Recently recovered Kenyapithecus mandible and its implications for great ape and human origins.

We report here a Kenyapithecus africanus juvenile mandible recovered from middle Miocene (ca. 14-16 million years) deposits of Maboko Island (Lake Victoria), Kenya. Symphyseal and dental attributes of the mandible distinguish K. africanus, a species widely regarded as the earliest known member of the great ape and human clade, from other Miocene large-bodied hominoids. The Maboko Island mandible exhibits a markedly proclined symphyseal axis, massive inferior transverse torus, mesiodistally narrow, high-crowned, and strongly procumbent lateral incisor, and molars with cingula restricted to the median buccal cleft. Although the presence of some of these conditions in Kenyapithecus was suggested earlier, the fragmentary and ill-preserved nature of previously known specimens led certain authorities to doubt their validity. Our assessment of mandibular and dental morphology indicates that K. africanus diverged after Proconsul and Griphopithecus but prior to the last common ancestor of Sivapithecus, extant great apes, and humans. The robustly constructed mandibular symphysis and anterior dentition suggest that incisal biting played as important a role as thick molar enamel in the dietary adaptations of K. africanus.