RELATIVE GROWTH AND SHAPE OF THE LOCOMOTOR SKELETON IN LESSER APES

This study addresses the question of whether the siamang can be accurately described as an overgrown or peramorphic version of the gibbon in terms of its locomotor skeleton. Lesser ape relative growth and skeletal design are also placed in a broader comparative context of all extant hominoids. With respect to thelar-gibbon and the siamang, the answer to this question is clearly negative;lar-gibbon ontogenetic trajectories do a poor job of predicting siamang body shape. Although there are some similarities in postnatal relative growth between the two, transpositional differences are most common. Siamang andlar-gibbon never overlap in overall shape regardless of size/age. This finding may be related to the highly derived position of thelar-gibbons relative to the evolutionary affinities of other lesser apes. The possibility cannot be ruled out that other gibbons such asHylobates hoolock, H. concolor and possiblyH. klossi are ontogenetically scaled-down (truncated) versions of the siamang. When all hominoids are considered together, patterns of relative growth in the postcranium appear to be much more closely related to locomotor function than to phylogenetic affinities. © 1992 Academic Press Limited.