[The anatomical and functional origin of the first bipedalism]

This communication is the synthesis of ten years of researchers of comparative anatomy done by the author or under his control on fossil Hominids, three million years old, found by his expeditions in Eastern Ethiopia. It brings, for the first time, the odd picture of a skeleton adapted to arboricolism and bipedalism together. The rachis has already the curves of an erect being but with at least a thoraco-lumbar cyphosis a bit more elongated than in our own rachis; the pelvis is wide and shallow like the pelvis of a biped but with many particular features like the width of the iliac wings, a great biacetabular diameter, the small size of the coxo-femoral joints; the femur is short with a special long neck, a very oblique diaphysis like in Man and an intercondylar fossa, deep and wide like in chimp; the tibia is also short, its spines very tight in such a way that the knee shows a great laxity. The foot is short and flat, with an abducted hallux and long curved toes; the scapular, elbow and wrist joints show, at the opposite of the knee joint, a great solidity, but both characteristics of the hind and fore-limb joints are not in contradiction: they are, as in chimpanzees again, functionally adapted to climbing and moving in the trees where are needed firm grip of the hands as well as mobility of the knee and of the foot. It seems that the early Australopithecine' bipedalism was original, different from ours and quite instable: short steps were necessary to maintain equilibrium as well as a strong rotation of the pelvis around the vertebral axis (50 to 60 degrees on each side). This analysis is then demonstrating a real evolution of bipedalism which was not at all, at once, the bipedalism of Homo sapiens, as it has been claimed. This paper is also showing that bipedalism anatomic organization is taking place from the pelvis to the foot and not the other way round. At last, as we have found, also in Ethiopia, stone-tools more than three million years old in association with Australopithecus, it seems that the very first made tools were the invention of prehumans who did not have yet the hands completely free from locomotion.