Meeting Abstract

P3.70  Saturday, Jan. 5  The effects of digitigrade cheiridial postures on speed and gait in infant baboons. ZEININGER, A.**; SHAPIRO, L.J.; RAICHLEN, D.A.; University of Texas at Austin; University of Texas at Austin; University of Arizona, Tucson azeininger@mail.utexas.edu

While digitigrade foot and hand (cheiridial) postures are common among mammals, they are rare within primates. It is currently unclear whether primates� lack of digitgrady is adaptive, or is simply a consequence of other biomechanical characteristics. For example, in mammals, the proposed function of digitigrady is to increase effective limb length (ELL) thereby increasing stride length and velocity. However, an increased ELL may raise the potential for limb interference during the distinctive diagonal sequence diagonal couplets primate walking gait, in which a hindlimb touches down before the ipsilateral forelimb lifts off. This study tests two hypotheses related to primate cheiridial postures, 1) primate digitigrady increases velocity and 2) primate digitigrady is preferred during lateral couplets rather than diagonal couplets walking gaits. An ontogentic study allowed for the latter comparison, as infant baboons, Papio cynocephalus, use both diagonal and lateral couplet gaits. Longitudinal kinematic data were collected on four infant baboons as they aged from 2-9 months, and again at 2-3 years. Cheiridial postures, dimensionless velocity, and gait number were calculated for 514 symmetrical walking strides. Contrary to predictions, digitigrady was not correlated with dimensionless velocity. Digitigrady in the foot and hand occurred during both lateral and diagonal couplets gaits, suggesting digitigrade postures are neither influenced by, nor preclude any particular gait. Thus, primates� general lack of digitigrade cheiridial postures does not appear to provide an adaptive advantage for either velocity or gait. It is possible that differences in distal limb morphology may account for the lack of digitigrady in primates.