Unlocking sexual dimorphism: geometric morphometrics analysis of the Atlas (C1) bone in Malaysian populations

Sexual identification is the most crucial step in the forensic anthropology field. Traditional morphometric techniques, involving caliper-based measurements, are often labor-intensive and time-consuming. In contrast, the geometric morphometric method (GMM) offers a more efficient approach, integrating qualitative and quantitative assessments of biological forms based on precise geometric characterizations of their shape. This study aimed to assess sexual dimorphism of the Atlas (C1) bone on lateral cervical radiographs using GMM. A cross-sectional design was employed, utilizinglateral cervical radiographs from a sample of 413 individuals, including 208 males and 205 females, age ranged between 35 and 45 years old. Six 2D landmarks were identified and marked on the digitalized radiographs using TPSDig2 (Version 2.31) software. GMM analysis conducted by MorphoJ software. Eight principal components (PC) accounted for 100 % of the shape variability produced. Procrustes ANOVA showed that centroid size and shape were significantly different between different sexes. Discriminant function analysis (DFA) revealed a correct classification rate for 87.9 % of cases, with an identification accuracy of 87.0 % for males and 88.8 % for females. There were significant differences among males and females in the height of the C1 vertebral body with p < 0.05 via independent t-test. In conclusion, there was a significant sexual dimorphism of the C1 vertebra by GMM, which could serve as an alternative method in physical anthropology and forensic medicine.