Crocodile

A crocodile (family Crocodylidae) or true crocodile is a large, semiaquatic reptile. It lives in warm places called the tropics in Africa, Asia, the Americas and Australia. Sometimes the word "crocodile" is used more loosely. It can include all living members of the order Crocodilia. That group includes the alligators and caimans (both in the family Alligatoridae), and the gharial and false gharial (both in the family Gavialidae). This article uses "crocodile" or "true crocodile" only for the animals in the Crocodylidae family, living or extinct.

Crocodiles differ in size, morphology, behaviour and ecology from one species to another. They also share many features. All crocodiles are semiaquatic. They usually gather in freshwater places such as rivers, lakes and wetlands. Sometimes they live in brackish water and saltwater.

Crocodiles are carnivorous animals, which means they eat meat. They mostly eat animals with backbones, such as fish, reptiles, birds and mammals. Sometimes they eat invertebrates like molluscs and crustaceans. What they eat depends on the species and how old the animal is.

All crocodiles are tropical species. Unlike alligators, they are very sensitive to cold.

Many crocodile species are at risk of extinction. Some are classified as critically endangered, which means they are in very great danger of disappearing.

Etymology

The word crocodile (croc.) came into English during the Middle English period. It comes from the transliteration krokódilos, a Greek word that means "stones worm." The word spread through Ancient Greece and the English language. Its Greek origins are linked to Anatolia. The earliest surviving Ancient Greek source is an Aesop's Fable from the sixth century BC, called Ἀλώπηξ καὶ κροκόδειλος. A century later, Herodotus thought the Greek word came from the Ionic period. The Latin language word crocodilus appears in the first century AD in the work Naturalis Historia by Pliny the Elder. Other forms, such as crocodillorum and crocodili, appear in writing from the sixth and seventh centuries AD. Words like corcodrillus and cocodrillus were used in Medieval Latin.

By around the 13th century, the Latin form appeared as cocodrille in the Old French work Li livres dou tresor. In that work, the crocodile is described as jaune (yellow). The earliest known English source is Kyng Alisaunder, written near the start of the 14th century. It is a magical romance poem written in rhyming couplets. Around 1483, Felix Fabri used the word in German and Latin after visiting the Holy Lands. By 1538 the modern English form was found in French. The word croc. appears in a poem by Edmund Spenser, thought to be written in 1579–80, and in the works of William Shakespeare, who died in 1616. The anatomical work of Andreas Vesalius, published in 1543, inspired new books about animals. These books helped the new science of zoology grow.

Taxonomy and phylogeny

Species

Scientists have found 18 living species of crocodile so far. More genetic study is needed to confirm the species proposed in the group Osteolaemus.

Tomistoma, also called the false gharial, is no longer thought to be a true crocodile. To learn more, see False gharial.

Species name	Distribution	Description/Comments
American crocodile (Crocodylus acutus)	Throughout the Caribbean Basin, including many of the Caribbean islands and South Florida.	A larger sized species, with a greyish colour and a prominent V-shaped snout. Prefers brackish water, but also inhabits lower stretches of rivers and true marine environments. This is one of the rare species that exhibits regular sea-going behaviour, which explains the great distribution throughout the Caribbean. It is also found in hypersaline lakes such as Lago Enriquillo, in the Dominican Republic, which has one of the largest populations of this species. Diet consists mostly of aquatic and terrestrial vertebrates. Classified as Vulnerable, but certain local populations under greater threat.
Hall's New Guinea crocodile (Crocodylus halli)	The island of New Guinea, south of the New Guinea Highlands	A smaller species that closely resembles and was long classified under the New Guinea crocodile, which it is now considered to be genetically distinct from. It lives south of the mountain barrier that divides the two species' ranges. It can be physically distinguished from the New Guinea crocodile by its shorter maxilla and enlarged postcranial elements. Cranial elements can still widely vary within the species, with populations from Lake Murray having much wider heads than those from the Aramia River.
Orinoco crocodile (Crocodylus intermedius)	Colombia and Venezuela	This is a large species with a relatively elongated snout and a pale tan coloration with scattered dark brown markings. Lives primarily in the Orinoco Basin. Despite having a rather narrow snout, preys on a wide variety of vertebrates, including large mammals. It is a Critically Endangered species.
Freshwater crocodile (Crocodylus johnstoni)	Northern Australia	A smaller species with a narrow and elongated snout. It has light brown coloration with darker bands on body and tail. Lives in rivers with considerable distance from the sea, to avoid confrontations with saltwater crocodiles. Feeds mostly on fish and other small vertebrates.
Philippine crocodile (Crocodylus mindorensis)	Endemic to the Philippines	This is a relatively small species with a rather broader snout. It has heavy dorsal armour and a golden-brown colour that darkens as the animal matures. Prefers freshwater habitats and feeds on a variety of small to medium sized vertebrates. This species is Critically Endangered and the most severely threatened species of crocodile.
Morelet's crocodile (Crocodylus moreletii)	Atlantic regions of Mexico, Belize and Guatemala	A small to medium sized crocodile with a rather broad snout. It has a dark greyish-brown colour and is found in mostly various freshwater habitats. Feeds on mammals, birds and reptiles. It is listed as Least Concern.
Nile crocodile (Crocodylus niloticus)	Sub-Saharan Africa	A large and aggressive species with a broad snout, especially in older animals. It has a dark bronze coloration and darkens as the animal matures. Lives in a variety of freshwater habitats but is also found in brackish water. It is an apex predator that is capable of taking a wide array of African vertebrates, including large ungulates and other predators. This species is listed as Least Concern.
New Guinea crocodile (Crocodylus novaeguineae)	The island of New Guinea, north of the New Guinea Highlands	A smaller species of crocodile with a grey-brown colour and dark brown to black markings on the tail. The young have a narrower V-shaped snout that becomes wider as the animal matures. Prefers freshwater habitats, even though is tolerant to salt water, in order to avoid competition and predation by the saltwater crocodile. This species feeds on small to mid-sized vertebrates.
Mugger crocodile (Crocodylus palustris)	The Indian subcontinent and surrounding countries	This is a modest sized crocodile with a very broad snout and an alligator-like appearance. It has dark-grey to brown coloration. Enlarged scutes around the neck make it a heavily armoured species. Prefers slow moving rivers, swamps and lakes. It can also be found in coastal swamps but avoids areas populated by saltwater crocodiles. Feeds on a wide array of vertebrates.
Saltwater crocodile (Crocodylus porosus)	Throughout Southeast Asia, Northern Australia and surrounding waters	The largest on average living reptile and most aggressive of all crocodiles. It is a big-headed species and has a relatively broad snout, especially when older. The coloration is pale yellow with black stripes when young but dark greenish-drab coloured as adults. Lives in brackish and marine environments as well as lower stretches of rivers. This species has the greatest distribution of all crocodiles. Tagged specimens showed long-distance marine travelling behaviour. It is the apex predator throughout its range and preys on virtually any animal within its reach. It is classified as Least Concern but with several populations under greater risk.
Borneo crocodile (Crocodylus raninus)	Island of Borneo in Southeast Asia	A freshwater species of crocodile that has been considered a synonym of the saltwater crocodile.
Cuban crocodile (Crocodylus rhombifer)	Found only in the Zapata Swamp and Isle of Youth of Cuba	It is a small but extremely aggressive species of crocodile that prefers freshwater swamps. The coloration is vibrant even as adults and the scales have a "pebbled" appearance. It is a relatively terrestrial species with agile locomotion on land, and sometimes displays terrestrial hunting. The snout is broad with a thick upper-jaw and large teeth. The unique characteristics and fossil record indicates a rather specialized diet in the past, preying on megafauna such as the giant sloth. This species sometimes displays pack-hunting behaviour, which might have been the key to hunting large species in the past, despite its small size. Today most prey are small to medium sized vertebrates. It is Critically Endangered, and the remaining wild population is under threat of hybridization.
Siamese crocodile (Crocodylus siamensis)	Indonesia, Brunei, East Malaysia and southern Indochina	A fairly small crocodile that prefers freshwater habitats. It has a relatively broad snout and olive-green to dark green coloration. It feeds on a variety of small to mid-sized vertebrates. Listed as Critically Endangered, but might be already extinct in the wild; status is unknown.
West African crocodile (Crocodylus suchus)	Western and Central Africa	Recent studies revealed that this is distinct species from the larger Nile crocodile. It has a slightly narrower snout and is much smaller compared to its larger cousin.
Osborn's dwarf crocodile (Osteolaemus osborni)	Western Africa	It is a heavily armoured species with uniform black coloration in adults, while juveniles have a lighter brown banding. Lives in the tropical forests of Western Africa. Feeds on small vertebrates and large aquatic invertebrates. It is a fairly terrestrial species and exhibits terrestrial hunting, especially at night.
Dwarf crocodile (Osteolaemus tetraspis)	Western Africa	It belongs to its own monotypic genus; however, new studies indicate there might be two or even three distinct species. It is a heavily armoured species with uniform black coloration in adults, while juveniles have a lighter brown banding. Lives in the tropical forests of Western Africa. Feeds on small vertebrates and large aquatic invertebrates. It is a fairly terrestrial species and exhibits terrestrial hunting, especially at night. This species is classified as Vulnerable.
West African slender-snouted crocodile (Mecistops cataphractus)	Western Africa	A medium sized species with a narrow and elongated snout. Lives in freshwater habitats within tropical forests of the continent. Feeds mostly on fish but also other small to medium sized vertebrates. It is a Critically Endangered species.
Central African slender-snouted crocodile (Mecistops leptorhynchus)	Central Africa	A medium sized species found in watery areas in dense rainforest. Feeds largely on fish. Insufficient conservation data, but was classified as Critically Endangered when lumped with M. cataphractus, although M. leptorhynchus is doing better in its home range.

Characteristics

Crocodiles are similar to alligators and caimans. For their shared traits and differences, see Crocodilia.

Crocodiles are large predator animals built for life in water. Their morphology shows that they are aquatic, and their streamlined bodies help them swim fast. While swimming, they tuck their feet to their sides to move through water more easily. Their webbed feet help them make quick turns and sudden moves, and in shallow water they sometimes walk. A palatal flap at the back of the mouth keeps water out. A special path runs from the nostril to the glottis and goes around the mouth. Their tongues are held in place, so they cannot stick them out. Like other archosaurs, crocodilians are diapsid, though their post-temporal fenestrae are reduced. Their backs have large osteoderms and scales that offer some protection, while their bellies and sides are smooth. A network of tiny capillaries lets blood absorb heat through the scales. Pores on the jaws are believed to sense movement, similar to the lateral line in fish.

Crocodiles vary greatly in size, from the dwarf crocodile to the saltwater crocodile, which can grow over 6 m (20 ft) long and weigh over 1,000 kg (2,200 lb). Males grow much larger and faster than females. Crocodiles start life at about 20 cm (7.9 in) long. The saltwater crocodile is the largest species and lives in eastern India, northern Australia, South-east Asia, and nearby waters. Two adult crocodiles had brain volumes of 5.6 cm³ for a spectacled caiman and 8.5 cm³ for a larger Nile crocodile. The largest crocodile ever kept in captivity was Yai, a saltwater–Siamese hybrid at the Samutprakarn Crocodile Farm and Zoo in Thailand. It measured 6 m (20 ft) long. The longest crocodile captured alive was Lolong, a saltwater crocodile that measured 6.17 m (20.2 ft) in the Philippines. Crocodiles are polyphyodonts, which means they can replace each of their 80 teeth up to 50 times over a lifespan of 35 to 75 years. Beside each tooth is a small replacement tooth and an odontogenic stem cell in the dental lamina. These can be activated when needed.

Biology and behaviour

Crocodiles are more closely related to birds and other dinosaurs than to most reptiles. They belong to the group Archosauria, which means "ruling reptiles." Crocodiles may look ancient, but they are among the more complex reptiles. Unlike other reptiles, they have a cerebral cortex and a heart with four chambers. Their eyes, ears and nostrils sit on top of their heads, so they can lie almost completely hidden under water. Crocodiles see very well at night and are mostly nocturnal hunters. They also have a strong sense of smell. Sensors in their skin can notice tiny changes in the water.

Crocodiles are ambush predators. They wait for fish or land animals to come close, then rush out to attack. They eat fish, amphibians, birds and mammals. What they eat depends on their species, size and age. Crocodiles have the strongest bite force of any animal. They can move quickly over short distances, and crocodiles may have a homing instinct. Most species can live for at least 30 to 40 years. Crocodiles are the most social of reptiles. The largest and heaviest males are at the top of their group's hierarchy. Females lay their eggs in nests. In many species, the temperature of the nest decides whether the young become male or female.

Relationship with humans

Large crocodiles can be dangerous to people. They can attack very quickly, before a person has time to react. The saltwater crocodile and Nile crocodile are the most dangerous. They have harmed many people in parts of Southeast Asia and Africa. The mugger crocodile and American crocodile can also be dangerous to people.

Crocodiles are protected in many parts of the world, but they are also raised on farms. Their skins are made into things like shoes and handbags, and their meat is eaten in some places. Aboriginal Australians hunted crocodiles in a way that kept their numbers healthy for thousands of years. Hunting grew much larger from the 1930s. Later, crocodiles were protected in many areas, including Western Australia and the Northern Territory. Crocodiles have been a protected species since the 1970s.

Further information: Crocodilia § Cultural depictions