The prehistoric ancestors of modern birds were equipped with teeth, but now, birds are left with merely a beak. New research has revealed when and why this happened.

Birds are the modern day ancestors of dinosaurs. But unlike their predecessors, birds nowadays no longer have teeth.

Until recently, scientists didn't know when or how. Now, after sequencing the genomes of 48 different bird species representing most avian orders, they were able to find when the switch happened from teeth to beaks.

The research was led by professor of biology Mark Springer, from the University of California at Riverside.

Upon examining the genomes, mutations were found amongst all them. This led scientists to believe it was a common ancestor of birds who eventually stopped producing enamel-covered teeth around 116 million years ago.

Still, it was an evolutionary change that occurred over time. Fossils found have shown that certain birds had beaks in the front of their mouths, and teeth in the back.

Many genes are required to form teeth, with six genes necessary to create dentin and enamel.

Beaks proved to be more useful, helping birds build nests, feed themselves and their young, and as a defense mechanism.

Of the findings, Springer said, "Our results highlight the power of DNA from the crypt to unravel the evolutionary history of vertebrates. Together, genomic fossils and fossils from rocks provide a powerful combination for reconstructing the past."