Australopithecus sediba from Malapa, South Africa

Abstract

First discovered in August of 2008, the site of Malapa, South Africa revealed two relatively complete partial skeletons that we assigned to a new species, Australopithecus sediba. Additional individuals have since been detected, and await excavation at the site. It appears that these hominins were washed into the cave through a deep vertical shaft, likely in a single depositional event resulting from a large storm inflow. Burial and cementation were rapid, occasioning the exceptional preservation of these skeletons. Uranium-lead and paleomagnetic dating combine to precisely constrain the age of the site to 1.977 ± 0.0015 Ma. Cranial and postcranial remains of A. sediba demonstrate numerous australopith-like features that denote a hominin at an australopith adaptive grade, prompting its inclusion in the genus Australopithecus. However, A. sediba also displays a series of characters that align it more closely with Homo than any other australopith species. We consider the evidence supporting the appearance of Homo prior to 1.977 Ma to be inconclusive, therefore we hypothesize that A. sediba from Malapa could be ancestral to Homo. Alternatively, if the existence of Homo prior to 1.977 Ma can be confirmed, this would not preclude a population of A. sediba that predated Malapa from occupying this role. Therefore we hypothesize that A. sediba indeed represents the ancestor of the genus Homo.