Today’s birds share a common ancestor that had a more toothy smile, suggests a recent study of fossil genes. Researchers led by biologists at the University of California Riverside and Montclair State University discovered through a fossil genetics investigation that the genes responsible for tooth development were turned off in birds and a few other vertebrates around 116 million years ago.

Edentulism, or the absence of teeth, is thought to have evolved on many different occasions in vertebrates including birds, turtles, and some mammals such as baleen whales, pangolins, and anteaters. There is an ongoing debate about when birds went “edentulist” because the fossil record is spotty.

Using the degraded remnants of tooth genes in birds, the investigators set out to determine when and how birds may have gave up their teeth. In a report published on December 12 in Science Magazine, the team suggests that the teeth were lost in birds as they shed weight in an effort to take to the skies in flight.

“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,” said Mark Springer, professor of biology and one of the lead authors of the study. “DNA from the crypt is a powerful tool for unlocking secrets of evolutionary history.”

The researchers focused their investigation on the fossil of Archaeopteryx, an ancestor of contemporary birds found in Germany, and found that tooth loss came down to the inactivation of six key genes.

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

Springer noted that the six genes responsible for tooth formation are expressed in the American alligator.