Figure 3

Shape deformations according to the first two dimensions of the PCA. The sequence of surface representations (from left to right) as deformations of the average shape correspond to increasing scores in PC 1 (a) and PC 2 (b) in Figure 2. The surface morphs differ from its neighbors by equal multiples of the standard deviation of the actual variability. The first and last column is extrapolated by 2 (a) and 4 (b) standard deviations, respectively. (a): Major variation in PC 1 lies in the relative length and curvature of the bill, in cranium height, in the position of the foramen magnum and in the position and orientation of the orbits. (b): Major variation in PC 2 lies in the angle between bill and cranium, in the position of the foramen magnum, in the position and orientation of the orbits and in bill-curvature.