Covariation between wrist bone morphology and maximal range of motion during ulnar deviation and supination in extant nonhuman primate taxa.

This study investigates the maximal range of motion (ROM) during wrist deviation and forearm rotation for five different primate genera and the possible correlation with the shape of the distal ulna, triquetrum and hamate. A two-block phylogenetic partial least square analysis was performed to test this covariation in a phylogenetic context, using shape coordinates and a matrix of maximal ROM data as input data. The results show that gibbons have the highest ROM for both ulnar deviation and supination, whereas Macaca exhibited the lowest ROM for supination, and Pan had the lowest ROM for ulnar deviation. These results can be attributed to differences in locomotor behaviour, as gibbons need a large wrist mobility in all directions for their highly arboreal lifestyle, whereas Macaca and Pan need a stable wrist during terrestrial locomotion. However, we found no correlation between distal ulna/triquetrum/hamate shape and maximal ROM during ulnar deviation and supination in the different primate taxa. A larger dataset, in combination with behavioural and biomechanical studies, is needed to establish form-function relationships of the primate hand, which will aid the functional interpretation of primate fossil remains.