Lucy's lower limbs: long enough for Lucy to be fully bipedal?

Abstract

The recent attempt to show that the Hadar australopithecine female ‘Lucy’ (AL 288-1) had hindlimbs too short to allow a modern pattern of striding bipedal gait¹ has important implications for understanding the origin of bipedalism, if not for the more general problem of hominid origins. Combined with previous claims that Lucy had a forelimb unusually long in proportion² and ape-like in morphology³, the additional contention of a relatively short hindlimb would suggest a very different pattern of gait from the norm of today because the effectiveness of the pendulum action of the lower limb during stride is a function of the amount of mass in the limb⁴, and because a short hindlimb would necessitate a short stride length¹. Yet, these contentions seem contradicted by the analyses of Lucy's pelvis (and the innomminates of other australopithecines)^4,5 that indicate a similar pattern of muscle use and imply a lack of significant gait differences. Are Lucy's legs too short to allow an effective stride, or is there a different solution to this contra diction? I propose here that there is.