alligator (genus Alligator), either of two crocodilians related to the tropical American caimans (family Alligatoridae). Alligators, like other crocodilians, are large animals with powerful tails that are used both in defense and in swimming. Their eyes, ears, and nostrils are placed on top of their long head and project slightly above the water when the reptiles float at the surface, as they often do. Alligators can be differentiated from crocodiles by the form of their jaw and teeth. Alligators possess a broad, U-shaped snout and have an “overbite”—that is, all the teeth of the lower jaw fit within (lingual to) the teeth of the upper jaw. The large fourth tooth on each side of the alligator’s lower jaw fits into a socket in the upper jaw. Usually, no lower teeth are visible when the mouth is closed. In contrast, crocodiles have a narrow, V-shaped snout, and the large fourth tooth on each side of the crocodile’s lower jaw projects outside the snout when the mouth is closed. Alligators are carnivorous and live along the edges of permanent bodies of water, such as lakes, swamps, and rivers. They commonly dig burrows in which they rest and avoid weather extremes. The average life span of alligators is about 50 years in the wild. However, there have been reports of some specimens living beyond 70 years of age in captivity.
The American alligator (Alligator mississippiensis), the larger of the two species, is found in the southeastern United States. It is black with yellow banding when young and is generally brownish when adult. The maximum length is about 5.8 metres (19 feet), but it more typically ranges from about 1.8 to 3.7 metres (6 to 12 feet). The American alligator has been hunted for its hide, and its young have been sold in large numbers as pets. It disappeared from many areas where it was once abundant and was later given legal protection from hunters, until it made an excellent comeback and limited hunting seasons were again established. The adult alligator feeds mainly on fishes, small mammals, and birds but may sometimes take prey as large as deer or cattle. Members of both sexes hiss, and the males also give loud roars that carry over considerable distances. During the breeding season, the female builds a mound nest of detritus and vegetation in which she buries about 20 to 70 hard-shelled eggs. She guards the eggs and may at this time be dangerous. Members of this species usually avoid humans.
The Chinese alligator (A. sinensis) is a much smaller, little-known reptile found in the Yangtze River region of China. It is similar to the larger form but attains a maximum length of about 2.1 metres (7 feet)—although usually to 1.5 metres—and is blackish with faint yellowish markings. It is considered endangered by the International Union for Conservation of Nature and Natural Resources (IUCN).