A Large Homo erectus Talus from Koobi For a, Kenya (KNM-ER 5428), and Pleistocene Hominin Talar Evolution

Abstract

KNM-ER 5428 is a very large probable Homo erectus talus from ~1.6 Ma deposits at Koobi Fora, Kenya. Though preliminarily described in 1985, here we provide a more detailed anatomical description and comparison of KNM-ER 5428 with fossil hominin, modern human, and extant ape tali. KNM-ER 5428 is exceptionally large, with body mass estimates >90kg—over 4 standard deviations larger than average H. erectus from the Early Pleistocene of Eastern Africa. Though human-like in most respects, KNM-ER 5428 and other Plio-Pleistocene hominins main-tained a mediolaterally wide but dorsoplantarly short talar body that contrasts with the relatively tall modern human talus. H. sapiens tali therefore have increased in volume through vertical expansion during the last 100 ka. Reasons for this dorsoplantar expansion of the talar body remain unclear.