Fossils have been found to prove this. All turtles are tootheless, but have a sharp-edged beak so that they can eat. This works ver well, especially for the Alliga tor Snapping Turtle, who can bite off a human finger in a single bite. Turtles also have a good sense of eyesight and smell. They can be sexually distinguished by their plastrons.
Males have concave plastrons, while females have flat ones.