Ontogenetic scaling of skeletal proportions in the talapoin monkey

The talapoin monkey is distinct from its close relatives in the genus Cercopithecus in a variety of morphological and ecological features, inclining some to place it in its own genus, Miopithecus. It is also the smallest of the extant catarrhines, and in this investigation the extent to which the morphological distinctions of the talapoin monkey are the result of allometric factors is analysed. A series of cranial and postcranial measurements were taken on the skeletons of young and adult talapoin monkeys (C. talapoin) and moustached monkeys (C. cephus). Ontogenetic scaling (i.e., allometric extrapolation) was utilized as a criterion of substraction in both bivariate and multivariate comparative allometric analysis. Adult cranial and postcranial proportions do differ significantly between C. talapoin and C. cephus, but in almost all cases these adult shape differences result from the sharing of common underlying patterns of ontogenetic allometry. Use of additional data from Verheyen's (1962) monograph suggests that the marked differences in skull form within the Cercopithecus group (from talapoin to patas monkeys) may also be primarily a product of ontogenetic scaling. The specific postcranial proportions seen in adult talapoins do not accord with expectations derived from several recent biomechanical models for primates which engage in frequent leaping and climbing behaviors, though the comparative growth allometric perspective utilized here does clarify these adult shape differences. The predominantly paedomorphic morphology of the talapoin monkey appears to be a direct and correlated allometric consequence of a decrease in overall growth rates and terminal body size, which may be related to increased propensities for leaping behavior and a more insectivorous diet.