A study suggests that ancient elephants used selective pressure to adapt a different set of teeth to graze in a habitat that changed from forest to grassland. Researchers studied fossilized elephant teeth to track the feeding behavior change, which occurred about 7 million years ago, and found that the elephants' teeth did not evolve until 3 million years later. "It only makes sense that behavior is a powerful driver of evolution, and that by taking the behavioral step to eat grass, it imposes the selection pressure for the right kind of teeth. ... This is the first example from the fossil record," said paleontologist Adrian Lister.