A morphometric study of limb proportions in leaping prosimians

Study of individual limb proportions - most notably, for instance, of the intermembral index - distinguishes from most other primates those various prosimians capable of leaping. The present investigation analyzes 24 measures of limb proportions from 161 specimens representing 12 species of prosimians, using the multivariate statistical method of multiple discriminant analysis. The results indicate that there are three major gradients: 1) indriids, 2) cheirogaleines, and 3) galagines plus Tarsius, radiating from a fourth centrally located group of species, Lemur, Lepilemur, and Hapalemur. It is likely that the morphometric relationships displayed here can be associated with behavioral (locomotor) parallels among these various forms. Though leaping is a most important adaptation among prosimians, it seems clear that it has evolved separately a number of times, and it seems at least likely that the biomechanical nature of the adaptation differs in different groups. The results, therefore, present certain new hypotheses about prosmian locomotion that can only be tested with further field and laboratory studies. This study also emphasizes the fact that anatomical adaptation is complex. Though the analysis of each anatomical region separately provides a similar qualitative picture of the variation among genera, it is only in the analysis of all measures taken together that the complete pattern described above appears. Though no new variables have been added in that analysis, new information is obviously contained within the results. Since this information stems from the interactions of the variables, it must be due to associations between these anatomical areas.