HOMINID RADIUS FROM THE MIDDLE PLIOCENE OF LAKE TURKANA, KENYA

A nearly complete left radius, KNM-ER 20419, was recovered from middle Pliocene sediments east of Lake Turkana, Kenya in 1988. Ape-like char acteristics of the fossil include an eccentrically positioned articula r fovea, relatively long radial neck, wide distal metaphysis, and larg e brachioradialis crest. The robustness of the radial neck in proporti on to the radial head, and the semilunar shape of the distal diaphysis , however, clearly distinguish KNM-ER 20419 as hominid. The distal art icular surface possesses a larger area for radius-lunate articulation than for radius and scaphoid, a radiocarpal arrangement that is associ ated with increased wrist adduction among quadrumanous climbers. Since this morphology is also found in hylobatids, Pongo, and other early a ustralopithecines, it is argued to be plesiomorphic for hominoids. Thi s further supports the argument that vertical climbing was an importan t locomotor behavior among both early hominoids and our more immediate prebipedal ancestors. (C) 1993 Wiley-Liss, Inc.