Investigating Variation among Arikara Crania Using Geometric Morphometry

Geometric morphometry has seen minimal application in studies of biological variability among subpopulations of humans. However, as landmark coordinates are highly effective for capturing information regarding size and shape variation, the tools of geometric morphometry are appropriate for investigating such questions. This research utilizes landmark coordinate data to quantify morphological variation among Arikara crania to evaluate the biological relationships between skeletal samples from late prehistoric, protohistoric and historic sites. These samples are derived from well documented archaeological contexts, and the presence of biological variability among them has been reported in previous studies. These factors make these samples appropriate for assessing the utility of geometric morphometry for investigating variation among subpopulations separated by time and space.

Forty cranial landmarks were recorded by three-dimensional coordinates on crania from 18 components from Extended and Post-contact Variants of the Coalescent Tradition of the Middle Missouri Region in the Great Plains. The coordinates were fitted employing general Procrustes analysis and the residuals from this procedure were subjected to traditional statistical analyses. Additionally, consensus configurations were employed to generate thin-plate spline transformation plots and comparative plots of Procrustes means depicting the morphological variation present among the various samples. This variation was interpreted in light of the results from analyses of the residuals and the known temporal, geographical and cultural contexts.

Canonical analysis and multiple matrix correlation (Mantel) tests indicate that geographic distance was the primary factor structuring morphological variation among the samples. Additionally, a statistically insignificant temporal trend is observed in the morphological variation across the samples.

This research demonstrates the utility of coordinate data for investigating biological variability and the relationships among human subpopulations based on cranial morphology. By retaining the geometric relationships among the coordinates, the geometric morphometric analyses of the configurations provide information about shape variation among all of the landmarks. While the nature of the variation detected in this study is similar to previous studies, the coordinate data permits the graphical representation of morphological patterns that allows for an appreciation of differences in landmark locations between configurations and a better understanding of morphological variation among these samples.