THE UNIVERSITY OF CALGARY Skull Morphology of the Ankylosauria by Matthew K. Vickaryous A THESIS SUBMITED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF BIOLOGICAL SCIENCES CALGARY, ALBERTA JANUARY, 2001 O Matthew K. Vickaryous 2001 National Library Bibliothéque nationale I*l of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON KIA ON4 Ottawa ON KIA ON4 Canada Canada Your Rie Votre rrlftimce Our fite Notre dfbrance 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. Abstract The vertebrate head skeleton is a fundamental source of biological information for the study of both modern and extinct taxa. Detailed analysis of structural modifications in one taxon frequently identifies developmental and / or functional features widespread amongst a more inclusive clade of organisms. Members of the Ankylosauria, a group of armoured, herbivorous dinosaurs, provide an opportunity to review innovative cranial architecture of a fossil taxon. The generalized skull condition of the Ankylosauria is surveyed, providing the first description of the basicranium, and a reappraisal of the palate and mandible. The previous identification of neomorphic cranial elements, such as "tabulars" and "prevomers", is not supported. Osteological terminology used to describe the Ankylosauria is reviewed in connection with the rnorphological overview. This descriptive evaluation establishes the foundation for subsequent detailed investigations of selected taxa. Euoplocephalus tutus Lambe (1 902),frequently regarded as the archetypal ankylosaur, is characterized by an akinetic craniurn with a distinctive pattern of cranial sculpturing, the presence of a modified "ciliary" supraorbital, and relatively small, fluted teeth. A new taon of ankylosaur, "Gobisaurus" gen. et sp. nov., is characterized by a narrow premaxillary rostrum, a prominent orbit, an enlarged nasal vestibule and an elongated rostral process of the vomer. The developmental processes giving rise to cranial ornarnentation are reviewed using the comparative approach, identifying two discrete rnechanisms that operate independently. A cladistic analysis of 22 ankylosaur taxa is conducted, thereby establishing a phylogenetic position for "Gobisaurus". The results of the cladistic analysis are compared with a consensus estimate of previously published hypotheses using a supertree analysis. The cladogram - supertree cornparison illustrates the importance of detailed cranial information in effectively clustering members of the Ankylosauria. ACKNOWLEDGEMENTS An enormous number of people played important roles throughout the course of this research, and many of them deserve special recognition. 1 would like to thank the members of my examination committee, Drs. A.P. Russell, P.J. Currie, M.A. Katzenberg, G. Pritchard and H. 1. Rosenberg, for carefully scrutinizing the penultimate product of my Master's research. My supervisor Dr. A.P. Russell has been particularly patient and longsuffering. Many thanks. Drs. A.P. Russell, P.J. Currie, H.I. Rosenberg, M.A. Katzenberg, B. Hallgrimsson, D.B. Brinkman (TMP) and LM. Witmer (Ohio University, Athens) al1 helped to mould, shape and pervert my knowledge of skeletal anatomy. Mr. W.D. Fitch kindly permitted me to play with, cut apart and yammer on about many of the fine specimens in his care at the University of Calgary, Museum of Zoology. 1 have no doubt benefited from the many frank and frequently perturbing conversations with my cohorts J.M. Lavigne (Talisman Energy, Calgary), M. Getty (Utah Museum of Natural History, Salt Lake City), K. Kucher (TMP), and L. Claessens (Harvard University, Cambridge). J.T. Lumb (Metafore, Calgary) and N. Rybczynski (Duke University, Durham) are to be congratulated not only for their years of polite discourse and encouragement, but also for their burliness in excavating ankylosaurs in the dark. My colleagues in the Vertebrate Morphology and Palaeontology Research Group have al1 contributed significantly to my current outlook. Thanks to G.L. Powell, L. McGregor, E. Snively, M.J. Ryan, M. Thompson, P.J. Bergmann, J. Peng, A.M. Gutierrez and T. Higham. Specimens studied during the course of this research came from a variety of institutions, and special thanks is owed to the following museum curators and collection managers: A. Newman, J.D. Gardner, J. Wilke, M. Laframbois and L. Cook (TMP); R.C. Fox (UAVLP); M.A. Norrell (AMNH); K. Carpenter (DMNH); K. Shepard (CMN); and Y. Kobayashi (FPDM). I also owe thanks to the staff of Prehistoric Animal Structures (East Coulee, Alberta) and Canada Fossils (Calgary, Alberta) for keeping me posted on ankylosaurs moving through their workspaces. Dr. R. Etheridge (San Diego State University) provided some crucial information iv about the development of ornamentation in squamates and supplementary information about ankylosaur material was gleaned through conversations with Drs. K. Carpenter (DMNH), J.I. Kirkland (Utah Geological Survey, Salt Lake City) and Mr. P. Penkalski (North Carolina State, Raleigh). The gurus of systematics, Drs. O.R.P. Bininda-Emonds (Leiden University, Leiden, The Netherlands) and S. Modesto (ROM),deserve special credit for permitting me to bother them so frequently. Thanks-eh! Ankylosaur cranial rnaterial was thin-sectioned with unparalleled skill by Mr. J. Resultay (University of Calgary, Department of Geology and Geophysics). Preparation of ankylosaur material at the TMP during the course of this research was conducted with prudence and finesse by Ms. W. Sloboda and Messrs. K. Kucher and M. Mitchell. Ms. D. Sloan (TMP), Dr. P. Johnston (TMP), Mr. G. Campbell and Mr. A.L. Vickaryous assisted with much of the photography and R. Humphries, L. Curtis and L. Morris performed the CT scanning at the Foothills Hospital, Calgary. This research was supported by the Duerksen Mernorial Scholarship, a Jurassic Foundation Grant, two Heaton Student Support Grants, a University of Calgary Graduate Scholarship, a University of Calgary Thesis I Dissertation Research Grant, an NSERC Operating Grant awarded to Dr. A.P. Russell and the infinite patience of J.T. Lumb. TABLE OF CONTENTS ... Abstract .............................................................................................................III Acknowledgements ...........................................................................................iv Table of Contents .............................................................................................. vi List of Tables .................................................................................................... xii... List of Figures .................................................................................................. xiii List Of ~ymbols.Abbreviations. And Nomenclature .......... Chapter 1. Introduction .......................... ............ ............ 1.1 Background Rationale...................................... 1.2 The Ankylosauria ............................................. 1.2.1 Euoplocephalus tutus Lambe (1902) .. 1.2.2 " Gobisaurus" gen. et sp . nov.............................................. 4 Chapter 2. Fossil Materials and Methods .................................................... 7 2.1 Specimens ........................................................................................ 7 2.1 .1 Post-mortem Deformation ..................................................9 2.1 -2 Euoplocephalus;A Question of Synonymy....................... IO 2.2 Methodology ................................................................................... II Chapter 3. Ankylosaur Head Skeleton Morphology ................................. 15 3.1 Overall Morphology ........................................................................ -15 3.2 Ossa Cranii ..................................................................................... 17 3.2.1 Rostral Region ............................................................. 17 3.2.1 .1 Os premaxillare ............................................... -18 3.2.1.2 Os maxillare (rostrodorsal secondary palate) .. -20 3.2.1.3 Osnasale ......................................................... 23 3.2.1.4 Os prefmntale ................................................. -24 3.2.1 .5 Os lacrimale .................................................... -25 3.2.2 Temporal Region............................................................. -26 3.2.2.1 Ossa supraorbitalia (processus cornuum supraonbitalia) ............................................. 26 3.2.2.2 Os postorbitale (lamina postocularis) ............... 28 3.2.2.3 Os jugale (arcusjugale) ..................................