Hand use and metacarpal robusticity in Catarrhini

Abstract

Recent studies,Rightmire (1972) andDay andScheuer (1973), have investigated the affinities of early hominid metacarpals from Swartkrans. Because of its extensive use in the analysis of metatarsals, the index of robusticity has also been applied to some fossil metacarpals. From the metatarsal analyses, it has been shown that within a group a variety of robusticity patterns exist with the average pattern occuring approximately 50 per cent of the time. This, coupled with the fact that it has also been shown that within the order Primates the pattern is not necessarily diagnostic of any locomotor category, has led us to investigate the usefulness of such an index in assessing primate metacarpals.

In this study, metacarpal robusticity patterns and the Total Robusticity Quotient are established for seven cercopithecoid genera and the results correlated with hand use. It is found that although patterns of robusticity are not diagnostic of locomotor categories, the TRQ relates well to hand use: low TRQ's are found in primates which use their hands to walk on a flat substrate, while high TRQ's are diagnostic of arm swinging animals. Primates with reduced thumb use in a precision grip and little manipulative use of the hand have higher TRQ's than those with a good precision grip. The model derived from our sample of Cercopithecoidea is tested with a hominoid sample of four genera and found to be similarly applicable.