Trabecular Bone Morphology and Locomotion in Extant Primates and Fossil Hominins

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This project develops a new approach to reconstructing gait and other aspects of behavior in fossils, and expands our understanding of the relationship between anatomical joint structure and function. The two main debates concerning gait in early fossil humans are over (1) the nature of their bipedal, upright walking gait (whether it was modern human-like or a gait with bent hips and knees), and (2) whether or not climbing and moving in trees remained an important part of the ecological behavior of these early species. Over the last decade, many researchers have acknowledged that these debates have reached an impasse, and that a resolution will require new kinds of data regarding fossil evidence of functional activity during life. Advances in imaging and analysis now permit researchers to capture and quantify the three dimensional (3D) structure of trabecular bone - the bone tissue most sensitive to loading history - in fossils and provide the kinds of evidence of joint loading during life needed to move beyond this impasse. The primary goals of this research are to examine the relationships between 3D trabecular structure and metacarpal (hand) and femoral (hip and knee) joint functions in higher primates. More specifically, this research aims to (1) establish the relationships between trabecular bone architecture and habitual joint posture in modern higher primates that differ in their manner of gait (e.g., involving more flexed or extended joints), (2) examine the relationships between trabecular bone characteristics of the joint and cross-sectional strength of the bone shaft. Establishing the nature of the relationship between habitual joint function and the structure of trabecular bone within the joint will then allow researchers to more accurately reconstruct gait in fossil species. This project will apply its findings to one hypothesis about functional behavior in fossils, namely whether Neanderthals used their hands in ways that differed from those of modern humans. This research entails the most comprehensive analysis to date of higher primate trabecular bone structure. This research also has several important broader impacts. The scans obtained in this research will be made publicly available to foster additional research. At least one doctoral student will gain training from this project. It will help to develop a new approach to behavioral reconstruction that will be of interest to paleontologists outside of anthropology. Finally, this proposal will foster interdisciplinary research between a geologist and two physical anthropologists, and international collaboration between researchers in the U.S. and Japan.