1Department of Paleoanthropology, Institut für Ur- und Frühgeschichte und Archäologie des Mittelalters, Eberhard Karls Universität Tübingen/Senckenberg Center for Human Evolution and Palaeoecology, 2Primatology, Max Planck Institute for Evolutionary Anthropology
Saturday All day, Plaza Level
Genetic evidence suggests that Pan troglodytes troglodytes, Pan troglodytes schweinfurthii and Pan troglodytes verus represent three different populations, with the latter possibly being a distinct species. Morphological differences, however, are not clear-cut and bear directly on questions concerning taxonomy, sexual dimorphism and phylogeny in extant hominoids and early human evolution. We re-examine Pan cranial variation using Procrustes-based geometric morphometrics to: 1) quantify and examine overall cranial shape variation among Pan species and sub-species; 2) investigate whether the face, basicranium and cranial vault can distinguish sub-species of Pan; this is because different regions of the cranium have shown to preserve phylogenetic information differentially.
Our dataset comprises 123 adult chimpanzees and 36 bonobos, and a total of 53 3-D landmarks. To analyze cranial shape variation, we conducted principal component (PCA) and canonical variate (CVA) analyses on Procrustes shape coordinates. The PCA of the full cranial landmarks set shows a separation between the Pan species, but not the sub-species. The CVA distinguishes bonobos from chimpanzees, and also shows subtle separation among the chimpanzee sub-species. In the separate face, basicranium and cranial vault analyses, bonobos are best distinguished from chimpanzees in aspects of the face and basicranium. Among the sub-species, P.t.verus and P.t.schweinfurthii are most disparate from each other, particularly in the face. P.t.troglodytes consistently overlaps with P.t.verus and P.t.schweinfurthii in all three cranial regions.
These results suggest population differences between the western and eastern chimpanzees, but do not indicate consistent separation of the western chimpanzees as suggested by the genetic data.
This study was funded by Marie-Curie (“EVAN”) Action grant MRTN-CT-2005-019564.