Assessing Social Behaviour, Ontogenetic Change and Taxonomic status in a Juvenile Gorgosaurus libratus (Dinosauria; Theropoda; Tyrannosauridae): A multidisciplinary analysis By Gavin Bradley A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Systematics and Evolution Department of Biological Sciences University of Alberta ©Gavin Bradley, 2015 Abstract The sparseness of the fossil record and the subjectivity of interpreting behaviour from morphological and taphonomic evidence have impeded studies on the behaviour of juvenile theropod dinosaurs. Most evidence for social behaviour in juvenile dinosaurs comes from multi individual bone beds or parent dinosaurs preserved while brooding on eggs or young. There is therefore a desire for alternative methods of assessing social behaviour, leading to the two key questions of this thesis: 1) can inferences about social behaviour be made using isolated specimens?, and 2) does gregariousness change with ontogeny in Gorgosaurus? A multidisciplinary study using isolated specimens of Gorgosaurus libratus, including a newly described juvenile specimen from Dinosaur Provincial Park in southern Alberta, was carried out in the hopes of answering these two questions. A review of social behaviour in modern animals suggests that gregariousness is gradational and varies from taxon to taxon, even within closely related groups such as Felidae. Inferences of social behaviour for dinosaurs based solely on phylogenetic bracketing is therefore not recommended. However, numerous analyses can be performed on isolated specimens in order to infer social behaviours including parental care, group living, sexual display and combat. For example, palaeopathologies may indicate intraspecific combat. Ontogenetic changes, such as growth curves, allometry of horns and crests, and changes in stable isotopes because of dietary changes may also indicate changing behavioural as well as ecological roles during development. Femoral circumferences are useful in inferring body mass of theropods, and in bone bed aggregations this can aid in studies of growth rates, which can inform social behaviour. Taphonomic damage can reduce sample sizes and make such studies problematic. Statistical analyses, however, suggest that three femoral-diameter-based estimation models may be used to predict femoral circumference measurements in tyrannosaurids. Ontogenetic morphological changes in Gorgosaurus may also inform inferences about social behaviour. Positive allometric growth of the lacrimal horns may imply a display function, as seen in modern bovid and cervid mammals. Slow maximum growth rates of juvenile Gorgosaurus, compared to other tyrannosaurids, calculated using lines of arrested growth and body mass estimations, may indicate social aggregation during early ontogeny in order to survive alongside faster growing and ii larger predators, such as Daspletosaurus or, alternatively, reduced growth due to nutritional stresses on juveniles. Macrowear patterns in the teeth of UALVP 49500 and UALVP 10, an adult specimen, exhibit four major types of tooth wear: enamel spalling, longitudinal facets, tip wear, and barrel-shaped puncture marks. Adult teeth were typified by tip wear, and juvenile teeth were typified by longitudinal wear facets. This is hypothesised to reflect a change in feeding behaviour during ontogeny, from shearing and slicing of meat, with high levels of tooth occlusion in the young, to the “puncture and pull” method previously hypothesized for adults. A slicing feeding method for juveniles is further supported by thinner teeth with higher denticle densities, smaller bite forces, and a more circular orbit shape that is less resistant to the strain of high bite forces on the skull. This multidisciplinary analysis shows that substantial ontogenetic change occurred in Gorgosaurus, and demonstrates that social behaviour may be inferred from isolated specimens. As well, a description of a juvenile Gorgosaurus libratus, UALVP 49500, presents the first examination of post cranial material in such a specimen, and supports a genus-level distinction between Albertosaurus sarcophagus and Gorgosaurus libratus. iii Preface The majority of chapter three of this thesis has been published in Cretaceous Research, although additional text has been added in the version seen in this thesis, to better contextualise the chapter within the overall goals of the masters research. The two co-authors of this manuscript are Michael Burns and Dr. Philip Currie. Both co-authors reviewed various stages of the manuscript and offered suggestions for improvements. The article was peer reviewed by one anonymous reviewer and by Dr. Nicolás Campione, whose suggestions were immensely helpful in the creation of the published version. The citation for the published version of the article is: Bradley, G. J., Burns, M. E., & Currie, P. J. (2015). Missing data estimation in tyrannosaurid dinosaurs: Can diameter take the place of circumference? Cretaceous Research, 55, 200-209. For chapter five, a manuscript has been submitted for publication to the Canadian Journal of Earth Sciences. An initial description of tooth wear in UALVP 10 was carried out over five years ago by James Glasier, but was redescribed by the author of this thesis based on both photographs of the specimen taken by Dr. Eric Snively and Dr. Ryan McKellar, my own physical examination of the teeth. James Glasier and Dr. Philip Currie will appear as co-authors on the manuscript, and both have provided initial reviews of the manuscript; some of the suggested changes have made their way into version submitted as Chapter 4 of this thesis. The article will be submitted in the following format: Bradley, G.J., Glasier, J. and Currie, P.J. Comparing tooth macrowear in a juvenile and adult specimen of Gorgosaurus libratus: changes in feeding behaviour throughout ontogeny in tyrannosaurids. Furthermore, the circumference prediction models produced in chapter two, and body mass estimation methods used in Chapter three were utilised in a publication that I co-authored. None of this data, however, is included in this thesis. The full citation for this article is: Funston, G. F., Persons, W. S., Bradley, G. J., & Currie, P. J. 2015. New material of the large- bodied caenagnathid Caenagnathus collinsi from the Dinosaur Park Formation of Alberta, Canada. Cretaceous Research, 54, 179-187. iv Dedication This thesis is dedicated to my family: Mum, Dad, Anna, Matt, and Andy, who have supported my every move thus far, even the one across the Atlantic Ocean. v Acknowledgements There are a great number of people who contributed in the writing of this thesis. Firstly, I would like to thank my girlfriend Kelsey Biggs, who has suffered more than anyone else at the hands of this thesis, but has shown phenomenal understanding and patience, even during late nights spent working in the lab. I would like to thank my supervisor, Dr. Philip Currie for accepting me into the lab, allowing me to work on such a remarkable specimen and for helpful reviews and comments on the various forms of this final work. Thanks also go to Dr. Eva Koppelhus for organising many of the administrative tasks associated with the thesis and for the support and understanding she has given me during my graduate studies. Immense thanks are owed to Michael Burns who not only dedicated a large portion of his time in supervising and teaching the histological portion of this thesis, but also reviewed chapters at various stages and made hugely useful comments, right down to the wire. I would also like to reserve special thanks for Dr. Nicolás Campione for sharing his expertise on MASSTIMATE, answering countless questions about statistics, and for a host of thoughtful and useful revisions on Chapter three. I am grateful to Dr. Ryan McKellar who gave me his only copy of Lawrence Lambe’s original Gorgosaurus manuscript to help guide my description, and who first introduced me to descriptions through the wonderful world of hymenopterans. I would like to show my appreciation for Ian MacDonald, who put in most of the hours preparing the skull material of Matilda; he did a wonderful job, and also managed to glue the bits I did back together. Thanks go to Clive Coy and Howard Gibbins for their help with all my collections queries, and for their part in the preparation of the salient specimen. I am also grateful to Dr. Michael Caldwell for the ongoing use of his camera equipment. Thanks also go to James Glasier, whose initial description of the teeth of UALVP 10 provided an excellent foundation for Chapter five, and to Dr. Eric Snively for providing pictures of tooth wear in UALVP 10. Access to UALVP 10 was provided by Andrew Locock and Lisa Budney for which I am grateful. I appreciate all the help provided over the past couple of years by Dr. Angelica Torices, who has taught me everything I know about tyrannosaurid teeth, but I suspect, not everything she knows, as it would take too long. Dr. Victoria Arbour and Scott Persons were also always there for me when I had questions, no matter how inane. No matter what the outcome of this thesis, I have been incredibly fortunate to have had the support of a phenomenal group of friends throughout. I’d like to thank Michelle Campbell for all the happy days we spent unwinding from thesis work by cutting out footprints, Hallie Street for being the only person to get my Terry Pratchett references, Jasmine Croghan for seeing me through my first year, Betsy Kruk for also being willing