CORTICAL BONE DISTRIBUTION IN THE FEMORAL-NECK OF HOMINOIDS - IMPLICATIONS FOR THE LOCOMOTION OF AUSTRALOPITHECUS-AFARENSIS

Contiguous high resolution computed Demography images were obtained at a 1.5 mm slice thickness perpendicular to the neck axis from the base of the femoral head to the trochanteric line in a sample of 10 specim ens each of Homo sapiens, Pan troglodytes, and Gorilla gorilla, plus f ive specimens of Pan paniscus. Superior, inferior, anterior, and poste rior cortical thicknesses were automatically measured directly from th ese digital images. Throughout the femoral neck H. sapiens displays th in superior cortical bone and inferior cortical bone that thickens dis tally. In marked contrast, cortical bone in the femoral neck of Africa n apes is more uniformly thick in all directions, with even greater th ickening of the superior cortical bone distally. Because the femoral n eck acts as a cantilevered beam, its anchorage at the neck-shaft junct ion is subjected to the highest bending stresses and is the most biome chanically relevant region to inspect for response to strain. As evinc ed by A.L. 128-1, A.L. 211-1 and MAK-VP-1/1, Australopithecus afarensi s is indistinguishable from H. sapiens, but markedly different from Af rican apes in cortical bone distribution at the femoral neck-shaft jun ction. Cortical distribution in the African ape indicates much greater variation in loading conditions consistent with their more varied loc omotor repertoire. Cortical distribution in hominids is a response to the more stereotypic loading pattern imposed by habitual bipedality, a nd thin superior cortex in A. afarensis confirms the absence of a sign ificant arboreal component in its locomotor repertoire. (C) 1997 Wiley -Liss, Inc.