Humans and many animals depend on their teeth for grinding and processing food but modern birds use their curved beaks and digestive tract for these purposes. Birds do not have teeth but this isn't the case 116 million years ago.

The discovery of the skeleton of the Archaeopteryx, a transitional species between feathered dinosaurs and present-day birds, in Germany in 1861 suggested that birds evolved from toothed reptile ancestors. Scientists are now aware that birds originated from theropod dinosaurs that include the likes of the Tyrannosaurus rex, carnivorous beasts characterized by a mouth full of sharp teeth for reaping the flesh of their prey.

Scientists did not exactly know what happened why the feathered animals developed edentulism, the condition of being toothless. Findings of a new study, however, shed light on what happened during the evolution of birds that could explains why they no longer have teeth.

For a new study published in the journal Science on Dec. 12, a group of researchers looked at the genes that play roles in tooth production. Six genes are involved in tooth formation among vertebrates and these govern the formation of the enamel, the tissue that coats and protects the teeth, and dentin, the calcified tissue covered by the enamel.

Study researcher Mark Springer, from the Department of Biology of the University of California, Riverside, and colleagues searched for mutation that could have inactivated these genes by using data from whole-genome sequencing of 48 species of birds that represent nearly every order of living birds and the American alligator to represent the order Crocodylia known to be the living relatives of the birds.

The researchers found that all of the bird species they looked at shared the same inactivating mutations in the dentin and enamel-related genes, which means that their common ancestor lost the capability to form teeth. The six genes, on the other hand, were all found to be functional in the American alligator.

"48 bird species share inactivating mutations in both dentin-related (DSPP) and enamel-related genes (ENAM,AMELX, AMTN, and MMP20), indicating that the genetic machinery necessary for tooth formation was lost in the common ancestor of all modern birds," the researchers wrote adding that the teeth's outer enamel covering was likely lost approximately 116 million years ago.

The researchers said that the mutations played a role in the development of the bird's beak, which essentially plays the role of the teeth among avian species and contributed to the diversification of the species.

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