BODY-SIZE AND LEAPING KINEMATICS IN MALAGASY VERTICAL CLINGERS AND LEAPERS

The locomotor category of vertical clingers and leapers has been domin ated conceptually from the beginning by its small-bodied representativ es, galagos and tarsiers. Over the years, great morphological diversit y has been documented within the group, much of it size-related. Corre sponding behavioral differences remain to be explored, in large part b ecause adequate data on the larger-bodied species were not available. The primary objective of this paper was to characterize the leaping ki nematics of indriid primates, the much neglected large-bodied vertical clingers and leapers. We videotaped leaps of four species of indriids at four different sites in Madagascar: Indri indri, Propithecus diade ma, Propithecus verreauxi, and Avahi laniger. Video images were evalua ted qualitatively and quantitatively after importing them into a compu terized measuring program. Ranges of motion at the hip joint (a combin ation of extension, adduction, and medial rotation) probably exceed th ose of tarsiers and galagos. The foot of indriids usually releases the grip around the support and contributes little or nothing to propulsi on, thus supporting the notion that indriids are ''hip'' leapers. With the forefoot stationary on the support, hindfoot eversion accommodate s the adduction and medial rotation at the hip during acceleration for take off. Indriid leapers can be characterized as ''tarsirotators'' i n contrast to ''tarsifulcrumating'' galagos and tarsiers. Size-related variation in hindlimb kinematics is surprisingly limited within the s ample of indriid leapers, although acceleration time (the duration of the push off) does increase with increasing body size. In addition, fo relimb kinematics reveal a clear size-related pattern; the smallest in driid species leaps with its arms tucked into the chest-like tarsiers and galagos--and the larger-bodied indriid species use their arms duri ng acceleration fbr rake off as well as to initiate body rotation whil e airborne. The small-bodied species rely exclusively on their tails f or this same purpose. Whereas relative tail length decreases with incr easing body size in vertical clingers and leapers, the relative weight of the forelimbs increases and makes their action more effective. (C) 1996 Academic press Limited