When Birds Lost Their Teeth

Image of the cover of Science Magazine, featuring Robert Meredith's research.Until recently, scientists studying the evolution of Earth's species had long wondered whether teeth were lost in the common ancestor of all living birds – or whether they were lost in independent bird lineages. That question was answered by researchers from Montclair State and the University of California, Riverside, who last year made the remarkable discovery that the common ancestor of all living birds lost its teeth roughly 116 million years ago.

Toothless vertebrates such as birds and turtles, along with such toothless mammals as anteaters and baleen whales, all descended from ancestors with enamel-capped teeth. Modern birds, which evolved from toothed theropod dinosaurs such as Tyrannosaurus rex, use a horny beak and muscular gizzard instead of teeth to grind up and process their food.

Until this discovery, information about when birds lost their teeth remained elusive. But through the sequencing of the genomes of 48 bird species, a research team — led by Montclair State Biology Professor Robert Meredith and collaborator Mark Springer, a biology professor at UC Riverside — was able to establish the evolutionary timeline regarding teeth. Their study, titled "Evidence for Tooth Loss and the Acquisition of a Horny Beak in the Common Avian Ancestor," published in the December 12, 2014, issue of Science, was a breakthrough in evolutionary science that opens up new areas of study.

For the past several years, Meredith has been involved in the Avian Genome Working Group, an international collaboration of researchers at universities and museums. "The group has been sequencing and analyzing the genomes of representatives of 48 major bird lineages, including ostriches, chickens, ducks, raptors and songbirds," Meredith explains.

"The group has been sequencing and analyzing the genomes of representatives of 48 major bird lineages."
–Robert Meredith

Meredith's research team examined remnants of tooth genes in living bird genomes to determine that bird edentulism – or absence of teeth – stems from a common ancestor.

All genomes of toothless vertebrates that the team has looked at so far have inactivating mutations in dentin and enamel-related genes that render them non-functional. "All bird genomes share inactivating mutations in some tooth-related genes, which provide the molecular evidence for our hypothesis that teeth — or at least the enamel caps — were lost in the common ancestor of modern birds."