The American alligator is the largest reptile in North America, weighing up to 500 pounds and growing up to fourteen feet long. It’s a member of the crocodylian family, which of course includes modern Nile crocodiles. Ancestors predate the dinosaurs, going back to creatures like Xilousuchus, a 3-foot-long hunter. More famous relatives include Deinosuchus a 35-foot croc that battled with T-rex. The supercroc Sarcosuchus may have been the largest ever, measuring around 40 feet long.