In the analysis of evolutionary changes in body structure, an underlying presumption is that a potential advantage of a modification is reduction in the amount of energy required to perform a particular task. For researchers in physical anthropology, energetic arguments regarding the costs of locomotion have only been considered in the study of the evolution of human bipedalism. The importance of energetics in the origins of the more generalized form of primate locomotion, quadrupedalism, has all but been ignored. This study will examine the role of energetics in the evolution of primate quadrupedalism. Since many regard quadrupedalism to have been an aspect of the locomotion favored by the earliest primates, and since it has been demonstrated that the form of quadrupedal locomotion displayed by primates differs both kinematically and kinetically from that of non-primate mammals, understanding the role energetics plays in primate quadrupedalism should provide new insights into the selection pressures acting during primate origins. Primates have muscles distributed closer to their hands and feet than other mammals due to their grasping extremities. This limb shape should theoretically cause muscles and tendons to use more energy during locomotion, thereby increasing locomotor energetic costs. Surprisingly, researchers have found that regardless of limb shape, animals of the same body size have the same energetic costs. Though there has been much debate in the literature, these results are as yet unexplained. This study proposes that animals with a greater proportion of muscle mass near their extremities will alter their gait in order to maintain similar energetic costs compared to animals of similar body mass. The relationship between limb shape and the mechanics and energetics of locomotion will be examined in a longitudinal sample of infant baboons (Papio cynocephalus). Because infants' limb shapes change with age, this study will be able explore how gait changes may offset the energetic costs of distally distributed limb mass allowing animals to do similar amounts of muscular work during locomotion. Results of this study will provide a new view of how competing selection pressures, such as grasping extremities and reduced locomotor costs, may have led to some unique aspects of primate gait. In addition to contributing to our understanding of primate locomotor evolution, this project will serve the community by taking an active role in undergraduate education. Two undergraduate assistants will be trained in techniques such as morphometric and kinematic data collection and analysis. Additionally, the CO-P.I. will be developing a kinematics laboratory based on this study for the P.I.'s undergraduate primate anatomy course. This lab will include computer-based instruction in locomotor research methodology and data analysis. By having undergraduate participation in this project, as well as integrating this project with the classroom, the proposed study promotes a greater understanding of the newest techniques used to answer questions about the evolution of primates. Finally, this study will foster inter-disciplinary relationships between colleges at The University of Texas at Austin.
