The 15-million-year-old American alligator (Alligator mississippiensis) name is probably an anglicised form of el lagarto, the Spanish term for the lizard, which early Spanish explorers and settlers in Florida called the alligator. The largest reptile in North America, it was first classified by French zoologist François Marie Daudin as Crocodilus mississipiensis in 1801.American alligators live in the freshwater rivers, lakes, swamps, and marshes of the south-eastern United States, primarily Florida and Louisiana. It is larger than the only other living alligator species, the Chinese alligator.