CRANIAL ANATOMY OF THE LATE PERMlAN DICYNODONT DIICTODON, AND ITS BEARING ON ASPECTS OF THE TAXONOMY, PALAEOBIOLOGY AND PHYLOGENETIC WATIONSHIPS OF THE GENUS by Corwin Sullivan A thesis submitted in conformity with the requirements for the degree of Master of Science, Graduate Department of Zoology, in the University of Toronto O Copyright by Corwin Sullivan 2000 National Library Biblioth&que nationale I*I of Canada du Canada Acquisitions and Acquisitions et Bibliographie SeMces services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Canada Cranial anatomy of the Late Permian dicynodont Diictodon, and its bearing on aspects of the taxonomy, palaeobiology and phylogenetic relationships of the genus Corwin Sullivan Master of Science 2000 Department of Zoology, University of Toronto ABSTRACT A study of the Late Permian dicynodont Diictodon confirrns suggestions that only one species, D. feliceps, can be presently recognized. The genus is charactenzed by features such as a palatal notch, a large dentary table with a media1 cutting blade. and the absence of postcanine teeth. Numerous anatomical variations exist within Diictodon, but many appear biologically insignificant. However, there is a clear distinction between specimens having canine tusks and those lacking hem, as tusked specimens are generdly larger and more likely to develop a pineal boss. This probably reflects sexual dimorphism, with the tusked sex almost certainly being the male. A phylogenetic analysis of dicynodonts indicates that previous analyses are correct in identifying Robenia as the sister-group of Diicfodon and Diqnodon and Aulacephalodon as close relatives of Lystrosaum .However, the results suggest that Endothiodon, rather than Eodicynodon, may be the most basai known dicynodont. TABLE OF CONTENTS Page Introduction 1 Materials 9 S ystematic Palaeontology 13 Osteological Description 19 Intrageneric Variation 9 1 Dicynodont Interrelationships 132 Acknow ledgements 160 Literature Cited 161 Appendix 1 - Information on Diictodon specimens examined in this study 177 Appendix 2 - Definitions of characters used in the phylogenetic analysis 182 Appendix 3 - Data matrix for the phylogenetic anaiysis 187 iii LIST OF UUSTRATIONS Page Figure 1. Biostratigraphy of the Beaufort Group Il Figure 2. Diictodon feliceps. Reconstruction of skull in dorsal view 23 Figure 3. Diictodon feliceps. Reconstruction of skull in lateral view 25 Figure 4. Diictodon feliceps. Reconstruction of skull in ventral view 27 Figure 5. Diictodon feliceps. Reconstruction of skull in occipital view 39 Figure 6. Diictoàonfeliceps. Reconstruction ol mandibic in donal view 3 1 Figure 7. Diictodon feliceps. Reconstruction of mandible in lateral view 33 Figure 8. Diictodon feliceps. Reconstruction of mandi ble in ventral view 35 Figure 9. Diictodon feliceps (R97.1). SkulI in donal view 37 Figure 10. Diictodon feliceps (R 97.1). Skull (with mandible) in lateral view 39 Figure 1 1. Diictodon feliceps (UT Von Huene 1922 r. 1-4). Skull in ventral view 4 1 Figure 13. Diictodon feliceps (UT Von Huene 1922 r. 1-4). Skull in occipital 43 view Figure 13. Diictodon feliceps (R 97.2 and SAM-PKX7730). Suborbital region in posterolaterai view 93 Figure 14. Diictodon feliceps (R 97.2 and SAM-PKX7730). Intertemporal region in donal view 95 Figure 15. Diictodon feliceps (R97.1 and SAM-PK-K7795). Snout in donal view 97 Figure 16. Reconstmcted skull of D. feliceps showing morphomeuic measuremen ts 106 Figure 17. Results of a principal components analysis of morphornetric cranial proportions in Diictodon feliceps 112 Figure 18. Cladogram showing dicynodont interrelationships (King, 1988) 134 Figure L9. CIadogram showing relationships among major groups of dicynodonts (Cox, 1998) 136 Figure 20. Cladogram showing dicynodont interrelationships as determined in this study 142 LIST OF TABLES Page Table 1. List of quditative and quantitative variations in the cranial anatomy of Diictodon feliceps 103 Table 2. Co-occurring matornical features in the skull of Diictodon feliceps 110 Table 3. Morphometnc principal components results for the skull of Diictodon fer iceps 114 Table 4. Statistical support for various clades obtained in a phylogenetic analysis of dicynodonts 144 Table A 1. Information on individual Diictodon feliceps specimens exmined in this study 178 Table A?. Data matrix for a phylogenetic analysis of dicynodont 188 interrelationships LIST OF ABBREViATIONS Abbreviations used in Figures A Angular ANT PL Antenor plate of sphenethmoid ANT R Anterior ridge (on palatal surface of premaxilla) ART Articular BO Basioccipital CULT PR Cultriform process (of pmbasisphenoid) D Dentary DEN TAB Dentary table ECT Ectopterygoid EO Exoccipi ta1 EP Epipterygoid F Frontal FEN OV Fenestra ovalis FOR MAG Forarnen magnum ICC Internai carotid canal INT VAC Interpterygoid vacui ty JU Jugal rCTG FOR Jugular forarnen L Lacrimai L FOR Lacrimai forarnen L FS Labial fossa L PAL FOR Laterd paiatal foramen M Maxilla MAN FEN Mandibular fenestra N Nasal N. VII Foramen for cranial nerve VI1 NAS BOSS Nasal boss P Parieta1 PAL Palatine PAL NO PaiataI notch PBS Parabasisphenoid PLANT Pila antotica PIN BOSS Pineal boss PIN FOR Pineai foramen PMX Premaxilla PO Postorbital POF Postfrontal POP Postparietal POS R Posterior ndge (on palatal surface of premaxilla) PP Preparie t al PR Pro0 tic PRF Prefron ta1 PRS Presphenoid PT Pterygoid PTF Posttempord fenestra Q Quacirate QJ Quadratojugal REF LAM Reflected lamina (of angular) SA Surangular sa Scleml ossicle SO Supraoccipi ta1 SP Splenial SQ Squarnosal ST Stapes T Tabular v Vomer VLTUB Ventrolaterd tubcr Institutional abbrevations AMNH Arnencan Museum of Natural History, New York Bm Namal History Museum, London BPI Bernard Price lnstitute for Palaeontological Research, Johannesburg BSP Bayerische Staatssarnrnlung fur Palaonto logie und historische Geologie, Munich rVPP Institute for Vertebrate Paieontology and Paleoanthropology, Beijing R Robert R. Reisz temporary field collection, Toronto RC Rubidge Collection, Wellwood, Graaff-Reinet SAM South African Museum, Cape Town TM Transvaal Museum, Pretoria WC University Museum of Zoology, Cambridge USNM Srnithsonian Institution, Washington, D.C. UT Universitat Tübingen Museum und Institute für Geologie und Palaontologie, Tübingen INTRODUCTION The Beaufort Group strata of South Ahica's Karoo basin have yielded the nchest and most diverse Late Perrnian terrestrial vertebrate palaeofauna in the world. These mainly fluvial deposits contain the remains of numerous species of synapsid amniotes, with less abundant diapsids, anapsids and anamniotes. As investigations of the Karoo pdaeoflora (e-g., Rayner, 1993) and sedimentology (e.g., Smith, 1993a) proceed dong with srudies of the fossil vertebrates, the emerging picture is that of an ancient ecosystem occupying a region of low-lying floodplains cut by a senes of extensive braided river channels. The vertebnte fauna was supported at the lowest trophic levels by plants ranging from the tree-like Glossopteris to the horsetail-like PlzyZZotlieca to a variety of fems, lycopods and mosses (Rayner, 1992) and was dorninated by a diverse array of therapsids. Most abundant of these were the dicynodonts, a clade of denved anomodonts that seem to have represented the fint major assemblage of terrestrial venebnte herbivores (Hotton, 1986) and were, therefore, of considerable ecological, as well as numencal, importance. Their stratigraphic range extends well into the Triassic and their distribution was more or less worldwide, with occurrences recorded on every continent (King, 1993). Although it is clear that dicynodonts were both highly diverse and highly abundant, exact quantification of either parameter is dificult. King (1993a) believed dicynodont taxonomy to be plagued by excessive splitting at the generic and particularly the specific levels, but nevertheless recognized no fewer than 35 valid genera. In terms of individual specimens, Watson (1948: p. 845) referred to one Beaufort stratigraphic interval as "the Endothiodon zone, where anornodonts swarm", whiIe Smith (1993b) found that over 90% of 329 vertebrate fossils he collecteci during a taphonomic study of three Beaufort cliff exposures were dicynodont rernains (mainly isolated skulls). The sheer number of Permian dicynodont fossils available for study is unparalleled in other Palaeozoic terrestrial vertebrate groups, and provides an opportunity to gather meaninghil data on intraspecific and perhaps even intrapopulational osteological variation. Such data are of obvious palaeobiological interest, but are aiso taxonornically useful in thar they may allow systematists to clearly cûstinguish genuine