Crocodilians.
Crocodilians first appeared about 200 million years ago and are believed to be the last remnants of the great age of reptiles. They originally lived on land and were lightly built, but soon diversified into water-dwelling, or aquatic, and amphibious forms. Except for the alligators and the American crocodile, crocodilians live in tropical 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 also 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 form a kind of armor in their thick skin. Their teeth, 30 to 40 in each jaw, are set into sockets in the jawbones and interlock when the mouth is closed; two of the bottom teeth protrude in all crocodilians except alligators. The jaws 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 it floats almost completely submerged, the crocodilian's 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. They move most quickly in a belly crawl, but can also walk mammal-like on all four legs.
Crocodilians are physiologically the most advanced reptiles; their internal anatomy resembles that of birds. They have a four-chambered heart and well-developed senses. Cold-blooded like all reptiles--their body temperature depends on the environment--crocodilians bury themselves in mud to estivate or hibernate; in warm regions they are dormant during droughts, in colder regions during winter.
Crocodilians are egg-laying, or oviparous, reptiles, reaching reproductive maturity at about the age of ten. The eggs, 20 to 90 in number and about the size of goose eggs, are buried in sand, mud, or vegetable debris, where they are left to hatch by the heat of the sun or of vegetable decomposition. Females of some species remain in the area to protect the nest and care for the newly hatched young, although many of the eggs and young are lost to predators. The parental behavior of crocodilians is unique among reptiles and points to their affinity with birds.
See ALLIGATOR; CAIMAN; GAVIAL,.
The Crocodile.
The crocodile genus includes the largest living reptiles. Crocodiles can be recognized by their long, triangular snouts, intermediate between the long, narrow snout of the gavial and the short, oval snout of the alligator. The saltwater crocodile, possibly the largest living reptile, ranges up to 9 m (30 ft) in length. It inhabits the coastal waters of India, southern China, and Malaysia. A smaller species, the swamp crocodile, or mugger, occupies the same area farther inland. The Nile crocodile of Egypt was revered by certain ancient Egyptian sects. In modern times this species has been hunted so extensively that few remain in the lower Nile, but they are still abundant in the upper Nile and southward in Africa to the Cape of Good Hope. Crocodiles found in the New World include three smaller species, restricted to Cuba, Central America, and Venezuela, and the largest species, the American crocodile (4 m/14 ft), ranging from Brazil as far north as Florida.
Crocodile eggs are used for food in some parts of the world, the skin is highly valued for leather, and the extract from the musk glands is used in the manufacture of perfume. Due to overhunting, the American and Nile crocodiles are considered endangered species.
For further information on this topic, see the Bibliography, section 470. Reptile and amphibian.
COMMON NAME FAMILY GENUS AND SPECIES Saltwater crocodile Crocodylidae Crocodylus porosus Swamp crocodile Crocodylidae C. palustris Nile crocodile Crocodylidae C. niloticus American crocodile Crocodylidae C. acutus