Ontogeny, Diversity, and Systematics of Pachycephalosaur Dinosaurs from the Belly River Group of Alberta by Ryan K. Schott A thesis submitted in conformity with the requirements for the degree of Master of Science Department of Ecology and Evolutionary Biology University of Toronto © Copyright by Ryan K. Schott 2011 Ontogeny, Diversity, and Systematics of Pachycephalosaur Dinosaurs from the Belly River Group of Alberta Ryan K. Schott Master of Science Department of Ecology and Evolutionary Biology University of Toronto 2011 Abstract Pachycephalosaur diversity and systematics is poorly resolved, mainly due to the incomplete nature of their remains. The largest sample of pachycephalosaurs is from the Belly River Group of Alberta, but this sample is also the most problematic in terms of alpha taxonomic diversity. Material from this assemblage has been proposed to represent from a single species to up to four distinct genera. Each of these views depends on different interpretations of morphology, ornamentation, ontogeny, and sexual dimorphism, but none have been adequately tested. Here I analyze the diversity of pachycephalosaurs with particular emphasis on Stegoceras validum and 'Prenocephale' brevis. The ontogeny of these species is described using comparative morphology, histology, and morphometrics. New specimens are described and the first detailed pachycephalosaur growth series supported by multiple, independent lines of evidence is presented. Phylogenetic analysis utilizing results from this study provides a new hypothesis for the evolutionary relationships of pachycephalosaurs. ii Acknowledgments I am indebted to all the individuals that have given me the supervision, guidance, and assistance that have made this Master's thesis possible. I am especially thankful to my supervisor David Evans, for first taking me in as an undergraduate student and providing me with the excellent projects that have culminated in this thesis. Without his support and guidance this would not have been possible. I am also grateful to my supervisory committee, Dan Brooks (co- supervisor), Tim Dickinson, and, especially, Mark Goodwin for their insight into my various projects. I am thankful to my external examiners, Deborah McLennan and Jason Head, for their comments and feedback on my work. Special thanks to the members of the Evans Lab, especially Nicolas Campione and Caleb Brown, for discussions and assistance with many aspects of this thesis. I thank Warren Fitch (UCMZ), Brandon Strilisky (TMP), Phil Currie (UALVP), and Kieran Shepherd (CMN), for access to collections and loans of material. Thanks to Caleb Brown for discovering UCMZ (VP) 2008.001, Miriam Reichel for discovering and preparing UALVP 49531, and Phil Bell for discovering UALVP 49440. Special thanks to the artists who provided the excellent scientific illustrations contained in this thesis, Caleb Brown, Johnathan Ho, Kurt Latanville, and Amy Janzen. Thanks to Ian Morrision for preparing UCMZ(VP) 2008.001 and numerous other specimens. I thank Nathan Scaiff for discussions and assistance regarding CT methodologies, Angel Ai for discussion regarding histology, and Bob Sullivan and Tom Williamson for discussions regarding pachycephalosaur morphology and systematics. Thanks to the University of Texas High-Resolution X-ray CT Facility for producing the HRCT images, and Arius 3D for the 3D surface scans and reconstruction of Foraminacephale brevis. Finally I would like to deeply thank my girlfriend, Alicia Dobbs; my parents, Daniel and Patricia Schott; my sisters Nicole and Natalie Schott; my grandparents, Ellen Duffy and iii Karl and Françoise Schott; and my great uncle, Robert Reid; for their love and support throughout my academic pursuits. iv Table of Contents Abstract.....................................................................................................................................ii Acknowledgments...................................................................................................................iii Table of Contents......................................................................................................................v List of Tables...........................................................................................................................vi List of Figures.........................................................................................................................vii List of Appendices...................................................................................................................ix Chapter 1: Introduction.............................................................................................................1 References............................................................................................................................4 Chapter 2: Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria) and the evolution of cranial doming and ornamentation in Pachycephalosauria........................6 1 Author Contributions.........................................................................................................6 2 Introduction.......................................................................................................................6 3 Systematic Paleontology.................................................................................................12 4 Description......................................................................................................................13 5 Taxonomic Assessment...................................................................................................22 6 Frontoparietal Allometry.................................................................................................25 7 Frontoparietal Bone Histology........................................................................................40 8 Squamosal Variation and Ontogeny................................................................................52 9 Discussion.......................................................................................................................60 References..........................................................................................................................69 Appendices.........................................................................................................................77 Chapter 3: Systematics and Ontogeny of Foraminacephale brevis gen. nov. (Ornithischia: Pachycephalosauria)...........................................................................................................81 1 Introduction.....................................................................................................................81 2 Taxonomic and Systematic History of Foraminacephale brevis....................................82 3 Systematic Paleontology.................................................................................................84 4 Description......................................................................................................................86 5 Frontoparietal Variation and Ontogeny.........................................................................112 6 Frontoparietal Histology...............................................................................................136 7 Phylogenetic Systematics..............................................................................................144 8 Discussion.....................................................................................................................150 References........................................................................................................................155 Appendices.......................................................................................................................159 v List of Tables Chapter 1: Introduction.............................................................................................................1 Table 1.1 A comparison of Belly River Group pachycephalosaur taxonomy.....................3 Chapter 2: Cranial Ontogeny in Stegoceras validum (Dinosauria: Pachycephalosauria) and the evolution of cranial doming and ornamentation in Pachycephalosauria........................6 Table 2.1 Reference and taxonomic assignment of Ornatotholus browni.........................11 Table 6.1 Allometric regression of Stegoceras validum frontoparietal ontogeny..............31 Table 6.2 Allometric regression of Stegoceras validum frontoparietal ontogeny excluding all specimens less domed than TMP 84.5.1................................................................34 Table 6.3 Allometric regression of Stegoceras validum frontoparietal ontogeny excluding all specimens less domed than TMP 84.5.1, except for three partially domed frontals .....................................................................................................................................35 Table 8.1 Allometric Regression of Stegoceras validum squamosal ontogeny.................57 Table 9.1 Ontogenetic changes in the morphology of Stegoceras validum.......................68 Chapter 3: Systematics and Ontogeny of Foraminacephale brevis gen. nov. (Ornithischia: Pachycephalosauria)...........................................................................................................81 Table 5.1 Allometric regression of Foraminacephale brevis frontoparietal ontogeny....121 Table 5.2 Allometric regressions comparing the