Geographic and sex differences in the 3D configuration of the human parietal bone

As a sizable component of the cranial vault, the parietal bone is essential for understanding the regional variation of cranial surface morphology. Predigital, traditional morphological studies have tended to underemphasize the role of parietal trait variation, particularly in identifying region-specific and/or sex-related differences in modern human populations. Consequently, the extent of morphological variation in the parietal bone among modern human populations remains insufficiently understood. In this study, we perform a three-dimensional (3D) geometric morphometric analysis of the external surface of the parietal bone, using microcomputed tomography data from 120 human crania (60 males and 60 females) sampled from European and Chinese populations. The analysis of the periosteal sur‍face of the parietal bone reveals significant sexual dimorphism in shape space. Specifically, the bi‍parietal distance between pterion landmarks is wider in Chinese males than in Chinese females. Re‍gional differences in parietal bone shape are more frequently statistically significant. Parietal bones of European populations tend to be wider and shorter, with less pronounced parietal eminences, whereas those from Chinese populations are relatively narrower and longer, exhibiting more prominent parietal eminences. When 3D geometric morphometric analysis is conducted in form space, which incorporates both shape and size, additional differences between sexes and populations become evident. Males exhibit significantly larger parietal bones than females, and individuals from European populations have significantly larger parietal bones than those from Chinese populations. Ultimately, differences in form space are more pronounced than those in shape space, emphasizing the importance of considering both shape and size in morphological analyses.