The Early Permian Reptile Acleistorhinus pteroticus and Its Phylogenetic Position Author(s): Michael Debraga and Robert R. Reisz Source: Journal of Vertebrate Paleontology, Vol. 16, No. 3 (Sep. 19, 1996), pp. 384-395 Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate Paleontology Stable URL: http://www.jstor.org/stable/4523731 . Accessed: 14/06/2011 04:38 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. 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The Society of Vertebrate Paleontology and Taylor & Francis, Ltd. are collaborating with JSTOR to digitize, preserve and extend access to Journal of Vertebrate Paleontology. http://www.jstor.org Journal of VertebratePaleontology 16(3):384-395, September 1996 C 1996 by the Society of VertebratePaleontology THE EARLY PERMIAN REPTILE ACLEISTORHINUS PTEROTICUS AND ITS PHYLOGENETIC POSITION MICHAEL DEBRAGA and ROBERT R. REISZ Department of Zoology, Erindale Campus, University of Toronto, Mississauga, Ontario, Canada L5L 1C6 ABSTRACT-Restudy of Acleistorhinuspteroticus indicatesthat this Early Permianamniote from North Americais the oldest known memberof Parareptilia.Despite its stratigraphicposition, Acleistorhinusis not a basal parareptile, and a phylogeneticanalysis of parareptileinterrelationships demonstrates that Acleistorhinusis a sister taxon to the Russianclade Lanthanosuchidae.This hypothesisof relationshipsis supportedby eleven synapomorphies.The presence of an Early Permianparareptile in North American sediments provides strong supportfor the recent hypotheses of amniotephylogeny that proposean extensive evolutionaryradiation for this group of reptiles. INTRODUCTION group. Contra Lee (1993), Laurin and Reisz have also restated the hypothesis of a sister-group relationship between procolo- For more than a century (Cope, 1881, 1896), many of the phonids and turtles. However, Laurin and Reisz did not attempt taxa now referred to Parareptilia were considered to be "stem" to evaluate the phylogenetic position of many problematic taxa reptiles (Cotylosauria) from which all other amniotes evolved. that have been frequently allied to Parareptilia (Ivakhnenko, Case (1911) tried to resolve some of the outstanding issues 1987) because detailed anatomical data were not available. surrounding the systematic position of many of these problem- One of these problematic taxa is Acleistorhinus pteroticus, atic taxa, but his systematic overview suffered from the pre- from the Lower Permian Hennesey Formation of southwestern cladistic era's indiscriminate mixing of plesiomorphic and apo- Oklahoma (Daly, 1969). Daly (1969) assigned her new taxon morphic features for diagnosing taxa and determining relation- to Procolophonoidea (sensu Romer, 1956). This assignment was ships. Case's Cotylosauria included a plethora of taxa including based on the overall shape of the skull and the orientation of pareiasaurs and procolophonids, presently assigned to Pararep- the paroccipital processes, which according to Daly (1969) rose tilia (Laurin and Reisz, 1995), along with numerous other taxa up to contact the enlarged supratemporals from below. Despite including Captorhinus, Bolosaurus, and the currently recog- its obvious significance as the oldest known "procolophonoid" nized anamniotes Diadectes, Seymouria, and Pantylus, to name Acleistorhinus has been ignored since Daly's original descrip- a few. tion. Carroll (1988) appears to have doubted Daly's (1969) as- Later, in perhaps the most thorough attempt at understanding signment of Acleistorhinus, and placed this taxon into the Cap- the phylogenetic position of many of these "stem" reptiles, torhinomorpha incertae sedis. Additional preparation and res- Olson (1947) implied that reptiles had a diphyletic origin, and tudy of the holotype and only known specimen of this enig- erected a new group, Parareptilia, within which he included matic fossil has yielded a great deal of new information on its seymouriamorphs, diadectomorphs, procolophonids, pareia- anatomy and phylogenetic relationships. Our work indicates not saurs, and chelonians. This diphyletic proposal did not meet only that Acleistorhinus is the earliest known member of the with much support and was later overwhelmed by Romer's Parareptilia, but also that it is the sister-taxon to the enigmatic (1956) classification. Romer's taxonomy placed most of Olson's Russian amniotes, the lanthanosuchids. Parareptilia back into that enigmatic basal group collectively referred to as "stem" reptiles or Cotylosauria. Heaton (1980), SYSTEMATIC PALEONTOLOGY after reviewing much of the earlier literature on Cotylosauria, concluded that all amniotes (his Reptilia) should be excluded PARAREPTILIA Olson, 1947 from that group. He did, however, include the Russian nycter- oleterids within his Seymouriamorpha, and hence within Co- Definition-The most recent common ancestor of mil- tylosauria and not Reptilia. Perhaps as a result of Romer's in- lerettids, Acleistorhinus, lanthanosuchids, Macroleter, Pro- terpretation, or because of the formerly politically isolated lo- colophonia, and all its descendants. cations (Russia, South Africa) where many of the key members Emended Diagnosis-A reptilian clade diagnosed by the of this assemblage are reposited, many of the parareptiles were following autapomorphies: anterolateral maxillary foramen ignored by North American paleontologists for much of the last present and significantly larger than all other foramina in four decades. maxilla; foramen orbitonasale entirely surrounded by bone; In a cladistic analysis of amniote interrelationships, Gauthier temporal emargination formed by quadratojugal and squamosal; et al. (1988) identified parareptiles as a monophyletic group. ectopterygoid teeth absent; paroccipital process-supratemporal More recently, Reisz and Laurin (1991) proposed that procol- contact present; sacral ribs only slightly in contact with one ophonids were a sister-taxon to Testudines. Spurred on by these another or not at all; and iliac blade dorsally expanded into fan- hypotheses, others have taken up the task of evaluating inter- like structure. relationships among parareptiles, and their relationship to turtles (Lee, 1993). As a precursor to the present study, Laurin and ANKYRAMORPHA, new taxon Reisz (1995), re-examined the interrelationships of basal am- niotes. Significantly, their analysis focused on evaluating par- Etymology-Ankyras, from the Greek for anchor, in refer- areptiles, a group which Gauthier et al. (1988) had found trou- ence to the anchor-shaped interclavicle. bling, and concluded that parareptiles formed a monophyletic Definition-The most recent common ancestor of Procolo- 384 DEBRAGA AND REISZ-ACLEISTORHINUS PTEROTICUS 385 phonia, Macroleter, Lanthanosuchidae, Acleistorhinus, and all orbit, and restricted to the lower half of the temporal region, its descendants. the skull possesses a single lateral temporal fenestra bordered Diagnosis-Members of Parareptilia exhibiting the following by the jugal anteroventrally, the quadratojugal posteroventrally, autapomorphies: dorsal process of premaxilla narrow; antero- and the squamosal posterodorsally. The orbits are circular and dorsal process of maxilla high and extending to the dorsal limit are equidistant from either end of the skull. of the external naris; posterior process of postorbital nearly as Although there are some important differences in the present wide as long; jaw articulation anterior to occiput; dermal sculp- skull reconstruction when compared to Daly's (1969) original turing on skull in the form of large tuberosities and pits; base interpretation, much of the overall configuration of the skull of quadrate ramus of pterygoid deeply excavated posteriorly; table has remained essentially unchanged. However, due to ectopterygoid, if present, contributing to outer-most border of more complete preparation, the interpretation of the occiput has transverse flange; cultriform shorter than the body of the para- been significantly altered. The most notable difference is in the sphenoid; paroccipital process antero-posteriorly expanded; composition of the quadrate which is here interpreted as a much quadrate condyle short and nearly flat antero-posteriorly; sur- smaller element; and the quadrate flange of the pterygoid which angular short and not extending anteriorly beyond the coronoid contributes an occipital flange to the region of the otic notch. eminence; prearticular short, terminating before coronoid emi- Furthermore, it has not been possible to corroborate