title: Complete fourth metatarsal and arches in the foot of Australopithecus afarensis.
abstract: The transition to full-time terrestrial bipedality is a hallmark of human evolution. A key correlate of human bipedalism is the development of longitudinal and transverse arches of the foot that provide a rigid propulsive lever and critical shock absorption during striding bipedal gait. Evidence for arches in the earliest well-known Australopithecus species, A. afarensis, has long been debated. A complete fourth metatarsal of A. afarensis was recently discovered at Hadar, Ethiopia. It exhibits torsion of the head relative to the base, a direct correlate of a transverse arch in humans. The orientation of the proximal and distal ends of the bone reflects a longitudinal arch. Further, the deep, flat base and tarsal facets imply that its midfoot had no ape-like midtarsal break. These features show that the A. afarensis foot was functionally like that of modern humans and support the hypothesis that this species was a committed terrestrial biped.
authors.affiliation: Department of Pathology and Anatomical Sciences, M263 Medical Sciences Building, University of Missouri, Columbia, MO 65212, USA. wardcv@missouri.edu
authors.forename: Carol V
authors.initials: CV
authors.lastname: Ward
authors.forename: William H
authors.initials: WH
authors.lastname: Kimbel
authors.forename: Donald C
authors.initials: DC
authors.lastname: Johanson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D005002:Ethiopia; D005528:Foot / Q000033:anatomy & histology* / Q000502:physiology; D005580:Fossils; D005684:Gait; D015186:Hominidae / Q000033:anatomy & histology*; D006801:Humans; D008124:Locomotion; D008682:Metatarsal Bones / Q000033:anatomy & histology*; D013640:Tarsal Joints / Q000033:anatomy & histology / Q000502:physiology