| Crocodilia Temporal range:
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|---|---|
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| Clockwise from top-left: saltwater crocodile (Crocodylus porosus), American alligator (Alligator mississippiensis), and gharial (Gavialis gangeticus) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Crocodyliformes |
| Clade: | Eusuchia |
| Order: | Crocodilia Owen, 1842 |
| Subgroups | |
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| Crocodylia distribution on land (green) and at sea (blue) | |
Crocodylia /krɒkəˈdɪliə/) is an order of semiaquatic, predatory reptiles 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. 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, it is less ambiguous to use "crocodilians".
Extant crocodilians have long flat heads with long snouts and tails 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, only show the upper teeth, while crocodiles usually have narrower V-shaped jaws with both rows of teeth visible when closed. Gharials have extremely slender and elongated jaws. 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. They have conical, peg-like teeth and a powerful bite. Like birds, crocodilians possess a four-chambered heart and lungs with unidirectional airflow. Like most other reptiles, they are ectotherms.
Crocodilians are found mainly in the warmer and tropical areas of the Americas, Africa, Asia and Oceania. They usually inhabit freshwater habitats, but some can live in saltier environments and even swim out to sea. They have a largely carnivorous diet. Some species like the gharial are specialized feeders, while others like the saltwater crocodile have generalized diets. Crocodilians are generally solitary and territorial, though they sometimes hunt in groups. During the breeding season, dominant males try to monopolize available females. Females lay their eggs in holes or mounds, and similar to many birds, care for their hatched young.
Some species of crocodilians (particularly the Nile crocodile) are known to have attacked humans. Humans are the greatest threat to crocodilian populations through activities that include hunting, poaching, and habitat destruction, but farming of crocodilians has greatly reduced unlawful trading in wild skins. Artistic and literary representations of crocodilians have appeared in human cultures around the world since Ancient Egypt.