Crocodile

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Crocodile Temporal range: Late Cretaceous - Recent

Nile Crocodile
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Crocodilia
Family:	Crocodylidae Cuvier, 1807
Genera
Crocodylus Osteolaemus See full taxonomy.

A crocodile is any species belonging to the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). The term can also be used more loosely to include all members of the order Crocodilia: i.e. the true crocodiles, the alligators and caimans (family Alligatoridae) and the gharials (family Gavialidae), or even the Crocodylomorpha which includes prehistoric crocodile relatives and ancestors. Crocodiles are large aquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. Crocodiles tend to congregate in freshwater habitats like rivers, lakes, wetlands and sometimes in brackish water. They feed mostly on vertebrates like fish, reptiles, and mammals, sometimes on invertebrates like mollusks and crustaceans, depending on species. They are an ancient lineage, and are believed to have changed little since the time of the dinosaurs. They are believed to be 200 million years old whereas dinosaurs became extinct 65 million years ago; crocodiles survived great extinction events.

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Biology and behaviour

Crocodiles are ambush hunters, waiting for fish or land animals to come close, then rushing out to attack. As cold-blooded predators, they are lethargic, therefore survive long periods without food, and rarely need to actively go hunting. Despite their slow appearance, crocodiles are top predators in their environment, and various species have been observed attacking and killing sharks. A famous exception is the Egyptian Plover which is said to enjoy a symbiotic relationship with the crocodile. According to unauthenticated reports, the plover feeds on parasites that infest the crocodile's mouth and the reptile will open its jaws and allow the bird to enter to clean out the mouth (Richford and Mead 2003).

Many large crocodilians swallow stones (called gastroliths or stomach stones) and they are believed to be of use in acting as ballast to balance their body. Other suggestions have been made that they may have a function similar to that of grit in birds, which is in crushing food.

Salt glands are present in the tongues of most crocodylids and they have a pore opening on the surface of the tongue. They appear to be similar to those in marine turtles, however these seem to be absent in Alligatoridae.

Crocodilians can produce sounds during distress and in aggressive displays. They can also hear well and the tympanic membranes are concealed by flat flaps that may be raised or lowered by muscles.

File:IMG 0428-Mexico.JPG

Crocodile farm in Mexico

Crocodiles eat fish, birds, mammals and occasionally smaller crocodiles.

Crocodiles are protected in many parts of the world, but they also are farmed commercially. Their hide is tanned and used to make leather goods such as shoes and handbags, whilst crocodile meat is also considered a delicacy. The most commonly farmed species are the Saltwater and Nile crocodiles, while a hybrid of the Saltwater and the rare Siamese crocodile is also bred in Asian farms. Farming has resulted in an increase in the Saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve crocodile habitat.

Crocodiles are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three being included in the group Archosauria ('ruling reptiles'). See Crocodilia for more information.

Crocodile embryos do not have sex chromosomes, and unlike humans sex is not determined genetically. Sex is determined by temperature, with males produced at around 31.6 °C, and females produced at slightly lower and higher temperatures. The average incubation period is around 80 days, and also is dependent upon temperature.

It has been observed that crocodiles may possess a form of homing instinct. Three rogue saltwater crocodiles were relocated 400 kilometres by helicopter in northern Australia but had returned to their original locations within three weeks, based on data obtained from tracking devices attached to the reptiles.

The land speed record for a crocodile is 17 km/h (11 mph) measured in a galloping Australian freshwater crocodile. Maximum speed varies from species to species. Certain types of crocodiles can indeed gallop, including Cuban crocodiles, New Guinea crocodiles, African dwarf crocodiles and even smaller Nile crocodiles. For most species, the fastest they can move is a kind of "belly run", where the body moves in a snake-like fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of 10 or 11km/h (around 7 mph) when they "belly run", and often faster if they're slipping down muddy tidal riverbanks. Another form of locomotion is the "high walk" where the body is raised clear off the ground.

Crocodiles do not have sweat glands, so they release heat through their mouths. Consequently, they often sleep with their mouth open and may even pant like a dog.

Danger to humans

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Main article: Crocodile attacks

The larger species of crocodiles are very dangerous to humans. The main danger that crocodiles pose is not their ability to run after a person but their ability to strike before the person can react. The Saltwater and Nile Crocodiles are the most dangerous, killing hundreds of people each year in parts of south-east Asia and Africa. Mugger crocodiles and possibly the endangered Black Caiman, are also very dangerous to humans. American alligators are less aggressive and rarely assault humans without provocation. The most deaths in a single crocodile attack incident may have occurred during the Battle of Ramree Island, on February 19, 1945, in Burma. Nine hundred soldiers of an Imperial Japanese Army unit, in an attempt to retreat from the Royal Navy and rejoin a larger battalion of the Japanese infantry, crossed through ten miles (16 km) of mangrove swamps which contained Saltwater Crocodiles. Twenty Japanese soldiers were captured alive by the British, and almost five hundred are known to have escaped Ramree. Many of the remainder may have been eaten by the crocodiles, although gunfire from the British troops was undoubtedly a contributory factor.

Taxonomy of the Crocodylidae

Most species are grouped into the genus Crocodylus. The other extant genus, Osteolaemus, is monotypic (as is Mecistops, if recognized).

Family Crocodylidae
- Subfamily Mekosuchinae (extinct)
- Subfamily Crocodylinae
  - Genus Crocodylus
    - Crocodylus acutus, American Crocodile
    - Crocodylus cataphractus, Slender-snouted Crocodile (studies in DNA and morphology suggest that this species may be more basal than Crocodylus, and therefore belongs in its own genus, Mecistops)
    - Crocodylus intermedius, Orinoco Crocodile
    - Crocodylus johnsoni, Freshwater Crocodile
    - Crocodylus mindorensis, Philippine Crocodile
    - Crocodylus moreletii, Morelet's Crocodile or Mexican Crocodile
    - Crocodylus niloticus, Nile Crocodile or African Crocodile (the subspecies found in Madagascar is sometimes called the Black Crocodile)
    - Crocodylus novaeguineae, New Guinea Crocodile
    - Crocodylus palustris, Mugger Crocodile, Marsh Crocodile, or Indian Crocodile
    - Crocodylus porosus, Saltwater Crocodile or Estuarine Crocodile
    - Crocodylus rhombifer, Cuban Crocodile
    - Crocodylus siamensis, Siamese Crocodile
  - Genus Osteolaemus
    - Osteolaemus tetraspis, Dwarf Crocodile (there has been controversy whether or not this is actually two species; current thinking is that there is one species with 2 subspecies: O. tetraspis tetraspis & O. t. osborni)
  - Genus †Euthecodon
  - Genus †Rimasuchus (formerly Crocodylus lloydi)
  - Genus †Asiatosuchus

Some of the extinct relatives of true crocodiles, members of the larger group Crocodylomorpha, were herbivorous.

Crocodile products

Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags, belts, hats, and shoes.

Crocodile is consumed in some countries, such as Australia, Ethiopia, Thailand, South Africa and also Cuba (in pickled form); it can also be found in specialty restaurants in some parts of the United States. The meat is white and its nutritional composition compares favourably with that of other meats. It tends to have a slightly higher cholesterol level than other meats. Crocodile meat has a delicate flavour; some describe it as a cross between chicken and crab. Cuts of meat include backstrap and tail fillet.

Crocodile oil has been used for centuries as a natural healing skin balm.

References

^ Grigg, Gordon and Gans, Carl (1993) Morphology And Physiology Of The Crocodylia, in Fauna of Australia Vol 2A Amphibia and Reptilia, chapter 40, pages 326-336. Australian Government Publishing Service, Canberra. PDF
Saltwater Crocodile, Saltwater Crocodile Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News - National Geographic
Britton, Adam. Estuarine Crocodile: Crocodylus porosus. Crocodilians: Natural History Conservation: Crocodiles, Caimans, Alligators, Gharials. Retrieved 4 January 2007.
Read MA, Grigg GC, Irwin SR, Shanahan D, Franklin CE (2007) Satellite Tracking Reveals Long Distance Coastal Travel and Homing by Translocated Estuarine Crocodiles, Crocodylus porosus. PLoS ONE 2(9): e949. doi:10.1371/journal.pone.0000949
Britton, Adam. "Crocodilian Biology Database FAQ, "How fast can a crocodile run?"". Retrieved 2008-02-02.
Anitai, Stefan. "14 Amazing Facts About Crocodiles - Living dinosaurs". Softpedia. Retrieved 2008-04-01.
McAliley, Willis, Ray, White, Brochu & Densmore (2006). Are crocodiles really monophyletic?—Evidence for subdivisions from sequence and morphological data. Molecular Phylogenetics and Evolution 39:16-32.

External links

Extant Crocodilian species

Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
(unranked): Archosauria
Superorder: Crocodylomorpha

Family Alligatoridae (Alligators and caimans)

Alligatorinae
(Alligators)

Alligator	American alligator (A. mississippiensis) Chinese alligator (A. sinensis)

Caimaninae
(Caimans)

Caiman	Spectacled caiman (C. crocodilus) Broad-snouted caiman (C. latirostris) Yacare caiman (C. yacare)
Melanosuchus	Black caiman (M. niger)
Paleosuchus	Cuvier's dwarf caiman (P. palpebrosus) Smooth-fronted caiman (P. trigonatus)

Family Crocodylidae (True crocodiles)

Crocodylinae

Crocodylus

Osteolaeminae

Mecistops	West African slender snouted crocodile (Mecistops cataphractus) Central African slender-snouted crocodile (Mecistops leptorhynchus)
Osteolaemus	Dwarf crocodile (O. tetraspis) Osborn’s dwarf crocodile (O. osborni)

Family Gavialidae

Gavialis	Gharial (G. gangeticus)
Tomistoma	False gharial (T. schlegelii)

Reptiles portal

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