Applying a geometric morphometric surface semilandmark-based approach for assessing sexual dimorphism in cranial bones

Abstract

Traditionally, sex estimation in human skulls has been carried out applying non-metric and inter-landmark distance approaches. Such estimation has substantially improved with the introduction of geometric morphometric semilandmark-based registration, representing a useful tool for capturing the complex morphology of 3D surfaces, particularly in human skulls. Taking in account these improvements, the main purpose of this study is to show the benefits of these techniques for assessing by means of a quantitative, hypothesis testing approach the differential phenotypic expression of sexual dimorphism in human cranial traits, using the frontal bone, the mastoid process of the temporal bone, and the zygomatic bone as proxies. According to our main results: i) accuracy and precision of sex estimation is higher when the shape variable is included in the analysis than when it is not, ii) numerical classification tends to be more accurate in males than in females for both shape and size components of sexual dimorphism, and iii) a single trait or two traits in combination would be more successful in sex classification than the three traits taken as a whole. The introduction in the present study of a surface semilandmark-based approach for quantitatively assessing sexual dimorphism in human skull considerably improves the capture of sexual dimorphic signatures, corroborating the importance of the information carried by the surface of the frontal bone, mastoid process, and zygomatic bone. Our results suggest that shape and size components should be considered as relevant factors in making a differential, bone- dependent sex assessment in human crania.

Keywords

• sexual dimorphism
• cranial trait
• geometric morphometrics
• 3D surface semilandmarks