The Mystery of the Avian Beak

How the modern bird lost all its teeth

One of the greatest mysteries that have confounded avian researchers is how and at what point birds lost their teeth. Since birds are the modern descendants of dinosaurs, they are likely to have once had teeth instead of beaks. This fact became known way back in 1861 when palaeontologists discovered a bird fossil, about 150 million years old, now classified as Archeopteryx, which had teeth.

But several questions have remain unanswered—when and why did this occur; did birds lose their teeth in a single event, meaning did a common ancestor of all living birds lose its teeth, or did edentulism happen independently along different lines of birds throughout history?

Researchers have now found that birds lost their pearly whites around 116 million years ago. According to the new study, conducted by researchers from the University of California, US, and published in the journal Science, around that time a common ancestor of all modern birds lost the ability to produce enamel-covered teeth.

In vertebrates, tooth formation involves six genes that are crucial for the formation of enamel and dentin, the building blocks of teeth. To figure out when birds developed edentulism, the researchers looked for mutations that might inactivate these six genes in the genomes of 48 modern bird species.

According to the researchers, such mutations would provide evidence that teeth were lost once by the common ancestor of all living birds. The researchers found mutations in every single genome. Based on the mutations they found, the researchers believe that a common ancestor of all birds lost the ability to produce enamel-covered teeth around 116 million years ago. In comparison, in alligators, which are the closest living reptilian relative of birds, all six genes are functional.

The shift from teeth to beaks is likely to have occurred over a period of time. According to the researchers, fossil and molecular evidence indicates that there was a first stage of tooth loss, when a partial beak began to develop in the anterior portion of both the upper and lower jaws of this ancestor. In the second stage, this tooth loss and beak development progressed to the back of the rostrum.

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