2004, pp 85-100

In What Manner Did They Walk on Two Legs?

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Abstract

When Mary Leakey and collaborators discovered the Laetoli footprints (Tanzania) in 1978-1979, they exhumed the direct evidence that a species of primate was able to walk bipedally 3.75 Mya. This evidence of an early bipedalism has also been corroborated by contemporary fossil bones, especially those of Australopithecus afarensis. But in what manner did these early hominids walk on two legs? This point remains the subject of discussion. Our purpose is to add pedal architectural data to the debate concerning the locomotor modalities in early hominids, especially in Australopithecus afarensis.

Australopithecine tarsal and metatarsal bones from Hadar are compared to a sample of Proconsul from Rusinga and Songhor (Kenya), other early hominids from Omo (Ethiopia), Olduvai (Tanzania), Koobi Fora, Ileret and Baringo (Kenya) and Kromdraai (South Africa), Neandertals and extant species (43 Homo, 36 Pan et 38 Gorilla). The architecture of the foot is assessed by examining proximodistal relationships, and by measuring angulations taken on the dislocated tarsometatarsal skeleton.

The architectural analysis of the Australopithecus afarensis hallucal tarsometatarsal complex suggests that the hallux was slightly abducted in neutral position and of a different pattern than in African apes. Furthermore, the Australopithecus afarensis foot is flat in neutral position, resembling the extant African apes condition. Although foot remains are too incomplete to propose a complete architectural pattern, architectural data strongly corroborate the uniqueness of the Australopithecus afarensis foot pattern, in which a slightly abducted hallux and no plantar vault in neutral position are associated. Accordingly, if Australopithecus afarensis were the makers of the Laetoli trails, as the Laetoli fossil bones suggest, then their bipedal locomotion would have necessitate a very strong muscular action. These features corroborate the idea of a very distinctive pattern of bipedality in Australopithecus afarensis.