Teeth to Beak: When Birds Lost Their Smile

When you see a bird beak, you may think it an adequate alternative to the good old pearly whites, but fossil records tell us that this wasn't always the case. Some birds ancestors boasted an unusual marriage between teeth and beak-like jaws. So when exactly did our avian friends lose their chompers for good? A new study investigates.

The study, recently published in the journal Science, details how the absence of teeth, called edentulism, occurred in one common bird ancestor more than 100 million years ago.

"Ever since the discovery of the fossil bird Archaeopteryx in 1861, it has been clear that living birds are descended from toothed ancestors," Mark Springer, a lead author of the study, said in a statement. "However, the history of tooth loss in the ancestry of modern birds has remained elusive for more than 150 years."

To finally uncover the truth about avian endentulism, Springer and his colleagues worked to identify and analyze the degraded remnants of tooth genes in modern birds' gene pool.

"One of the larger lessons of our finding is that 'dead genes,' like the remnants of dead organisms that are preserved in the fossil record, have a story to tell," Springer explained. "DNA from the crypt is a powerful tool for unlocking secrets of evolutionary history."

The team highlighted six genes that are essential for the proper formation of dentin and enamel - factors of tooth production that have long been "shut off" in the avian genome, but are still present.

Some researchers had suspected that edentulism had occurred late in the evolution of birds, with various ancient bird lineages losing their ability to make teeth with different times and conditions.

However, this latest research shows that among 48 species of modern birds, all shared the same mutations that shut off their teeth-crafting genes. This suggests that edentulism developed in one common ancestor - one that likely lived about 116 million years ago, according to Springer.

Amazingly, the team found that the same six genes are still present and active in crocodylia - the closest relatives to modern birds - while inactive versions of these genes boasting very different mutations can be found in other toothless animals, such as turtles and anteaters.

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