The distortion caused by projecting all landmarks onto this plane will have greatest effect on the landmarks of the acromion and metacromion, which are separated laterally from the blade.
This warp also includes displacements of the extreme points on the acromion and metacromion. W5 is a much more localized warp that primarily represents a contrast between displacements of the landmarks near the middle of the dorsal margin.
On W3, the center includes the dorsal edge of the acromion, whereas on W4, the center includes the posterior tip of the metacromion. The ends are also slightly different; and W4 covers a smaller portion of the blade.
The remaining principal warps, W6, W7, and W9, complete the series of deformations coveting progressively smaller portions of the acromion, metacromion, and ventral blade.
Chipmunks have +y loadings reflecting dorso-ventral compression of the supraspinous fossa with tilting of the acromion and lower metacromion. Ground squirrels have the opposite transformation, and a particularly large -y loading distinguishes Sp.
striatus, are characterized by dorso-ventral compression of the acromion and ventral metacromion. In contrast, these structures tend to be expanded along the antero-posterior axis in ground squirrels, although some ground squirrels retain shapes that are very similar to tree squirrels.