Sexual dimorphism using elliptical Fourier analysis: shape differences in the craniofacial complex

The assessment of sexual dimorphism plays an essential role in numerous disciplines such as: (1) forensics, with its concern with skeletal identification, including sexing; (2) archeology, where the sexing of skeletal materials is an essential aspect; (3) primatology, where sex differences are diverse; (4) paleoanthropology, where the identification of sex can influence taxonomic and phylogenetic decisions, and (5) growth and development, where one strives to identify differences before and after puberty. Other disciplines where sexual dimorphism plays an important function include orthodontics, gerontology, nutrition, and medicine. Quantitative studies of morphological forms in general, and sexual dimorphism in particular, is not a trivial endeavor in that at least two aspects are involved, namely size and shape. Focusing on the human skeletal system, sexual dimorphism affects all bones, including the cranium, pelvis, long bones, and vertebral column. However, the overwhelming numbers of studies of sexual dimorphism are based solely on size differences. These studies have repeatedly demonstrated that males are larger for most dimensions. The question of shape differences, if indeed present, cannot be readily inferred from these studies. Consequently, a number of studies were initiated, over some 20 years duration, that specifically focused on the presence of sexually dimorphic shape changes in the skeletal craniofacial complex. The following anatomical structures were examined: (1) the human nasal bones, (2) the primate cranial base, (3) the human cranial base, (4) the human dental arch, (5) the human mandibular arch, and (6) the human cranial vault. These six datasets involved 16 samples for a total of 1110 specimens. Every dataset generated statistically significant sexually dimorphic differences in shape. Thus, it is apparent that the craniofacial complex not only exhibits size differences but also specific shape differences.