CONICET | Buscador de Institutos y Recursos Humanos

Cranial sexual dimorphism is a characteristic commonly evidenced in Primates. However, the mode in which such differences are reached is poorly known in several species of New World monkeys. In this study, we analyzed the allometric growth of 17 linear variables in the skull of two species of New World monkeys, namely, Cebus apella (50 males, 50 females) and Allouata caraya (27 males, 37 females), belonging to two different families, Cebidae and Atelidae, We used three different approaches: univariate (t-test), bivariate (RMA), and multivariate analyses. For the univariate analysis, we proposed age classes based on tooth eruption and wear. Sexual dimorphism between adults in both species arises through extension of the growth trajectory common to both sexes, and through differences in the rate of growth between males and females, indicating that some cranial measurements are not adjusted to ontogenetic scaling. The expectation that the ontogenetic bases of adult dimorphism vary interspecifically is well supported by the present study. C. apella and A. caraya do not share all allometric trends, and the latest species exhibit a transitional strong dimorphism in subadult stages. Although the presence of bimaturism is very common and highly variable among Primates, the dimorphism is also illustrated by numerous cases in which sex differences in rate of growth occur in most of cranial measurements. These results also suggest that there are potentially very marked differences in the ways that neotropical primates attain adult dimorphism.