Comparing frontal inclination angles measured from digital 3D models and 2D photographs of dry male and female crania from Croatia

The frontal bone is one of the sexually dimorphic elements of the human skull that can be used for sex estimation of unidentified human remains. Numerous morphological features of the frontal bone, such as its angle of inclination, maximum anterior projection (glabella), and rounded elevations (frontal eminences) have been shown to differ between males and females. Various approaches have been developed to assess the frontal inclination in particular, and recently a method has been proposed where the angle of the frontal slope is measured from snapshots of digital three-dimensional (3D) models of human crania. However, as 3D-based investigations of skeletal material can be time-consuming and expensive, we here compare measurements of frontal angle inclination from 3D model snapshots to measurements from 2D photographs for a large sample (61 females and 61 males) of dry archaeological crania from medieval Croatia. Although angles measured from 3D snapshots and 2D photographs produced discriminant functions that classified crania by sex with similar accuracy (around 73%), the angles recorded from the 2D photographs were systematically one degree smaller than the angles recorded from the 3D images. Thus, even though both data sets were useful for sex estimation, we conclude that angles measured with the two different techniques should not be combined.