The common name used for 15 species of large reptiles included in the family Crocodylidae, one of the three families of the order Crocodylia, which also includes the alligators, caimans, and gharials (also known as gavials). Like all crocodilians, the crocodiles are distributed throughout the tropical and subtropical regions of the world. Species occur in both saltwater and freshwater habitats. Crocodiles are generally carnivorous, feeding on invertebrates, fish, other reptiles, amphibians, birds, and mammals. A few, very narrow snouted species are believed to subsist primarily on fish. Crocodiles are primarily aquatic and nocturnal, leaving the water only to bask by day or to build their nests. Some species construct burrows into the banks of rivers or lakes where they spend part of their time.