Evaluation of Mastoid Process as Sex Indicator in Modern White Americans using Geometric Morphometrics

Conventional methods for evaluating the mastoid as a sex indicator cannot determine whether mastoid shape is an independent and reliable sex indicator. Here, shape differences between the mastoids of 100 male and 100 female modern white Americans were statistically analyzed and visualized using the geometric morphometric method. Discriminant analysis was performed on mastoid size and shape. The relation between size and shape was analyzed to examine the effect of size on shape. In the results, mastoid size and shape were statistically significant sex indicators, while size factor explained 87.3% of the total variance of the shape variables. Nevertheless, females had relatively broader and shorter mastoid shape than males regardless of size, reflecting 12.7% of the total variance of the shape variables. In conclusion, mastoid size and shape were statistically significant sex indicators, while size may matter more in the mastoid than in other cranial parts in terms of sexual dimorphism.