Meeting Abstract
44.4 Wednesday, Jan. 5 The biomechanics of arboreal stability in cebid monkeys. YOUNG, J. W.; NEOUCOM jwyoung@neoucom.edu
Broad consensus states that unique aspects of primate postcranial morphology (e.g., clawless grasping extremities) and locomotor behavior (e.g., the use of distinctive gait patterns) are part of a suite of adaptations that facilitate movement in a fine-branch arboreal niche, where the maintenance of stability is paramount. Here, I test this hypothesis by combining data on gait kinematics with quantitative measures of locomotor stability in two cebid primates, squirrel monkeys (Saimiri boliviensis) and tamarins (Saguinus oedipus). Callitrichine primates, such as tamarins, are unique among extant anthropoids in possessing claws on all non-hallucial digits, presumably limiting grasping ability in a fine-branch setting. Six squirrel monkeys (N strides: 275) and three tamarins (N strides: 77) were filmed as they traversed a 3.2cm pole into which two force transducers were incorporated. Force and kinematic data were combined to calculate the angular momentum of the center of mass about the pole (i.e., Lsup), a quantitative measure of stability. Results showed that average Lsup magnitudes were inversely proportional to the time spent on contralateral fore- and hind limb pairs, supporting predictions that primates’ habitual use of “diagonal” footfall patterns enhances arboreal stability. Although squirrel monkeys and tamarins were equally adept at maintaining balance on the 3.2cm pole, tamarins preferentially used gaits that maximized contralateral limb support durations, improving stability despite potentially limited grasping abilities. The results of this study broadly support the hypothesis that grasping extremities and distinctive gait patterns represent adaptations to facilitate stability when primates are moving on narrow branches. Research supported NEOUCOM and the Leakey Foundation.
