Quantifying male and female shape variation in the mastoid region of the temporal bone

Abstract

The shape of the temporal bone of the adult human cranium, specifically the mastoid region, is documented widely in past literature as a measure of sexual dimorphism within and among human populations. Yet, past research focuses primarily on the qualitative assessment of the size of the mastoid region as it varies between males and females. This thesis explores both standard qualitative and standard and nonstandard quantitative measures of variation, in both size and shape, of the inferiorly projecting cone-shaped process of the temporal known as the mastoid process. A set of eight measurements, two of which use five non-metric scores, are recorded for 100 male and 100 female adult White crania from the Hamann-Todd Osteological Collection at the Cleveland Museum of Natural History. It is hypothesized that a quantitative approach will either exceed or provide greater consistency in identification than the qualitative characterization of the mastoid region, as it is used almost exclusively in current practice. Descriptive statistics demonstrate patterns of sexual dimorphism in the mastoid region and univariate statistics reveal significant differences between the measurements among males and females. A nonstandard measure of the height of the mastoid process, mastoid radius, is tested against the standard measurement, mastoid height. Descriptive statistics reveal a strong correlation between the two measurements. Univariate statistics show significant differences between the two measurements and variances around the mean suggest that the mastoid radius provides greater consistency as a measure of size than does the standard mastoid height measurement. The results from this study indicate that quantitative analysis of the mastoid process correctly classifies more individuals than qualitative scoring. Further, scoring the size of the supramastoid crest produces a greater percentage of correct sex identification than the qualitative scoring the overall size of the mastoid process.