Crocodylia

Crocodylia is a clade of large, semiaquatic reptiles that includes all living crocodilians: alligators, caimans, crocodiles, and gharials. It represents the crown group of crocodilians and includes three living families—Alligatoridae, Crocodylidae, and Gavialidae—as well as numerous extinct relatives.

They inhabit tropical and subtropical regions across Africa, the Americas, Asia, and Australia, occupying rivers, swamps, marshes, lakes, estuaries, and coastal habitats. They are highly aquatic in habit, with eyes and nostrils positioned on top of the head, a strong, laterally compressed tail, and a powerful bite. Their skin bears thick osteoderms for protection.

Crocodilians are ectothermic carnivores with diverse feeding strategies, ranging from ambush hunting to active pursuit depending on species and habitat. They prey on fish, reptiles, birds, and mammals. Reproduction is oviparous; many species construct nests and exhibit extensive maternal care, guarding eggs and assisting hatchlings to water. In many crocodilians, incubation temperature influences the sex of offspring—an example of temperature-dependent sex determination.

The fossil record shows crocodilians originated in the Late Triassic, with the three modern lineages diverging in the early to middle Cenozoic. Today about 23 living species are recognized, distributed across Africa, the Americas, Asia, and Australia, ranging from small caimans to the large saltwater crocodile and the gharial.

Conservation concerns are common, as habitat destruction, hunting, pollution, and water management pressures affect many species. A number of crocodilians are protected, and several are listed as threatened or endangered by IUCN assessments.