Geometric Morphometry Analysis of the Scapula: Implications for the Determination of Sex and Ancestry

The nascent but growing field of geometric morphometrics has proved to be a useful tool in the investigation of shape differences of skeletal elements of various populations. Until recently, most anthropological studies using geometric morphometrics have focused on shape differences of the skull, largely to the neglect of the postcrania. This research uses coordinate data derived from three-dimensional digitizing to quantify morphological variation in left and right scapulae of Blacks and Whites of both sexes. The sample analyzed was from a collection of present day Americans, making it particularly germane for forensic applications. Left and right scapulae of Black males, Black females, White males, and White females were digitized, producing three-dimensional coordinates that were subsequently subjected to Procrustes analysis, and residuals were analyzed by traditional statistical analyses. Consensus configurations were superimposed using thin-place splines to investigate shape variability among groups. Canonical discriminant function analysis suggested that shape differences exist between scapulae of Blacks and Whites and between the sexes. Principal component analysis showed that principal components loaded differently on the canonical discriminant functions of left and right scapulae. Centroid sizes effectively discriminated between males and females but did not discriminate between Blacks and Whites. The success of this study in differentiating shape variability between scapulae of males and females and between Blacks and Whites demonstrates the benefit of using geometric morphometry to examine biological variability of human subpopulations. In addition, the use of non-traditional landmarks allowed for a more complete analysis of scapular shape. The use of non-traditional landmarks showed that much of the variability in scapular shape between the sexes and between Blacks and Whites lies in previously neglected areas of the scapula.