Crocodilians Crocodilians first appeared about 200 million years ago and are believed to be remnants of the great age of reptiles. Their ancestors originally lived on land and were lightly built, but they soon diversified into water-dwelling, or aquatic, and amphibious forms. Except for the alligators, crocodilians live in tropical and subtropical areas of the world. Modern crocodilians are amphibious, spending much of their time in water, where they swim with rhythmic strokes of the tail. The tail is sometimes used to capture prey, sweeping it from shallow to deeper water, where it can be devoured more easily.
Crocodilians are well-adapted as predators, with few natural enemies.
Bony plates, called osteoderms, form a kind of armor in their thick skin. Their teeth, about 30 to 40 in each jaw, are set into sockets in the jawbones and interlock when the mouth is closed. The jaws of crocodilians are powerful enough in closing to crush the bones of small animals, but so weak in opening that they can be held together by hand. As the crocodilian floats almost completely submerged, its protruding nostrils and eyes and a portion of its back are the only parts visible as it stalks its prey. Crocodilians are the most vocal reptiles, producing sounds from quiet hisses to fearsome roars and bellows, usually during the mating season.