TUPAIID MASTICATORY ANATOMY AND THE APPLICATION OF EXTANT ANALOGS TO RECONSTRUCTING PLESIADAPIFORM JAW ADDUCTORS by Heather L. Kristjanson A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor of Philosophy Baltimore, Maryland June 2019 © 2019 Heather L. Kristjanson All Rights Reserved i v Abstract The plesiadapiforms, archaic stem primates first appearing in the Paleocene 66-63 Ma), are integral to investigating the ecological context for primate origins emphasizing diet as a key factor. Fossil evidence comprised almost entirely of jaw fragments has led to dental analyses dominating most dietary research. Yet despite a tremendous diversity in jaw morphologies, no analyses have focused on quantifying the functional morphology of non-dental parts of the plesiadapiform masticatory apparatus, resulting in a chronic deficit in the study of mandibular morphology and muscles of mastication. Non-dental parts of the masticatory apparatus refine dental-based dietary inferences. This project aims to reconstruct plesiadapiform muscles of mastication using both a tupaiid (treeshrews: Order Scandentia) and strepsirrhine (lemurs, lorises and galagos: Order Primates) model. These two taxa form an extant phylogenetic bracket around plesiadapiforms and will serve as extant analogs during reconstruction of their masticatory muscles. Jaw adductor muscles of tupaiid treeshrews were dissected and their architecture described. Muscle mass and fiber architecture were measured and used to calculate the physiological cross-sectional area (PCSA). Results indicate that tupaiid jaw adductor muscle mass, fiber length, temporalis muscle PCSA, and masseter muscle PCSA scale positively and allometrically to jaw length, while medial pterygoid PCSA scales isometrically. Diffusible Iodine-based Contrast-enhanced ii MicroCT scans of two tupaiid specimens show promise as an alternative method to traditional dissection. PCSA in tupaiids was found to correlate to mandibular muscle insertion area, which was then combined with strepsirrhine data to infer jaw adductor dimensions in a sample of plesiadapiform primates. Reconstructing PCSA in this sample suggests niche partitioning in insectivorous species, dental convergence in frugivorous species and specialization in folivorous species. From the reconstructed PCSA, bite force was estimated along the tooth row for plesiadapiforms and compared to estimates in treeshrews and strepsirrhines. In all cases, bite force increased distally along the tooth row and was greatest in specialized extant folivores and weakest in insectivorous plesiadapiforms. Incorporating data from a variety of sources including dental, mandibular, muscular, and biomechanical metrics provides a more comprehensive picture of the challenges and opportunities proffered by a unique mandibular morphology than can be painted by looking at dental evidence alone. iii Thesis Committee Members Jonathan Perry, Ph.D. (dissertation advisor) Associate Professor, Center for Functional Anatomy and Evolution Johns Hopkins University School of Medicine Siobhán Cooke, Ph.D. Assistant Professor, Center for Functional Anatomy and Evolution Johns Hopkins University School of Medicine Sharlene Santana, Ph.D. Associate Professor, Department of Biology Curator of Mammals, Burke Museum University of Washington Eric Sargis, Ph.D. Professor, Department of Anthropology Curator of Mammals and Vertebrate Paleontology, Yale Peabody Museum of Natural History iv Acknowledgements I thank the American Museum of Natural History and the Staatliches Museum Fur Naturkunde (R. Ziegler) for access to plesiadapiforms in their care. I thank the United States National Museum of Natural History-Smithsonian Institution (D. Lunde), Yale University (G. Aronsen and E. Sargis), and the Max Planck Florida Institute for Neuroscience for access to treeshrew specimens. I thank the Shared Materials Instrumentation Facility at Duke University (D. Boyer, J. Gladman) and the Gignac Lab at Oklahoma State University (P. Gignac) for the use of their facilities. I thank the American Museum of Natural History, American Association of Anatomists, and Society for Vertebrate Paleontology for funding. I thank the members of my committee, Drs. Siobhán Cooke, Sharlene Santana, and Eric Sargis, and Drs. Mary Silcox, Doug Boyer, Paul Gignac, and Chris Kirk for helpful advice. I would also like to thank Arlene Daniel, current and former faculty members Kenneth Rose, David Weishampel, Valerie DeLeon, Chris Ruff, Elizabeth St. Clair, Janine Chalk, and Terry Mitchell, as well as former and current students from the Center for Functional Anatomy and Evolution for their friendship, expertise, and advice over the years. A special thank you to my fieldwork companions Heather Ahrens, Stephanie Canington, Tony Harper, Katrina Jones, Kristen Prufrock, Nicky Squyres, and Kaya Zelazny for the good times and memories. v I would especially like to thank my advisor, Dr. Jonathan Perry, for all of his advice and friendship over the years; it was a lot of fun bonding over our shared pop-culture references and love of all things purple. To my family, who supported me on my journey in the pursuit of knowledge, it was your love, encouragement, and stability that made this possible. In particular, I thank my dad for instilling in me the curiosity to embark upon this path and my mom for the perseverance to see it through. These acknowledgements would not be complete without thanking my friend and fellow student, Rachel, for her confidence in me, her support both as a colleague and friend, and always providing an excuse to drink tea. Whether it was a midnight dissection or midnight wedding flower arranging, you were always there for me. Finally, I thank my husband, Steve, for being an invaluable source of encouragement and support; it seems fitting that it was anatomy that brought us together and I am very grateful to always have you by my side. vi Contents Abstract .......................................................................................................................................................... ii Acknowledgements ................................................................................................................................... v List of Tables ............................................................................................................................................ xiii List of Figures ............................................................................................................................................ xv Chapter 1: Introduction ....................................................................................................................... 19 1.1 Primate origins and the case for diet .............................................................................. 19 1.2 Introduction to plesiadapiforms ....................................................................................... 22 1.2.1 Overview ................................................................................................................................ 22 1.2.2 Previous dietary research on plesiadapiforms ..................................................... 24 1.3 Relationships between primate morphology and diet ............................................ 27 1.3.1 Categorizing diet ................................................................................................................ 28 1.3.2 Muscles of Mastication ..................................................................................................... 30 1.3.2.1 Applications of iodine staining for reconstructive work ......................... 31 1.3.2 The primate mandible...................................................................................................... 32 1.3.2.1 Corpus ............................................................................................................................ 33 1.3.2.2 Symphysis ..................................................................................................................... 35 1.4 Non-dietary factors influencing primate mandibular morphology ................... 36 1.4.1 Food material properties ................................................................................................ 37 1.4.2 Sexual dimorphism and size ......................................................................................... 38 1.5 Reconstructing diet in the primate fossil record ....................................................... 40 vii 1.5.1 Establishing modern analogs for plesiadapiform by constructing an extant phylogenetic bracket ................................................................................................................... 42 1.5.1.1 Plesiadapiform reconstruction ............................................................................ 44 1.5.2 Introduction to tupaiids .................................................................................................. 45 1.5.2.1 Systematics and ecology ......................................................................................... 45 1.5.2.2 Tupaiid suitability as an extant analog ............................................................ 47 1.6 Goals and hypotheses ............................................................................................................. 49 1.6.1 Goals and Hypotheses: Chapter Two ........................................................................