Crocodiles are the largest reptiles in the world and the closest living relatives of birds. Both descend from archosaurs. The saltwater crocodile is the most dangerous of all crocodiles. It holds the record for the largest crocodile: it can weigh up to one ton, as much as a small car. While most crocodiles live in rivers and lakes, the saltwater crocodile is the only one that can thrive in both freshwater and the saltwater of the seas. In addition to the saltwater crocodile, there are many other species, totaling 25. These include the Nile crocodile, the freshwater crocodile, alligators, and caimans.