Crocodilia

Crocodilia Temporal range: Late Cretaceous – Present PreꞒ Ꞓ O S D C P T J K Pg N
Clockwise from top-left: saltwater crocodile (Crocodylus porosus), American alligator (Alligator mississippiensis), and gharial (Gavialis gangeticus)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Crocodylomorpha
Clade:	Crocodyliformes
Clade:	Eusuchia
Order:	Crocodilia Owen, 1842
Subgroups
Alligatoroidea Alligatoridae Longirostres Gavialoidea Gavialidae Crocodyloidea Crocodylidae †Mekosuchinae †?Planocraniidae †Pristichampsidae †Prodiplocynodon †Asiatosuchus †Brachyuranochampsa †"Crocodylus" affinis †"Crocodylus" acer
Crocodylia distribution on land (green) and at sea (blue)

Crocodilia (/krɒkəˈdɪliə/) is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchian, a subset of archosaurs that appeared about 235 million years ago and were the only survivors of the Triassic–Jurassic extinction event. While other crocodylomorph groups further survived the Cretaceous–Paleogene extinction event, notably sebecosuchians, only the crocodilians have survived into the Quaternary. The order includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharial and false gharial (family Gavialidae). Although the term "crocodiles" is sometimes used to refer to all of these families, the term "crocodilians" is less ambiguous.

Extant crocodilians have flat heads with long snouts and tails that are compressed on the sides, with their eyes, ears, and nostrils at the top of the head. Alligators and caimans tend to have broader U-shaped jaws that, when closed, show only the upper teeth, whereas crocodiles usually have narrower V-shaped jaws with both rows of teeth visible when closed. Gharials have extremely slender, elongated jaws. The teeth are conical and peg-like, and the bite is powerful. All crocodilians are good swimmers and can move on land in a "high walk" position, traveling with their legs erect rather than sprawling. Crocodilians have thick skin covered in non-overlapping scales and, like birds, crocodilians have a four-chambered heart and lungs with unidirectional airflow.

Like most other reptiles, crocodilians are ectotherms. They are found mainly in the warm and tropical areas of the Americas, Africa, Asia, and Oceania, usually occupying freshwater habitats, though some can live in saline environments and even swim out to sea. Crocodilians have a largely carnivorous diet; some species like the gharial are specialized feeders while others, like the saltwater crocodile, have generalized diets. They are generally solitary and territorial, though they sometimes hunt in groups. During the breeding season, dominant males try to monopolize available females, which lay their eggs in holes or mounds and, like many birds, they care for their hatched young.

Some species of crocodilians, particularly the Nile crocodile, are known to have attacked humans, which through activities that include hunting, poaching, and habitat destruction are the greatest threat to crocodilian populations. Farming of crocodilians has greatly reduced unlawful trading in skins of wild-caught animals. Artistic and literary representations of crocodilians have appeared in human cultures around the world since Ancient Egypt.