Avian dentition really is as rare as proverbial hen’s teeth. While birds’ dinosaur ancestors had gnashers aplenty, as did the earliest birds, the lineage lost them about 100 million years ago as they developed their horny beaks.
But evolution has a long memory, and birds have retained most of the genetic instructions for building teeth. These can be activated in chickens by geneticists, causing embryos to grow reptilian, peg-like teeth, but those individuals don’t survive to hatching.
Beaks perform many of the functions fulfilled by teeth. They are less adept at chewing and grinding food, but the gizzard, a muscular section of the gut often filled with swallowed stones, can help there.
Sometimes, though, only teeth – or something like them – will do. Goosanders and other sawbill ducks have tooth-like serrations along the edges of their bills to grip slippery fish. And some birds, such as flamingos, geese and penguins, have teeth-like barbs on their tongues or in their throats.