Craniodental Variation in the African Macaque, with Reference to Various Asian Species

Abstract

Based on twenty-seven craniodental measurements and ratios derived from them, the relationship between the African macaque (M. sylvanus) and the others in Asia were examined with principal components analyses (PCA) and Euclidean distance analysis based upon prior discriminant function analyses (DFA). Results based on analyses of raw measurements indicate that the variation between species lies in the first axis of PCA; the species are dispersed according to their differences in size. The variation between sexes (sexual dimorphism) lies in the second axis. In the analyses of ratio variables, though these two patterns of separation remain orthogonal, they lie at approximately forty-five degrees to each axis. Variables relating to anterior teeth were found to play an important role in variation analysis, and this may be related to the special food preferences of these monkeys: more frequent usage of the incisor teeth for processing frugivorous diets than in other primates that are mainly folivorous. The results from Euclidean distance analyses indicate that the average distance of species within the Asian group is shorter than that between Asian and African groups regardless of sex and variable type. In addition the variation between African and Asian groups is larger than that within Asian group. Thus, it is reasonable to suggest that the African macaque has a range of measurements and ratios quite distinct from the species found in Asia (though the greatest separations result from the analyses of ratio data). These results therefore support the view that M. sylvanus may be regarded as an independent species group in the genus Macaca as proposed by Delson [1980].