Sexual dimorphism in shape and size of the neurocranium

Sex identification is a primary step in forensic analysis of skeletal remains. The accuracy of sex estimation methods greatly depends on the sexual dimorphism manifested by the target anatomical region. The study aims to evaluate the sexual dimorphism in shape and size of the neurocranium and to compare the potential of shape and size of different cranial regions to classify correctly the male and female crania. The study was carried out on computed tomography images of 373 Bulgarian adults (161 males and 212 females). Three-dimensional coordinates of 32 landmarks were acquired. The landmarks were arranged in 4 configurations: neurocranium, frontal bone, parietotemporal region, and occipital bone. For each configuration, the presence of significant sex differences in shape and size was tested. Principal component analysis (PCA) was applied to explore the shape variation. The classification power of size and shape was tested using discriminant analysis and k-means clustering. The neurocranium shows significant sex differences in shape and size. The parietotemporal region is the most dimorphic neurocranial part in size and the frontal bone is the most differing one in shape. The size of the parietotemporal region and frontal bone classifies correctly more than 80% of the crania. The discrimination ability based on shape is rather low as the highest values of about 70% are obtained for the frontal and occipital bone. The PCA plots show large overlapping of the male and female crania. It can be inferred that the sex-specific size differences in the neurocranium are more important than the shape differences.