There was time when birds had teeth. Evolutionary biologists now have a date for when teeth disappeared in birds – 116 million years ago.
One bird’s fossil told researchers living birds descended from an ancestor with teeth. The discovery of the Archaeopteryx fossil in 1861 made that clear. “However, the history of tooth loss in the ancestry of modern birds has remained elusive for more than 100 years,” said Mark Springer, a lead author on the study.
The research team – with biologists from the University of California, Riverside and Montclair State University, NJ – used the remnants of tooth genes in birds to determine the time frame.
“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 Springer
These remnant genes are “a powerful tool for unlocking secrets of evolutionary history,” according to Springer.
A press release from the UC Riverside explains what is needed for teeth to form.
Tooth formation in vertebrates is a complicated process that involves many different genes. Of these genes, six are essential for the proper formation of dentin (DSPP) and enamel (AMTN, AMBN, ENAM, AMELX, MMP20).
48 birds species were studied for inactivating mutations. They discovered the 48 bird species shared mutations in dentin and enamel-related genes. This means the “genetic machinery” needed for teeth to form was lost in the common ancestor of today’s birds.
“The presence of several inactivating mutations that are shared by all 48 bird species suggests that the outer enamel covering of teeth was lost around ~116 million years ago,” Springer said.
With teeth out of the equation, the beak evolved. The research team believed the loss of teeth and the beak evolved at the same time.
“In the first stage, tooth loss and partial beak development began on the anterior portion of both the upper and lower jaws. The second stage involved concurrent progression of tooth loss and beak development from the anterior portion of both jaws to the back of the rostrum,” reads the study abstract.
You can read the full study here.