Sex Determination of Human Crania Using 3D Surface Scanning of the Mastoid Process

Abstract

Historically, sex determination of human skulls has been dependent on visual examination and qualitative scoring of sexually dimorphic features such as the mastoid process. The accuracy of this method relies heavily on observer experience. We report a new method for sex determination based on quantitative analysis of the mastoid process. A Polhemus FastScan 3D laser scanner is employed to capture cranial surface morphology. The scan protocol generates 2 mesh models that are imported and aligned using Geomagic Design X64 software to create a single digital model per cranium. From the model, the mastoid process is isolated and its volume measured. Total cranial volume is also estimated from the model, allowing computation of a mastoid ratio (mastoid volume:cranial volume) for each specimen. A pilot study was performed utilizing a small sample of crania from known-sex Medieval Nubian individuals. Results demonstrate little overlap in the range of male vs female absolute mastoid volume. Intra-observer measurement error is low. A t-test shows significant differences (p < 0.05) between male and female mastoid ratios, demonstrating the utility of this method for sex determination. Moreover, the new method is advantageous because the scan protocol is quick; it captures a permanent record of each specimen; and unlike qualitative scoring, it can be executed consistently with minimal training. Future work will focus on evaluating inter-observer error, testing the method across population samples, and devising protocols for other dimorphic features, with the goal of developing a comprehensive multivariate method for sexing skulls based on 3D surface scanning.