There are several differences between alligators and crocodiles. Alligators have shorter and wider snouts. They prefer fresh water to saltwater. Crocodiles have a gland that removes much of the salt. Alligators do not have this gland. In alligators, the fourth tooth of their lower jaw fits into a pit in the upper jaw. In crocodilians this tooth fits into a groove on the outside of the jaw. Alligators are also less aggressive than crocodilids. Usually only the largest of the species are a threat to humans.