Functional capabilities of modern and fossil hominid hands: three-dimensional analysis of trapezia.

Three-dimensional (3D) trapezium mod- els from Homo sapiens, Gorilla gorilla, Pan troglodytes, Australopithecus afarensis (A.L.333-80), and Homo habi- lis (O.H.7-NNQ) were acquired through laser digitizing. Least-square planes were generated for each articular surface, and the angles between the planes were com- pared. Each extant species displays an overall pattern that distinguishes it from the others. The observed angles in G. gorilla and P. troglodytes are more similar to one other than either is to H. sapiens. Our results, obtained from using new 3D modeling and analytical tools, raise interesting questions about the functional capabilities of the fossil trapezia. Multivariate statistical analyses indi- cate that A.L.333-80 is morphologically more similar to that of modern humans, whereas the O.H.7 trapezium is more similar to that of the gorilla. Significant differences between A.L.333-80 and the extant species occur, but some similarities to humans suggest the ability to form the distinctively human forceful pad-to-side and three-jaw chuck grips. Some key morphological differences from hu- mans highlighted and quantified by our research suggest limitations in the functional capabilities of the O.H.7 tra- pezium, particularly in those that facilitate pronation at the base of the second metacarpal. If the O.H.7 trapezium represents part of the hand responsible for manufacturing and using the stone tools found at Olduvai, our results suggest that the hand manipulated the stones in a way for which we have no modern analog. Alternative consider- ations are that the O.H.7 trapezium is not representative of other trapezia from its species (i.e., N 1), or that it represents another primate or hominid species. Am J Phys Anthropol 122:101-112, 2003. © 2003 Wiley-Liss, Inc. Major anatomical differences between the hands of humans (Homo sapiens), chimpanzees (Pan trog- lodytes), and gorillas (Gorilla gorilla) relate to dif- ferences in hand functions and use. While modern humans use the hand entirely for object manipula- tion, the hands of the African apes are used for manipulation and also for locomotion. The human hand displays numerous specialized features, some of which are shared with the African apes, while others are distinct and significantly enhance human grasping capabilities (Lewis, 1989). In this study, attention is focused on the trape- zium, the most lateral bone in the distal carpal row. This bone lies at the base of the thumb and articu- lates with the scaphoid, trapezoid, and first and second metacarpals. In comparative analyses of pri- mates, the trapezium shows great variation in shape (Napier and Davis, 1959). The irregular shape of the trapezium, in combination with the large amount of inter- and intraspecies variability, has made quan- titative analyses of its morphology difficult. The main differences reported in the literature among extant hominids in trapezium morphology relate to the first and second metacarpal joints (Kuc- zynski, 1972; Lewis, 1989; Marzke, 1992; Susman and Creel, 1979; Trinkaus, 1989). The trapezium- trapezoid and trapezium-scaphoid joints have gen- erally not received the same attention as the trape-