New York: Using the degraded remnants of tooth genes in birds to determine when birds lost their teeth, researchers have found that teeth were lost in the common ancestor of all living birds more than 116 million years ago.
The absence of teeth or "edentulism" has evolved on multiple occasions within vertebrates including birds, turtles and a few groups of mammals such as anteaters, baleen whales and pangolins.
As far as the case of early birds is concerned, the fossil record is fragmentary.
Now, a research team led by biologists at University of California (UC)- Riverside and Montclair State University, New Jersey, has found an answer.
"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 professor Mark Springer, one of the lead authors from UC - Riverside.
Springer explained that "edentulism" and the presence of a horny beak are hallmark features of modern birds.
All toothless and enamel-less vertebrates have descended from an ancestor with enamel-capped teeth.
In 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 which involves many different genes.
Of these genes, six are essential for the proper formation of dentin and enamel.
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.
Springer and Robert Meredith from Montclair State University found that 48 bird species share inactivating mutations in both dentin-related and enamel-related genes, indicating that the genetic machinery necessary for tooth formation was lost in the common ancestor of all modern 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 noted.
The study appeared in the journal Science.