Morphometric disparities in skull size and shape of capuchin monkeys (Cebidae: Cebus) in northern South America and Central America.

Abstract

Taxonomic classifications of the gracile capuchin monkeys, Cebus, have traditionally been based on cranio-dental and pelage characters. Advances in molecular biology have provided information on the evolutionary history of the genus but the taxonomy and distribution limits of taxa in the northern Andes are still under debate. To assess morphometric disparities and compare the results with hypotheses based on genetic evidence for Cebus taxonomy, we used 2D geometric morphometrics on 206 adult specimens (127 males, 77 females, 2 unsexed) belonging to 12 taxa by assigning Type I landmarks in the frontal (11), lateral (18) and ventral (16) views of the skull, and 14 in the mandible. Our results show that skull shape is more variable than centroid size and that morphometric disparities exist across and within all three geographic groups (Central America, Andes, and Amazon). Although skull shape in Cebus tends to vary slightly, our results suggest differences among some taxa and highlight the utility of studying shape in addition to methods that have focused on size. Some results concur with the taxonomic classifications based on molecular evidence but it is important to note that Cebus species are wide-ranging with high inter- and intraspecific phenotypic variability in diverse ecological conditions. This makes it difficult to provide species diagnoses based just on morphometric or morphological characters and suggests the need to integrate different sources of evidence to resolve uncertainties about the taxonomy and the evolutionary relationships in the genus.