Answer:
The American alligator, Alligator mississippiensis, sometimes referred to colloquially as a gator or common alligator, is a large crocodilian reptile native to the Southeastern United States and northeastern Mexico.
I believe it is the last one. Thi is because Alligators are chordates and therefore vertebrates; this means they have backbones. And we all know that an alligator is a reptile.