Figure 2. Principal components analysis (PCA) of human craniofacial shape variation.

Panels show (A) PC1 by PC2, (B) PC1 by PC3, and (C) wireframes illustrating craniofacial shape change associated with the first three principal components in right lateral, superior, and frontal views. The left and right columns of wireframes represent the negative and positive ends of each component, respectively, scaled to their respective axes. The 10 unique landmarks with the highest loadings for each component are highlighted using a red ellipse on the midline and right side. A single ellipse was used to circle multiple landmarks if they were located close together. Shape differences toward the positive end of PC 1 include: a vertically shorter face with a more projecting brow ridge, a longer and more projecting palate, a more vertical frontal bone that is narrower at pterion, a vault that is expanded posteriorly, and a lower temporal line at stephanion. Shape differences toward the positive end of PC 2 include: a longer cranium with a wider frontal bone, a vault that is angled more postero-inferiorly, wider orbits and a superiorly shifted nasal aperture, and an antero-posteriorly shorter temporal bone. Shape differences toward the positive end of PC 3 include: higher temporal lines at stephanion, a shorter and more orthognathic subnasal region with a less projecting palate, a more inferiorly positioned TMJ, and a more inferiorly positioned midline cranial base.