1Anthropology, Modesto College, 2Anthropology, University of California, Santa Cruz
Friday All day, Plaza Level
Infant and juvenile chimpanzees face locomotor challenges as they develop their motor skills. Shifts in body proportions and tissue components underlie the observed transformation during locomotor development. We present anatomical data on 7 female Pan paniscus of known age (2 infants, 2 juveniles, 3 adults) based on whole body dissections that quantify body segments, muscle mass and bone tissues. Our results show that the limbs of infants under a year of age weigh 27.7% of total body mass, with significant mass to the distal segments, the hands and feet. They have only 22.0% total body muscle and of this, a remarkable 82.7% is in their limbs. In juveniles, limbs are nearly double, at 41.0% of body mass. Muscle increases to 43.5% of total body mass, with a similar proportion of muscle to the limbs at 83.8%. However, in contrast to infants, juveniles have heavy proximal segments (arms and thighs) with a decrease to hands and feet. Locomotor observations in captive Pan paniscus groups parallel these anatomical findings, demonstrating that each life stage has a distinguishing signal of behaviors (Zihlman, unpub; Grote et al, 2011, AJPA Suppl). Infants emphasize suspensory behavior and juveniles are more agile in the trees, whereas adults are less suspensory. These behaviors are consistent with field observations on Pan troglodytes where juveniles most often climb and jump, activities emphasizing different muscle groups than in infants or adults.