Abstract:
Cercopithecoids represent an essential component of the Plio-Pleistocene faunal assemblage. However, despite the abundance of the
cercopithecoid fossil remains in African Plio-Pleistocene deposits, the chronological and geographic contexts from which the modern
baboons (i.e. Papio hamadryas ssp.) emerged are still debated. The recently discovered Papio (hamadryas) angusticeps specimen (U.W.
88-886) from the Australopithecus sediba-bearing site of Malapa, Gauteng, South Africa, may represent the first modern baboon occurrence in the fossil record. Given the implication of U.W. 88-886 for the understanding of the papionin evolutionary history and the
potential of internal craniodental structures for exploring evolutionary trends in fossil monkey taxa, we use X-ray microtomography to
investigate the inner craniodental anatomy of this critical specimen. Our goal is to provide additional evidence to examine the origins of
modern baboons. In particular, we explore (i) the tissue proportions and the dentine topographic distribution in dental roots and (ii) the
endocranial organization. Consistent with the previous description and metrical analyses of its external cranial morphology, U.W.
88-886 shares internal craniodental anatomy similarities with Plio-Pleistocene and modern Papio, supporting its attribution to Papio
(hamadryas) angusticeps. Interestingly, average dentine thickness and distribution in U.W. 88-886 fit more closely to the extinct Papio
condition, while the sulcal pattern and relative dentine thickness are more like the extant Papio states. Besides providing additional
evidence for characterizing South African fossil papionins, our study sheds new light on the polarity of inner craniodental features in
the papionin lineage.
