The Morphology and Evolution of the Primate Brachial Plexus
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City University of New York (CUNY) CUNY Academic Works All Dissertations, Theses, and Capstone Projects Dissertations, Theses, and Capstone Projects 2-2019 The Morphology and Evolution of the Primate Brachial Plexus Brian M. Shearer The Graduate Center, City University of New York How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/gc_etds/3070 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] THE MORPHOLOGY AND EVOLUTION OF THE PRIMATE BRACHIAL PLEXUS by BRIAN M SHEARER A dissertation submitted to the Graduate Faculty in Anthropology in partial fulfillment of the requirements for the degree of Doctor of Philosophy, The City University of New York. 2019 © 2018 BRIAN M SHEARER All Rights Reserved ii THE MORPHOLOGY AND EVOLUTION OF THE PRIMATE BRACHIAL PLEXUS By Brian Michael Shearer This manuscript has been read and accepted for the Graduate Faculty in Anthropology in satisfaction of the dissertation requirement for the degree of Doctor in Philosophy. William E.H. Harcourt-Smith ________________________ ___________________________________________ Date Chair of Examining Committee Jeffrey Maskovsky ________________________ ___________________________________________ Date Executive Officer Supervisory Committee Christopher Gilbert Jeffrey Laitman Bernard Wood THE CITY UNIVERSITY OF NEW YORK iii ABSTRACT THE MORPHOLOGY AND EVOLUTION OF THE PRIMATE BRACHIAL PLEXUS By Brian Michael Shearer Advisor: William E. H. Harcourt-Smith Primate evolutionary history is inexorably linked to the evolution of a broad array of locomotor adaptations that have facilitated the clade’s invasion of new niches. Researchers studying the evolution of primates and of their individual locomotor adaptations have traditionally relied on bony morphology – a practical choice given the virtual non-existence of any other type of tissue in the fossil record. However, this focus downplays the potential importance of the many other structures involved in locomotion, such as muscle, cartilage, and neural tissue, which may each be influenced by separate selective forces because of their different roles in facilitating movement. This dissertation is an investigation into the evolution of primate anatomy with an emphasis on the peripheral nervous system, particularly that of the brachial plexus, its intraspecific patterning, and its interactions with muscle in relation to changes in locomotion across clades. As the primate nervous system directs voluntary motor movement to the limbs thereby facilitating locomotion, its morphology may be expected to vary with primate locomotor proclivities and/or limb anatomy. This prediction has not been explicitly tested. The anatomy of the peripheral nervous system was studied using a comparative approach both within 29 genera of primates and among non-primate clades via extensive primary dissection and a broad literature search in order to better understand its evolution. Data on spinal iv nerve level contributions, axon combination and branching morphology, nerve distribution pattern, and neural relationships with other soft tissues are detailed with photographs and standardized descriptions for 79 specimens and 123 individual plexuses. 99 characters generated from observations made during dissection were then analyzed using a parsimony-based phylogenetics approach to evaluate the evolutionary patterns presented by the brachial plexus in primates. The phylogenies generated with the brachial plexus characters did not perfectly mirror commonly accepted primate phylogenies, suggesting that while there is some evolutionary signal contained in the plexus, its morphology may also be influenced by forelimb function. As robust hypotheses exist regarding extant primate phylogenetic relationships and evolutionary histories, character evolution was mapped onto existing molecular trees to better understand how the individual structures that comprise the brachial plexus may evolve independently or in concert at different taxonomic levels. The rate of brachial plexus evolution in clades and leaf taxa was then assessed, demonstrating a marked heterogeneity in the structure both within and among clades. Taxa that have undergone recent locomotor shifts since divergence from their most recent common ancestor, and particularly those who exhibit some amount of suspensory behaviors, exhibit the highest rates of evolution observed here. Notably, several ape genera exhibit brachial plexus evolutionary rates significantly higher than the primate mean, running counter to the notion that hominoids have undergone an evolutionary slowdown relative to other primates. As the true unit of homology in the peripheral nervous system is a subject of ongoing debate, several levels of discussion are necessary to understand the variation in primates and their place in the broader spectrum of tetrapod diversity. Macroanatomy, microanatomy, development, and comparative anatomy are explored in a broad context to evaluate the evolutionary trends of the primate peripheral nervous system and are discussed in detail. v Acknowledgments This dissertation is the culmination of (too many) years of work and would not have been possible without the guidance and support of numerous people. I extend my thanks and sincere gratitude to them here, mostly in chronological order. First and foremost, I would like to thank the members of my dissertation committee, William Harcourt-Smith, Christopher Gilbert, Jeffrey Laitman, and Bernard Wood, for taking the time to read and provide comments. Additional many thanks are due to the funding agencies that supported my research. This project would not have been possible without funding from CUNY and NYCEP, the Wildlife Conservation Society, the CUNY GC DSRG, and the National Science Foundation Graduate Research Fellowship Program. I owe much to the various teachers I have had in the circuitous path through my education thus far. I would not be where I am without their belief in me and encouragement to try for greater heights than I naturally aspire to. At Chaffey Community College, I would like to thank Dan Loomis for teaching me to take my education seriously after I nearly failed out of high school. I would especially like to thank Marc Meyer for mentoring me early in my career. I took Marc’s introduction to Physical Anthropology class when I was deciding what I wanted to major in, and his enthusiasm for the subject reminded me of the passion that I had for paleontology in my youth. Though I no longer specialize in paleontology/paleoanthropology as a primary interest, his course was an excellent reminder of how fascinating the history of the natural world is, and I aspire to replicate his enthusiasm for education in my own teaching. At UC Santa Barbara, I would like to thank my undergraduate advisor, the late Phil Walker, for encouraging my interest in biological anthropology and for inviting me into his lab to participate in research. I will always be grateful to him for his kindness. My deepest thanks vi also to the Walker Lab (Sabrina Sholts, Susan Kuzminsky, Zach Hubbell, Louise Flores, Sebastian Wärmländer) for their support. I would also like to thank Muhammad Spocter for always making time to sit and talk with me after his class and for encouraging my interest in research. Through the New York Consortium in Evolutionary Primatology, I have had the exceptional opportunity to take courses and seek knowledge from many leading scholars in the fields of vertebrate paleontology, morphology, and primate evolution. I am especially grateful to Eric Delson for giving me the opportunity to participate in his consortium and for helping to train me as a researcher. Eric has been extremely helpful and full of insight, all while doing the work of a small administrative team for NYCEP and also managing to be one of the most knowledgeable scientists I have had the pleasure of knowing. Many thanks to my advisor, William E.H. Harcourt-Smith, for providing the support and freedom to explore my work unhindered. Will has always encouraged my research and has unceasingly offered constructive compliments to build the confidence of an unsure graduate student, and for that I will always be grateful. Thank you also to all the NYCEP faculty that have helped train me through formal coursework or informal discussions through the years, and for providing a valuable sense of community and continuity. I would like to thank those that have facilitated my career as an anatomist. I am grateful to Jeffrey Laitman and Joy Reidenberg at the Icahn School of Medicine at Mt. Sinai for helping teach me human anatomy, allowing me to participate in teaching a few generations of medical students, and for providing me with an avenue and skill set with which to build a career. I would further like to thank Anthony Pagano for referring me to my current anatomy job at NYU School of Medicine, where I’ve had the opportunity to cut my teeth on being a real anatomy professor vii for the last few years. Anthony is a rare colleague that understands the importance of lifting others as you climb and has always encouraged my application to bigger and better things. I try to emulate this attribute and encourage others to do so from his example. I owe him many thanks for his kindness when none was necessary. I am grateful to Eugene Harris, Charles Roseman, Rick Madden, and John Polk for facilitating