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Copyright by Blake Russell Chapman 2018 The Senior Honors Thesis Committee for Blake Russell Chapman Certifies that this is the approved version of the following Thesis: A new Assemblage of Mosasaurs from the Upper Cretaceous Savoy Pit, Austin Chalk, Northeast Texas APPROVED BY SUPERVISING COMMITTEE: Christopher J. Bell, Supervisor Christopher Lowery Charles Kerans A new Assemblage of Mosasaurs from the Upper Cretaceous Savoy Pit, Austin Chalk, Northeast Texas by Blake Russell Chapman Senior Honors Thesis Presented to the Faculty of the Jackson School of Geosciences of The University of Texas at Austin in Partial Fulfillment of the Requirements for the University Honors Research Program The University of Texas at Austin May 2018 Acknowledgements I thank my graduate student mentor Joshua Lively for the many hours he spent familiarizing me with the anatomy of lizards and mosasaurs, answering my numerous questions on mosasaur ecology and evolution, introducing me to mechanical preparatory work, and guiding my way as a paleontologist. I thank my undergraduate adviser Christopher J. Bell for all the knowledge he shared on the proper procedures for conducting science and ethics, spending long days and nights revising my abstracts and research thesis, and for his repeated financial support during my undergraduate career. I also thank Christopher Lowery, Charles Kerans, Michael J. Polcyn, and the Bell Lab Group for guidance and assistance on this project. Preparation that I did not complete myself was performed by Kenneth Bader, Alana Self, Paul Redman, Chase Shelburne, and Michael Chiappone. I thank Deborah E. Wagner for her advice on fossil preparation. I also thank the collections managers and staffs of the following institutions for J. Lively’s access to collections which by extension also benefitted me: Chris Sagebiel of the Vertebrate Paleontology Laboratory at The University of Texas at Austin, Dale A. Winkler of the Schuler Museum of Paleontology at Southern Methodist University Kansas University, Laura E. Wilson of the Sternberg Museum of Natural History at Fort Hays State University, Darrin Pagnac of the Museum of Geology at South Dakota School of Mines and Technology, Hans-Dieter Sues of the National Museum of Natural History at the Smithsonian, Michael J. Novacek of the American Museum of Natural History, Tim White of the Yale Peabody Museum, Ned Gilmore of The Academy of Natural iv Sciences of Drexel University, Mary Beth Prondzinski of the Alabama Museum of Natural History at The University of Alabama, Lamar Smith at the McWane Science Center, Rodney Scheetz of the Museum of Paleontology at Brigham Young University, Brandon Strilisky of the Royal Tyrrell Museum of Palaeontology, Michael W. Caldwell of the University of Alberta Laboratory for Vertebrate Paleontology, Patrick Leiggi of the Museum of the Rockies at Montana State University, Courtenay and District Museum and Palaeontology Centre, and Richard Hulbert of the Florida Museum of Natural History at the University of Florida. This work was partially funded by grants to J. Lively from the Evolving Earth Foundation, The Geological Society of America, The Texas Academy of Science, and the Jackson School of Geosciences. Additional financial support was provided by C. Bell. v Abstract A new Assemblage of Mosasaurs from the Upper Cretaceous Savoy Pit, Austin Chalk, Northeast Texas Blake Chapman, B.S. The University of Texas at Austin, 2018 Supervisor: Christopher J. Bell The fossil assemblage at the Savoy Pit (Fannin County, Texas) was collected in 1940 by participants in the Works Progress Administration working alongside personnel from the Bureau of Economic Geology at The University of Texas at Austin. The locality is contained within the Ector Chalk (lower Coniacian), an argillaceous limestone, of the Austin Group. Previously published taxa from the site include the bird Ichthyornis and fish such as Belonostomus and Laminospondylus transversus; several types of shark teeth and invertebrates (e.g., crustaceans, asteroids, and bivalves) also have been found. Several mosasaur specimens are present at the site and include isolated elements and associated skeletons that have yet to be described. My collaborator Joshua Lively and I scored the material from the Savoy Pit using published and novel morphological characters and compared our results to about 250 mosasaur specimens from North America and Sweden. We then ran a phylogenetic vi analysis using maximum parsimony to hypothesize the taxonomic composition of the mosasaur assemblage. At least three taxa are identified: a russellosaurine represented by a frontal resembling Russellosaurus coheni, an undetermined basal mosasaurine represented by a partial skull and vertebrae, and Tylosaurus nepaeolicus based on a premaxilla and quadrate. The mosasaurine possesses a unique combination of characters including synapomorphies of both Mosasaurinae (e.g., striated quadrate tympanic rim, dorsally constricted suprastapedial process) and Russellosaurina (e.g., short premaxilla- maxilla suture, low surangular coronoid buttress). In our phylogenetic analysis, we recovered this specimen as a basal mosasaurine that does not align with any published genus, and we recognize it as a new taxon. The russellosaurine synapomorphies possessed by the new taxon may represent the plesiomorphic state of Mosasaurinae; some of those characters are shared with Kourisodon puntledgensis. The presence of a russellosaurine resembling Russellosaurus coheni may extend the range of this species into the Coniacian. The new taxon helps to fill a stratigraphic gap of approximately six million years between the earliest known mosasaurine, Dallasaurus turneri, and ‘Clidastes liodontus.’ Identification of Tylosaurus nepaeolicus at the Savoy Pit extends the lineage into the Early Coniacian and represents one of the earliest occurrences of that genus. vii TABLE OF CONTENTS LIST OF FIGURES .............................................................................................................x INTRODUCTION ...............................................................................................................1 GEOLOGIC CONTEXT AND LOCALITY INFORMATION ..........................................3 MATERIALS AND METHODS .........................................................................................6 SYSTEMATIC PALEONTOLOGY AND DESCRIPTION...............................................7 TMM 31051-84, The new taxon .................................................................................7 Systematic Paleontology ....................................................................................7 Description .........................................................................................................9 Skull ..........................................................................................................9 Maxilla .............................................................................................9 Prefrontal........................................................................................12 Jugal ...............................................................................................13 Squamosal ......................................................................................14 Postorbitofrontal ............................................................................16 Palatine ...........................................................................................17 Pterygoid ........................................................................................18 Quadrate .........................................................................................19 Coronoid ........................................................................................21 Surangular ......................................................................................22 Angular ..........................................................................................25 Post-cranial Skeleton ..............................................................................25 Atlas ...............................................................................................26 viii Post-atlas Vertebrae .......................................................................27 Cervical Vertebrae ................................................................28 Trunk Vertebrae ....................................................................29 Ribs ................................................................................................30 TMM 31051-64, Tylosaurus nepaeolicus .................................................................31 Systematic Paleontology ..................................................................................31 Description .......................................................................................................31 Premaxilla ...............................................................................................31 Quadrate ..................................................................................................33 TMM 31051-59, Yaguarasaurinae cf. Russellosaurus coheni ..................................36 Systematic Paleontology ..................................................................................36 Description .......................................................................................................36 Frontal .....................................................................................................36