Sexual dimorphism in southeast Asian crania: a geometric morphometric approach

Despite a number of studies stating that sexual dimorphism is population specific, sexual differences in Southeast Asian populations have received little attention. Previous studies in this region have focused on samples from Thailand or East Asian populations from China and Japan, examining sexual dimorphism predominantly of the postcranial bones, teeth and mandible with comparatively few cranial studies. These earlier studies have used traditional methods to metrically assess differences between the sexes. The aim of this study is to use geometric morphometric methods for the first time to quantify sexual dimorphism of Southeast Asian crania and extend knowledge of cranial sexual dimorphism beyond China, Japan and Thailand. A total of 35 unilateral and midline landmark coordinates were collected from 144 mainland and island Southeast Asian crania (89 male, 55 female). Using the shape analysis software Morphologika, principal components analysis and thin plate splines allowed for the statistical and visual exploration of shape differences. Differences included relative facial breadth, particularly across the zygomatic and postorbital regions and cranial vault breadth. Significant size dimorphism was also apparent. Overall expected accuracies were highest in the discriminant analysis using both shape and centroid size (86.8%).