Anatomy of the mandibular symphysis of extant cercopithecids: taxonomy and variation

The symphyseal anatomy of extant and fossil cercopithecids has not yet been demonstrated as a useful tool for taxonomic discrimination, and the source of variation in cercopithecid symphysis has not been addressed on a broad taxonomic scale. Here, we used linear and angular dimensions to quantify symphysis shape. Using univariate, multivariate data and allometric regressions (partial least squares and phylogenetic generalized least square regressions), we addressed the hypothesis that extant cercopithecids can be distinguished by symphysis shape. Significant differences in univariate and multivariate data and allometric regressions permitted to distinguish cercopithecids at the subfamilial, tribal, and genus levels. We showed that multivariate data followed the distribution expected under Brownian Motion and significantly discriminates taxa at different taxonomic levels. Colobine symphysis are characterized by developed inferior transverse tori, short planum alveolare, and short symphysis, whereas cercopithecine symphysis are characterized by developed superior transverse tori, long planum alveolare, and long symphysis. Exceptions to this pattern exist within each subfamily, and this study underlines the particular anatomy of Colobus and Presbytis among the colobines, Allenopithecus among the Cercopithecini, and Theropithecus and Lophocebus among the Papionini. We also demonstrate that the relative development of the transverse tori, the relative length of the planum alveolare and symphyseal inclination are dimorphic traits. Specifically, we show that the symphysis of Procolobus verus, Nasalis larvatus, and Papio anubis is strongly dimorphic.