Crocodilians have heavily armored bodies. Parts of their skin are hardened into individual hard scales made of fingernail material (keratin) and usually reinforced with bony plates. What they do provide is a tough but flexible body covering. Flexibility is essential for a predator that relies on quick maneuvering. The position of crocodilian eyes and nostrils on top of their heads allow them to lie camouflaged just under the water surface. When prey is near enough to ambush, crocodilians lunge out of the water and clamp down with powerful jaws. While a crocodilian is a great lunger, it cannot sustain long-distance movements. Huge tail and leg muscles help the crocodilian lunge quickly, then twist and pull heavy prey underwater. These characteristics of crocodilians are ancient, as they have retained nearly the same body form during 200 million years on Earth.