Uniqueness of primate forelimb posture during quadrupedal locomotion

Among the characteristics that are thought to set primate quadrupedal locom otion apart from that of nonprimate mammals are a more protracted limb post ure and larger limb angular excursion. However, kinematic aspects of primat e or nonprimate quadrupedal locomotion have been documented in only a handf ul of species, and more widely for the hind than the forelimb. This study p resents data on arm (humerus) and forelimb posture during walking for 102 s pecies of mammals, including 53 nonhuman primates and 49 nonprimate mammals . The results demonstrate that primates uniformly display a more protracted arm and forelimb at hand touchdown of a step than nearly all other mammals , Although primates tend to end a step with a less retracted humerus, their total humeral or forelimb angular excursion exceeds that of other mammals. It is suggested that these features are components of functional adaptatio ns to locomotion in an arboreal habitat, using clawless, grasping extremiti es. (C) 2000 Wiley-Liss, Inc.