Age and Sex Differences in the Locomotor Skeleton of Australopithecus

Abstract

Skeletons of juvenile hominoids recovered from the past can provide much information about locomotor patterns, including when and in what order adult morphology appears in the skeleton, how locomotor repertoire during growth affects the skeleton, and how ontogeny relates to the evolution of new locomotor behaviors. The goal of this review is to assess whether the pattern of growth in the Australopithecus skeleton as can now be perceived provides insight into previously developed locomotor hypotheses derived from the adult skeleton. Hypotheses about the developmental underpinnings of skeletal differences between Australopithecus, apes, and humans are also explored. Based on current evidence reviewed here, Australopithecus afarensis, Australopithecus africanus, and Australopithecus garhi were habitually bipedal, but incorporated arboreal grasping postures into their behavior, whether locomotor or positional. Finally, the proposal that hind limb growth in recent Homo species is heterochronic extension of the Australopithecus pattern is probably oversimplified and is confounded because the phylogenetic relationship among A. afarensis, A. africanus, A. garhi, and Homo is not understood.