Hominin fossils from Kromdraai and Drimolen inform <i>Paranthropus robustus</i> craniofacial ontogeny.

Abstract

Ontogeny provides critical information about the evolutionary history of early hominin adult morphology. We describe fossils from the southern African sites of Kromdraai and Drimolen that provide insights into early craniofacial development in the Pleistocene robust australopith <i>Paranthropus robustus</i>. We show that while most distinctive robust craniofacial features appear relatively late in ontogeny, a few do not. We also find unexpected evidence of independence in the growth of the premaxillary and maxillary regions. Differential growth results in a proportionately larger and more postero-inferiorly rotated cerebral fossa in <i>P. robustus</i> infants than in the developmentally older <i>Australopithecus africanus</i> juvenile from Taung. The accumulated evidence from these fossils suggests that the iconic SK 54 juvenile calvaria is more likely early <i>Homo</i> than <i>Paranthropus.</i> It is also consistent with the hypothesis that <i>P. robustus</i> is more closely related to <i>Homo</i> than to <i>A. africanus</i>.