Most crocodiles are more aggressive than the related alligators . The two forms are distinguished by the long lower fourth tooth: in crocodiles, but not in alligators, this tooth protrudes on the side of the head when the mouth is closed. Also, the snouts of most crocodiles are narrower than those of alligators.
Small crocodiles feed on fish and small aquatic animals; larger ones also catch land mammals and birds that approach the water. Members of some large species sometimes attack and eat humans. The female crocodile deposits her eggs, usually about 20 in number, in a nest of rotting vegetation or in a shallow pit on the river bank, and digs them up when she hears them hatching.
In most species the average adult length is between 6 and 10 ft (1.8–3 m). The largest crocodile (the saltwater crocodile) is often 14 ft (4.3 m) long and may exceed 20 ft (6 m) in length. The Nile, American, and Orinoco crocodiles are commonly 12 ft (3.7 m) long, and specimens up to 23 ft (7 m) long have been reported for the last two species. The extinct Sarcosuchus imperator, which lived during the Cretaceous period, may have approached 40 ft (12 m) in length. The smallest crocodile (the Congo dwarf crocodile) averages 3 1⁄2 ft (105 cm) long.
With the exception of the two African dwarf crocodiles ( Osteolaemus ) and the so-called false gavial ( Tomistoma ) of Asia, crocodiles are classified in the genus Crocodylus, with about a dozen species. The Nile crocodile ( C. niloticus ) is found in fresh- and saltwater throughout S and central Africa. In early historic times it ranged N to the Nile delta and the Mediterranean coast. It sometimes attacks humans, as does the saltwater crocodile ( C. porosus ), found on islands and in straits from SE Asia to Australia and Melanesia. The marsh crocodile, or mugger ( C. palustris ), is a freshwater species of India and Sri Lanka, regarded as sacred in some regions. The American crocodile ( C. acutus ) is found in fresh- and saltwater in S Florida, the West Indies, Central America, and NW South America. It does not attack humans without provocation. The Orinoco crocodile ( C. intermedius ) is a freshwater species of the Orinoco basin of Colombia and Venezuela. Two smaller species are found in limited areas of Central America and Cuba.
Crocodiles are classified in the phylum Chordata , subphylum Vertebrata, class Reptilia, order Crocodilia, family Crocodilidae.
See also gavial .
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