Earliest complete hominin fifth metatarsal : implications for the evolution of the lateral column of the foot

StW 114/115, from Sterkfontein, South Africa, is the earliest complete hominin fifth metatarsal. Comparisons of StW 114/115 to modern humans, extant apes, and partial hominin metatarsals AL 333-13, AL 333-78, SKX 33380, OH 8, and KNM-ER 803f reveal a similar morphology in all six fossils consistent with habitual bipedality. Although StW 114/115 possesses some primitive characters, the proximal articular morphology and internal torsion of the head are very human-like, suggesting a stable lateral column and the likely presence of lateral longitudinal and transverse tarsal arches. We conclude that, at least in the lateral component of the foot of the StW 114/115 individual, the biomechanical pattern is very similar to that of modern humans. This, however, may not have been the case in the medial column of the foot, as a mosaic pattern of hominin foot evolution and function has been suggested. The results of this study may support the hypothesis of an increased calcaneo-cuboid stability having been an early evolutionary event in the history of terrestrial bipedalism.