Single-limb force data for two lemur species while vertically clinging

Objectives Vertical clinging and climbing have been integral to hypotheses about primate origins, yet little is known about how an animal with nails instead of claws resists gravity while on large, vertical, and cylindrical substrates. Here we test models of how force is applied to maintain posture, predicting (1) the shear component force (F_s) at the hands will be higher than the feet; (2) the normal component force (F_n) at the feet will be relatively high compared to the hands; (3) the component force resisting gravity (F_g) at the feet will be relatively high compared to the hands; (4) species with a high frequency of vertical clinging postures will have low F_g at the hands due to relatively short forelimbs. Materials and Methods Using a novel instrumented support, single-limb force data were collected during clinging postures for the hands and feet and compared across limbs and species for Propithecus verreauxi (N=2), a habitual vertical clinger and leaper, and Varecia variegata (N=3), a habitual above-branch arboreal quadruped. Results For both species, hand F_s were significantly higher than at the feet and F_n and F_g at the feet were significantly higher than at the hands. Between species, P. verreauxi has relatively low F_g at the hands and F_n at the feet than V. vareigata. Discussion These results support previous models and show that hindlimb loading dominance, characteristic of primate locomotion, is found during clinging behaviors and may allow the forelimbs to be used for foraging while clinging. These findings provide insight into selective pressures on force distribution in primates and primate locomotor evolution. Am J Phys Anthropol 158:463-474, 2015.