Ontogenetic niche shifts in megaherbivorous dinosaurs of Late Cretaceous North America and their ecological implications by Taia Wyenberg-Henzler A thesis submitted to the Faculty of Graduate and Postdoctoral Affairs in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences Carleton University Ottawa, Ontario © 2020, Taia Wyenberg-Henzler Abstract Despite megaherbivore ontogeny being relatively well-studied, little research has been conducted on the ecological implications of growth stages. Using ecomorphological dietary correlates, investigations into potential ecological differences between mature and immature ceratopsids and hadrosaurids were undertaken. The results suggest that juvenile megaherbivores selectively consumed softer, lower-growing vegetation than their adult counterparts, which likely reduced intra-specific competition. Ecomorphological investigations into the potential for competition between juvenile megaherbivores and small ornithischians, and investigations into relative abundances, were conducted to test the competition and taphonomic hypotheses. An overlap in results indicated a potential for competition between juvenile megaherbivores and leptoceratopsids, and as predicted by the competition hypothesis small ornithischians were generally less abundant than megaherbivores. Other groups showed separation in the ecomorphospace and some distributions showed similar abundances between groups as predicted by the taphonomic hypothesis. Thus, size differences were important for resource partitioning, and competition and taphonomy both influenced observed Late Cretaceous size distributions. ii Acknowledgements I would like to than Dr. Jordan Mallon and Dr. Tim Patterson for their supervision and guidance throughout this project, and Dr. Gabriel Blouin-Demers, Dr. Michael Ryan and Dr. Andrew Simons for their feedback. I would also like to thank Dr. Danielle Fraser and Dr. Nicolas Campione for their help and suggestions with R. Thanks to staff and students of Carleton University, especially my colleagues in the Carleton University Palaeontology program, for their support and encouragement. I would like to acknowledge NSERC, the Dinosaur Research Institute and Jurassic Foundation as funding sources that made the travel necessary for the completion of this project possible. My thanks also goes to the curators and assistants at the American Museum of Natural History, Museum of the Rockies, Royal Ontario Museum, Royal Tyrrell Museum of Palaeontology, Smithsonian National Museum of Natural History and University of Alberta Laboratory for Vertebrate Palaeontology for providing access to their collections. I thank Dr. Corwin Sullivan, Dr. David Evans, Amanda Millhouse and David Trexler for providing and/or facilitating access to restricted-access specimens. Thanks to Andrew Knapp for providing CT data on AMNH 5401 and AMNH 5402, Dr. Michael Ryan for photos of the MNHCM Prenoceratops from which measurements were taken, and staff at the Canadian Museum of Nature, Dr. Michael Ryan and Dr. Frank Varriale for providing help and suggestions on methods to remove bubbles from epoxy casts. Special thanks goes to my family who helped and supported me throughout this entire process. iii Institutional Abbreviations ACM, Beneski Museum of Natural History, Amherst College, Amherst; AMNH, American Museum of Natural History, New York, New York; ANSP, Academy of Natural Sciences of Philadelphia, Philadelphia, Pennsylvania; BHI, Black Hills Institute, Hill City, South Dakota; BMNH, British Museum of Natural History, London, U.K.; CMN, Canadian Museum of Nature, Ottawa, Ontario; CM, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania; CCM, Carter County Museum, Ekalaka, Montana; DMNH, Denver Museum of Nature and Science, Denver, Colorado; FMNH, Field Museum of Natural History, Chicago, Illinois; GPDM, Great Plains Dinosaur Museum, Malta, Montana; IMNH, Idaho Museum of Natural History, Pocatello, Idaho; LACM, Natural History Museum of Los Angeles County, Los Angeles, California; MNHCM, Mokpo Natural History and Culture Museum, Mokpo, Korea; MCSNM, Museo Civico di Storia Naturale di Milano, Milan, Italy; MOR, Museum of the Rockies, Bozeman, Montana; NCSM, North Carolina Museum of Natural Sciences, Raleigh, North Carolina; NHMUK and NHM Natural History Museum, London, U.K; NMMNH, New Mexico Museum of Natural History, Albuquerque, New Mexico; NSM PV and NMST, National Museum of Nature and Science, Tokyo, Japan; OTM, Old Trail Museum, Choteau, Montana; RAM, Raymond M. Alf Museum of Paleontology, Claremont, California; ROM, Royal Ontario Museum, Toronto, Ontario; RSM, Royal Saskatchewan Museum, Regina, Saskatchewan; SM – Senckenberg Museum, Frankfurt, Germany; TMM, Texas Memorial Museum, Austin, Texas; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta; TLAM, Timber Lake and Area Museum, Timber Lake, South Dakota; TCMI, The Children’s Museum of Indianapolis, Indianapolis, Indiana; UALVP, iv University of Alberta, Edmonton, Alberta; UC, University of Calgary, Calgary, Alberta; UCMP, University of California Museum of Paleontology, Berkeley, California; UMMP, University of Michigan Museum of Paleontology, Ann Arbor, Michigan; USNM, Smithsonian Institution, National Museum of Natural History, Washington, D.C.; UTEP, University of Texas, El Paso, Texas; YPM, Peabody Museum of Natural History, Yale University, New Haven, Connecticut; YPM PU, Peabody Museum of Natural History, Yale University, New Haven, Connecticut, Princeton University Collection. v Table of Contents Abstract .............................................................................................................................. ii Acknowledgements .......................................................................................................... iii Institutional Abbreviations ............................................................................................. iv Table of Contents ............................................................................................................. vi List of Tables ..................................................................................................................... x List of Illustrations .......................................................................................................... xii List of Appendices .......................................................................................................... xvi Chapter 1: Introduction ................................................................................................ 18 1.1 Background................................................................................................................... 18 1.2 Taxonomy ..................................................................................................................... 19 1.3 Coexistence................................................................................................................... 22 1.4 Ontogenetic Niche Shifts .............................................................................................. 23 1.4.1 Ontogenetic Niche Shifts in Extant Taxa ................................................................. 25 1.4.2 Ontogenetic Niche Shifts in Dinosaurs .................................................................... 29 1.5 Structure and Aims of Thesis ....................................................................................... 33 Chapter 2: Ontogenetic niche shifts in hadrosaurids of Late Cretaceous North America ............................................................................................................................ 34 2.1 Introduction .................................................................................................................. 34 2.1.1 What is a hadrosaurid? ............................................................................................. 34 2.1.2 Hadrosaurids and ontogenetic niche shifts ............................................................... 35 2.1.3 Chapter goals ............................................................................................................ 38 2.2 Methods ........................................................................................................................ 39 2.2.1 Skull allometry ......................................................................................................... 40 2.2.2 Snout shape .............................................................................................................. 46 vi 2.2.3 Tooth wear analysis .................................................................................................. 49 2.3 Results .......................................................................................................................... 53 2.3.1 Skull allometry ......................................................................................................... 53 2.3.2 Snout shape .............................................................................................................. 58 2.3.3 Microwear ................................................................................................................ 58 2.3.3.1 Scratch orientation and distribution ................................................................. 61 2.3.3.2 Scratches and pits ............................................................................................ 65 2.4 Discussion....................................................................................................................