http://www.newsweek.com/evolution-birds-dinosaurs-941329

Birds don’t have teeth, and believe it or not, we’re still not entirely sure why. A new study, however, has an impressive theory on what happened to our winged friends, and suggests how going toothless gave them, and their dinosaur ancestors, an evolutionary edge.

The study, published online in Biology Letters Wednesday, suggested that birds lost their teeth so that incubating babies could hatch quicker. This challenges past theories that suggested birds lost their teeth to aid in their ability to fly or to improve their ability to eat. However, some flying dinosaurs did have teeth and some meat-eating dinosaurs also lost theirs. For this reason, faster incubation appears to be the most sensible answer.