The lower limb of Ardipithecus ramidus

Abstract

The Early Pliocene hominin Ardipithecus ramidus recovered from the Middle Awash, Ethiopia study area had a mixed locomotor anatomy that retained a capacity for arboreal clambering and adaptations to terrestrial bipedality. The first functional analyses of the Ar. ramidus (Lovejoy et al., 2009a-b, Science, v. 326) lower limb identified an ape-like talo-crural orientation and the foot’s elongated and rigid midtarsus, dorsiflexion at the lateral metatarsophalangeal joints, and an abducent great toe that lacked evidence of hallucal fulcrumation. Here, we review the lower limb anatomy of the ca. 4.5 Ma Ardipithecus ramidus partial skeleton from Gona, Ethiopia and how it broadens our understanding of the locomotion in this species. This includes anatomical regions not previously known for Ar. ramidus including the proximal femur and distal fibula. The Gona fossil has many similarities with the Middle Awash sample including overall size, but exhibits notable functional differences – such as a more vertical talocrural orientation and regular recruitment of the hallux during bipedal propulsion in the Gona individual – that document notable variation in the locomotion adaptations of this early hominin despite occupation of a similar landscape.