Toward the locomotion of two contemporaneous Adapis species

Abstract

The morphological differences between the limb bones of two Adapis species from two localities in Southern France are analyzed for their functional significance. The study focuses on the distal humerus, proximal femur, astragalus and calcaneum. The Escamps species Adapis aff. betillei shows more extreme flexion at the elbow, lateral mobility at the hip, and more rotation at the calcaneocuboid joint than in the other species. The species from Rosières 2 A. cf. parisiensis shows increased emphasis on parasagittal movements, restrictions of lateral mobility in the hindlimb, enhanced capacity for rapid flexion and powerful extension of the thigh, and powerful rapid foot extension. The Rosières species probably engaged in more frequent branch walking and running, and the Escamps species probably included more climbing in its locomotor repertoire. In the general Adapis genus morphology, the large tuber calcanei, short astragalus, and the presence of a calcaneal "pressure facet" are similarities shared with living cercopithecids. Along with other characters, these suggest that horizontal running was possibly an important means of locomotion in the Adapis and adapine morphotypes, and may even indicate a degree of terrestraility. Contrary to the most common view, the euprimate morphotype was probably not a specialized leaper.