Evolution of teeth in frogs has long interested scientists why some species have teeth on the upper jaw, others only have fangs, some and completely toothless, and the fourth has teeth on both jaws? To find out, the authors studied MRI scans of almost all living amphibians, about 20,000 specimens, and turned to a genetic-based map of evolutionary relationships among amphibians.
It turned out that frogs lost and re-grew teeth more than 20 times over the course of evolution than any other vertebrate group. Diet played an important role: teeth were lost in those who ate small insects like ants and termites.
Having teeth on the jaw to grasp and hold prey becomes less important, as frogs feed on very small invertebrates that they can send into their mouths with their tongue, the researchers explain. This seems to relieve the pressure of natural selection to retain teeth.
Similar changes have occurred with other amphibians, such as salamanders, the scientists note. The insect-eating mammals pangolins and anteaters also lack teeth.
In the future, questions about the genes associated with the presence and absence of teeth remain to be clarified. It is also unclear whether the denticles on the jaws of some frog species that have lost their teeth in the past can be considered teeth. Scientists hope that modern technology will allow them to fill in the gaps in animal knowledge.