THE RELATION BETWEEN HAND MORPHOLOGY AND QUADRUPEDALISM IN PRIMATES

Primate hands can be classified into two broad categories on the basis of ray proportions and other features, Ectaxonic hands are characteri zed by a longer fourth ray and are found in most strepsirhines. Most h aplorhines possess mesaxonic hands which are characterized by a longer third ray. Preuschoft et al, ([1993] in H. Preuschoft and D.J. Chiver s (eds,): Hands of Primates. Berlin: Springer-Verlag, pp. 21 - 30) pro posed a biomechanical model which predicts that, during quadrupedalism , a mesaxonic hand should be held in a more neutral position with resp ect to the forearm, whereas an ectaxonic hand should be more ulnarly d eviated, The relation between hand positioning and the mesaxony/ectaxo ny categorization is investigated for 27 primate taxa. Videotapes were recorded for each species walking quadrupedally on arboreal supports, Several species were also videotaped during ground quadrupedalism. Th e degree of deviation of the hand relative to the substrate and the gr ips utilized were quantified for 18 species from the videotapes, Prima tes with mesaxonic hands use deviated hand positions and grips, especi ally when walking quadrupedally on small poles. Several species with e ctaxonic hands use neutral hand positions and grips when walking quadr upedally on similar supports. Also, several primates, with either ecta xonic or mesaxonic hands, display a combination of deviated hand posit ions and grips when on arboreal substrates and neutral hand positionin g when on the ground, The statistical results indicate that hand posit ioning during quadrupedal walking Is more variable than expected based on the mesaxony/ectaxony classification, Furthermore, radiographic da ta suggest that primates evolved at least two different mechanisms of hand ulnar deviation. (C) 1998 Wiley-Liss, Inc.