The evolutionary radiation of birds has produced incredible morphological variation, including a huge range of skull form and function. Investigating how this variation arose with respect to non-avian dinosaurs is key to understanding how birds achieved their remarkable success after the Cretaceous–Paleogene extinction event. Using a high-dimensional geometric morphometric approach, Felice et al. quantified the shape of the skull in unprecedented detail across 354 extant and 37 extinct avian and non-avian dinosaurs. Comparative analyses reveal fundamental differences in how skull shape evolved in birds and non-avian dinosaurs. The authors find that the overall skull shape evolved faster in non-avian dinosaurs than in birds across all regions of the cranium. Taken together, the remarkable cranial shape diversity in birds was not a product of accelerated evolution from their non-avian relatives, despite their frequent portrayal as an icon of adaptive radiations. The image shows 3D digital models of the skulls of a selection of avian and non-avian dinosaurs. Clockwise from center top: Outer circle: Anhinga anhinga, Pandion haliaetus, Triceratops horridus, Probosciger aterrimus, Diplodocus carnegii. Inner circle: Allosaurus fragilis, Anser anser.

Image Credit: Ryan N. Felice