The climbing ability and locomotor efficiency of australopithecine species, particularly Australopithecus afarensis, remain controversial despite decades of research. The hip joint is an informative area of anatomy in this regard: determination of relative hip mobility contributes significantly to reconstructing climbing ability, because a mobile hip joint is useful in navigating discontinuous arboreal substrates. This study quantified the distribution of subchondral bone on the femoral head and/or acetabulum in A. afarensis, Australopithecus africanus and Australopithecus robustus and used it to infer range of movement and loading environment at the hip. Animation of three-dimensional computer models was used to estimate maximum range of abduction For one complete A. afarensis hip (AL 288-1). AU of the hominid species had a preponderance of articular surface on the anterior aspect of the femoral head, a morphology associated with moderate hip mobility, and a more adducted femur. Although there was variation in the degree of development of this trait, all of the hominids differed from Pan which has a femoral articular surface which is distributed uniformly about the fovea capitis. The cranial acetabular articular surface of early hominids was expanded, with the exception of AL 288-1, which did not possess the same degree of cranial acetabular development. Greater cranial expansion in the acetabulum of A. robustus as compared with A. afarensis may be indicative of a greater habituation to the cranially directed forces generated by bipedal gait. However, despite evidence for variation in the pattern of bipedal hip use among australopithecines, three-dimensional simulations of posture and maximum abduction indicate that AL 288-1 had an adducted hip and a limited range of abduction, similar to modern humans and less than chimpanzees and some monkeys. Limited hip abduction probably reflects a diminished ability to climb and cross substrate gaps using the hindlimb, alternatively, it may signify that climbing kinematics in A. afarensis differed from that of non-human anthropoids. (C) 1996 Academic Press Limited
