Morphological correlates of substrate use in didelphid marsupials: implications for primate origins

The ability of some mammals to forage on vines or terminal branches depends upon their grasping extremities. This study tests the functional link betw een use of small-diameter supports and grasping abilities by comparing hand and foot proportions in didelphid marsupials. Metapodials and phalanges we re measured for the hands and feet of six didelphid taxa characterized by d ifferent patterns of substrate use. Comparisons of hand and foot proportion s demonstrate that Marmosa and Caluromys, didelphids that rely on vines or terminal branches, possess more prehensile extremities than Monodelphis, Di delphis, and Philander, which travel and feed mainly on the ground. Moreove r, the proportions of the hand and foot of Marmosa and Caluromys are more s imilar to those of cheirogaelid primates than those of other didelphids. Th ese morphological data corroborate the suggestion that the use of branches of small diameter was an important factor in the development of prehensile hands and feet in early primates.