Crocodilia

Crocodilia; Temporal range:
	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 (or Crocodylia, both /krɒkəˈdɪliə/) is an order of egg-laying, mostly semiaquatic, predatory reptiles known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds, both being the last surviving Archosaurs. Crocodilians are a type of Crocodylomorph Pseudosuchian, a subset of Archosaurs that appeared about 235 million years ago in the Late Triassic period and were the only survivors of the End-Triassic Extinction Event. The order Crocodilia includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharial and false gharial (family Gavialidae). Notable extinct groups include the Mekosuchines, a diverse lineage of semiaquatic and terrestrial crocodiles from Australasia, and potentially the Planocraniids, a terrestrial, hooved lineage adapted for running on land. Although the term crocodiles (or crocs) is sometimes used to refer to all of these, it is less ambiguous to use the term “crocodilians” when talking about this group.

Solidly built animals, extant crocodilians have long flattened snouts and laterally compressed tails, with their eyes, ears, and nostrils at the top of the head. They are good swimmers and can move on land in a “high walk” position, traveling with their legs erect rather than sprawling. While most can’t do it for long, many species can gallop. 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. Still, like most other reptiles, they are ectothermss.

Crocodilians are found mainly in lowlands in the tropics, but alligators also live in the southeastern United States and the Yangtze River in China. They have a largely carnivorous diet, feeding on animals such as fish, crustaceans, mollusks, birds, and mammals. 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 are known to have attacked humans. The largest number of attacks comes from the Nile crocodile. 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. The earliest known mention of the story that crocodiles weep for their victims was in the 9th century; it was later spread by Sir John Mandeville in 1400 and then by William Shakespeare in the late 16th and early 17th century.