Positional and Morphological Development of Wild Chimpanzees, Pan Troglodytes.

This project explores the relationship between form and function through an integrated study of chimpanzee osteological and behavioral development. Unlike most mammals, chimpanzees go through several locomotor transitions during development, making them excellent candidates to investigate how changes in behavior influence changes in morphology. The aim of this study was to identify anatomical features that are induced by loading during suspensory and knuckle-walking behavior that can then be used to reconstruct fossil behavior. This task was accomplished by examining the positional behavior of wild chimpanzees at Ngogo, Kibale National Park, Uganda, in tandem with the morphological analysis of wild-caught skeletal specimens from museums. Chimpanzee positional behavior was found to proceed developmentally through a number of distinct stages, each characterized by its own loading regime. Specifically, chimpanzee infants principally used their upper limbs in locomotion and posture with the loading environment changing to hindlimb dominated knuckle-walking as individuals aged. The most dramatic transitions in behavior occurred during juvenility and adolescence. Infants displayed more diversity in their forms of positional behavior than did members of any other age-sex class. Metacarpal morphology and long bone midshaft cross-sectional properties were examined to see if they tracked behavioral changes. The third metacarpal is a weight-bearing conduit in knuckle-walking. Two changes in this bone provide added stability during knuckle-walking: distal ridge formation and increased shaft curvature. Increased curvature and ridge formation occurred at juvenility and adolescence in chimpanzees, the same developmental periods where shifts in behavior occurred. Changes in femoral and humeral bone strength and shape over the course of development were also tracked, since both features are likely influenced by locomotor behavior. A general trend of increased femoral relative to humeral strength was found, in concert with the advent of hindlimb-dominated locomotion. The femur also became more elliptical with age while no such shape change occurred in the humerus. It is proposed that, since the timing of the development of these features occurs together with behavioral transitions, the behaviors themselves are influencing bone development. These features can now be used with confidence to reconstruct locomotion in fossil species.PhDAnthropologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98074/1/rens_1.pd