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Resumo

The discovery ofPanin the Middle Pleistocene deposits of the Kapthurin Formation of the Tugen Hills (McBrearty and Jablonski: Nature 437 (2005) 105–108) inspires new interest in the search for other chimpanzee fossils in the East African Rift Valley. Craniodental evidence of an eastward excursion of chimpanzee populations in the Plio‐Pleistocene goes undetected in other hominin sites, but one enigmatic postcranial fossil, the Olduvai Hominid 36 ulna, has many chimp‐like features. Analyses by Aiello et al. (Aiello et al.: Am J Phys Anthropol 109 (1999) 89–110) reveal that it is similar to extantPanin some respects, but it also has unique traits not seen in other hominoid species. They refer it toParanthropus boisei. In this study, we reassess the affinities of OH 36 using a different data set that includes more recently discovered hominin fossils including those attributed toParanthropus. Despite its superficial resemblance to modernPan, our results agree with those of Aiello et al. (Aiello et al.: Am J Phys Anthropol 109 (1999) 89–110) that OH 36 is distinctly different from modern chimpanzees. By default, it is reasonable to assign this specimen toP. boisei, but it is not at all similar to other ulnae referred to this genus. Ulnae attributed toParanthropusfrom South Africa, Kenya, and Ethiopia are morphologically more heterogeneous than those within species of large‐bodied Hominoidea. Although there are many apparent shared derived traits justifying a monophyleticParanthropusclade, most if not all of these traits are related to a single functional complex (hypermastication) that may have evolved in parallel and thereby constituting a paraphyletic group of species. Am J Phys Anthropol, 2007. © 2007 Wiley‐Liss, Inc.

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