The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

A large 1.5 million-year-old hominin radius from Koobi Fora, Kenya


1Pathology and Anatomical Sciences, University of Missouri, 2Anatomical Sciences, Stony Brook University, 3Cell and Neurobiology, University of Southern California, 4Anthropology, University of Arkansas, 5Anatomy, Ross University

March 27, 2015 2:45, Grand Ballroom E/F/G Add to calendar

A nearly complete hominin radius dated to 1.5 Ma was found in 2008 at Ileret, East Turkana, Kenya (KNM-ER 48100) (Kirera et al 2009 AJPA S48:165). It is unassociated with craniodental remains, and thus its taxonomic attribution has remained uncertain. The OH 80-11 radius from Olduvai Gorge (Domingez-Rodrigo et al 2013 PLoS One) is securely attributed to Australopithecus boisei based on association with teeth, providing a chance to re-evaluate the taxonomic attribution and evolutionary significance of KNM-ER 48100.

KNM-ER 48100 has a head with deep, straight sides, a neck that is relatively round in cross-section, differing from the narrow, beveled radial head margin and compressed neck of OH 80-11, morphologies also seen in the diminutive KNM-ER 1500 specimen often attributed to A. boisei as well. This, and its large size, indicate that KNM-ER 48100 is most likely attributable to Homo erectus.

The most notable feature of KNM-ER 48100 is its impressive size, with a head diameter overlapping that of female gorillas. Its length is estimated at about 300 mm. This is longer than the radius of almost any human in the comparative sample, substantially larger than that of the KNM-ER 15000 Homo erectus radius, and comparable to the length of the Omo L40-19 ulna. Published stature regression formulas yield stature estimates of over 188 cm. The KNM-ER 48100 radius indicates the presence of very large Homo erectus individuals in East Africa around 1.5 Ma, also suggested by a metacarpal from West Turkana and other penecontemporaneous Koobi Fora fossils.

Research supported by the Wenner Gren Foundation, LSB Leakey Foundation and Turkana Basin Institute