Metatarsals

Full-time bipedalism requires a sturdy base for shock absorption and forward motion. The development of specially adapted foot arches has enabled modern humans to be successful bipeds. Recent research has revealed that australopithecines had a similar metatarsal arrangement allowing them to also walk upright.  According to Ward, Kimbel, and Johanson, the evolution of permanent transverse and logitudinal foot arches is unequivocal evidence for bipedalism (2011). Until very recently the fossil record has been too incomplete to allow for a comprehensive study of australopithecine pedal bone physiology. In 2000, excavations in Hadar, Ethiopia revealed an intact fourth metatarsal bone. There are pronounced differences between humans and apes in the fourth metatarsal, and it is this bone that offers the most definitive pedal evidence for bipedalism (Ward, Kimbel, & Johanson, 2011). The fourth metatarsal is slightly rotated in australopithecines, as it is in modern humans, to produce a walking surface that is strongly supported by a pedal arch (Ward, Kimbel, & Johanson, 2011). The degree of rotation found in the recent Hadar specimen provides further evidence for a transverse pedal arch.  The longitudinal arching of the pedal bones, particularly the fourth metatarsal, and the tarsometatarsal joints provide foot stability and lateral rigidity, two pedal characteristics that are not present in apes (Ward, Kimbel, & Johanson, 2011). It seems likely that Australopithecines had developed human-like pedal structures that were permanently in place for full-time bipedal locomotion.