Do birds have teeth?
Birds used to have teeth ... more than 100 million years ago. Over the centuries they lost their teeth and developed beaks instead. (Sometimes beaks are called bills). They are the only class of vertebrates not to have teeth. (Actually, do birds have tongues? What do you think?)
A bird’s beak shows many variations: pointed or blunt, small or large, and it comes in many colours. The beaks are adapted to the kind of food they eat: to probe flowers for nectar, to crack nuts and seeds, or to catch insects and fish.
Beaks are present in a few invertebrates (e.g., cephalopods and some insects), some fishes and mammals, and all birds and turtles. Many dinosaurs were beaked. So birds are not the only animals with beaks. But birds have no other choice with which to eat food. How do we know that birds had teeth and why did they lose them?
To answer ths question scientists looked at the genetic evolution of birds, going millions of years all the way back to dinosaurs, which are their ancestors. In 2006, scientists at the University of Manchester and the University of Wisconsin managed to manipulate a chicken’s genes so that it actually grew teeth. So scientists found an incredible thing: there is a gene that de-activates the formation of teeth and all birds carry this gene. Moreover, the scientists found that the gene had appeared in birds that lived as long ago as 100 million years back.
There are two genes of interest: one that is responsible for producing dentin, of which teeth are mostly made. The other gene is responsible for the enamel coating that covers teeth. Enamel is the hardest substance in the human body. Its job is to protect the inner layers of the teeth from injury. The scientists reasoned that if birds had genes to produce dentin and enamel, surely they would have had teeth as well.
They classified all birds, ancient and modern, into those that had these genes and those that didn't. They found that the mutations to disable or deactivate these genes developed 100 million years ago.
The loss of teeth and the development of the beak happened almost simultaneously. For instance there is a fossil species of bird called Ichthyornis. It has a partial beak in the front of the mouth and teeth in the back. The teeth were present only in the middle portion of the upper and lower jaws (see picture). The jaw tips had no teeth and were covered in a beak.
So it is in-between in the evolution of the beak.
Of course, now we know when the teeth were lost, but we still do not know why it happened. Perhaps there was some advantage to birds growing a beak instead of teeth.
A modern view is that birds gave up teeth to speed up hatching of their eggs. While it took several months for a dinosaur egg to hatch, modern birds eggs hatch in a few days or weeks. This speeding up happens because it takes 60% of the development time for the embryo to develop teeth.
An older theory said that perhaps birds lost their teeth in order to lighten their skeleton so they could fly better, think some scientists. However, birds developed the ability to fly at a different time from developing teeth. For instance an ancient bird called Archaeopteryx had wings, could fly and had teeth.
But teeth were replaced by beaks and that exchange was surely insufficient for weight loss. Perhaps birds didn't lose teeth but gained a beak because it was advantageous for them by being more versatile.
The true reason is still not known. Meanwhile birds continue to fascinate us with their varied plumage and beaks.
Adapted from https://www.audubon.org/news/how-birds-lost-their-teeth