How Birds Lost Teeth Explained By Biologists

Scientists have known that avian ancestors once had teeth. But where have all the teeth gone to birds of today? How birds lost their teeth? Were teeth lost in the common ancestor of all living birds or convergently in two or more independent lineages of birds?

A new study conducted by biologists from UC Riverside and Montclair State University suggested that the common ancestor of all living birds lost the ability to produce teeth, and the answer to exactly how this happened can be found in modern-day birds’ genes.

Using the degraded remnants of tooth genes in birds to determine when birds lost their teeth, the team reports in the Dec. 12 issue of Science that teeth were lost in the common ancestor of all living birds more than 100 million years ago.

“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, a professor of biology and one of the lead authors of the study along with Robert Meredith at Montclair State University who was previously a graduate student and postdoctoral researcher in Springer’s laboratory. “DNA from the crypt is a powerful tool for unlocking secrets of evolutionary history.”

Springer explained that edentulism and the presence of a horny beak are hallmark features of modern birds.

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

All toothless/enamelless vertebrates are descended from an ancestor with enamel-capped teeth. In the case of birds, it is theropod dinosaurs. Modern birds use a horny beak instead of teeth, and part of their digestive tract to grind up and process food.

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).

The researchers examined these six genes in the genomes of 48 bird species, which represent nearly all living bird orders, for the presence of inactivating mutations that are shared by all 48 birds. The presence of such shared mutations in dentin and enamel-related genes would suggest a single loss of mineralized teeth in the common ancestor of all living birds.

The study was published in the journal Science on December 12, 2014.