Reptile of the genus Alligator, related to the crocodile. There are only two living species: A. mississipiensis, the Mississippi alligator of the southern states of the USA, and A. sinensis from the swamps of the lower Chang Jiang River in China. The former grows to about 4 m/12 ft, but the latter only to 1.5 m/5 ft. Alligators lay their eggs in waterside nests of mud and vegetation and are good mothers. They swim well with lashing movements of the tail and feed on fish and mammals but seldom attack people.

The skin is of value for fancy leather, and alligator farms have been established in the USA. Closely related are the caymans of South America; these belong to the genus Caiman. Alligators ranged across northern Europe from the Upper Cretaceous to the Pliocene period.

Alligators differ from caymans by having a bony septum between the nostrils; they differ from crocodiles by having a broad head, depressed and obtuse muzzle, and unequal teeth, the fourth from the front on each side of the lower jaw being elongated and fitting into a cavity in the upper jaw when the mouth is closed.