The Forelimb and Pectoral Girdle of Pachyrhinosaurus lakustai (Ceratopsia, Centrosaurinae) by Rebekah Marion Vice A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Systematics and Evolution Department of Biological Sciences University of Alberta © Rebekah Marion Vice, 2020 Abstract Ceratopsidae is a group of non-avian dinosaurs known for their distinctive cranial ornamentation and horns. This ornamentation has become the focal point of ceratopsid research and therefore has led to a state of affairs in ceratopsid palaeontology in which taxa are diagnosed on the basis of cranial morphology and the postcranial skeleton is generally neglected and assumed to be unimportant. However, recent studies have begun to alter this situation by introducing descriptions of articulated or associated ceratopsid skeletons. This thesis sets out to build on previous understandings of ceratopsid postcranial elements in order to detect, and distinguish between, intraspecific and interspecific variation within Ceratopsidae. This sample was drawn from the upper Campanian Pipestone Creek Bonebed in the Wapiti Formation near Grande Prairie, Alberta, where hundreds of Pachyrhinosaurus lakustai elements have been collected over the past few decades, making this species an ideal focal point for the present study. Morphological and allometric analyses of the forelimb and pectoral girdle of P. lakustai revealed multiple characters potentially unique to the species, as well as variation within the genus Pachyrhinosaurus. Other characteristics of the scapula and humerus that differentiate Centrosaurinae from Chasmosaurinae, including the ratio of the anterior and posterior widths of the scapula to the midshaft width, were identified. Such characters are key to identifying ceratopsid skeletons as accurately as possible when cranial material is not available. Furthermore, histological sampling was used in this study to determine the growth trajectory and age range of specimens from the Pipestone Creek Bonebed. This revealed an that juveniles were more abundant in the sample than subadults or adults. The youngest individual was determined to be under a year old, and the oldest at least 21 years old. The overall growth ii curve of P. lakustai is typical for non-avian dinosaurs in being sigmoidal, the rate of body mass increase greatest in subadults. Lastly, P. lakustai manual pathologies apparently resulting from stresses produced during normal locomotion were discovered and described. This is the first description of this pathology in a centrosaurine ceratopsid, but similar pathologies have been documented in Chasmosaurinae. CT analyses and morphological comparisons suggested that these pathologies were consistent with the unique step cycle described by Thompson and Holmes (2007) for Chasmosaurus irvinensis, therefore expanding the potential scope of this kinematic hypothesis to centrosaurines. Overall, this comparative study of the forelimb and pectoral girdle of ceratopsids revealed taxonomically significant characteristics that may be used in the identification of ceratopsid material in the absence of the cranium. These analyses have implications for understanding the behaviour and ecology of these animals, underlining the importance of studying the postcrania of ceratopsids and paving the way for future studies on this topic. iii Preface This thesis is an original work by Rebekah Vice. No part of this thesis has been previously published. C. Sullivan was the supervisor for this thesis and was involved with concept formation and manuscript edits for all chapters. iv Acknowledgements First and foremost I would sincerely like to thank my supervisor, Dr. Corwin Sullivan. Thank you for your constant help and support over the last few years and of course for making this entire thesis possible. Prior to graduate school I was fortunate enough to have a few amazing mentors over the years. Mrs. Beverley Jealous, who taught me the benefit of hard work and dedication, not to mention how to play the instrument that got me through some of the hardest days. Ms. Redmond and Mrs. Schneider, who pushed me to always do my best. And of course, Dr. Hillary Maddin and Dr. Michael Ryan; you both are the reason I have gotten where I am today. Your mentorship and guidance gave me the confidence and knowledge to pursue this dream. I would also like to thank Dr. Philip Currie for his feedback and assistance throughout my degree. A huge thanks to Darren Tanke, Brandon Strilisky and all the collections staff at the Royal Tyrrell Museum of Palaeontology for allowing me to visit their collections and thin section material for this project. Thanks as well to Derek Larson, Calla Scott, Jackson Sweder and Cam Reed at the Philip J. Currie Dinosaur Museum for allowing me to visit the collections and to join the field crew at the Pipestone Creek Bonebed. Margaret Currie and Kieran Shepard from the Canadian Museum of Nature, and Dr. Kevin Seymour at the Royal Ontario Museum, thank you all for your assistance during collections visits to your respective institutions. Thank you to Dr. Michael Doschak in the Faculty of Pharmacy and Pharmaceutical Sciences at the University of Alberta, for devoting your time and resources to CT scanning a specimen for me. Thank you to Dr. David Evans and the palaeontology graduate students at the University of Toronto and Royal Ontario Museum for hosting the palaeohistology workshop and allowing me to use your equipment, and to Clive Coy, Howard Gibbins, Robin Sissons, and all the volunteers v in the University of Alberta Laboratory for Vertebrate Palaeontology for your constant hard work and help in preparing my material. And a huge thank you to the entire palaeontological community at the University of Alberta; graduate students and professors, and everyone in between. Thanks especially to Dr. Aaron LeBlanc for teaching me how to make histological sections and answering my many questions along the way. Of course, none of this would have been possible without the endless support from my family and friends. To all my friends, both old and new, who have kept a smile on my face through the insanity of school. To my partner, Sam, who has been my biggest cheerleader these past few years, and who has been by my side every step of the way. To my family; Mum, Dad, Moriah and Lianna; thank you for always believing in me, for listening to every rant, every problem, sharing in all the good times and the bad times too. Thank you to everyone who has supported me through it all. Here is to you all. vi Table of Contents Abstract ........................................................................................................................................... ii Preface............................................................................................................................................ iv Acknowledgements ......................................................................................................................... v List of Tables ................................................................................................................................. ix List of Figures ................................................................................................................................. x List of Institutional Abbreviations ................................................................................................. xi Chapter 1 – Introduction ................................................................................................................. 1 A History of Pachyrhinosaurus .................................................................................................... 2 Geology and Taphonomy of the Pipestone Creek Bonebed ........................................................ 6 A Problem in Ceratopsid Palaeontology .................................................................................... 6 Current Study ............................................................................................................................ 10 Chapter 2 - Osteology of the Forelimb and Pectoral Girdle of Pachyrhinosaurus (Ceratopsia: Centrosaurinae) ............................................................................................................................. 11 Introduction ............................................................................................................................... 12 Materials and Methods .............................................................................................................. 16 Specimen Selection and Linear Measurement Data Collection ............................................ 16 Anatomical Orientation ......................................................................................................... 18 Testing Allometry Throughout Ontogeny ............................................................................. 18 Description ................................................................................................................................ 19 Scapula................................................................................................................................... 19 Coracoid................................................................................................................................. 26 Humerus................................................................................................................................