LAMMERS, A.R.: The effects of incline and branch diameter on the kinematics of arboreal locomotion

It is likely that the common ancestor of Mammalia was small, quadrupedal, and scansorial. To better understand the kinematics of arboreal locomotion in a primitive, scansorial mammal, I examined the effects of branch angle and diameter on limb posture, speed, gait and duty factor in the South American possum Monodelphis domestica. Animals were filmed (250 f/s) walking up artificial branches of different angles and diameters. Kinematic data were then measured from the videos. Data indicate that branch angle (up to 45 degrees) has little effect on limb kinematics for these small mammals. These results may explain why Taylor et al. (1972, Science 178:1096) found that low substrate incline had less metabolic effect on running mice compared to chimpanzees; furthermore, Vilensky et al. (1994, J. Hum. Evol. 28:375) found kinematic differences with substrate incline in squirrel monkeys. Therefore, as mammals become larger over evolutionary time, the effects of gravity and mass appear to cause changes in arboreal kinematics.