An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator (Alligator mississippiensis) and the Chinese alligator (Alligator sinensis).
The name alligator is an anglicized form of el lagarto, the Spanish term for "lizard", which early Spanish explorers and settlers in Florida called the alligator.
Alligators have a variety of successful adaptations to their ecological niche that have allowed these reptiles to remain almost unchanged for 200 million years.
Font: http://en.wikipedia.org/wiki/Alligator (5 years and 2125 days ago)