Predictable value of cranial traits used in the visual assessment of sex: a Geometrics Morphometrics analysis.

Sex assessment it’s one of the cornerstones for any investigation in physical anthropology. It can be realized by means of visual examination of the cranium or the hip bone. Populational validation for these methods it’s perform by experienced observers estimating the sex in osteologycal collections with known sex. A problem with these methods it’s that they are validated minimizing the interobserver error for sex assessment and not by the biological varibility measurement of these traits. Five cranial traits for sex determination (glabella, mastoid process, zygomatic process of the temporal, zigomatic bone and orbital form) were recorded in a set of 3D landmark coordinates and analized by geometrics morphometrics. The aim of this investigation was the metric assessment for the reliability of these traits for sex visual assessment. The coordinates set for each trait were statistically compare between females and males, and by Generalised Procustes analysis (GPA) and thin-plate splines for size and shape variables to carry out a discriminant analysis and to visualize they morphological variation. Significant differences between sex were found for glabella, mastoid process, zygomatic bone and zygomatic process of the temporal. Discriminant analysis for size and shape variables gave significant clasification for sex over 89% of the sample. 3D thin-plate splines visualization of form for these traits described the morphological variation from hyperfeminine to hypermasculine cases. These results may improve visual methods to sexing skulls and demostrate that geometrics morphometrics could be a powerful tool for populational validation of these methods.

Keywords: sex estimation, sexual dimorphism, geometrics morphometrics, populational validation