Morphometric variation of the frontal bone in an adult South African cadaveric sample

Recent developments in geometric morphometrics enabled reassessment of features of the cranium in a more robust, objective and quantitative manner. Previous studies show that morphological variation of not only the cranium as a whole, but also parts thereof are useful in differentiating between sex and population groups. The present study used geometric morphometrics to assess variation of frontal bone morphology and its use in estimation of sex and ancestry. Frontal bones of 777 Black, Coloured and White South African adults were digitized and superimposed through Generalized Procrustes Analysis. Centroid sizes and morphological variation between groups were assessed. Accuracy of distinction between groups was assessed using Discriminant Function Analysis and leave-one-out cross-validation. Male frontal bones were more robust and sloped, compared to more gracile, rounded frontal profiles of females, resulting in classification accuracy of 79.3%. Morphological variation related to ancestry was found in the slope and width of the frontal bones, allowing distinction of the groups with 85.9% accuracy, even when including the heterogeneous Coloured group. When assessed according to sex and ancestry combined, 83.3% accuracy was achieved with the six sex-ancestry groups. These results show that variation in frontal bone morphology is sufficient to allow accurate distinction between these closely related groups, with accuracies compatible or exceeding those obtained when using the entire cranium of the same sample. Future studies may be able to investigate similar use of morphological variation of other cranial bones for estimation of sex and/or ancestry for use when the cranium is damaged or fragmented.