The Evolution of Snout Shape in Eudromaeosaurians and Its Ecological Significance by Mark James Powers
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The Evolution of Snout Shape in Eudromaeosaurians and its Ecological Significance By Mark James Powers 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 © Mark James Powers, 2020 Abstract Dromaeosaurids were small to medium sized theropod dinosaurs that diversified during the Late Cretaceous, reaching a near cosmopolitan distribution. They were diverse in morphology from the small four-winged gliders of Microraptorinae, to the bear-sized giant ‘raptors’ like Achillobator or Utahraptor from the Eudromaeosauria. Eudromaeosauria and its constituents that make up the general public’s view of ‘raptor’ dinosaurs. This group comprises the medium to large dromaeosaurids with pronounced teeth and claws to fill their respective predatory niches and were largely restricted to Laurasia. The known diversity of this clade has increased dramatically since the 1990s, new species described almost yearly. Except for a few nearly complete skeletons, eudromaeosaurians are represented by limited material used in diagnosing distinct species. The maxilla has been given a lot of phylogenetic and ecological weight due to its complexity and its relation to feeding behaviour. This creates an image of eudromaeosaurian systematics that is largely based on one element of the skeletal anatomy. It is important then to have the most complete understanding of the morphology of this one element and how it varies among specimens. This can be difficult as individual bones within a species can show ontogenetic, sexual and/or individual variation. Additionally, taphonomic processes can influence our understanding and interpretations of features affected by deformation. Once these factors are assessed, the level of phylogenetic and ecological inference can be better hypothesized. In this thesis project, I acquired computed tomography data of eudromaeosaurian maxillae to study these elements within this clade. This allowed me to perform a thorough examination of the morphology of internal features and suture patterns and attempt to retro- deform areas that were distorted during the fossilization process. Previous morphological ii descriptions were expanded on and modified as needed. Morphological variation of the maxilla was examined with an emphasis on the ingroup variation of Eudromaeosauria. Linear measurements were taken from a wide range of eudromaeosaurian maxillae for bivariate and principal component analyses to test for trends. Maxillary characters that are ratio-based were examined to look for natural breaks in the range of variation observed to assess the validity of character state thresholds. The characters were then either dropped or adjusted to fit the data. Using the same methods, the range of variation within Velociraptor was examined, coupled with a description of a previously undescribed specimen, to develop a baseline for intraspecific variation. Complex morphology of the maxillary sinus system is demonstrated to be shared among North American eudromaeosaurians from the Late Cretaceous. The sinus systems are noticeably different in related Asian taxa. Ratio-based maxillary characters pertaining to the anterior ramus overshadowed phylogenetically informative features previously not coded. Reinterpretation of the maxilla of Deinonychus revealed a morphology more in line with other North American dromaeosaurids, and thereby changed its close phylogenetic placement to Asian taxa. PCA analysis of the maxillae across eudromaeosaurian species shows clear distinction between Asian and North American morphologies. Asian taxa are shallow and elongate while North American taxa have either stout maxillary morphologies or intermediate between the extremes. The gradient of maxilla elongation across PC 1 possibly represents adaptations for prey selection. Maxillary variation within specimens previously identified as Velociraptor mongoliensis suggests one specimen falls outside a conservative range of variation and should be classified as a new species -- Velociraptor vadarostrum sp. nov. Supported by discrete autapomorphies of the frontal and pelvis, V. vadarostrum sp. nov. fits well in the trend in maxillary morphology in iii Asian velociraptorines, possessing the most elongate form compared to Linheraptor and Tsaagan, which possess the least elongate maxillae of the Asian velociraptorines. The consistency of elongate snout morphology in derived Asian eudromaeosaurians supports a monophyletic Velociraptorinae. Persistence of this trait may have been driven by environmental pressures of predominantly arid to sub arid environments which define the Djadokhta Formation of Mongolia and equivalent sediments in China. These arid environments would not support a high diversity of large animals and would cause pressure on Asian eudromaeosaurians to specialize in hunting and eating smaller, more abundant prey. The maxilla is an informative element due to its importance in theropods, for interacting with its lifestyle and environment. Therefore, ecological pressures and vicariance were likely driving eudromaeosaurian biodiversity and morphological disparity during the Late Cretaceous of Laurasia. iv Preface Chapter 3 (“Re-examining ratio based premaxillary and maxillary characters in Eudromaeosauria (Dinosauria: Theropoda): divergent trends in snout morphology between Asian and North American taxa”) was published in Palaeogeography, Palaeoclimatology, Palaeoecology on March 24, 2020. The manuscript and its contents were originally produced by me, and the co-authors (Drs. Philip Currie and Corwin Sullivan) provided valuable discussion and edits to improve the quality of the manuscript. The content of this chapter – including its tables, figures, and appendices – have only been altered to reflect the data presented in chapter 2 and formatted to fit the thesis document. The introduction of the published manuscript has been modified and included in the introductory chapter of this thesis, and the introduction for Chapter 3 has been abbreviated. Powers M. J., Sullivan C., and Currie P. J. 2020. Re-examining ratio based premaxillary and maxillary characters in Eudromaeosauria (Dinosauria: Theropoda): divergent trends in snout morphology between Asian and North American taxa. Palaeogeography, Palaeoclimatology, Palaeoecology 547:1-20. v Dedication “Perfection? I don’t want that … cuz that would mean stopping. Standing in place. I’m always aiming higher.” – Son Goku, Dragon Ball Super manga Ch. 39 “The only constant in life is change. One’s ability to adapt to those changes will determine your success in life” – Benjamin Franklin To everyone I have met along the way and how they have changed me. I would not be here if it were not for them. To my mother, Barbara Powers. You were the fire under my ass mom, and you pushed those around you to do better – be better. Were you still with us today I have no doubts this thesis would have been finished months ago. vi Acknowledgements Funding for Chapter 3 was in part provided by the Natural Science and Engineering Research Council of Canada (NSERC), Canadian Graduate Scholarship – Master’s (CGS-M) award. I would like to thank the Natural Science and Engineering Research council of Canada (NSERC), for the Canadian Graduate Scholarship – Master’s (CGS-M) award, which allowed me to have teaching relief for a year while writing this thesis. I like to thank the Dinosaur Research Institute for providing funding to travel to various museums and look through collections to collect data for this study. For collections visits I would like to thank TMP curator Donald Brinkman, collections manager Brandon Strilisky, and collections staff Becky Sanchez, Rhian Russell and Tom Courtenay for access to and assistance with specimens of Atrociraptor and Saurornitholestes and facilitating the acquisition of CT scanning these specimens for whom I would like to thank the technician Lynn Kostenuk at Mayfair Diagnostics; BYUVP collections manager Rodney Scheetz and graduate student Rebecca Esplin for access to Utahraptor material; CEUM curator Kenneth Carpenter and collections staff member Katherine Corneli for access to Geminiraptor and Utahraptor material; AMNH fossil Fish, Amphibians, Reptiles and Birds collections manager Carl Mehling, and curator Mark Norell, for access to Bambiraptor, Tsaagan, and Velociraptor specimens and allowing access to the Tsaagan scans as well as authorizing the scanning MPC-D 100/982; YPM assistant professor and curator Bhart-Anjan Bhullar, and his PhD student Matteo Fabbri, for access to Deinonychus material and for scanning Deinonychus and Velociraptor material, and museum assistant Daniel Brinkman for facilitating the collections visit to the YPM; and ROM collections manager Kevin Seymour, collections technician Brian Iwama, and curator David Evans for access to the Acheroraptor and providing scans of the vii holotype specimen, and access to various other comparative dromaeosaurid material. I would also like to thank Dr. Gregory Funston and Dr. Philip Currie for providing photos of Velociraptor specimens from the MPC, and for discussion their discussions and mentorship. For valuable skills learned and mentorship I would like to thank Dr. Michael Caldwell and Dr. Corwin Sullivan. I thank the committee members for reviewing this behemoth of Appendices and them plus the chair for sitting through the impending defence. For discussion I would also like to thank Gavin Bradley, Meghan Dueck, Aaron