested that conodonts might be an extinct eralogyto the radular teeth and, particularly, group of the invertebrate superphylum termed the buccalmandiblesofthe Aplacophora.They Irphophorata or Tenkculata by various aunote,asI havein a previousparagraph,that the thors and composedat presentof the phyla principal reasonfor rejecting a rnolluscanaffin- Brachiopoda,Bryozoa, and phoronida. Conity for conodontsis the argumentthat mollusks way-Morris's suggestionis basedon his interare incapable of secretingphosphatic hard pretation of a curious little fossil from the faparts.However,Tillier and Cuifhave subjected mous Middle Cambrian Burgess Shale of the radular teeth and buccal mandibles of British Columbia as a vagrant tophophorate, Chevrodermaturnerae (a prochaetodermatid and on his interpretationofimpressionsin the caudofoveate) to both X-ray microdiffraction supposedlophophoreof that oryamsmas conand microprobeanalysisand have discovered odont elements.Unfortunately,the conical elethat both teethand mandiblesincludesubstan- mentssupposedto havesupportedlobes ofthe tial amountsofcalcium phosphate,as is prob- lophophore of the creature Conway-Morris ably also the casewith the radular teeth of at named.Odontogiphus omalius have all been least certain scaphopods.(Gastropodradulae dissolvedaway,and the fossilis from rocks far studied thus far seemto lack phosphate,and older than thoseyielding the oldestspecimens the external spiculesof the Aplacophoraare I would regardas conodonts.Thus,in addition aragonitic. ) to questioningthe realsignificance ofa vagrant, The featuresjust summarizedled Tillier and or swrmming,lophophorate,I disqualifyOdonCuif to commentthat if conodontswereapla- togriphusas a seious contributor to our undercophoranmollusks,it would be normal for the standingof conodontaffinities. phosphaticbuccalmandibles,at least,to be fosLindstrijm (1973), on the other hand, silized even though the aragonitic dermal pointed out featuresthat suggestconodont elespiculesmight recrystallizeand be unrecogniz- ments were internal (not external)structures; able as conodontelements.They thereforere- noted a generaltendencyin the evolution of gard the Conodontaas a potentialclassof the conodonB toward an increasein surfaceareaof Mollusca, most closelyrelated to one or an- elements;and suggested that pits in the upper otherofthe groupsincludedin the paraphyletic surfacesof certain conodont elementsmight Aplacophora. have been the sites of muscle attachment. Theseobservationsled him to suggest that conodont elements might have served as intemal E.3-3 Connections with otherinvertebrates supportsfor a muscle-operated tentacularapMiiller (in Clark et al., l98l) lists a largenum- paratus, or lophophore, and this led to the furber ofadditional invertebrategroupsthat have ther suggestion that beenconsideredappropriate,for one r€asonor another,as taxonomicreceptacles for the con- anceslors of the co[odont stock and those of the braodonts.In addition to the arthropods,annelids, chiopod stock were closely related at some relatively late
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3 aITOWWOrInS d this zoologiE the category 1982) demonr structure bed early Ordor assigned to tEs of Sagitta L I s'as partict tbat the conEDic and early Eognalha bed I had used thar group in lin anomalies dOrdovician , srrh the apt study, many lscovered the rs. however, t rle Chaetoirbs in distrid structure of
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Phakelodusand,Sagia4 elements.I am not c€r_ rmens and concluded that they were ,,. . . frag_ tain that any oftheseproblemsis fatal,but thev ments of the hard, crustaceousends of the all diclate caurion. For example.the graspin! segmentsof some trilobite.,, In apparentdef_ spinesofall living chaetognaths areentirelyor_ erence to that opilrion, which he did not at_ ganic in composition, whereasall specirnens tempt to refute, Pander remarked somewhat that I regardas skeletalelementsofconodonts wistfully that (my translation)... . . Complete are thoroughly phosphatized.Furthermore, al_ conviclion that theseremainsarereallyteeihof thoughBengtson(1976)has outlined the steDs extinct fishes could be reachedonly if similar by which the transition from organismswiih structures could be demonstratedin living an_ elementslike those of phakelodusto thosewith imals of the sarneclass." elements with the internal structure of all known conodontsmight havebeenmade,that transition has not yet been objectivelydocu_ E.4.2 Newberry,Hinde, Huxley and Myxine mented.Thus it is my perhapsultraconserya_Newberry (1875), on his own account. and trye conclusion that phakelodus and other or_ Hinde (18?9). on the adviceof Huxlev.congamsms with skeletal elements of similar cluded apparentlyfrom shapeand lusteralone lntemal structure(the paraconodontidaof the that the conodont elements they examined Treatise classjfic.ation)are not conodonts. If were so closely similar to the teeth of the hae_ that is the case,then identity in structureof frsh,Myxine (Fig.8.2). as to be indistinsuishaPhakelodus and Sagi a elementshas no bear_ ble. In fact. Huxley is reported ro have in_ lng on the question of conodont affinities. althoughit may suggesrthal rootsoflhe Chae_ tognathaare to be found in the paraconodon_ Fig. 8.2.. Myxine glutinosa, a hagish (o, slime eel), tida, a goup formerly assignedto the Cono_ reprcsents the chordate division to which many believ; donta on the basis of gross morphology of conodonts to be mosl closely related. Redrawn from Miiller (1836). skeletalelements. 8.4 Conodontsas Chordates Only a few studentsofconodontshayetakena firm stand regarding the biologic affinities of condonls.and most of them favor an assign_ ment rn or nearthephylum Chordata.It is thus ofinterest to look criticaltyat the evidenceon which that assignmenthasbeenbased. 8.4.1 Theopinionsof pander Pander(1856),who coinedthe nameand pro_ vided the first diagnosesand descriptioni of conodonts,included those diagnosesand de_ scnptrons rn a monogaph that dealt Drimarilv with fossil 0shes. Throughout rhai pioneei monograph,Pandertreated conodontsas the hard parts, possiblythe teeth and jaws, of a group of extinct fisbes, prirnarily, it seemsto me becausethat is what they looked like to him. Panderdid not seriouslyconsiderassign_ rng the conodonts to any group other lhan the Chordata, but he noted that Murchison, Bar_ rande,and Carpenterhad examinedsomesDec_
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THE PHYLUM CONODONTA
ber ditrerent lErs on con1986).
kr rpressed the ah and derI necessarily osever, that nrily (if not riS' in exters the teeth the teeth of n frnd no evI of the sublructure deil by Pander.
d basalbony rt elements rbrns in the lone of censome of the |t tbe baseto in color and derm bone. @inion that have been : he was unD include all r later, Bar1 (1982)deel ptatesof drs- a genus dy in the rs together rrespond in I Osreocyres, tov and his rE bone and I remalns. rred in the tqts as the r€d to have never pre6 Kirk had I did many
yearslater),that many ofthe elementsthey collected from the Middle Ordovician Hardins Sandslone oIcentralColoradowereattached ai the baseto a substancethat ".. . appearsbony but does not have the structure of ordinary bone." Bransonand Mehl's (1933) comment that ". . . the materialsto which the conodonts are attachedcould not be from annelids or from anlthing but vertebrates..." takes on considerableimportance becauseit was the conclusionof a pair of trained vertebratepaleontologists;but it can hardly be acceptedas evidenceofaffinity in the absence offurther description, illustration, or histologic analysis. Possiblythey werereferringto materialsuchas that describedfrom Siberiaby Barskov,Moskalenko,and Starostina(1982),but this will alwaysbe uncertain.
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Ulrich and Bassleron little evidenceother than comparativegrossmorphology. 8.4.7 Interpretations of the Scottish Carboniferousspeci mens
The most recentdiscussionsofconodont amnities (Briggser al., t983; Aldridge er al., 1986) are concemedprimarily with appropriate interpretation of the four Scottish Carboniferous specimens,to which I have alreadymade repeatedreference.Briggs et al. comparedthe first-discoveredand best-preservedScottish specimen with the cephalochord.ateBranchiostoma(FiE.8.lA),the ammocoetelarva of lampreys, and arTowworms of the invertebrate phylum Chaetognarha (Fig. 8.lC). Their conclusionwasthat neithera chordatenor a chaetognath model ". . . provides a satisfactoryanswerto the questionofconodont amnity." 8.4.6 Compositionand growthof etements Following description of three additional Ellison (1944),and Hassand Lindberg (1948) specimensin 1986,however,Aldridge and his clearedup long-standingconfusionabout the colleagues concludedthat conodontsrepresent chemical composition of conodont elements a group ofjawless,craniatechordates seDarate and pointed out that the phosphaticminerals from previouslydescribedgroupsbut perhaps they identified were the sameas those in fossil rnost closelyrelatedto the hagfishes(Myxinoand recent bones and teeth. However, Gross idea). A similar conclusionis expressed, but (1954),a studentoffossil fishes,madethe im- just in passing,by Jeferies(1986),who notes portant determinationthat conodontelements that the hypotheticalanimal ..s" proposes he as are not composedof dentineand lack features the first "crown vertebrate,,resembles the Scotthat could be interpretedas either a purpa or tish Carboniferousconodontanimal described dentine channels. Furthermore, Gross pre- by Briggset al. (1983).However,in the nearly paredthin sectionsofthe Pa elemenlsof Ozar- three pagesJetreriesdevotes to listing the charkodina murchisonl (Pander)and determined actersof this hypotheticalcreature, I find onlv frorn the arrangementoftheir lamellaethat the six that might be more or less objectivelyrepelementsmust havegrownby accretionofnew resentedin (or by) the Scottishspecimens(mamaterial to their outer surfaces,not by addition rine habitat, eel-shapedbody, head-trunk-tail, ofnew lamellaeon the inner surfaceofthe ele- rasprngtee1h,?lensless pairedeyes,?somites).I ment, as Pander(1856)had concludedwasthe suggestthat, as Jefferiesintimates, the resemcase.Gross vr'asthus able to assertwith some blance betweenhypotheticalanimal ..s,'and confidencethat conodont elementswere not the Scottishconodontsmay be so striking bethe teeth or derrnal scalesof vertebrates.nor cause the latter were used as a general model werethey componentsof the vertebrateendo- for the former. skeleton,which should show evidenceof ossiIn reachingtheir conclusionson conodontaffication about a core of spongy, cartilagenous finities, Aldridge er al. (1986) and Jefferies tissue.Gross concludedfrom his studiesthat (1986) clearly identiry with Pander, Huxley, conodonts were primarily soft-bodied chor_ Newberry,Macfarlane,and Ulrich and Bassler, datesassignable to a distinct branchofthe Ae- althoughtheir reasoningis somewhatdifferent. natha. lt is ironic. I suppose,that his detail; Becausethe Scottishspecirnenslack any evistudiesled Grossto conclusionsvery similar to denceofjaws or a bony skeleton,it is the opinthose advancedby Huxley, Macfarlane,and ion of Aldridgeand his coauthon that
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the chordate feature to which the conodont appamtus shows the greatest similarity is the lingual structure of hagfishes. . . in which the rows ofteeth are not opposed when at resl, but are evefted by protractor muscles in such a way thal the action is bilateral rather than vertical.
basal plate, which supports the floor of the mouth and is the rigid, immovable site of at_ tachmentofthe jaw muscles. Contraction of prolractor muscles attached, to its anterior end causesthe dental plate to slide forward in the grooved upper surface of Sincethis is alsothe chordatefeatureto which the basalplate. As it doesso, its sidesflatten Huxley, Newberry, Macfarlane, and Ulrich and and the rows of lingual teeth above it are Basslerassignedconodontelements,and a fea- raised, spread laterally, and eyerted from the ture of Jeferies' (1986) hypothetical animal mouth (Fig. 8.3, upper left). Dawson (1963) "s," the first cro\ln vertebrate,a briefreyiew of likens this sequence ofevents to the openingof its charactersis in order. a book. Contractionofmusclesattachedto the posteriorend of the dental plate efects retraction of the plate, closingof the book, and ap8.4.8 The lingual apparatusofVyxine proximation of the teeth in a graspingmove_ Figure8.3includesventral viewsofthe headof ment. Repeatedprotraction and retraction of Myxine glutinosa, a typical hagfish, drawn to the lingual apparatus altemately spreads and show the toothed lingual structure everted(left, approximatesthe rows of teethand is effective above) and retracted(right, above).The sagittal in tearing food and conducting it into the and transversesectionsbelow these two views mouth. During theseripping motions,the lone provide schematicinformation on the anange- palatal tooth may serve as a gaff by impaling ment of supporting plates and principal rnus- chunksof foodstuffand therebykeeping them cles.Accordingto Dawson(1963),the lingual from slippingout ofthe mouth during prorracslructule of Myxine has four primary compo- tive moyementsofthe dentalplate. nents. Above the mouth there is a single,backIndividual lingual teeth of Myxine glutinosa wardly directedpalatal tooth,which is median (Fig. 8.4A) are complexstructuresmade up of in position and firmly attachedto an overlying an outer horn cap separatedby an epithelial plate of palatal cartilage. The laterally com- layer from an inner conethat includesdistincpressed,slitlike mouth is flanked by flaps of tive, goblet-shaped pokal cells.In the centerof mucousmembrane,which arecontinuationsof each tooth is a mesodermalpulp cavity. The the cephalicepidermisand fold into and line base of the outer horny cap is embedded in a the oral cavity.Embeddedin the mucousmem- groove in the mucous membrane of the oral brane on either side of the oral cavity are two cavlty, exceptlaterally,whereit joins adjacent longitudinal rows of sevento nine yellowish- teeth. Dawson (1963) notes that severalaubrown, horny teeth,which are conicalin shape thors believe that growth of the horn cap takes and joined at their basesto form a tooth comb- place by cell division and keratinization in this When the lingual apparatus is retracted (Fig. basalgroove.Cells in the epithelial layer be8.3, upper right), the tooth combslie flat, and tweenthe apexofthe horn cap and that ofthe apicesof their componentdenticlespoint in- inner pokal-cell cone appearpl/.led.apart, as if ward and posteriorly. they had been stretchedbetweena horn cap The lingual teeth of Myxine are firmly at- that gIew more rapidly than the underlying tachedto a cartilaginols dental plate (FiE. 8.3), pokal-cellcone.The latter,composedofwhite, which is a troughlike structure of V-shaped opaque,resilientectodermalcells,is peculiar to crosssectionthat lies just below the mucous the Myxinoidea and surroundsa small pulp, membraneof the oral cavity. Its longitudinally which contains blood vesselsand nerve fibers. keeledundersidemoves forward and backward Various authors have speculatedthat the in the grooved upper surfaceof a cartilaginous pokal-cellcone might be a replacement tooth,
Fig.8.3.. .Myxine glutrroJa. Top two views show venrral side of head,with lingual apparatusextended(left) and retracted (dght). central and bottom figures are tralsverse and sagittal sections-of t}re rieao to strow erem'enti a.J ' musculatureofthe lingual apparatus.Rledrawnfrom oa*son fts65i_
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rhich are the donts collected rtilaginous pala are required . in Myxine. I brtable just to eiltrer. That is, tEerve rmpresI havebeeninnld have been American Silu:served of the Ens preserves n might be inal;' three likely natus designed imately ingest herd grasping F,ir€(d lalam.I join Dawson trses of any of cuetoped inde-
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pendentlymany times. If so, similarity in me- the repositoryfor the Conodonta or its sister chanical action, even if real, may not imply group. very much about biologicafiniries. Without in any way minimizing the possible signilicance of the bonelike features reported by Barskov, Moskalenko, and Starostina 8.4.9 Summaryoffeaturcsindicatingchordate (1982) from the basalplate of severalMiddle qlfinities Ordovicianelernentsfrom Siberia,it shouldbe In summary. evidencetaken by previous au- notedthat no suchfeatureswerenotedin cornthors to suggestchordate (or vertebrate) affiri- parableparts of any of the conodontelemeqts ties for conodontsconsistsof (l) similarity in studiedby owig (195t), Gross(1954),Miiller chemical composition of conodont elements and Nogami(1971),or in the closelysimilareleand the mineralizedtissuesof yertebrates;(2) ments of ArchaeognathusrccEntly analyzed in the shapesofconodontelements,which suggest detail by Klapper and Bergstrtim(1984).The that they functionedas teeth or jaws; (3) the affinities of Coleodus, to which the Siberian presencewithin the basalplatesof severalSi- specimenshave been assigned, are unknown berian Ordovician specimens of structures amongconodonts;and the Siberianfossils are suchasthosethat characterize vertebratebone; diferent enough from the tlpe of Coleodusto (4) tlte chevron-shaped impressionsin the pos- raiseat leastmodestdoubt about their identiterior half of seyeral Scottish Carboniferous lication.In short,the featuresnotedby Barskov specimens,which have beeninterpretedto be and his coauthorsmay indicatethat the basal myotomes comparableto those of Branchio- plates of the specimensin which they found stoma(:Amphiorus); and (5) imptied similar- them are bone.But it is not entirelyclear that ity of function betweenlhe cephalic apparatus the specimensare conodont elements! Nor of conodonts and the lingual apparatusof have those featuresbeen seen in the basal Myxine and.other hagfishes. platesof elementsrepresenting other species. With respectto compositionalsimilarity, it Orvig (1951)notedthat someofthe conodont has been noted repeatedly that phosphate elementsin his collectionfrom the Silurian of mineralizationis widespreadwithin the animal Estoniaand the middle DevonianofOhio have kingdom and henceis not, ofitsell evidenceof "a baseconsistingofa substancewhich differs anything more than an enzymatic system that . . . frorn. . . materialof the tooth-likecusps.. . hasnot beencompletelymodifiedto permit ac- but in this substance oneis not concernedwith cumulationofcarbonateminerals.Note,in this any kind of bone tissue."He also pointed out regard,the recent determination by Tillier and that the Middle OrdovicianHardingSandstone Cuif(1986) that the buccalelementsof certain of Colorado, which yields elementsof Coleodus aplacophoranand scaphopodanmollusks are and a greatvarietyofother typesofconodonts, phosphatic. also yieldsspecimensassignedto the ostmcodWith respectto shape,I needonly point out erms Astraspis and. Eriptychius that exhibit that teeth,graspingspines,copulatoryhooklets, practicallyall the typesofhard tissueknown in and the like, have similar shapesin whatever vertebrates.To my mind, this statementis siganimal body they are formed becausethoseare nificant becauseit suggests that conodontelethe shapesthat do the job, not becauseall or- ments with superficiallybonelikematerials a1 ganismswith teeth,graspingspines,and copu- the baseand specimenscomposed of real bone latory hooklets are closely related. In addition occur in collectionsfrom the samebeds and to those formed in various ways by diferent that tbey may be readily distinguishedby one groupsofchordates,structurcsthat are similar with a trained eye. to chordate teeth in form and function are Finally, anyone familiar with the elegant ilfound in distantly relatedgroupssuchas mol- lustration of Myxine glutinosa in Miiller's lusks, arthropods,trematodes,nemertineans, (1836) famous monograph on the hagfishes gnathostomulids,and chaetognaths. It is thus (Fig. 8.2)is boundto be struckby the many feano surpnsethat someone,sometime,has con- tures that seemto be sharedwith the best Dresideredone or anotherofthose groupsaseither servedof lhe ScottishCarboniferoussoecimens
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THE PHYLUM CONODONTA
.rc be€n trying h Chordataor crtebratephyla, rsrated convic'organizational E a aroselate in c Paleozoicand since Han. However, -tracted) lin the late Prely of metazoan le such organihve survived, hce" between ruch less than rvrvors. rtte idea(albeit t-aflhropod" is I independently te gradesof ord rhat at least confiisingcomthn characters, fled to survive lested recently ne members of lave been aslbn to several :nlatlves, may organizational rtitrgdom!)that mmotiids and rps. And it has tt eventhe l/enD mor€ than a hates and verhtives may reI of the "chortral sides into €-, the Echinor phyla, or even r-Yof trying to : bas done little ipeness. Their ftatures of the le1- have comr linle hard in-
183
formation we have on soft-part anatomy Branson,E. B., and Mehl, M. G. (1933).Conodont StudiesNo. l. Univ. Missouri Studiest, speaksto us in severaltongues.Thus, I am 5-72. comfortablein consideringthe Conodontaan Briggs,D. E. G., Clarkson,E. N. K., and Aldridge, extinctphylum of small.solitarymarineaniR. J. (1983). The conodont aqimaL Lethaia mals,with compressed or depressed vermifom 16,t-14. bodies that were soft except for a variously dif- Ctark, D. L., Sweet, W. C., Bergstriim, S. M., Klapper, G., Austin, R. L., Rhodes, F. H. T., ferentiated assemblageof phosphatizedepithelial elementsin the cephaliclobe.The elements Mtiller, K. J., Zieg)er, W., Lindstriim, M., Miller, J. F., and Harris, A. G. (1981). Conby which conodontsare represented in the fosodonta. Pt. W, Suppl. 2 il Trcatiseon Invertesil record may have functioned as grasping brate Paleontology(ed. R. A. Robison), Geol. spinesand buccal or pharyngealteeth. And the Soc.America and Univ. Kansas,202 pp. cosmopolitanand broadly facies-independentConway-Morris, S. (1976). A new Cambrian lophophorate from the BurgessShale of British distributionofmany speciessuggests they were Columbia. Palaeontology 19, 199-222. pelagicanimals, probably nektonic, although Dawson, J. A. (1963). The oral cavity, the'jaws' others,of more limited distribution and facies and the horny teeth of Myxine glutinosa. Pp. dependence,may have been nektobenthicor 231-255 il The Biology of Myxlze (ed. A. Brodal and R. Fange).Universitetsforlaget,Oslo. even benthic. Conodonts were probably a minor phylum.neverparlicularlyconspicuousDubois, E. P. (1943). Evidence on th€ nature of conodonts. Pal. 17. 155-159. componentsof Paleozoicor Triassic marine Ellison, S. P., "L Jr. (1944).The composition ofconfaunas.Their ultimate extinctionat the end of odonts. J. Pal. lE, 133-140. the Triassicwasprobablythe cumulativeresult Gross, W. (1954).Zur Conodonten-Frage.,SerrckenbergianaLethaea 35, 73-85. of a long decline through the Carboniferous Harley, J. (1861).On the Ludlow bone-bedand its and Permianand a gradualreductionin genocrustaceanremains.Q. L Geol,Soc.London 11, mic diversity. In spite of their probablerarity 542-5s2. in Paleozoicand Triassic seas,conodontsare Hass, W. H., and Lindberg, M. L. (1946).Orientation of crystal units ofconodonts. J. Pal.20, abundantand commonasfossilsright up to the 501-504. top ofthe Triassic,probablybecausethey were Hinde, G. J. (1879). On conodonts from the blessedwith heala, chemicallyresistantskeleChazy and Cincinnati group of the Cambro-Sital elementsthat providedthem a placein poslurian, and from the Hamilton and Geneseeterity denied to other less suitably endowed shaledivisions ofthe Deyonian in Canadaand groups. the United States. 0. "/. Geol. Soc. London 35,
351-369. Hubrecht, A. A. W. (1883).On the ancestralform of the chordate. Q. J. Microsc. Soc. 23, 349References 368. Aldridge,R. J., Briggs,D. E. c., Clarkson,E. N. (1887). The relation of the Nemertea to K. and Smith, M. P. (1986).The amnitiesof the Vertebrata.Q. J. Microsc. Sci.21,605-644. conodonts-new evidencefrom the Carbonif- Hyman, L. H. (1951). The Invertebrqtes:Plqtyerousof Edinburgh,ScotLand. Lethaia19,| -l 4. helminthes and Rhynchocoela-The acoeloAldridge,R. J., Srnith,M. P., Norby,R. D., and mate Bilateria.y.lL Mc Graw-Hill. New York. Briggs,D. E. G. (1987).The architectureand 550 pp. polygnathacean functionof Carboniferous (1959). The Invertebrates: Smaller Coelocon- odontapparatuses. Pp. 63-75in Palaeobiology mate Groups. V. 5. Mc Graw-Hill, Ne\ryYork, of Conodonts(ed. R. J. Aldridge). Ellis Hor783 pp. wood,Chichester, 180pp. James,U. P. (1884).On conodontsand fossil anBarskov,I. S.,Moskalenko, T. A., andStarostina, nelidjaws. Cincinnati Soc.NaL Hist. J.7. 143prinadlezh- 149. L. P. (1982).NorTe dokazatel'stva nosti konodontoforid k pozvonochnym.Pal Jefferies,R. P. S. (1986). The Ancestryofthe VerZhur. 19E2,80-86. [English translation in Patebrates. Carnbidge Univ. Press, Cambridge, leontologicallournal 1982,82-90.1 376 pp. Bengtson, S. (1976).The structureof someMid- Kirk, S. R. (1929).Conodontsassociatedwith rhe dle Carnbrianconodonts,and the earlyevolu- Ordovician fish fauna of Colorado-A prelimtion of conodont structure and function. Iernary roe. Am. J. Sci.Ser.5, 18(108),493-496. thaia7, 185-206. Klapper, G., and Bergstriim, S. M. (1984). The
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APPENDIX A. A SUMMARY CLASSIFICATIONOF THE CONODONTA
Phylum ConodontaPander,1856 ClassCar.idonti,new Order Proconodontida. new Family ProconodontidaeLindstr6m, t970 E oconodont us Miller, 1980 Miller, 1969 Proconodontus Family Cordylodontidae Lindstriim,
r970 CambrooistodusMiller, I 980 CordylodusPzndet 1856 I apetognathus Ianding, | 982 Family FryxellodontidaeMiller, l98l Fryxel lodontus Miller, I 969 Family PygodontidaeBergstriim,198I N eri codus Li'j.ds1'Jom,| 955 PolonodusDzik, 1976 PygodusI-amont and Lindstriim, 1957 Order Belodellida, new Family BelodellidaeKhodaleyich and Tschernich,1973 B eIodeIIa Ethi'lgtoll, 1959 Coelocerodontus Ethington, 1959 Dvorakia Klapper and Barrick, 1983 Stoladus Lindstrdrn, 1955 Il aIIiserodus Serpagh,| 967 Family Ansellidae Fihraeus and Hunter, 1985 AnsellaFirhtaeu;s andHunter, 1985 Yiira, 1975 Hamarodus 2 n€w Dapsilodontidae, Family BesselodusAJdridge,1982 Dapsi lodus Cooper, | 9-l6 ClassConodontiBranson,1938 Order Protopanderodontida,new Family Protopanderodontidae Lindsrrtim, 1970 Glypt oconus KenJc,dy, 1980 M onocostodus M.rller, 1980 OneotodusLindstriim, I 955 Landing, 1982 Parutahconus ProtopanderodusLlndstriim, I 97I
Drygant, 1974 2Pseudooneotodus ScabbardeIIa Orchard, I 980 SemiacontiodusMiller, I 969 Stauferella Sweet,Thompson, and Satterfield,1975 2Strachanognat hus Rhodes,1955 Teridontus Miller, 1980 TropodusKennedy, 1980 UtahconusMiller. 1980 VaiabiloconusLanding,Bames,and Stevens.1986 FamilyClavohamulidae Lindstrdm, t970 Clavohamulus Fumish, | 938 H i rsutodont us Mjlle\ | 969 Seftat ognathus I-fJe,| 970 ?Paraserratognat hzs Yang, 1986 Family AcanthodontidaeLindstrtim, t970 Acanthodus Fu;mish, | 938 Cor nuodus F ahrircrs, | 966 D repanodusPander, 1856 Parapaltodus Stov$e, 1984 ScalpellodusDzik, 1976 Ulric hodina Furnish, | 938 Family DrepanoistodontidaeFihraeus and Nowlan, 1978 D repanoistodusLindstrdm, I 97I Paltodus Pande\ 1856 ParoistodusLindstrttm, I 97I Order Panderodontida,new Family Panderodontidae Lindslriim,
r9'10 BeIodi na EthilJigton,| 959 CulumbodinaMoskalenko,1973 N eopanderodus Ziegler and Lindstrtim, 1971 PanderodusEthinglon, 1959 Parabelodina Sweet,| 9'l 9 ParapanderodusStouge,I 984 PlegagnathusEthington and Fumish, 1959 Pseudobelodina Sweet, 1979
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A SUMMARY CLASSIFICATION OF THE CONODONTA
llae Bergstrilm, r6m, 1983 r. 1966 ftr. 1935 he Harris, mson and L 1 938 rb and Harris, ton and Clark, ad Harris, -,genusfor Ete P t5 B5 33 r llass, 1959 t935 rd Mehl, : Lindstriim, a|IOmand rrp.elj, 1974 E- Mehl, and dstrdm, 1970 rtu. l97l I Etrson and nd Mehl, ud Mehl, I Mehl, 1933 sler. 1925 Dd Mehl, tL 1982
Hibbardella Bassler,1925 I dioprioniodusGlnnell, 1933 Kl adognathus Rexroad, I 958 OulodusBrarson and Mehl, 1933 Prio ni odina Bassler,1925 PristognathusStone and Furnish, 1959 ?Ligo nodina Bassler,1925 ?Lonchodina Bassler,1925 Family BaclrognalhidaeLindstriim, t9'70 Bactrognathus Bransonand Mehl, 194l DoliognathusBransonand Mehl, t94l Dollymae Hass, 1959 Eotaphrus Pierce and Langenheim, t97 4 E mbaysgnathus Metcalfe,I 98I ScaliognalhusBransonand Mehl, t94l Staurognathus Branson and Mehl, 194l Family EllisoniidaeClark, 1972 EllisoniaMij.ller,1956 Furnishius Clark, 1959 GladigondoIelIa Miiller, I 962 Hadrodontina Staesche,I 964 Metillina Kozur and Mock, 1974 Pachycladina Staesche,I 964 SweelinaWardlawand Collinson, 1986 Family GondolellidaeLindstrdm, l9'10 CarinellaBt trov,1973 CypridodeIla Moshey 1968 EpigondoIella Mosher I 968 Gondolella Statffer and Plummer, 1932 Misikella Kozur and Mock, 1974 Mosherella Kozur, 1972 NeogondolellaBender and Stoppel, r965 Neospathodus Mosher, I 968 Platyvillosus Clark, Sincavage,and Stone1964 Pseudolurnishiusvan den Boogaard, 1966 Xaniognathus Sweet,1970 Order Ozarkodinida Dzik, 1976
t 87
Family Spathognathodontidae Hass, l9s9 Amydrotaxis Klapper and Murphy, 1980 AncyrodellaUlich and Bassler,1926 A ncyrodeIloides Bishoff and Sannemann, 1958 AphelognathusBranson,Mehl, and Branson,l95l BispathodusM.ilrlle4 | 962 E ognathodusPhllip, | 965 Lochriea Scott, 1942 Mehlina Y oungquist, 1945 OzarkodinaBransonand Mehl, 1933 PandorinelIi na M;jller and Miiller, t95'l ?"Plectodina" (new genusfor specres without pastinateP elements) PolygnathoidesBranson and Mehl, t933 Pseudopolygnathus Branson and Mehl, 1934 Rhachistognat hus Dunn, I 966 Scaphignathus Helms, 1959 Torlodus Weddige, 1977 VogelgnathusNorby and Rexroad, 1985 Yaoxianognathus An, | 985 Family KockelellidaeKlapper, l98l A ncoradelIa W zlliser, 1964 KockeIella W alliser, 195'1 Family Pterospathodontidae Cooper, 1977 Apsidognalhus W alliser,1964 Astropentagnat husMostler, 1967 AulacognathusMostler, 1967 Carniodw Wallisel 1964 Johnognathus Mashkova,I 977 PterospathodusW alliser, I 964 Family PolygnathidaeBassler,1925 Ancyrognalhus Bransonand Mehl, 1934 ?A ncyroIepis Ziegle4 1959 PolygnathusHindq | 879 PolylophodontaBranson and Mehl, t934 Family Palmatolepidae,new Klapperina l-ane, Miiller, and Ziegler,1979 MesotaxisKlaEEerand Philip, 1972
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APPENDIX B. STRATIGRAPHICRANGE CHARTS in and
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I Mirchell, tin and lin and d Mehl, h and
Alekseev,
In charts on the next 14 pagesI indicate the slraligraphicrangesof 562conodontspeciesin a biostratigaphicframeworkthat includes156 conodont-definedbiozonesand, in the Lower and Upper Carboniferous, severalintervals for which there are currently no widely accepted In choosingwhich conodont-biozonal schemes. of the nearly 5000namedconodontspeciesto include in the following charts,I followed no particular guidelines. By and large I have included specieswhose first and/or last occurrencesdefineboundariesin the biozonal framework, and I haye omitted species with exceptionallylong rangesand/or poorly known or morphologically nondescript apparatuses. Representativespecimensof many of the species included are illustrated in Chapter 5.
I and 938 t 1933 f,ehl, Xehl,
Mark Kleffner, a doctoral student at The Ohio State University, generously abstracted information on the rangesof important Silurianspecies from the much more inclusivecomposite slandard section he has assembledby graphic means.In compilingotherchartsin this appendix I have supplementedmy own recordswith information from sourceslisted below. Thus authors of those rcports must be credited for most of the hard work that went into building the charts in which their data are used. Of course,they must alsosharesomeofthe blame for any errors!
References Higgins, A. C., and Austin, R. L., editors (19E5). A Strutigraphkal Index of Conodonts. Ellis Horwood, Chicheste\ 263 W. Klapper, G., and Johnson, J. G. (1980). Endemism and dispenal of Devonian conodonts."[ PaL 54(2), 400-455. Klapper, G., arld Ziede\ W. (1979). Devonian conodont biostratig.raphy. Spec. Papers in PoIqeont. 23, 199-224. Kovacs, S., and Kozur, H. (1980). Stmtigaphische Reichweite der wichtigsten Conodonten (ohne Zahnreihenconodonten)der Mittelund Obertrias. Geol. Paliiont. Milt. Innsbruck
r0(2),4't-'18.
I-ane, H. R., Sandberg,C. A., and Ziegler, W. (1980). Taxonomy and phylogeny of some Lower Carboniferous conodonts and preliminary standard post-Siphonodella zonation. Geol. et Palaeont.14, ll'l-168. I-ane,H. R., and Struka,J. J., (1974).I-ate Mississippian and early Pennsylvanian conodonts, Arkansas and Oklahoma. Geol. Soc.America Spec.Paper 152, 144 ppRitter, S. M. (1986). Taxonomic revision and phylogeny of post-Early Permian crisis bisseliwhitei Zone conodontswith commentson Late Paleozoicdiversity. Geol et Palaeont. 20, 139165. Wardlaw, B. R., and Collinson, J. W. (1986). Paleontology and deposition of the Phosphoria Formation. Contr. Geol. Univ. Wyoming 24(2), to7 -142.
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Ranges of selected Triassic conodont species.
Index
Absarokasequ€nce,132, Acanthodontidae,54, lE5 Acanthodus,54, l85, FiE. 5.7 Acodus,6l "Acodtu," 60 Acontiodus,53 Adcarinal trough, 100 Adenticulate process, I 6 Adetognathus,120, l2l, 122, 136, 137, 160, 16l, 163, 188,Fig. 5.s7 Aethotaxis,ll5,ll7,137,161, 164,I87, Fig. 5.54 Agnatha, 177 Alate g€niculateconiform el€ment, 16 Alat€ nongeniculateconiform element, 16 Alale ramiform element, 17 Albid (crowns),13, 14,52 Alternognathus,89,96, IO1, loE, 188,Fig. 5.49 pseudoslrigosus, 107, 108,Fig. 5.49 Ambalodusgalerus,99 Ammocoetelawa, 177 Amoryhognathus,63, 64,7l, 134, 156, 165, 186,Fig. 2. 11, 5. 15 ordovicicus, 26 Afi p hioxus. See B ruhchtostoma Amydrctaxis, 89, 93, 95, 99, 135, 187,Figs. 5.39,5.40 Anchiglathodontacea, I I 7 Anchignarhodontidae,90, 92, 1t 5, I17, 188 Ahchignathodus,l17 typicalis, ll7 Ancoradella,89,93, 98, 187 ploeckehsis, 98 Ancyrodella,89, 96, 106, 135, l4l, 187,Figs. 5.39,5.41 Ancyrodelloides,89, 93, 95, 96, 98, 99, 106, 135, l4l, 187,Fiss. 5.39, 5.40 Ancyrognalhus,lO2, 187,FiE, 5.46 Ahcyrclepis,187 Angulatepectiniform element,2l Annelids,l7l, t72 Ansella,49,50,167,185,Fig 5.3 Ansellidae,42, 49, 185 Anterior process,16 Antler flysch trough, 157 Antognathus,69, 10, 186 Apatognathus,81, I16, 186,Fig. 5.30 Aphelognathus,73,91,93, 134, 154, 155, 156, 187,Fig. 5.37 "Aphelognathus,"9l, |86 gigas,9l kimmsv/ickensis, 9l Aplacophora, 172, 173 Appalachignathus,15, 16, 186,Fie. 5.26
Apparatuses, 38 of, 142 €laboration reductionof, 143 Apsidognathus, 99, 187,Fig.5.43 173,I82 Archaeocyathida, Archeognathus, 123,l8l, 188,Fig.5.59 | 73 Aschelminthes, AshlockFormation,155 Aslraspis,l8l Astropentaghathus, 99, 187,Fig.5.43 40 Altachmentsurfac.e, Aulacognathus, 99, 187 Au lobodui, 186 Bactrognathidae, 83, 145,156,187 Bactrognathus, 83,84, 136,159,lE1,Fig.5,32 anchorarius,84 excavatut,84 hamatus,84 Balognathidae, 63,64,1l,15, 144,186 Balognalhus, 63 Baltoniodus,63, 64,65,186,Fig.5.15 Eovince, 167 Baltoscandic Bars,15,16 Basalcavily,13,15,40 Basalfilling,12 Basalpit, 13,22 Basalplate,179 Base,13,15 Belodella, 45,49,185,Fig.5.3 42,45,49, 133,185 B€lodellida, 42,49, 185 Belodellidae, Belodia,18,55,57,58,141,185,Fig.5.10 57 calciprcminens, comprcsso, 58 monilorcnsis, 58 Berys!rcemoghathus, 75,76,186,Fig.5.26 extensus,l6 Besselodus,50, 51, 185,Fig.5.3 Bimembrateskeletalappalatus,24 iamiformelement,18,24 Bip€nnate Bnksleldia,65 pectiniformelement,22 Bisegminiscaphat€ Bispathodui, 89,90,94,96,97,136,l4l, 159,187, Fi gs.5.39,5.41 aculealus,96 biswthodus,96 s,96 spinulicostat 109,I12,Fie.5.50 stabilis,96,97, utahensis, 96, 159 Blades,15,20 205
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INDEX Distacodidae,36 Distacodontacea,41, 42, 5l Distacodontidae,36, 5l Distacodus,51,54 Distomodontidae,67, 68,11, 134, l4l, 144, 167, 186 Distomo&rs, 66, 61, 68,1 l, 98, 186,Fie. 5.19 kentuckyensis,61, 68 Diversity cycles,130 firsr-order, 130, 132, 133 long-term, 130, 132, 133 second-order,13l, 133, l 40, 146 Dolabrate coniform elemcnt, l8 Dolabrateramiform elemenl, 18, 24 Doliognathus,83, 84, 136, 159, 187,Fig. 5.32 Do ytnae, 83, 136, 187 Drakes Formation, 154 Drcpanodus,54, 185,Fig. 5.? slrkttus,56 Drepanoistodontidae,54, 185 Drepanoistodus,54, 55, 59, 134, | 57, 185,Fig. 5.8 sp. aff. suberectus,23 Dvorakia, 45, 149, 185,Fig. 5.3
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Il. 137,139,
Echinodermata,173, 182 EinfacheZahne, 15, 35 Element, I I Elictognathidae,89, 96, 106, 136, 188 E lictoghathus, 106, 107 Elltsonia,83,85, 86, 89, 137,138,139,161,163,187, Fig. 5. 33 teichefti, Il7 ttiassica,86,87 Ellisoniidae,83, 85, 142,166, 187 Embaysgnathus,84, 18?,Fig. 5.32 Enanliognathus,18, 83 Eobelodina,5T Eoconodontus,46, 47, 185,Fig. 5.2 Eognathodus,89, 93, 94,95, 96,91, 135, l4l,181, Fies . 2. 11, 5. 39, 5. 41 sulcalus,26,96 Eoneop oniod s,72 EopIacognathus, 1 l, 72, 102, | 43, 186,Fie. 5.21 Eotaphrus,83, 136, 159, 187 Epigondolella,87, l3'1,142,146, 187,Fig. 5.35 ,g/rkd, 81, 186,Fig. 5.30 divaricala, 8l Eriplychius, l8l Eismod s, 18,79,81,134,186,Frg-5.29 quadridactylus, 79 Erratrcodon, 78, 79, 81, 85, 186,Fig.5.29 palu, 79 Euconodontelement,42 Euconodonts,4l Evolutionary index. ,SeeIndex ofevolutron Exoc hognot hus exwnsu-s, 68 Extensiformdigyrateelement, 18, 24 Fairview Formation, 155 Falcodus, lO4, 106, loj anguhts, lO7 Fibrous elements,?9, 81, 165
207
Fibrous struclure, 14 Flotant marsh, 164 Form taxonomy, 5, 35 Freeblade,I13, ll7 Fryxellodontidae,48, 185 Fryxellodontus, 48, 185, Fig. 5.2 Fumishinacea,42 Furnishiut,85,86, 138,187,Fig. 5.33 Fus€dcluster,24, 3?, 41, l7l GamachighalhrLt,64, 65, 67, 186,Fig. 5.15 Geniculateconiform element, 15, 16, 25 Germanic Province, 168 Gladigondolella,87, 138, l8?, Fig. 5.34 meeki, 81 tJtY?toconus, )J, l6)! frg. ).) quadruplicatus,53 Gnathodontidae, 89, 95,96, lO9, ll2,I13, 135,l8E Gnathodus, 109, Ill,ll2, 136,14l, 159,t88, Fig. 5.50 austi L lll bilineatus, IIO, I I t, 112,Fig. 5.50 anneifurmis,109,Fig. 5.50 delicarus,109,t1l, Fig.5.50 girtyi, l l l,137, Fig. 5.50 praebilineatu,s,lll p nctalus, lO9,I10, Fig. 5.50 semiglaber,111,Fig. 5.50 texaws,lll,Fit 5,50 typicus, 109, I10, Fig. 5.50 Gnathostomulids,173 Gondolella,81,88, 89, 137, 138, 142, 16I, 162, 163, 165,166,187,Fig. 5.35 navicula,1'l Gondolellacea,41, 42, 78 Gondolellidae,78, 83, 87, 88, 89, 138,142,146, 166, 187 Gondwanaglaciation, 134 Grant Irke Formation, 155 Grier Member (of Lexington Limestone),155 Habit (ofconodon$), 148, 150 benthic,152 nektobenthic,l5O, 152, 164 pelagic,150,152,164 Hadrcdoatina,85,86, 138,187,Fig.5.33 Hadrcgnalhus,68, l4l sta rcgnathoides,68 Hagfrsh. See Myxine Hamarcdus,49,50,185,Fig. 5.3 Harding Sandstone,l?7 Hemichordata, 173 Heterochrony,145 H ibbardella, 11, 8 | , 82, 84, 187, Frg. 5.29 angulata,8l Hibbardellacea,42, 7E Hindeodus,l15,l16, l17, l18, 120,137,139,I40, 159, 1 6 0 ,1 6 l , 1 6 4 ,1 8 8 uassidenlatus,I 15, 116,Fig. 5.54 crlstulus, | 16, I l'1, Fig. 5.54 jufensis, I 17 minulus, lI7
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L 1,14,150,
t 5.52
Neomuhioistodus,2L,72,73, 186,FiE 5.22 clypeus,73 Neopanderodus, 55, 57, 185 Neoptioniodus,82,83 Neospathodus,87, 137, 138, 142, lE7, Fig. 5.35 ll7, ll9, 131,138, 188,Fig. 5.55 Neostteptognathodus, Neoteny, 146 Ne codl,ts,48,185 Neurodontiformes,14, 36, 79, 81, 155 Noixodonlus,64, 186 Nongeniculateconiform elemenl, 15, 16 Nonh American Midcontinent Province, 167 Nonh Atlanric Provinc€, 167 Nolhognathella, 104 Octimembrateapparatus,64 Odontogtiphus, 28, l'l 3 omolius,173 Oelandodus,61,185, Fig. 5.13 Oepikodut,63, 186,Fig. 5.14 Otrshorefauna, 165 Ohio Valley Province, 167 Oistodontidae,42, 50, l4l, 186 Oistodontinae,61, 186 Oistodus,61, 186,Fig. 5-l3 Oneotodontidae,52 OneotodtLt,52, 53, 185, Fig.5.5 Origination-extinctionratio. SeeIndex of evolution Ostracoderms,176 Oulodw 18,81,154,155,156, l81,Fie. 5.29 se atus,8l Outsideshale,161,163 Ozarkodina,91, 92,93, 95, 96, 98,99, l2O, 115, 142, 187,Figs.5.38,5.39 abrupta,97 confluens,33 inclinata,92,94 murchisoni, 177 n. sp. of Bergstritm,9l renscheideksis, 95 sannemana,96 se$,93,94,95,99 semialtemens,93, 106 tortilis, 37 Ozarkodinida, 42, 45, 75,89,90,lJ4,135, 140,l4l, 187 P position (or element),24 Pa position (or element),24, 30 Pachycladina,85, 86, 138, 187,Fig. 5.33 Paedomorphosis,145, 146 Palataltooth, 179 Palmatodella, lO4 Palmatolepidae, 89, 102,106,135,187
Palmatolepis,102, 104, 105, 135, 136, 145, 188,Figs. 5.44,5.4',7 pe obata,105 rugosa, 105 rugosa ampla, 105 rugosa lrachyleru, 105 Itia gula s, lO5 PaLodus,53,54, 185, Fig. 5.8 Pander,Christian Heinrich, 3 PanderSociety,7 Panderodontacea, 4l Panderodonlida,42, 45, 55,56, l4l, 185 Panderodontidae,56, 167, 185 Panderodus, 55, 57, 58, 59, l4l, 156,167,170,185, Fig.5.9 berystrcerni,56,58, 141 gr4cuts,zJ, rtE z.t sulcatus,5l unicostatus,32, 57, Frg. 3.3 Pahdetulepis, lO5 Pandotinellina, 92,93, 95, 96, 107, 123, 136, 142, | 59, l8?, Fis. 5.37 insita,93,96,l2l, 123 Parubelodiha,18, 55, 58, l4l, 185,Fig.5.l0 denticulata,56, l4I Paruchtognathus, 79 Paraconodonta,4l Paraconodontida,41, 42, 45, 175 Paraconodonts,28, 41, 42 Paragnalhodus,lll Parupaltodus,54, 185 Parupandetudus,55, 56, 185,Fig. 5.9 asymmetficus, 56, 51 striatus,56 Parapet,109 Paruprioniodus,73, 134, 186,Fie. 5.22 costalus,73, l4l Paraserrutognathus, 185 Psroistodus,54,55, 185,Fig. 5.8 horridus, 55 Porutahconus, 53, 185 Pastinatep€ctiniform element,2l Pastiniscaphate pectiniform element, 22 Patrcgnathus,96, 120,122, 136,I88, Fig. 5.57 Pb position (or element),24, 30 Pectinat€t€eth, 19 Pectiniform elem€nt, 15, 20, 24, 36 Peda s, 65, 66,67, 68,7L, 134,135,146,l86,Fi& 5.18 lalialalus,7I Pelelcysgnathus, 60, 65, 65,69,70,71, 135, 136, l4l, 142, t46, t86,Fie. 5.20 csakyi,lO inclinatus,70 index, 70, Il, l4l "Pelekysgnathus," 7o Peiodon, 18, 35, 16, 77, 156, 186,FLl- 5.27 acuteal4, to, t t '17 Jlabellum, gtanats, | |
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INDEX
5-47
) l zl l, 1 45,
t 3 3,l4l, Lll
45. Fis.5.2 188.Fig.5.50
rt5
Fr. 5.10 13i
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Rabeignathus,117, I19, 188,Fig. 5.56 Radular teeth, 172 Ramiform element, 15, 16,24 Rastrat€element, 15, 18, 55, 57 Recapitulation,145 Recurrentgroup, 39, 40, 4l Red River Province, 167 Rhachistognathus,97, 136, 137, l4l, 187, Figs. 5.39, 5.41 Rhipidognathidae,62,7 5, 99, 186 Rhrpidog4athu:, 15,16, 155,156,157,l86,Figs.2.ll, 5.26 \ slmmetricttl;,l54 Rhodesognathui564,134, 156, 186,Fig. 5.16 Rhynchocoela,3l! 176, 182 Robtglicoslatusstiock(of Polygnalhus),99,100, l0l Rossods,53,60,61,133, 186,Fig. 5.12 Rostral ridge, 102 Rostrum, 102 Rotundacodina, 67, 68, 186,Fig.5.19 dubius,68,7l,146 S position (or element),24,25, 30 Sa position (or element),25 Sagiua,41,174, l'l5 Sagittodohtina,64, 67, t86, Fig.5.l5 Sannemannia,65, 66, 186 pesanse s, 66 Sauk sequence,132,133, 134 Sb position (or element),25 Sc position (or element),25 Scabbardella,53, 185,Fig. 5.5 kaliognath s, 33,84, 159, 187 Scalpellodus,54, 185,Fig. 5.7 Scandodus, 54 Scaphaleattachments!fiace, 15,22 Scaphignathus,96, 107, 123, l4l, 187,Fig. 5.41 Schmidtognathus,102, 104, 106, 135, 188,Fig. 5.47 Scolopodontidae,52 Scolopodri, 53 gracilis,56 Sclttula, lO4 Scyphiodtu,73,'14, 143, 186 primrs,74,Fig. 5.25 Sd position (or element),25 Secondaryprocess,21 Segminate pectiniform element, 22 sefitacon oaus,)2, )J, )o, t6), l.lg. ).) Septimembrate skeletal appamtus, 24 Serratognalhus,53, 185,Fig. 5.6 Seximembrate sk€letal apparatus, 24 Siphonodella,89,96, 99, 106, 107, 108, 136, 188, Figs. 5. 48, 5. 49 duplicala, 109 pruesulcata,107, 108, 109 sulcato, 107, IO9 Siphonognathui, 106 Skeletalappararus,23, 37, 38 Skeletalelemenl, 11 Solenogastres, 172, 173 Somites,29, l7l
2tl
Spathodus,ll5 Spathognathodontidae, 89, 90, 91, 94, 95, 96, 97, 106, tt2, t34, 116,t4t, 144,167,t87 Spathognalhodtls,ll5 Spatula,I I ? SlauflercL\a,53,185,Fig. 5.5 Staurcghathla,83, 84, 136, 187,Fig. 5.32 Stellatepectiniform element,21 Steptotaxis,65,66, 186,Fig. 5.18 fumishi grotrp, l4l Steteocohtls,123, 188, Fig. 5.59 Stolodus,49, 185,Fig. 5.3 Sttuchahoghath s, 185 Strcptognathodl,ts, ll4, ll5,137,146, 150,l6l, 163, 188,Fig. 5.52,5.53 Subbryantodus,I 15, 116, 188 Survivorship curves, 139 Sweetina,85, 137, | 38, 187,Fig. 5.33 Sw€erognathidae, 90, 92,96, ll2,ll7, 188 Sweetognathinae,I l7 Sweelognathus,89, 117, l19, 137, 138, 188,Fig. 5.55 menilli, l19,131 whitei,IL9,l2O Symmetry,classesof, 25 Symmetry-tran$ition series,22 Synpioniodina, lO4 TanglewoodMember (of Lexington Limestone), 155 Tangshanodus, 186 Taphrognalhus,l2O, 122, l88, Fle. 5.57 Tenraculata. See Lophophorata Teridonlidae, 52 Teridontus,45, 52, 5!, 133,142, 157, 185,Fig. 5.5 Tertiopedateramiform element, l7 Tethyan Prcvince, 168 Tippecanoesequence,132, 134 Tooth comb, 179 Tortodus,93,94, 187,Figs. 5.39,5.41 Ttiangulodus, T2 Trichonodello, 11 2expansa,68 T gonodur,12 Trimembrate skeletal apparatus, 24 Tipodellus, IO5 Tripodontinae, 62, 186 Tripodus,60,61,62, 63,72,13,75, 133,14l, 185,Fig. 5.t2 deltotus, '12 Trisegminiscaphate pectiniform element, 22 I ropodus,)5, lu), nrg. ).) complus,53 Truchercgnalhus, 79 True conodonts,4l Ulrtchodina,54, 185,Fig. 5.? Unimembrate skeletal apparatus, 24 Utahfonus,53, 185,Fig. 5.5 "Utica" Shale,155
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