Fig. 2: Endocranial shape variation in extant birds, non-avian dinosaurs, and American alligator.

Morphospaces constructed from first two principal components (PC) axes of (a) total endocast shape (inset images along axes illustrate extremes of shape changes along PC1 and PC2 axes; green, blue, and purple arrows show the general ontogenetic direction of Alligator, Psittacosaurus, and Gallus, respectively); b cerebrum shape; c cerebellum shape; d optic lobe shape; e brainstem shape. The regional shape data were extracted by performing local Procrustes alignment within each region.