Facial patterns in Cercopithecoidea and Hominoidea: a geometric approach

The maxillofacial and orbital compartments of the primate skull contribute to the ontogenetic and phylogenetic variability of the viscerocranium and are of crucial evolutionary relevance. As the form of organisms changes depending on endo- and exogenous factors, metrical evaluation of specific adaptations and incorporation of the results into a biological framework could be helpful in identifying valid characters for separation of taxa (e.g. family, genus, and species) and in understanding divergence and convergence. During the last two decades a morphometric "revolution" heralded by Rohlf & Marcus (1993), Adams et al. (2004) and Oxnard (2004) brought about a synthesis of traditional quantitative-morphometrical with modern methods. This approach is called "Geometric Morphometrics (GM)" and constitutes the coremethod applied here. Based on standardized photographs (in Norma frontalis), landmarks (LM) were set and two-dimensional coordinates (X, Y) recorded for the facial cranium in selected representatives of the superfamilies Cercopithecoidea and Hominoidea. The comparison of two datasets by means of factor analysis and distance computation for the complete maxillofacial complex on the one hand, and circumorbital and orbital features on the other, indicate that morphological differences between super-families and genera are valid for separating them even in a heterogeneous sample like the one presented here. Including more landmarks and therewith capturing the morph in a more complex way optimizes separation within the sample.