Chicken embryos with dinosaur-like faces provide clues as to how bird beaks evolved from dinosaur snouts.

Early in bird evolution, the twin bones that form the snout in dinosaurs and reptiles — the premaxillae — grew longer and joined together, eventually forming the beak. Bhart-Anjan Bhullar, now at the University of Chicago in Illinois, Arhat Abzhanov at Harvard University in Cambridge, Massachusetts, and their colleagues analysed the development of beaks in embryonic chickens and emus, and snout development in reptiles such as alligators.

They found that two proteins involved in facial development, FGF and Wnt, might have a role in beak evolution. When they inhibited these genes in developing chicken eggs — making the expression pattern more like that of reptiles and other vertebrates — the premaxillae were separate and much shorter in some chicken embryos than in others. (None was allowed to hatch.)

X-ray scans of the embryonic skulls showed that they more closely resembled the bones of early birds and dinosaurs than those of modern chickens.

Evolution http://dx.doi.org/10.1111/evo.12684 (2015)