Geometric Morphometric and Traditional Morphometric Analyses of Secular Changes in the Craniofacial and Anterior Cranial Base Shapes of Modern Euro-Americans

Prior research has identified that the cranial vault has become taller and narrower and the mandible has decreased in breadth and become longer over time among Americans (Angel, 1976; Jantz and Meadows Jantz, 2000; Jantz, 2001; Martin and Danforth, 2009; Jantz and Meadows Jantz, 2016). Studies of the cranial vault also suggest narrowing of the face. However, research investigating secular changes in craniofacial morphology is lacking. Because the cranium is a complex of integrated modules with different trajectories and patterns of ontogeny and development, modular accommodation during growth is critical for the cranium to maintain functionality as a unit. This dissertation utilizes craniometric data from documented 19th and 20th century skeletal collections to investigate whether changes in craniofacial morphology have occurred concomitantly with those of the vault, and if so, whether those changes are related to changes in cranial base shape.Geometric morphometric analysis was performed using 21 digitized craniometric landmark data from a sample of n=662 White males and females. Generalized Procrustes Analysis was utilized to fit the three-dimensional coordinate data into a common coordinate system for the execution of further multivariate analysis. Principal components analysis and canonical variates analysis were executed to ascertain the presence of secular changes in craniofacial and base shape. Subsets of the 21 craniometric landmarks were analyzed to facilitate separate examinations of the face and base.Two-dimensional interlandmark distance data obtained from the same individuals were analyzed using correlation analysis, principle components analysis, and regression to corroborate the results of the geometric morphometric analysis. The use of non-traditional craniometric measures proved instrumental for identification of specific areas and directions of shape change.Lastly, a series of traditional cranial angle data obtained from a larger sample of n= ~1,500 individuals were analyzed using regression analysis. The examination of the cranial angle data served to substantiate the results obtained from the prior analysis and to further delineate secular changes in morphology.Results suggest that the faces of American White males and females have become more leptoprosopic (tall and narrow) and the cranial vault has become more dolichocephalic (longer and narrow) over time.