Have you ever thought of why birds don’t have teeth? Evolutionary scientists say the birds’ ancestors possessed teeth. But the million dollar question arises when did birds lose their teeth?

A team of biologists at the Montclair State University and the University of California in Riverside examined the fossil record of birds and analyzed the tooth genes that were degraded in bird DNA.

During the analysis, the researchers found strong clues confirming that one of the common ancestors of birds made the switch over100 million years ago.

In a press release, lead study investigator Mark Springer said, “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 is a professor of biology at University of California, Riverside.

The birds are not the only species to give up teeth but turtles have also tried for the beak, while several mammal groups like anteaters, pangolins and baleen whales have also developed alternate oral feeding tools.

According to Springer, each of these animals has a common ancestor possessing teeth. When talked in the case of birds, it is theropod dinosaurs.

But, the scientists say at some point between the theropods and the first birds’ species, the avian ancestors started swapping out teeth for a beak. Following analysis of the decaying nature of six genes associated with the teeth formation, the scientists indicated the transformation was solidified by 116 million years ago.

According to Springer, this progression ultimately led to a complete horny beak that replaced the teeth effectively and most likely have contributed to the diversification of living birds.

The study’s findings were detailed on Monday in the journal Science.