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Comparative Forefoot Kinematics and Bone Architecture in Extant Hominids Open Access

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Habitual bipedalism is a key hominin adaptation. Traditionally, functional assessments of the external structure of the bones of the lower limb have been at the center of debates over whether early hominins walked with a modern human-like gait and whether climbing was an important part of their locomotor behavior. However, these approaches have proved to be inconclusive, especially regarding the functional implications of forefoot morphology among early hominins. This obstacle is further compounded by the lack of data on forefoot function and structure in living great apes and modern humans. This dissertation investigates the relationship between characteristics of in vivo function and bone structure in the great ape and modern human forefoot in order to provide a more solid basis for interpreting early hominin locomotion. The primary goal is to define differences in forefoot function in modern humans and great apes by quantifying specific aspects of the first and second metatarsophalangeal joints (MTPJ) that are related to range of motion and loading in dorsiflexion during terrestrial gait. This thesis comprises an Introduction, the reports of three individual research projects (Chapters One to Three), and a Conclusion. Chapter One represents the first study to quantitatively measure in vivo MTPJ dorsal excursion during gait in humans and the great ape taxon, Pan paniscus, and this study serves as a partial basis for the next two projects of this thesis. Chapter Two demonstrates that though dorsal canting of the first and second proximal phalanx can distinguish taxa based on forefoot function, this trait may not distinguish more subtle functional differences such as those that exist between the digits or the sexes. In Chapter Three, predictions are made about the micro-anatomy of the first and second metatarsals based on measures of joint motion and loading during terrestrial gait. The results reveal that absolute differences in the preferential alignment of trabeculae distinguish habitual, metatarsi-fulcrimating humans from great apes which lack a metatarsi-fulcrimating foot and also have a more diverse locomotor regime. The outcome of this study encourages the investigation of micro-architecture of fossil metatarsals for the purpose of predicting forefoot loading patterns and gait.

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