According to a recent study conducted by a team of biologists from the University of California, Riverside and Montclair State University in New Jersey, it appears that birds descended from a toothed reptile, and that different species of birds slowly developed genetic mutations that didn’t allow them to develop tooth enamel, thus causing too many dental problems to sustain a full set of teeth.

By looking at six different genes that affect tooth growth and maintenance in all species, researchers examined 48 different species of living birds and found that the birds all had mutations in the genes that affect the production of enamel (the hard outer covering of a tooth) and dentin (the hard calcified material underneath the enamel).

Scientists have known for a while that modern bird species descended from ancient bird-reptile hybrids (LiveSciencespecifically notes the 1861 discovery of the famous bird-reptile Archaeopteryx fossil), and they knew that these ancestors were most likely toothed carnivores. But it has never been clear if birds slowly evolved into toothless animals, or if the earliest bird ancestor lost its teeth before evolving into separate species of birds.

Although each modern species in the study shared the same genetic mutation, researchers noted that the closest reptilian relative of birds — alligators — have all genes without mutations. The scientists concluded, therefore, that the mutation must have occurred early enough to affect so many species, but late enough that it didn’t affect the bird-reptile ancestors that branched off into modern reptile species too.

Ultimately, the scientists concluded, the mutation probably occurred around 116 million years ago.

As Latin Post reporter Chaka Phillips notes, the study has revealed some important details about the evolution of birds, specifically pertaining to when and how they branched away from other reptiles. Nevertheless, scientists still don’t know why the loss of teeth wasn’t a bigger problem for birds.

When tooth loss occurs in other animals, the results are often catastrophic; when a human loses multiple teeth or experiences tooth decay, for example, the body’s entire health starts deteriorating — something that has influenced the rise of specialized dental practices for tooth reshaping, bonding, and even replacement dentures or implants.

Birds, on the other hand, managed to develop curved beaks and well-functioning digestive systems to make up for their tooth loss.

But perhaps the answer to that question is the responsibility of another research team; for now, anyone interested in the specifics of the study can find the group’s official report in the December 12 issue of Science.