Abstract: The frontal bone is the important cranial part that connects the facial and neurocranial parts of the cranium. Little is known about the variance of the frontal shapes of the major populations in the world. In addition, the complicated surface morphology of frontal bone limits the possibility of further research. The current study aims to investigate the morphological variation of the frontal bone of East Asian modern human population, and the comparisons with other major modern human populations of geographically dispersed locations (Europe, Southeast Asia, America, Africa and Australia), using three-dimensional surface landmarks based geometric morphometric methods. 11 landmarks, 31 curve semi-landmarks and 418 surface semi-landmarks on the frontal bone for each specimen. We then performed 3D geometric morphometric analyses to quantify the frontal shapes. Within the populations included in this study, the main variation is exhibited in following ways: 1) the robusticity of the frontal tubercle of the frontal squama and the relative width of the frontal bone; 2) the development of the superciliary arches, frontal tubercles, and mid-sagittal crest. To further explore the relationships between the frontal morphology of the East Asian population and other populations, we carried out analyses of frontal size and comparisons. The results show that East Asian and European modern human populations exhibits the greatest median of the centroid size of the frontal bone, and Australian the smallest. Permutation test shows that the East Asian and Indian American populations share the closest frontal morphology in terms of Procrustes distance. Statistically significant differences were observed between Australian aboriginals and all the other populations. And the frontal morphology of the East Asian population exhibit significant difference between Australian aboriginals, Europeans and African modern humans. The current study also tested the association between frontal morphology and the genetic distance. The result shows that they are significantly correlated (r=0.214, p=0.002), suggesting that the morphological differences reflect genetic differences to some extent. The frontal morphologies of East Asian population show unique features in the comparison to all the populations included in this study, possibly suggesting a relatively isolated evolutionary history for the East Asian population. Future analyses of geometric morphometrics on the frontal surface will continue to explore the difference between specimens of different gender, and evolutional stage through expanding the sample size of cranial materials.

Key words: Frontal bone; modern human; three dimension; geometric morphometrics