A nearly complete foot from Dikika, Ethiopia and its implications for the ontogeny and function of <i>Australopithecus afarensis</i>.

Abstract

The functional and evolutionary implications of primitive retentions in early hominin feet have been under debate since the discovery of <i>Australopithecus afarensis</i>. Ontogeny can provide insight into adult phenotypes, but juvenile early hominin foot fossils are exceptionally rare. We analyze a nearly complete, 3.32-million-year-old juvenile foot of <i>A. afarensis</i> (DIK-1-1f). We show that juvenile <i>A. afarensis</i> individuals already had many of the bipedal features found in adult specimens. However, they also had medial cuneiform traits associated with increased hallucal mobility and a more gracile calcaneal tuber, which is unexpected on the basis of known adult morphologies. Selection for traits functionally associated with juvenile pedal grasping may provide a new perspective on their retention in the more terrestrial adult <i>A. afarensis</i>.