Non-metric traits of the cranium: are they related one with each other? A novel approach to skeletal variants

Non-metric traits are anatomical variants of the human skeleton that are commonly used as morphological descriptors and have shown potential for personal identification. Although their frequencies are reported for different contemporary and archaeological populations, very little is known about their origins and even less is reported about their reciprocal correlations. This study aims at assessing the possible correlation among 21 different non-metric traits of the cranium (12 pair and symmetric, 9 unpaired and median) to verify if they are correlated one with each other. The variants were observed on 733 CT-scan collected from the radiological databases of two Italian hospitals. A pairwise correlation analysis among features was performed using Pearson’s correlation index (|r|). Results show that only four significant positive correlations were found, namely between number of septa and scallops in the frontal sinuses, between the pneumatization of pterygoid processes and greater wings bilaterally, and between the pneumatization of greater wings and clinoid processes on the left side with a |r| between 0.333 and 0.650. The single negative correlation was between metopism and number of scallops in the frontal sinuses with a |r| of -0.408 (p < 0.05). This study shows that most of anatomical variants are largely independent one from the others: this novel information represents a starting point for an in-depth study on the origin of non-metric traits and confirms their potential for personal identification.