Relative facial width, and its association with canine size and body mass among chimpanzees and bonobos: Implications for understanding facial width-to-height ratio expression among human populations.

Objectives: Facial width-to-height ratio (fWHR) has been widely investigated in the context of its role in visual communication, though there is a lack of consensus about how fWHR serves as a social signal. To better understand fWHR variation in a comparative context, we investigate the associations between fWHR and canine crown height (CCH) and body mass, respectively, among two chimpanzee subspecies (Pan troglodytes schweinfurthii, Pan troglodytes troglodytes) and bonobos (Pan paniscus).

Materials And Methods: We collected landmark data from 3D surface models of 86 Pan cranial specimens to quantify fWHR and upper CCH, and to estimate body mass.