Functional capabilities of modern and fossil hominid hands: Three‐dimensional analysis of trapezia

Abstract

Three-dimensional (3D) trapezium models from Homo sapiens, Gorilla gorilla, Pan troglodytes, Australopithecus afarensis (A.L.333-80), and Homo habilis (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 compared. 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 indicate 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 humans highlighted and quantified by our research suggest limitations in the functional capabilities of the O.H.7 trapezium, 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 considerations are that the O.H.7 trapezium is not representative of other trapezia from its species (i.e., N ϭ 1), or that it represents another primate or hominid species. Am J Phys

Estimating thumb–index finger precision grip and manipulation potential in extant and fossil primates

“…Furthermore, Au. afarensis Mc1 and trapezium articular morphology suggests that range of motion at this joint may have been more similar to Pan [50,67] and thus it is possible that Au. afarensis may have had a smaller thumb-index manipulation WS than later rsif.royalsocietypublishing.org J. R. Soc.…”

Evidence in hand: recent discoveries and the early evolution of human manual manipulation

“…scaphoid-trapezoid) and carpometacarpal (e.g. capitate-Mc2) articulations, and the development of a styloid process on the base of the Mc3, together help to better distribute across the wrist and palm the large loads incurred by the thumb during tool-related behaviours [31,[58][59][60][61].…”

Investigating interrelationships between Lower Palaeolithic stone tool effectiveness and tool user biometric variation: implications for technological and evolutionary changes

“…Relationships with specific biometric traits would, however, have been both task and tool dependent. This is of potential importance to our understanding of early human tool use behaviours, particularly if the first (flaked) stone-tool use is considered to be undertaken by hominins displaying restricted precision manipulative force potential (e.g., Tocheri et al, 2003Tocheri et al, , 2008Marzke, 2013;Rolian and Gordon, 2013;Kivell, 2015). Indeed, the reduced importance of manipulative strength potential during the cutting of relatively small material masses suggests that hominins displaying such traits may have been more favourably equipped for the processing of smaller material masses (e.g., scavenging meat scraps off carcasses) relative to larger, more resistant materials (e.g., whole carcasses).…”