Crocodile

This is an old revision of this page, as edited by 75.183.27.139 (talk) at 19:12, 9 December 2007. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Revision as of 19:12, 9 December 2007 by 75.183.27.139 (talk)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff) For other uses, see Crocodile (disambiguation).

{{Taxobox | color = pink | name = Crocodiles | fossil_range = Late Cretaceous - Recent | image = NileCrocodile.jpg | image_caption = Nile Crocodile | regnum = Animalia | phylum = Chordata | classis = [[Reptiley O Fondia | ordo = Crocodilia | familia = Crocodylidae | familia_authority = Cuvier, 1807 | subdivision_ranks = Genera | subdivision = }}

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. Some species, notably the Saltwater Crocodile of Australia, Southeast Asia and the Pacific islands often live along the coastal areas. They are also known to venture far out to sea. They mostly feed on vertebrates like fish, reptiles, and mammals, sometimes with 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.

Description

Crocodiles, like dinosaurs, have the abdominal ribs modified into *gastralia*

Crocodiles are among the more biologically complex reptiles despite their prehistoric look. Unlike other reptiles they have a four-chambered heart, diaphragm and cerebral cortex. Their external morphology on the other hand is a sign of their aquatic and predatory lifestyle. A crocodile’s physical traits allow it to be a successful predator. They have a streamlined body that enables them to swim faster. They also tuck their feet to their sides while swimming, which makes the animal even faster, by decreasing the water resistance. They have webbed feet which, although not used to propel the animal through the water, allow it to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallower water where the animals sometimes move around by walking.

Crocodiles are very fast over short distances, even out of water. They have extremely powerful jaws capable of biting down with immense force, by far the strongest bite of any animal. The crocodile's bite force is more than 5,000 pounds per square inch, comparing to just 335 psi for a rottweiler, 690 psi for a large great white shark, or 800 psi for a hyena. They have sharp teeth for tearing and holding on to flesh, but cannot open their mouth if it is held closed, because the crocodile is evolved for biting down; the muscle space inside the skull is used up for muscle that closes the jaws. Zoologists will often subdue crocodiles for study or transport by taping their jaws or holding their jaws shut with large rubber bands cut from automobile inner tubes. All crocodiles also have sharp and powerful claws. They have limited lateral movement in their neck, so on land, protection can be found by getting even a small tree between the crocodile's jaws and oneself.

Age

There is no reliable way of measuring crocodile age, although several techniques could be used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth - each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons. Bearing these inaccuracies in mind, the oldest crocodilians appear to be the largest species. C. porosus is estimated to live around 70 years on average, and there is limited evidence that some individuals may exceed 100 years. One of the oldest crocodiles recorded died in a zoo in Russia apparently aged 115 years old.

A male freshwater crocodile at the Australia Zoo is estimated to be 130 years old. He was rescued from the wild by Bob Irwin and Steve Irwin after being shot twice by hunters. As a result of the shootings, this crocodile (known affectionately as "Mr. Freshy") has lost his right eye.

Size

File:LargeCroc.jpg

Large Crocodile in captivity in Australia

Size greatly varies between species, from the dwarf crocodile to the enormous saltwater crocodile. Large species can reach over 5m long and weigh well over 1200 kg (2,640 lb). Despite their large adult size, crocodiles start their life at around 20 cm (8 inches) long. The largest species of crocodile is the Saltwater Crocodile, found in northern Australia and throughout South-east Asia.

The largest recorded crocodile is a giant saltwater crocodile measured at 8.6 meters (28.2 feet) shot in Australia, by a school teacher who later became a conservationist. The largest living crocodile is a 7.1 m (23.3 ft) long saltwater crocodile, in Orissa, India. It lives in Bhitarkanika Wildlife Sanctuary and in June 2006, was entered in the Guinness Book of World Records.

The other two larger certifiable records of complete crocodile are both of 6.2 m crocodiles. The first crocodile was shot in the Mary River in the Northern Territory of Australia in 1974 by poachers and measured by wildlife rangers. The second crocodile was killed in 1983 in the Fly River, Papua New Guinea. In this latter crocodile it was actually the skin that was measured by zoologist Jerome Montague, and as skins are known to underestimate the size of the actual animal, it is possible this crocodile was at least another 10 cm longer.

File:Sweetheart.gif

Sweetheart, a large saltwater crocodile that attacked boats

The largest crocodile ever held in captivity is an Estuarine/Siamese hybrid named Yai (Thai: ใหญ่, meaning big) (born 10 June, 1972) at the famous Samutprakarn Crocodile Farm and Zoo, Thailand. This animal measured 6 m in length and weighs 1,114.27 kg (2,450 lb.).

Another huge captive specimen was a salt water crocodile named Gomek. Gomek was captured by George Craig in Papua New Guinea and sold to St. Augustine Alligator Farm in Florida. Gomek died of heart disease in February 1997. By this stage, he was a very old crocodile. When he died, he was 5.5 m long - as confirmed by St. Augustine Alligator Farm - and probably between 70 and 80 years old.

Wildlife experts, however, argue that the largest crocodile so far found in the Bhitarkanika was almost 7.62 m which could be traced from the skull preserved by the Kanika Royal Family. The crocodile, probably was shot dead near Dhamara during 1926 and later its skull was preserved by the then Kanika King. The crocodile experts said the crocodile would be about 7.62 m since the size of the skull was measured one seventh of the total length of the body.

Etymology

A statue of Saint Theodore of Amasea treading on a crocodile (Venice, Italy)

The crocodile gets its name from the Greeks who observed them in the Nile river. The Greeks called them krokodilos, a compound word from kroke, which means "pebbles" and drilos, which means "worm". To the Greeks, this "worm of the stones" was so named because of the crocodiles habit of basking in the sun on gravel-covered river banks.

Petsuchos was the name given by the Greeks to the live crocodile at Crocodilopolis in Ancient Egypt, which was worshipped as a manifestation of the Egyptian god Sobek; the deification of crocodiles.

During a voyage in 1585-1586, Sir Francis Drake named the Cayman Islands after the islands' 10-foot crocodiles, called "Caymanas" by the native Caribs.

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.

File:IMG 0428-Mexico.JPG

Crocodile farm in Mexico

Crocodiles eat fish, birds, mammals and occasionally smaller crocodiles. Wild 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 in many parts of the world. 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 degrees celsius, 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.

Danger to humans

Main article: Crocodile attacks

The larger species of crocodiles can be very dangerous to humans. 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 what is now Myanmar. 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 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. Crocodiles are the leading cause of animal related deaths as of 2001.

Taxonomy of the Crocodylidae

Most species are grouped into the genus Crocodylus. The two other living genera of this family are both monotypic: Osteolaemus and Tomistoma.

Family Crocodylidae
- Subfamily Mekosuchinae (extinct)
- Subfamily Crocodylinae
  - Genus Euthecodon (extinct)
  - Genus Rimasuchus (extinct, formerly Crocodylus lloydi)
  - Genus Osteolaemus
    - Dwarf Crocodile, Osteolaemus tetraspis (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 Crocodylus
    - Crocodylus acutus , American Crocodile
    - Crocodylus cataphractus , Slender-snouted Crocodile (Recent DNA studies suggest that this species may actually be more basal than Crocodylus, and belong in its own genus, Mecistops)
    - Crocodylus intermedius , Orinoco Crocodile
    - Crocodylus johnstoni, 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
- Subfamily Tomistominae (recent studies may show that this group is actually more closely related to the Gavialidae)
  - Genus Kentisuchus (extinct)
  - Genus Gavialosuchus (extinct)
  - Genus Paratomistoma (extinct)
  - Genus Thecachampsa (extinct)
  - Genus Rhamphosuchus (extinct)
  - Genus Tomistoma
    - Tomistoma schlegelii, False gharial or Malayan gharial
    - Tomistoma lusitanica (extinct)
    - Tomistoma cairense (extinct)
    - Tomistoma machikanense (extinct, Pleistocene species from Japan)

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

Differentiation from alligators

While often confused with each other, alligators and crocodiles belong to two quite separate taxonomic families, and are more distinct from one another than humans are from gorillas. As for appearance, one generally reliable rule is that alligators have U-shaped heads, while crocodiles' heads are V-shaped.

Crocodile products

Crocodile leather can be made into a variety of goods, such as wallets, briefcases, purses, belts and hats. 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 more traditional meats. It does tend to have a slightly higher cholesterol level than other meats. Crocodile meat has a delicate flavour and its taste can be complemented by the use of marinades. Choice cuts of meat include backstrap and tail fillet.

References

National Geographic documentary; "Bite Force", Brady Barr.
Britton, Adam. Crocodilian Biology Database, FAQ. "How long do crocodiles live for?". Retrieved 9/11/2006.
Britton, Adam. Crocodilian Biology Database, FAQ. "How long do crocodiles live for?". Retrieved 9/11/2006.
profile of Mr Freshy at Australia Zoo website, accessed 1 February 2007
http://animals.nationalgeographic.com/animals/reptiles/saltwater-crocodile.html?nav=A-Z
"Orissa crocodile recognised as world's largest". Reuters. 2006-06-16. Retrieved 2006-06-18. {{cite news}}: Check date values in: |date= (help)
Cayman Islands Government (2005). Cayman Islands History. Retrieved 4 January 2007.
http://animals.nationalgeographic.com/animals/reptiles/saltwater-crocodile.html?nav=A-Z
Britton, Adam. Estuarine Crocodile: Crocodylus porosus. Crocodilians: Natural History Conservation: Crocodiles, Caimans, Alligators, Gharials. Retrieved 4 January 2007.
Mercer, Phil (27 September 2007). "Homing crocodiles defy relocation". BBC News. Retrieved 2007-09-27. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
"Homesick crocs hightail it home". Sydney Morning Herald. 26 September 2007. Retrieved 2007-09-27. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)

External links

Categories:

Misplaced Pages