The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


A new ~1.5 Ma hominin distal humerus from Ileret, Kenya

MICHAEL R. LAGUE1, BRIAN G. RICHMOND2,3, DAVID J. GREEN4, DAVID R. BRAUN2, JOHN W.K. HARRIS5, EMMA MBUA6 and HABIBA CHIRCHIR7.

1School of Natural Sciences & Mathematics, The Richard Stockton College of New Jersey, 2Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 3Human Origins Program, National Museum of Natural History, Smithsonian Institution, 4Anatomy Department, Midwestern University, 5Anthropology Department, Rutgers University, 6Department of Palaeontology, National Museums of Kenya, 7Hominid Paleobiology Doctoral Program, Department of Anthropology, The George Washington University

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Although variation among Plio-Pleistocene hominin distal humeri tends to be subtle, previous studies have identified unique morphology shared by several 2-1.5 Ma specimens from Koobi Fora. Here, we analyze a new 1.51-1.53 Ma hominin distal humerus (KNM-ER 47000) from the Koobi Fora Fm, Kenya (FwJj 14E, Area 1A). KNM-ER 47000 is an associated right upper limb that includes portions of the scapula, humerus, ulna, and hand. The entire distal half of the humerus is preserved apart from the capitulum and part of the trochlea. Using linear dimensions and landmark data, we compare KNM-ER 47000 to extant hominoids and a wide range of Plio-Pleistocene hominins.

Transverse diaphyseal sections of KNM-ER 47000 yield extremely high values for total cortical area (CA) and percent cortical area (%CA) that exceed those reported for a wide range of fossil Homo species, suggesting extreme strength in axial loading. In other aspects, KNM-ER 47000 is most comparable to the 2-1.5 Ma Turkana humeri, particularly to KNM-ER 739. Similarities include: deeply grooved trochlear central sulcus, highly projecting medial epicondyle, relatively shallow olecranon fossa, relatively wide medial and lateral pillars, salient lateral supracondylar ridge (indicative of a powerful m. brachioradialis), and unusual posterior surface convexity of the distal shaft. Given their morphological resemblance and shared spatiotemporal context, it is likely that KNM-ER 739 and KNM-ER 47000 are conspecific. KNM-ER 47000 thereby expands the sample size of the enigmatic set of Koobi Fora humeri and links this unusual elbow morphology to that of other skeletal regions.

This research was supported by grants from the National Science Foundation (BCS-9712585, BCS-0647557, BCS-0924476, BCS-1128170, DGE-0801634), a grant from the Wenner-Gren Foundation (to J.M. Plavcan & C.V. Ward), and the University Facilitating Fund (UFF) at George Washington University.

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