Krapina and other Neanderthal clavicles: A peculiar morphology?

The clavicle is the less studied element of the shoulder girdle, even if it is a very important bone for human evolution because it permits all movements outside the parasagittal plan. In this work, clavicle curvatures are studied by projecting them on a cranial and a dorsal plan, which are perpendicular: In cranial view, there is no difference within the genus Homo, and Neanderthal clavicles are not more S-shaped than modern human ones. On the contrary, the dorsal view allows to distinguish two human groups. The first includes Homo habilis, Homo ergaster and Neanderthal. Their clavicles are characterized by two curvatures, an inferior one at the acromial end and a superior one at the sternal end. The second group includes only modern human, whose clavicles are characterized by the presence of the inferior curvature only. The shape of the clavicle in dorsal view is associated to the position of the scapula in regard to the thorax. Two curvatures are associated to a high scapula, and, on the contrary, a unique curvature is associated to a scapula in a low position in regard to the thorax. Moreover the two curvatures of the modern human clavicle in dorsal view constitute an apomorphic character in regard to the other human species.