Postnatal growth allometry of the extremities in Cebus albifrons and Cebus apella: A longitudinal and comparative study

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Abstract
C. albifrons and C. apella, partially sympatric capuchin monkeys from South America, differ substantially in adult body mass and bodily proportions. C. apella possesses a robust, stocky build in contrast to the more gracile, relatively longer limbed body design of C. albifrons. Average birth weights and adult body lengths of these 2 congeners are remarkably similar and do not serve to distinguish them. This study examines longitudinal growth rates and patterns of ontogenetic scaling in the extremities (humerus radius, hand, femur, tibia, foot) in order to document the nature and magnitude of skeletal changes associated with increasing age and body mass. The growth rates of the 6 skeletal components of the limbs differ only slightly and somewhat inconsistently between the 2 spp. Body mass increases at a consistently faster rate in C. apella. Relative to body mass the extremities of C. albifrons scale much faster than those of C. apella. This implies that at any given postnatal body mass, C. albifrons is longer limbed than C. apella. C. dpella is heavier than C. albifrons at any given limb length or age. Such differences in body mass distribution are causally related to differences in locomotor behavior and foraging strategies. Specifically, the relatively long-limbed C. albifrons is probably more cursorial and tends to travel longer distances each day than C. apella. C. apella is a much more deliberate quadruped and is characterized by especially vigorous and powerful foraging and feeding behaviors. The results to other (mostly cross-sectional) studies of skeletal growth allometry in nonhuman primates.