Pliocene hominid postcranial fossils from the Middle Awash, Ethiopia

This dissertation presents the description and analysis of the hominid postcranial fossils recovered from the 2.5 million year-old deposits of the Middle Awash area of Ethiopia. These fossils, labeled here as the "Hata postcranial fossils" after the Hata beds of the Middle Awash, are the MAT-VP-1/1 distal humerus, the BOU-VP-11/1 proximal ulna, the BOU-VP-35/1 humerus shaft, and the BOU-VP-12/1 partial skeleton (humerus shaft, proximal radius, ulna shaft, proximal hand phalanx, femur shaft, fibula shaft, and mandible fragment). The Hata postcranial fossils significantly expand the sample of available postcranial material from the crucial 2--3 million year time period in East Africa. As such, they provide insight into several aspects of Pliocene hominid evolution.; The descriptive component of this study provides extensive written descriptions of the Hata postcranial fossils, supplemented by measurements, photographs, and radiographs. The morphology of the Hata postcrania is compared with that of over 220 hominid fossils from Plio-Pleistocene Africa, as well as with samples of modern hominoids. The precise and accurate documentation of morphology requires greater methodological attention than is commonly practiced. Failure to adequately describe hominid fossils has compromised several previous interpretations of human evolution.; The theoretical component of this study examines the methodological basis for the inference of taxonomy and for the inference of function and phylogeny. For taxonomy, it is shown here that the taxonomic assignment of isolated hominid postcrania has previously been done in a largely ad hoc fashion, often without any apparent consideration of the fundamental methodological principles involved. When such principles are considered, it is clear that the potential for making such identifications is more limited than currently appreciated. As such, a "morphogroup" approach is proposed here. This would group isolated postcrania together based solely on morphology, using the variation seen in a reference sample of Homo sapiens as a benchmark for the degree of variation allowable within a single morphogroup. Among other advantages, this would result in more objective groupings based on more explicit criteria whose significance would be unambiguous. Importantly, such morphogroups, and the attendant explicit criteria for membership, would allow the recovery of new specimens to serve as tests of explicit a priori hypotheses. (Abstract shortened by UMI.)...