Alligator mississippiensis is in the family Crocodylidae. This family has existed since the upper Triassic period, but the modern family members appear in the fossil record as little as 80 million years ago. There are three subfamilies, Alligatorinae, Crocodylinae, and Gavaialinae. Some people also include a fourth subfamily, Tomistominae, which contains a single species, the False Gharial. Alligatorinae includes the American and Chinese alligators and the caimans. Crocodylinae includes the crocodiles. Gavaialinae contains the gharials (or gavials). The alligators are unusually tolerant of cold and have been fou