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Michelle Maxine Mekarski The Origin and Evolution of Aquatic Adaptations in Cretaceous Squamates by Michelle Maxine Mekarski A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Systematics and Evolution Department of Biological Sciences University of Alberta © Michelle Maxine Mekarski, 2017 i ABSTRACT Three species of Cretaceous marine squamates are described or redescribed. The first, Pontosaurus ribaguster is described from a relatively complete specimen discovered on Hvar Island, Croatia. Preservation of identifiable nektonic teleosts within the gastric cavity (the first identifiable gastric contents described from a dolichosaur) provide strong evidence of a primarily piscivorous diet. The second described species is a new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergi, from the Cenomanian-Turonian (U. Cretaceous) of Dugi Otok, Croatia. The specimen preserves an exquisite forelimb showing a unique anatomy that appears to be transitional between Aigialosaurus and Mosasaurus. The new and unique limb anatomy contributes to a revised scenario of mosasauroid paddle evolution, whereby the abbreviation of the forelimb and the hydrofoil shape of the paddle evolves either earlier in the mosasaur lineage than previously thought, or more times than previously considered. The third description is a reassessment of the lizard Aphanizocnemus libanensis. Re-examination suggests that characters cited as supporting varanoid-dolichosaur affinities are misinterpreted, are common to many squamates, or are homoplastic and tightly linked to aquatic adaptation. Available data support the conclusion that Aphanizocnemus is not a dolichosaur, a varanoid, nor in fact an anguimorph, but may represent a new form of aquatic scincomorph, a group not previously recognized as having evolved aquatic adaptations. The three descriptions highlight morphological data that has been erroneously used, or were unavailable for, previous studies. A systematic analysis of the Pythonomorpha (inclusive of Pontosaurus ribaguster and Pontosaurus krambergi¸ and exclusive of A. libanensis) shows strong evidence for a monophyletic Aigialosauridae from which the hydropedal mosasauroid condition evolved at least twice. The results also support dolichosaurs as a non-monophyletic assemblage that form successive sister ii taxa to the derived ophidians. The relationship between mosasauroids (Aigialosauridae) and ophidiomorphs is less conclusive, recovering the ophidiomorph lineage as arising from within the Mosasauroidea, most often as a sister group to the Mosasaurinae. To provide context for their evolutionary history, non-ophidian ophidiomorphs are further investigated through paleobiogeography. Fragmentary discoveries suggest that dolichosaurs originated in the Valanginian (Early Cretaceous) or even the latest Jurassic. Diversity and density peaked in the Cenomanian as a result of a large radiation in the Tethys and Western Interior Seaway. This radiation was likely interrupted by the Cenomanian-Turonian Boundary Event, an extinction event which caused a considerable drop in diversity. Non-ophidian ophidiomorphs persist until the Maastrichtian, while achieving their largest geographical distribution: spanning Europe, North America and South America. Their fossil record indicated that this geographically widespread group inhabited nearshore and offshore marine environments, and made several independent radiations into freshwater environments. Their radiative success was driven by features that were predisposed to functionality in the marine environment. Such ‘preadaptive’ features could explain the propensity of the pythonomorph lineage to invade the water, as evidenced by multiple lineages independently radiating into the marine environment. Fast evolution of aquatically adapted features would subsequently allowed them to colonize the aquatic environment worldwide. iii PREFACE Some of the research conducted for this thesis forms part of an international research collaboration, led by Dr. Michael Caldwell at the University of Alberta, with the Croatian Natural History Museum (Hrvatski prirodoslovni muzej), Zagreb, Croatia. Chapters two and three represent two manuscripts written, figured, and analyzed by M. Campbell Mekarski. M. Caldwell was the supervisory author; K. Krizmanić supervised the curation and management of the specimens; and D. Japundžić assisted with the review and interpretation of Croatian literature, assisted with some anatomical interpretation, and prepared the specimen described in Chapter two. Chapters one and four through seven are my original work. Chapter two of this thesis is in preparation for submission as M. Campbell Mekarski, D. Japundžić, K. Krizmanić, and M. Caldwell “A new Cenomanian-Turonian Pontosaurus from the Dalmatian Coast, Croatia, and the first described ‘dolichosaur’ stomach contents” PLoS One. M. Caldwell assisted with manuscript composition and editing; D. Japundžić contributed to geological review and manuscript edits; and K. Krizmanić contributed to manuscript edits. Chapter three of this thesis is in preparation for submission as M. Campbell Mekarski, D. Japundžić, K. Krizmanić, and M. Caldwell “Description of a new basal mosasauroid with comments on the evolution of the mosasauroid forelimb” Journal of Vertebrate Paleontology. M. Caldwell assisted with manuscript composition, D. Japundžić and K. Krizmanić contributed to manuscript edits. Chapter seven was originally researched and written for a much more general audience as two parts of the University of Alberta MOOC ‘Ancient Marine Reptiles, PALEO 203’. Though all the original writing and the bulk of the background research is all my own, H. Street helped iv with literature review, and T. Onuczko, M. Caldwell, and H. Street contributed to edits. The included text is all my own original work, and has been greatly edited and supplemented for this thesis from its original format. The novel taxonomic binomials introduced in chapters two and three are not official under the International Code of Zoological Nomenclature and should not be considered valid at this time. v ACKNOWLEDGEMENTS First and foremost, I would like to thank Dr. Michael Caldwell for his supervision, guidance, and friendship during my stay at the University of Alberta. He was willing to take a student fresh from medical oncology research, who had very little prior knowledge of paleontology, and work with me to make my degree a success. I am extremely grateful for his faith and patience. The many discussions (in the lab, in hallways, and in kitchens and restaurants with wine in hand) greatly influenced my thinking as a person and a scientist, and I look forward to a lifetime of mentorship, friendship, and collaboration. I would also like to thank Rob Holmes, Alison Murray, and John Acorn, who were involved in the supervision of my Ph.D. and who were always ready to help me out. I also want to thank Hans Larsson, the external member of my Ph.D. jury, for reading and evaluating my thesis, and for his suggestions. I gratefully acknowledge the funding agencies which supported me financially throughout: Natural Sciences and Engineering Research Council, the University of Alberta Faculty of Science and Department of Biological Sciences, and the Government of Alberta. I would like to give a special thanks to my colleagues at the Croatian Natural History Museum, especially Dražen Japundžić, Katarina Krizmanić and Davorka Radovčić. Without them, access to the specimens which formed the backbone of this thesis would not have been possible. I wish to thank them for their generosity and hospitality during my visits, for inviting me into their homes, offices, cafes, and soccer fields, and introducing me to Croatian culture. Allan Lindoe deserves praise and thanks for his preparation of Portunatasaurus. Al is a constant source of comedic relief and stories, and has been a wonderful friend and mentor. The graduate students of the Biological Sciences department, and especially the members of the UofA Laboratory for Vertebrate Paleontology have been co-conspirators in both science vi and procrastination. In no particular order, thanks are offered to: Phil (we almost took over the world!), Michelle, Michele, Van, Josh2, Kyle, Fran, Trish, Jess, Katie, Kristina, Miriam, Robin, Jasmine, Stephanie, Kelly, Paulina, Thodoris, Juan, Gavin, Tiago, Julien, Betsy, Tetsuto, Victoria, Scott, Mike, Aaron, Angelica, Greg, Sydney, Matt, Brennan, Aaron, Sinjini, Oksana, Ilaria, and Katherine. An extra special thank you goes to Hallie Street, who picked me up from the airport and let me sleep in her living room during my first week in Edmonton, who guided me in my early struggles with anatomy and geology, answered countless questions, who has been a collaborator, travel companion, trusted second opinion, and my closest friend in Edmonton. For celebrating the good times, and distracting me during the bad: thank you to all my friends (especially Jess, Chris, Jessie, Logan, Amy, Caroline, Mike, and the Crossfit Lineage and Edmonton Water Polo communities), and most especially my family. My mother, father, and brother watched me leave to start this journey, and I have two mothers, fathers, and brothers cheering for me at its completion. To Mom, Dad, Iain, Pawel, Sean, Liv, Chris and Barb, Tom, Aunt Heather, Oma and Grandad, Grandma and Grandpa, cousins, aunts, and uncles. Even being so far away, you were all very present during every step of my Ph.D. studies. Thank you for all the love and support
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