NORTHWESTERN UNIVERSITY Morphology of the Hindlimb and Correlations to Locomotor Tendencies in Platyrrhines A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS For the degree DOCTOR OF PHILOSOPHY Field of Driskill Graduate Program in the Life Sciences By Michael Scott Mutehart EVANSTON, ILLINOIS September 2018 2 © Copyright by Michael S. Mutehart 2018 All Rights Reserved 3 Abstract Platyrrhines are an enigmatic and intriguing radiation of New World monkeys that currently inhabit the western hemisphere from Argentina to Mexico. Platyrrhini, a taxonomic parvorder within Primates, is their formal taxonomic designation, as they represent the sister group of the Catarrhini or all of the Old World monkeys and apes. These platyrrhine monkeys are diverse in terms of body size, their ecology, and in their movement patterns. From the smallest anthropoid, Cebuella pygmaea, to the large bodied Brachyteles, platyrrhines inhabit the Amazon rain forest basins, the Atlantic coastal forests of Brazil, and the Central American rain forests. Their locomotor abilities range from arboreal quadrupedalism, to climbing and leaping preferences, to forelimb suspensory behaviors. It is the intention of this study to identify anatomical correlates in the hind limb of these New World monkeys relative to their respective movement patterns. Forty-five species of platyrrhines, representing hundreds of individual specimens, were measured and analyzed to determine if morphology of the hip and pelvis, thigh and proximal femur, and/or knee, could be mapped to their known locomotor behavior. The features examined were chosen on the basis of previous studies conducted on platyrrhine primates or other mammals where hindlimb anatomy had been correlated with positional behavior. Behavioral studies that included quantified and qualitative descriptions were examined. Statistical analyses, including regressions and the analysis of variance were employed to determine if correlations between morphology and movements could be specified. 4 Results from this study indicated that morphological adaptations for leaping are more generalized within platyrrhines than in “prosimian” primates. Dorsal ischial projection was found to be a good indicator of (vertical) leaping in pithecids for example, but not among callitrichids nor among platyrrhines as a whole. There are elements of the platyrrhine postcranium that are linked to climbing including a wide pubis, robust intertrochanteric crest and posteriorly placed lesser trochanter. The New World brachiators have increased their joint excursion range at the hip and evidence two features of the knee, a wide patellar groove and gracile medial condylar lip, that help to distinguish them morphologically from the other groups. Overall, this study demonstrates that the hindlimb morphology of the platyrrhines examined here are more generalized in nature and they are not as strongly indicative of the distinctive movement patterns as has been noted previously in “prosimian” primates or for the brachiating apes. Callitrichids, in particular (excluding Cebuella, the pygmy marmoset), although exhibiting differences in frequency and style of locomotor behaviors, actually do not vary very much morphologically in their hindlimb anatomy. While several monkeys, including Cebuella and Ateles species, stand out as being genuinely unique morphologically and do not fit the expectations of the movement hypotheses developed in this study. In the end, this project has identified features of the hindlimb that are indicative of certain locomotor behaviors, while also illustrating platyrrhine locomotor behavior in terms of a rather generalized hindlimb morphology. 5 Acknowledgements This work would not have been possible without the help and support of many individuals and institutions. I am grateful to the Driskill Graduate Program in the Life Sciences for their support throughout my graduate career. I am especially indebted to the program committee members and Dr. Steve Anderson for their unending guidance and patience throughout my time in the program. Special thanks to the Field Museum in Chicago, the National Museum (Smithsonian) and the American Museum in New York for giving me access to their collections. I would like to extend specific thanks to Dr. Martha Tappen for allowing me access to the Neil Tappen primate collection housed at the Department of Anthropology at the Univeristy of Minnesota. This journey began many years ago when I was an undergraduate at Northern Illinois University. I would like to extend my gratitude to my undergraduate professors who made me believe that a career in primate studies was possible. Thanks to Dr. Leila Porter for showing me that primate behavior and ecological studies should be on the same level as morphology and for fostering in me a desire to learn as much as possible about the platyrrhines. I would not have survived graduate school without the help and inspiration of my colleague and lab partner, Dr. Denitsa Savakova. Thank you for all the fun times, interesting conversations and unique experiences that made the graduate school years bearable. I am grateful for our friendship. I would not have been able to make this study work without the help, insight, perspective, and guidance of my dissertation committee. Dr. Dan Gebo provided years of inspiration and I am 6 forever grateful for your guidance during my undergraduate years. Dr. Larry Cochard, thank you for your unique perspective to research and teaching. Dr. Brian Shea, thanks for all the advice and help from day one. I will forever remember our conversations, which, I believe have covered every topic imaginable. I am forever indebted to my thesis advisor, Dr. Marian Dagosto. Marian, you have provided me with years of friendship, immeasurable support, mentorship, and shared with me your vast knowledge and intellect. Thank you for all of your support and for guiding me through this turbulent process. Your example of a quiet and mature demeanor and years of scholarship has not gone unnoticed. My family has been by my side throughout this process and I am grateful for all of their support. My parents have been helpful in so many ways and I will always cherish their love. My wife and daughter were brought into this through no fault of their own, and have always been completely devoted to helping me through to the the finish line. Thank you. Lastly, I would like to thank the many dozens of researchers who have come before me who spent their time and money studying primates in the wild, obtaining behavioral and body weight data. That research and data is invaluable and this study would be impossible without it. 7 Dedication To my daughter, Eva Bear When you were born, I had a ‘legitimate’ reason to buy everything monkey! To my wife, Brandy Even in the difficult times, you made me believe in myself! You both have my unending and complete love. 8 Table of Contents Abstract ......................................................................................................................................................... 3 Acknowledgements ....................................................................................................................................... 5 Dedication ..................................................................................................................................................... 7 Table of Contents .......................................................................................................................................... 8 List of Tables and Figures ............................................................................................................................ 13 Chapter 1 ..................................................................................................................................................... 22 Introduction ................................................................................................................................................ 22 Objectives................................................................................................................................................ 24 Significance ............................................................................................................................................. 24 Positional and Locomotor Behavior ........................................................................................................ 26 Previous work...................................................................................................................................... 26 Definitions of Locomotor Behavior ..................................................................................................... 30 Morphological Studies ........................................................................................................................ 34 The Hip ............................................................................................................................................ 34 The Knee ......................................................................................................................................... 36 Studies Incorporating Morphology and Behavior ........................................................................... 36 Hypotheses ............................................................................................................................................. 39 Leaping: