NovAMERICANitatesMUSEUM PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2770, pp. 1-41, figs. 1-14 November 8, 1983 Colosteus scutellatus (Newberry), a Primitive Temnospondyl Amphibian from the Middle Pennsylvanian of Linton, Ohio ROBERT W. HOOK' CONTENTS Abstract ..................................................................... 2 Introduction .................................................................. 2 Acknowledgments ........................................................... 2 Abbreviations ............................................................... 3 Methods .................................................................... 3 Review of Previous Work .................. .................................... 4 Systematics ................................................................... 6 Description ................................................................... 7 Skull Roof.................................................................. 7 Palate .................................................................... 12 Parasphenoid and Braincase ............... ................................... 16 Mandible ................................................................... 16 Dentition ................................................................... 18 Dermal Sculpture and Lateral Line Canals ..................................... 19 Branchial Arches ............................................................ 20 Postcranial Remains ........................ ................................. 21 Occurrences of Colosteid Remains ............ .................................. 29 Characteristics and Composition of the Colosteidae ............................... 29 Shared Derived Characters of the Family ...................................... 29 Relationships Within the Family ............ .................................. 31 Relationships of the Colosteidae ........................................ ... 32 The Status of the Order Temnospondyli ................... ............ 32 The Development of the Temnospondyl Otic Notch ............................ 33 Colosteids, Edopoids, and Trimerorhachoids ................................... 34 Systematic Conclusions .................... .................................... 35 Appendix ..................................................................... 35 Literature Cited ............................................................... 37 ' Coal Geology Research Group, Department of Geology, University of Kentucky, Lexington, Kentucky. Copyright © American Museum of Natural History 1983 ISSN 0003-0082 / Price $3.40 2 AMERICAN MUSEUM NOVITATES NO. 2770 ABSTRACT Colosteus scutellatus (Newberry), known exclu- (Tatarinov, 1964) is recommended in the absence sively from the classic Coal Measure locality of of shared derived characters indicating a close re- Linton, Ohio, is the genotype and youngest rep- lationship between the colosteids and any other resentative ofthe Colosteidae, an archaic group of known temnospondyls. The structure ofthe stapes temnospondyls that also includes Pholidogaster and and skull roof suggests that the colosteoids may Greererpeton. The colosteids are a monophyletic represent the plesiomorphic sister group ofall oth- group distinguished from other temnospondyls by er temnospondyls. massive stapes and no otic notch; elongate pre- An overview ofthe status ofthe Temnospondyli frontal contacting narial border, premaxilla, and indicates that exclusion of the loxommatoids is maxilla; intertemporal reduced or absent with justified, but that a possible microsaur-temno- broad postorbital-parietal contact; single pair of spondyl relationship circumvents the possibility premaxillary tusks; and single, elongate Meckelian of temnospondyl monophyly. fenestra. The use of the superfamily Colosteoidea INTRODUCTION The Temnospondyli are the largest and burkemorani Romer, a Colosteus-like form possibly most diverse order of fossil am- from the Mississippian of West Virginia, it phibians. Despite an impressive representa- became evident that the colosteids represent tion of Late Paleozoic and Triassic forms, an archaic lineage that might provide insights temnospondyls older than Pennsylvanian or into the early evolution of temnospondyls, if Westphalian age are virtually unknown. Con- not all Paleozoic amphibians. Subsequent sequently, the astonishing array of temno- study of additional colosteid material (Ro- spondyls that first appears in the Coal Mea- mer, 1972; Panchen, 1975; Smithson, 1982) sures of North America and Europe has has identified the need for a more detailed consistently frustrated paleontologists who understanding of the genotype of the family. wish to incorporate at least a modicum of The objective of the present paper is to phylogeny in their classifications ofthe order. provide a thorough description of the genus The variety and abundance of Pennsylva- Colosteus and an accurate characterization of nian temnospondyls is nowhere better doc- the Colosteidae. Although the affinities ofthe umented than in collections acquired from family are also considered, re-evaluation of the once-active coal mines of Linton, Ohio. other primitive temnospondyls is necessary In addition to a dozen species of fishes and before the problem of interrelationships can a score ofother tetrapods, this prolific locality be fully addressed. has produced seven temnospondyl genera, four of which are unique to Linton (Hook, ACKNOWLEDGMENTS 1981). The most common of these indige- nous temnospondyls is Colosteus scutellatus, I am greatly indebted to Dr. Donald Baird, a heavily scaled amphibian with an elongate whose commitment over the past 30 years body and diminutive limbs. Because similar to the collection, preparation, and identifi- forms are unknown from younger deposits, cation ofLinton fossils made the present study such as the Texas redbeds (Romer, 1935), possible. I am also grateful to Dr. Robert R. early workers generally considered Colosteus Reisz for support and thoughtful criticism. as a novel adaptation to the coal swamp en- My thanks are due to Dr. Andrew R. Mil- vironment. Thus, after a somewhat check- ner, Messrs. John Chom, Stephen Godfrey, ered taxonomic history, Colosteus and the Timothy R. Smithson, and Carl F. Wellstead family to which it gives its name, the Colos- for free exchange of information on unpub- teidae, were removed from the main line lished material; to Dr. Robert L. Carroll for of temnospondyl evolution (Romer, 1947, initially directing my attention to the need 1966). for a review of the Linton colosteids and for With the 1969 description of Greererpeton making available unpublished drawings by 1983 HOOK: COLOSTEUS SCUTELLA TUS NEWBERRY 3 Mrs. Pamela Gaskill; to Drs. Richard Lund YPM, Peabody Museum of Natural History, Yale and Kathy V. Bossy for loans of peels of Lin- University ton specimens; to Dr. Malcolm J. Heaton for interest in my work and advice on the prep- ANATOMICAL aration of specimens and figures; to Ms. Di- a, angular ane Scott for helpful suggestions in the pro- a.p.f., anterior palatal fenestra duction of illustrations; and to Mr. Steven art, articular Jaunzems for expert photographic services. c, clavicle I also thank Drs. Anne E. Fry and Dennis cb, ceratobranchial ossifications Radabaugh of Ohio Wesleyan University for ch, choana their in c.r., conical recess assistance recovering Dr. Baird's peels ct, cultriform process from the research materials of the late Dr. cth, cleithrum John N. Chase. Dr. Robert W. Morris of Wit- co, coronoid tenberg University and Mr. Michael C. Han- d, dentary sen of the Ohio Geological Survey provided ect, ectopterygoid valuable guidance in the early stages of this eo, exoccipital work. f, frontal It is similarly a pleasure to acknowledge h, humerus the assistance of individuals at institutions hb, hypobranchial cartilage where I have studied Linton material. These i, interclavicle ic, intercentrum include Drs. Eugene S. Gaffney and John G. im.f., intermandibular fenestra Maisey, American Museum of Natural His- j, jugal tory; Dr. Angela C. Milner, British Museum 1, lacrimal (Natural History); Dr. David S. Berman, Car- m, maxilla negie Museum of Natural History; Dr. Mi- n, nasal chael E. Williams, Cleveland Museum of p, parietal Natural History; Dr. John R. Bolt, Field Mu- pal, palatine seum of Natural History; Dr. Donald Brink- pa.f., para-articular foramen man and Mr. Charles R. Schaff, Museum of pra, prearticular Comparative Zoology, Harvard University; pc, pleurocentrum pf, postfrontal Dr. Stig M. Bergstrom, Orton Museum, Ohio pl, pleuracanth shark tooth State University; and Ms. Ruth L. Elder, Mu- pm, premaxilla seum of Paleontology, University of Michi- po, postorbital gan. pp, postparietal Drs. C. S. Churcher, Thomas S. Parsons, prf, prefrontal and P. J. Pointing read an early version of pt, pterygoid the manuscript. The suggestions of Drs. qj, quadratojugal Baird and Milner improved the final draft. r, radius sa, surangular ABBREVIATIONS sp, splenial spp, postsplenial INSTITUTIONAL st, supratemporal t, tabular AMNH, American Museum of Natural History u, ulna BM[NH], British Museum (Natural History) u.p., uncinate process CM, Carnegie Museum of Natural History v, vomer FMNH, Field Museum of Natural History of manus MCZ, Museum ofComparative Zoology, Harvard I-IV, digits University OSU, Orton Museum, Ohio State University METHODS PU, Museum of Natural History, Princeton Uni- versity Vertebrate remains from Linton