The functional morphology of the primate shoulder as revealed by comparative anatomical, osteometric and discriminant function techniques

A background to assessments of the ecological adaptations of fossil primates is the relationship of the detailed shape of bones in living forms to their known locomotor patterns, and this has been here attempted for the shoulder. Within the locomotion of the primates the function of the shoulder varies according to the extent to which the trunk is suspended by the arms. An analysis of the differences in the shoulder muscles has shown that much of their quantitative variation is mechanically in phase with these functional differences. A series of features of the shoulder bones, chosen because of their association with the mechanically meaningful features of the musculature, have been found to vary (a) in association with the known contrasts in locomotion and (b) in such a way as to render more efficient mechanically the associated muscular structure. Investigation of bony dimensions “residual” to such a study has shown that they are not highly correlated with primate locomotion but are, in contrast, associated with the commonly accepted taxonomic grouping of the order. The combination by discriminant functions of such sets of “locomotor” and “residual” dimensions reveals unsuspected information for living primates and might well allow more precise definition of the functional and taxonomic status of a fossil. The experimental testing of functional inferences from morphology is a necessary part of such studies, and preliminary reports of experimental stress analysis utilising the photoelastic technique confirm and reinforce their validity.