title: Long bone cross-sectional properties reflect changes in locomotor behavior in developing chimpanzees.
abstract: OBJECTIVE
  Recent studies indicate that the locomotor behavior of wild chimpanzees changes during development. Before transitioning to quadrupedal knuckle-walking in adulthood, young chimpanzees engage in a significant amount of upper limb loading suspensory behavior. We investigated whether these dramatic changes in locomotion influence the strength and shape of chimpanzee long bones.
  
  
  METHODS
  We examined changes in chimpanzee arboreal locomotion over the course of development using behavioral data collected on wild chimpanzees. We measured the midshaft geometric properties of femora and humeri of wild-caught individuals housed in museum collections using micro computed tomographic scans.
  
  
  RESULTS
  Chimpanzees spent less time moving arboreally as they aged. Femoral/humeral strength ratios also increased with age, as predicted by the changing loading environment during development. Additional analyses revealed that femoral shape, but not humeral shape, varied across chimpanzee age classes. Adult femora were more elliptical compared with those of infants. This change in adult femora is consistent with the observation that adult chimpanzees spend most of their time moving terrestrially and consequently experience a less variable loading environment than do infants.
  
  
  CONCLUSIONS
  Taken together, these findings contribute to our understanding of how ontogenetic changes in function affect form. As similar changes may have characterized the behavioral and skeletal ontogeny of extinct hominoids including hominins, these findings furnish a potential means to make inferences about the behavior of fossil taxa based on the structural properties of their bones.
authors.affiliation: Evolutionary Studies Institute, Palaeosciences Centre, University of the Witwatersrand, Johannesburg, South Africa.|University of Maryland University College Europe, PE28 4DE, England.
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Sarringhaus
authors.affiliation: Department of Anthropology, University of Michigan, Ann Arbor, MI, 48109.
authors.forename: Laura M
authors.initials: LM
authors.lastname: MacLatchy
authors.affiliation: Department of Anthropology, University of Michigan, Ann Arbor, MI, 48109.
authors.forename: John C
authors.initials: JC
authors.lastname: Mitani
mesh_terms: D000367:Age Factors; D019412:Anatomy, Cross-Sectional; D000818:Animals; D005269:Femur / Q000033:anatomy & histology* / Q000502:physiology*; D006811:Humerus / Q000033:anatomy & histology / Q000502:physiology; D008124:Locomotion / Q000502:physiology*; D002679:Pan troglodytes / Q000033:anatomy & histology* / Q000502:physiology*
keywords: Pan; femur; humerus; ontogeny; shape; strength