AMERICAN MUSEUM Novttates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2902, pp. 1-12, figs. 1-3, table 1 December 30, 1987 Trematops milleri Williston, 1909 Identified as a Junior Synonym of Acheloma cumminsi Cope, 1882, with a Revision of the Genus DAVID W. DILKES1 AND ROBERT R. REISZ2 ABSTRACT The Early Permian temnospondyl amphibians shelf, an internal naris with an anteroposterior Acheloma cumminsi Cope, 1882 and Trematops length less than that of the posterior division of milleri Williston, 1909 of the family Trematop- the external naris, and a median septum of the sidae prove, upon reexamination ofthe holotypes, vomers that contacts the roof of the antorbital to be indistinguishable. Since the former name has region. priority, Trematops milleri is declared to be a sub- The slitlike, dorsally convex otic notch ofAche- jective junior synonym of Acheloma cumminsi. loma cumminsi is unique among labyrinthodont The family name Trematopsidae is retained. amphibians. The dimensions of this otic notch The generic diagnosis ofAcheloma cumminsi is suggest that the tympanum, if present, was simi- revised to emphasize the presence of a slitlike, larly reduced and could not have been part of an posteriorly closed otic notch, a supratympanic efficient impedance-matching hearing apparatus. INTRODUCTION The family Trematopsidae is a small group Trematops. A third, Trematopsis (= Tre- of poorly known terrestrially adapted am- matopsoides Romer, 1966), erected by Olson phibians of the order Temnospondyli col- (1956) on the basis ofa fragmentary skeleton, lected from North American deposits of has been reduced recently to subjectivejunior Lower Permian age. At present, the-family is synonymy with Cacops cf. C. aspidephorus composed of the two genera Acheloma and by Milner (1985a). Actiobates peabodyi Ea- I Department of Zoology, Erindale Campus, University of Toronto, Mississauga, Ontario L5L 1C6, Canada. 2 Associate Professor, Department of Zoology, Erindale Campus, University of Toronto. Copyright © American Museum of Natural History 1987 ISSN 0003-0082 / Price $1.70 2 AMERICAN MUSEUM NOVITATES NO. 2902 ton (1973), a Late Pennsylvanian dissoro- argued that the unusually acute angle between phoid, has been placed provisionally within the scapula and coracoid was merely an ar- the family Trematopsidae by Berman et al. tifact of the poor postcranial ossification of (1985) and Milner (1985a, 1985b). The type the specimen and, thus, did not constitute a and only known specimen of Actiobates is valid diagnostic feature. Watson accepted thought by the former to exhibit features Cope's statement that Acheloma lacked otic suggestive of a juvenile and by the latter to notches and, recognizing the taxonomic sig- possess a combination of primitive dissoro- nificance of this character, placed Acheloma phoid and advanced trematopsid features. within a new family, the Achelomidae. Eaton (1973) did not comment on the on- It was not until a review of the family togenetic status ofActiobates but presumably Trematopsidae by E. C. Olson in 1941 that considered it to be an adult. Actiobates is the affinities of Acheloma were properly es- currently being studied by Ms. Eleanor Daly tablished. After a reexamination of the type of the Mississippi Museum of Natural Sci- material, Olson concluded that it possessed ence. the same elongate external naris and slitlike, E. D. Cope (1882) first describedAcheloma closed otic notch as Trematops and, accord- cumminsi and placed it within the family ingly,' expanded the family Trematopsidae to Eryopidae. Cope distinguished Acheloma include Acheloma. Olson interpreted the from Eryops primarily on the basis of a sca- Trematopsidae as carnivores that were closely pulocoracoid with a scapular blade tilted me- related to the family Dissorophidae, a mor- dially and posteriorly at a 300 angle to the phologically diverse group of terrestrially coracoid, the apparent absence ofotic notch- adapted temnospondyls that occupied a span es on the skull, and the absence of articular of time from the Middle Pennsylvanian condyles on the humeri. (Westphalian D) to Upper Permian. Trematops milleri, also from the Lower The possible synonymy of Acheloma and Permian red beds of Texas, was initially de- Trematops has not been studied in detail un- scribed by S. W. Williston in 1909. The til now. Although expressing some doubt, unique attributes of Trematops include an Williston (1909) accepted Cope's description elongate external naris occupying most ofthe ofAcheloma as accurate and concluded that antorbital region and a slitlike, posteriorly each was a valid genus. Romer (1935) stated closed otic notch. Williston (1910) subse- that Trematops was probably synonymous quently erected the monogeneric family with Acheloma but did not elaborate. Fol- Trematopsidae to house this unusual am- lowing Olson's review of the family, Romer phibian. (1947) apparently reversed his opinion and Following the discovery of Trematops mil- retained Acheloma and Trematops as distinct leri, the taxonomic position of Acheloma genera, a conclusion unquestioned to the cumminsi was reevaluated as part of inde- present. pendent studies of Williston (1916) on the tetrapods of the Permian and Carboniferous ACKNOWLEDGMENTS ofNorth America and Watson (1919) on the early evolution ofamphibians. Although nei- We wish to express our thanks to Dr. Eu- ther author was apparently able to examine gene Gaffney of the American Museum of firsthand the holotype of Acheloma, each Natural History for arranging the loan of the considered it to be sufficiently distinct from holotype of Acheloma cumminsi, to Ms. Eryops to warrant its removal from the fam- Charlotte Holton, also ofthe AMNH, for her ily Eryopidae. They differed, however, in their assistance to the first author during his visit final taxonomic conclusions. Williston chose to the museum, and to Dr. John Bolt of the to assign Acheloma to the family Trematop- Field Museum of Natural History for allow- sidae, but made this decision with extreme ing us to examine the holotype of Trematops reservations because he was unsure of the milleri. Support for this study was provided true nature ofthe external naris and otic notch. by a grant from the Natural Sciences and En- Watson, on the basis of illustrations of the gineering Research Council of Canada pectoral girdles of Acheloma (Case, 1911), (A0077). 1987 DILKES AND REISZ: ACHELOMA AND TREMATOPS 3 ABBREVLATIONS The left quadratojugal is complete, although slightly damaged, whereas the right quadra- Institutional tojugal is fragmentary. The left quadrate is AMNH American Museum ofNatural His- complete. Both lower jaws are in place and tory lack the section beneath the external naris. FMNH UC Field Museum of Natural History The dermal sculpturing exhibited by each ele- Anatomical ment consists of a uniform pattern of round pits at the ossification center and slightly oval a angular pp postparietal d dentary prf prefrontal pits at the periphery. The prominent ridges ect ectopterygoid pt pterygoid and protuberances characteristic of many f frontal q quadrate dissorophids (Carroll, 1964; DeMar, 1968; in.f. internarial fenestra qj quadratojugal Berman et al., 1981) and commonly found mI. jugal sa surangular along the margins ofthe skull table, the cheeks, lacrimal sm septomaxilla or the medial rim of the orbit are m maxilla sp splenial absent in n nasal spp postsplenial Acheloma. There are no lateral line grooves p parietal sq squamosal or pits. pal palatine st supratemporal A large internarial fenestra is situated near pf postfrontal t tabular the tip of the snout, opening below into a pm premaxilla v vomer Po postorbital small, median, internarial pit. The position of the partial posteromedial rim of the right REDESCRIPTION OF external naris indicates that the external naris HOLOTYPES is greatly elongated posteriorly. An elongate external naris is a feature found in Descriptive statements are derived given below the limited to those characters that are relevant trematopsids, dissorophid Ecolsonia to the taxonomic reevaluation of the holo- (Vaughn, 1969; Berman et al., 1985), and types. Actiobates (Eaton, 1973). Medial to the rim of the right external naris is a partial narial Acheloma cumminsi (AMNH 4205) flange consisting of a laterally concave sheet of bone projecting down and inwards from Many ofthe details ofcranial morphology, the roofofthe snout. As preserved, this flange in particular the pattern ofskull roof sutures, is composed ofseparate sheets from the nasal were unknown to earlier workers because and prefrontal that abut against each other AMNH 4205 had been only partially pre- with no sign of overlap. Although the narial pared. Extensive mechanical and chemical flange is incomplete anteriorly and poste- preparation allows, for the first time, a critical riorly, the nasal portion probably continued comparison of the two holotypes. forward underneath the nasal. The prefrontal The holotypic skull ofAcheloma cumminsi portion of the flange, curving laterally to fol- (fig. 1) has suffered significant dorsoventral low the rim of the narial opening, probably crushing with a slight increase in width ofthe reached the narrow antorbital bar that sep- temporal region. The majority of the dermal arates the orbit and external naris. The height skull elements are preserved. The left tabular, of the narial flange increases posteriorly, re- left supratemporal, left postfrontal, and both ducing the space between the