A Biomechanical Investigation into the Absence of Leaping in the Locomotor Repertoire of the Slender Loris (Loris tardigradus)

Abstract

Unlike all other primates, members of the subfamily Lorisinae are never seen to leap. To investigate the anatomical specializations that are behind the absence of leaping in their locomotor repertoire, a predictive mechanical model of leaping was developed using the lesser bushbaby, Galago moholi, as a size-matched leaping prosimian comparison. This enabled the required limb movements for a leaping slender loris to be calculated, and hence the torque and power requirements at each of the hindlimb joints. From this information, the maximum feasible leap was calculated for the slender loris morphotype; and it was found that this alone would prevent the animal from leaping a greater distance than it could walk over, so that the reduction in fitness due to an apparent loss of leaping from the behavioural repertoire can be considered to be very small.