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crocodile

crocodile, large, carnivorous reptile of the order Crocodilia, found in tropical and subtropical regions. Crocodiles live in swamps or on river banks and catch their prey in the water. They have flattened bodies and tails, short legs, and powerful jaws. The eyes, ears, and nostrils are located near the top of the head and are exposed when the crocodile floats on the surface of the water. The ears and nostrils have valves that close when the animal is submerged.

Most crocodiles are more aggressive than the related alligators. The two forms are distinguished by the long lower fourth tooth: in crocodiles, but not in alligators, this tooth protrudes on the side of the head when the mouth is closed. Also, the snouts of most crocodiles are narrower than those of alligators.

Small crocodiles feed on fish and small aquatic animals; larger ones also catch land mammals and birds that approach the water. Members of some large species sometimes attack and eat humans. The female crocodile deposits her eggs, usually about 20 in number, in a nest of rotting vegetation or in a shallow pit on the river bank, and digs them up when she hears them hatching.

In most species the average adult length is between 6 and 10 ft (1.8–3 m). The largest crocodile (the saltwater crocodile) is often 14 ft (4.3 m) long and may exceed 20 ft (6 m) in length. The Nile, American, and Orinoco crocodiles are commonly 12 ft (3.7 m) long, and specimens up to 23 ft (7 m) long have been reported for the last two species. The extinct Sarcosuchus imperator, which lived during the Cretaceous period, may have approached 40 ft (12 m) in length. The smallest crocodile (the Congo dwarf crocodile) averages 31/2 ft (105 cm) long.

With the exception of the two African dwarf crocodiles (Osteolaemus) and the so-called false gavial (Tomistoma) of Asia, crocodiles are classified in the genus Crocodylus, with about a dozen species. The Nile crocodile (C. niloticus) is found in fresh- and saltwater throughout S and central Africa. In early historic times it ranged N to the Nile delta and the Mediterranean coast. It sometimes attacks humans, as does the saltwater crocodile (C. porosus), found on islands and in straits from SE Asia to Australia and Melanesia. The marsh crocodile, or mugger (C. palustris), is a freshwater species of India and Sri Lanka, regarded as sacred in some regions. The American crocodile (C. acutus) is found in fresh- and saltwater in S Florida, the West Indies, Central America, and NW South America. It does not attack humans without provocation. The Orinoco crocodile (C. intermedius) is a freshwater species of the Orinoco basin of Colombia and Venezuela. Two smaller species are found in limited areas of Central America and Cuba.

Crocodiles are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Crocodilia, family Crocodilidae.

See also gavial.

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crocodile

croc·o·dile / ˈkräkəˌdīl/ • n. a large predatory semiaquatic reptile (Crocodylus and two other genera, family Crocodylidae) with long jaws, long tail, short legs, and a horny textured skin. ∎  leather made from crocodile skin, used esp. to make bags and shoes. ORIGIN: Middle English cocodrille, cokadrill, from Old French cocodrille, via medieval Latin from Greek krokodilos ‘worm of the stones,’ from krokē ‘pebble’ + drilos ‘worm.’

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crocodile

crocodile Carnivorous lizard-like reptile found in warm parts of every continent except Europe. Most crocodiles have a longer snout than alligators. All lay hard-shelled eggs in nests. Length: up to 7m (23ft). There are about 12 species including two dwarf species in Africa. The Asian saltwater crocodile (Crocodylus porosus) sometimes attacks humans. Family Crocodylidae.

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crocodile

crocodile a person making a hypocritical or malicious show of sorrow, often by weeping crocodile tears. These are said to be named from a belief that crocodiles wept while devouring or alluring their prey.

In Barrie's Peter Pan, Captain Hook is stalked by, and finally falls victim to, the crocodile which has previously bitten off his hand.

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crocodile

crocodile. XIII ME. coko-, cokadrille — OF. cocodrille (mod. crocodile) :- medL. cocodrillus, for crocodīlus — Gr. krokódīlos, for *krokódrīlos ‘worm of the stones’, f. krókē pebble + drîlos worm. The present form, assim. to L., appears XVI.

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Crocodile

Crocodile

a long line of persons or things, c. 1870.

Example: a crocodile of schoolgirls.

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crocodiles

crocodiles See CROCODILIA; CROCODYLIDAE.

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crocodile

crocodileaisle, Argyle, awhile, beguile, bile, Carlisle, Carlyle, compile, De Stijl, ensile, file, guile, I'll, interfile, isle, Kabyle, kyle, lisle, Lyle, Mikhail, mile, Nile, pile, rank-and-file, resile, rile, Ryle, Sieg Heil, smile, spile, stile, style, tile, vile, Weil, while, wile, worthwhile •labile, stabile •immobile, mobile •nubile • aedile • crocodile • cinephile •profile • audiophile • bibliophile •Francophile • Anglophile •technophile • necrophile •Russophile •paedophile (US pedophile) •agile, fragile •chamomile •penile, senile •juvenile • stockpile • isopropyl •woodpile • sterile • febrile • virile •puerile • facile • decile • flexile •extensile, prehensile, tensile •fissile, missile •domicile • docile • reconcile

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Crocodile

CROCODILE

CROCODILE (Heb. תַּנִּיך or תַּנִּים), the largest surviving reptile, with a length of as much as 23 feet (7 m.) or more. The tannim or tannin of the Bible refers to the Nile crocodile (Crocodylus niloticus) and also to gigantic mythological animals said to have rebelled at the time of the creation against their Creator and hence to have been punished with extinction (Isa. 51:9; Ps. 74:13–14; Job 7:12); similar myths are found also in Ugaritic epics. The reference may be to prehistoric reptiles, remains of whose bones have been uncovered in various places in the Middle East region and which may have stirred the imagination of the ancients and formed the basis of these legends. Footprints of a prehistoric reptile have been discovered at Bet Zayit in the vicinity of Jerusalem. Tannim also refers to another gigantic, non-reptilian animal, the whale (cf. Lam. 4:3), usually called *leviathan, which word, however, also denotes a crocodile, as in Job 40:25–41:26, where the description, although poetical and mythical, applies to a crocodile. Thus, it is stated there that the leviathan has a tongue, a nose, enormous teeth, and shining eyes. Its head and neck are covered with protective scales impenetrable to spears. It is fearless and attacks every other animal. Mention is also made there of a bird that plays with it and of the covenant between them: this may refer to the crocodile plover (Pluvianus aegyptius) which pecks at the throat and teeth of the crocodile. This reptile was sacred to the Egyptians; hundreds of embalmed crocodiles have been found in cemeteries specially set aside for them. Plutarch relates that the Egyptians ascribed to them powers of prescience in that the female lays its eggs on the high water mark of the Nile. As it was a sacred animal, the Egyptians protected it, and it multiplied undisturbed in the country's waters. The sign performed by Aaron with his rod which became a tannin – a crocodile – (Ex. 7:9–10) may have been intended as a protest against its sanctity. Ezekiel calls Pharaoh king of Egypt "the great tannim that lieth in the midst of his rivers" (Ezek. 29:3; cf. Isa. 27:1), while Jeremiah (51:34) likens the king of Babylonia to a crocodile that preys on human beings. No longer found in the Nile, the crocodile is at present indigenous only in Central Africa. At the end of the 19th century crocodiles were still found in Ereẓ Israel, and a river in the Sharon is called Naḥal ha-Tanninim.

bibliography:

Lewysohn, Zool, 220 no. 271; F.S. Bodenheimer, Animal and Man in Bible Lands (1960), 65; J. Feliks, Animal World of the Bible (1962), 94–95.

[Jehuda Feliks]

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Crocodiles

Crocodiles


The largest of the living reptiles, crocodiles inhabit shallow coastal bodies of water in tropical areas throughout the world, and they are often seen floating log-like in the water with only their eyes and nostrils showing. Crocodiles have long been hunted for their hides, and almost all species of crocodilians are now considered to be in danger of extinction . Members of the crocodile family, called crocodilians (Crocodylidae), are similar in appearance and include crocodiles, alligators, caimans, and gavials. A crocodile can usually be distinguished from an alligator by its pointed snout (an alligator's is rounded), and by the visible fourth tooth on either side of its snout that protrudes when the jaw is shut.

Crocodiles prey on fish, turtles, birds, crabs, small mammals, and any other animals they can catch, including dogs and occasional humans. They hide at the shore of rivers and water holes and grab an animal as it comes to drink, seizing a leg or muzzle, dragging the prey underwater, and holding it there until it drowns. When seizing larger animals, a crocodile will thrash and spin rapidly in the water and tear its prey to pieces. After eating its fill, a crocodile may crawl ashore to warm itself and digest its food, basking in the sun in its classic "grinning" pose, with its jaws wide open, often allowing a sandpiper or plover to pick and clean its teeth by scavenging meat and parasites from between them.

The important role that crocodiles play in the balance of nature is not fully known or appreciated, but, like all major predators, their place in the ecological chain is a crucial one. They eat many poisonous water snakes, and during times of drought , they dig water holes, thus providing water, food, and habitat for fish, birds, and other creatures. When crocodiles were eliminated from lakes and rivers in parts of Africa and Australia , many of the food fish also declined or disappeared. It is thought that this may have occurred because crocodiles feed on predatory and scavenging species of fish that are not eaten by local people, and when left unchecked, these fish multiplied out of control and crowded out or consumed many of the food fish.

Crocodiles reproduce by laying eggs and burying them in the sand or hiding them in nests concealed in vegetation. Recent studies of the Nile and American crocodiles show that some of these reptiles can be attentive parents. According to these studies, the mother crocodile carefully watches over the nest until it is time for the eggs to hatch. Then she digs the eggs out and gently removes the young from the shells. After gathering the newborns together, she puts them in her mouth and carries them to the water and releases them, watching over them for some time. American crocodiles are very shy and reclusive, and disturbance during this critical period can disrupt the reproductive process and prevent successful hatchings.

In recent decades, crocodiles and other crocodilians have been intensively hunted for their scaly hides, which are used to make shoes, belts, handbags, wallets, and other fashion products. As a result, they have disappeared or have become rare in most of their former habitats. As of 2001, 12 crocodile species have been designated endangered. These species are found in Africa, the Caribbean, Central and South America, the Middle East, the Philippines, Australia, some Pacific Islands, southeast Asia, the Malay Peninsula, Sri Lanka, and Iran. They are endangered primarily due to overexploitation and habitat loss.

The American crocodile (Crocodylus acutus ) occurs all along the Caribbean coast, including the shores of Central America, Colombia, Cuba, Hispaniola, Jamaica, Mexico, extreme south Florida, and on the Pacific coast, from Peru north to southern Mexico. The United States population of the American crocodile consists of some 5001,2000 individuals. This species breeds only in the southern part of Everglades National Park , mainly Florida Bay, and perhaps on nearby Key Largo, and at Florida Power and Light Company's Turkey Point plant, located south of Miami. The population is thought to be extremely vulnerable and declining, mainly due to human disturbance, habitat loss (from urbanization, especially real estate development), and direct killing such as on highways and in fishing nets. Predation of hatchlings in Florida Bay mainly by raccoons may also be a factor in the species' decline.

[Lewis G. Regenstein ]


RESOURCES

BOOKS

Crocodiles: Their Ecology, Management and Conservation. A Special Publication of the Crocodile Specialist Group. Gland, Switzerland: IUCN-The World Conservation Union, 1989.

Ross, C. A., ed. Crocodiles and Alligators. New York: Facts on File, 1989.

Thorbjarnarson, J., comp. Crocodiles. An Action Plan for Their Conservation. Gland, Switzerland: IUCN-The World Conservation Union, 1992.

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Crocodiles

Crocodiles

Biology of crocodilians

Species of crocodilians

Crocodilians and people

Resources

The crocodile order (Crocodylia) consists of several families of large, unmistakable, amphibious reptiles: the crocodiles (Crocodylidae), gavials (Gavialidae), and the alligators and caimans (Alligatoridae). Although these animals look superficially like lizards, they are different in many important respects, and are believed by biologists to be the most highly evolved of the living reptiles.

Crocodilians are amphibious animals, spending most of their time in water but emerging onto land to bask in the sun and lay their eggs. Their usual habitat is in warm tropical or subtropical waters. Most species occur in freshwater, with only the saltwater crocodile being partial to marine habitats. Fish are the typical food of most adult crocodilians, but the biggest species will also eat large mammals, including humans. Younger crocodilians eat invertebrates and small fish.

Crocodilians are economically important for their thick, attractive hide, which can be used to make fine leather for expensive consumer goods, such as shoes, handbags, and other luxury items. Wild crocodilians are hunted for their hide wherever they occur, and in some areas they are also raised on ranches for this purpose. Crocodilian meat is also eaten, often as a gourmet food.

Most populations of wild crocodilians have been greatly reduced in size because of overhunting and habitat loss, and many species are endangered.

Biology of crocodilians

Among the more distinctive characteristics of the crocodilians are their almost completely four-chambered heart, teeth that are set into sockets in the jaw, a palate that separates the mouth from the nasal chambers, and spongy lungs. These animals also have a protective covering of partially calcified, horny plates on their back. The plates are notconnected with each other, and are set into the thick, scaly skin, allowing great freedom of movement. Crocodilians have a heavy body with squat legs and a large, strong, scale-ridged tail.

Sinusoidal motions of the powerful tail are used to propel the animal while swimming. The tail is also a formidable weapon, used to subdue prey and also for defense. Although they appear to be ungainly and often spend most of their time lying about, crocodilians can actually move quite quickly. Some crocodilians can even lift their body fully above the ground, and run quickly using all four legs; a human cannot outrun a crocodile over a short distance on open land.

Crocodilians have numerous adaptations for living in water. They have webbed feet for swimming

slowly and their nostrils, eyes, and ears are set high on the head so they can be exposed even while most of the body and head are below the surface. When a crocodilian is totally submerged, its eye is covered by a semi-transparent nictitating membrane, and flaps of skin seal its nostrils and ears against water inflow. Crocodilians often float motionless in the water, commonly with the body fully submerged and only the nostrils and eyes exposed. To accomplish this behavior, crocodilians regulate their body density by varying the amount of air held in the lungs. Also, the stomach of most adult crocodiles contains stones, to as much as 1% of the animals total body weight. The stones are thought to be used as buoyancy-regulating ballast.

Crocodilians are poikilothermic, meaning they do not regulate their body temperature by producing and conserving metabolic heat. However, these animals are effective at warming themselves by basking in the sun, and they spend a great deal of time engaged in this activity. Crocodilians commonly bask through much of the day, often with their mouths held open to provide some cooling by the evaporation of water. Only when the day is hottest will these animals re-enter the water to cool down. Most species of crocodilians are nocturnal predators, although they will also hunt during the day if prey is available.

Stories exist of birds entering the open mouths of crocodiles to glean leeches and other parasites. This

phenomenon has not been observed by scientists, although it is well known that crocodiles will tolerate certain species of birds picking external parasites from their skin, but not necessarily inside of their mouth.

Male crocodilians are territorial during the breeding season, and chase other males away from places that have good nesting, basking, and feeding habitat. The male animals proclaim their territory by roaring loudly, and sometimes by snapping their jaws together. Intruders are aggressively chased away, but evenly matched animals may engage in vicious fights. Territory-holding males do not actively assemble females into a harem. Rather, they focus on chasing other males away from a territory. Females will enter the defended territory if they consider it to be of high quality.

All crocodilians are predators, and they have large, strong jaws with numerous sharp teeth for gripping their prey. Crocodiles do not have cutting teeth. If they capture prey that is larger than they can eat in a single gulp, it is dismembered by gripping strongly with the teeth and rolling their body to tear the carcass. Some crocodiles will opportunistically cooperate to subdue a large mammal, and then to tear it into bits small enough to be swallowed. However, extremely large animals with tough skin, such as a dead hippopotamus, will be left to rot for some time until the carcass softens and can be torn apart by the crocodiles.

All crocodilians are oviparous, laying hard, white-shelled eggs. The nest may be a pit dug into a beach above high water, or it may be made of heaps of aquatic vegetation, which help to incubate the eggs through heat produced during decomposition. Often, a number of females will nest close to each other, but each builds a separate nest. The nesting grounds are used by the same females, year after year. In many species the female carefully guards and tends her nest. Fairly open, sandy beaches are generally preferred as sites upon which to build the nest or nest mound.

Typically, 20-40 eggs are laid at a time, but this varies with species and the size of the female. Incubation time varies with species and temperature, but ranges, in the case of the Nile crocodile, from 11 to 14 weeks. Predators as diverse as monitor lizards, mongooses, dogs, raccoons, and even ants seek out crocodile nests to eat the eggs and newly hatched young.

An infant crocodilian has a small, so-calledegg toothat the end of its snout, which helps it to break out of the shell when ready to hatch. All of the baby crocodilians hatch within a short time of each other, synchronized in part by the faint peeping noises they make during the later stages of incubation. In some crocodilians, the mother assists her babies in hatching, by gently taking eggs into her mouth and cracking them with her teeth. The mother also may guard her offspring for some time after hatching, often allowing them to climb onto her body and head. Female crocodiles are very aggressive against intruders while their eggs are hatching and newborn babies are nearby, and under these circumstances they will even emerge from the water to chase potential predators away. Nevertheless, young crocodilians are vulnerable to being eaten by many predators, and this is a high-risk stage of the life cycle.

Potentially, crocodilians are quite long-lived animals. Individuals in zoos have lived for more than 50 years, and the potential longevity of some species may be as great as a century.

Species of crocodilians

The gavial or gharial (family Gavialidae) is a single species, Gavialus gangeticus, which lives in a number of sluggish, tropical rivers in India, Nepal, Bangladesh, and Indochina. Gavials have a long, slender snout, and are almost exclusively fish eaters, catching their prey with sideways sweeps of the open-mouthed head. Gavials can attain a length of about 20 ft (6 m). They are considered holy in the Hindu religion, and this has afforded these animals a measure of protection in India. Unfortunately, this is not sufficiently the case anymore, and gavials have become endangered as a result of overhunting for their hide.

The true crocodiles (family Crocodylidae) include about 14 species that live in tropical waters. Crocodiles are large, stout animals, with a much heavier snout than that of the gavial. The main food of crocodiles is fish, but some species can catch and subdue large mammals that venture close to their aquatic habitat, or attempt to cross rivers in which the crocodiles are living. Perhaps the most famous species is the Nile crocodile (Crocodylus niloticus ) of Africa, which can grow to a length of 23 ft (7 m). This crocodile can be a predator of unwary humans, although its reputation in this respect far exceeds the actual risks, except in certain places. This species used to be very abundant and widespread in Africa, but unregulated hunting, and to a lesser degree habitat loss, have greatly reduced its population.

The most dangerous crocodilian to humans and the largest crocodilian is the estuarine or saltwater crocodile (Crocodylus porosus ), which lives in salt and brackish waters from northern Australia and New Guinea, through most of Southeast Asia, to southern India. This species can achieve a length of more than 23 ft (7 m). Individuals of this crocodile species sometimes occur well out to sea.

Other species are the mugger crocodile (Crocodylus palustris ) of India, Bangladesh, and Ceylon; the Australian crocodile (C. johnsoni ) of northern Australia; and the New Guinea crocodile (C. novaeguineae )of New Guinea and parts of the Philippines.

The American crocodile (Crocodylus acutus ) is a rare and endangered species of brackish estuaries in southern Florida, occurring more widely in central and northwestern South America and the Caribbean. This species can achieve a length of 20 ft (6 m). The Orinoco crocodile (C. intermedius ) occurs in the Orinoco and Amazon Rivers of South America.

The false gavial (Tomistoma schlegelii ) is a slender-snouted species of Southeast Asia.

The alligators and caimans (family Alligatoridae) are eight species that occur in freshwater, with a broader head and more rounded snout than crocodiles. The American alligator (Alligator mississipiensis ) can achieve a length of 13 ft (4 m), and occurs in the southeastern United States as far north as South Carolina and Alabama. This species was endangered by unregulated hunting for its hide. However, strict conservation measures have allowed for a substantial recovery of the species, and it is now the subject of a regulated hunt.

The Chinese alligator (Alligator sinensis ) occurs in the lower reaches of the Yangtze and Kiang rivers in southern China, and it is the only member of its family to occur outside of the Americas. The Chinese alligator can grow as long as 6.5 ft (2 m).

Caimans are animals of freshwater habitat in South and Central America. The black caiman (Melanosuchus niger ) can achieve a length of 16 ft (5 m). The spectacled or common caiman (Caiman crocodilus ) and the broad-nosed caiman (C. latisrostris ) of eastern Brazil can both grow somewhat longer than 6.5 ft (2 m). The dwarf caiman (Paleosuchus palpebrosus ) and the smooth-fronted caiman (P. trigonatus ) live in more swiftly flowing streams and rivers and are relatively small species that do not exceed about 5 ft (1.5 m) in length. The Yacaré (Caiman yacare ) has the southernmost distribution of any caiman and is found in Brazil, Argentina, Bolivia, and Paraguay. This species reaches lengths of (2.53 m) and eats a variety of aquatic animals, especially snails and fish.

Crocodilians and people

The larger species of crocodilians are fierce predators. In particular, crocodiles have posed a longstanding risk to domestic livestock that try to drink from their aquatic habitat as well as to unwary humans. For this reason, crocodiles are commonly regarded as dangerous pests, and they are sometimes killed to reduce the risks associated with their presence.

Because some species of crocodilians are dangerous, they are greatly feared in many places. This fear is justified in some cases, at least in places where large human-eaters are abundant. In some cultures, the deep fear and revulsion that people have for dangerous crocodilians has transformed into an attitude of reverence. For example, a pool near Karachi, Pakistan, contains a number of large mugger crocodiles, which are venerated as priest-like entities and worshipped by pilgrims. In other places, human sacrifices have been made to crocodiles to pacify animist spirits.

The skins of crocodilians can be used to make a very tough and beautiful leather. This valuable product is widely sought for use in making expensive shoes, handbags, wallets, belts, suitcases, and other items. Crocodilians are readily hunted at night, when they can be found using searchlights that reflect brightly off

KEY TERMS

Endangered Refers to species or populations of organisms that are so small that there is a likelihood of imminent local extirpation, or even global extinction over its entire range.

Extirpated The condition in which a species is eliminated from a specific geographic area of its habitat.

Nictitating membrane An inner eyelid.

Overhunting Hunting of an animal at a rate that exceeds its productivity, so that the population size decreases, often to the point of endangerment.

Oviparous This refers to an animal that lays eggs, from which the young hatch after a period of incubation.

Poikilotherm Refers to animals that have no physiological mechanism for the regulation of their internal body temperature. These animals are also known, less accurately, ascold-blooded.In many cases, these animals bask in the sun or engage in other behaviors to regulate their body temperature.

their eyes. In almost all parts of the range of crocodilians, they have been hunted to endangerment or extirpation. Most species in the crocodile family are endangered to some degree.

In a few places, however, strict conservation regulations have allowed the populations of crocodilians to increase from historically depleted lows. This has been particularly true of the American alligator, which was considered to be an endangered species only a few decades ago, but has now recovered sufficiently to allow for a carefully regulated sport and market hunt.

Some species of crocodilians are also ranched, usually by capturing young animals in the wild and feeding them in confinement until they reach a large enough size to slaughter for their hide. The meat of crocodilians is also a saleable product, but it is secondary in importance to the hide.

Crocodilians are sometimes used to entertain people, and some species are kept as pets. The Romans, for example, sometimes displayed Nile crocodiles in their circuses. To amuse the masses of assembled people, the crocodiles would be killed by humans, or alternatively, humans would be killed by the crocodiles.

In more modern times, alligator wrestling has been popular in some places, for example, in parts of Florida. The key to successful alligator wrestling is to hold the jaws of the animal shut, which can be accomplished using only the hands (but watch out for the lashing tail!). Crocodilians have very powerful muscles for closing their jaws, but the muscles to open their mouth are quite weak.

Resources

BOOKS

Alderton, D. Crocodiles and Alligators of the World. New ed. New York: Facts on File, 2004.

Dudley, K. Alligators and Crocodiles. New ed. London: A & C Black, 2000.

Grenard, S. Handbook of Alligators and Crocodiles. New York: Krieger, 1999.

Halliday, T.R., and K. Adler. The New Encyclopedia of Reptiles and Amphibians. New York: Oxford University Press, 2002.

Messel, H., F.W. King, and J.P. Ross, eds. Crocodiles: An Action Plan for Their Conservation. Gland, Switzerland: IUCN, 1992.

Webb, G., S. Manolis, and P. Whitehead, eds. Crocodiles and Alligators. Australia: Surrey Beatty, 1988.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd ed. New York: Academic Press, 2001.

Zweifel, R.G., H.G. Cogger, and D. Kirshner, eds. Encyclopedia of Reptiles and Amphibians. 2nd ed. Academic Press, 1998.

Bill Freedman

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Crocodiles

Crocodiles

The crocodile order (Crocodylia) consists of several families of large, unmistakable, amphibious reptiles : the crocodiles (Crocodylidae), gavials (Gavialidae), and the alligators and caimans (Alligatoridae). Although these animals look superficially like lizards, they are different in many important respects, and are believed by biologists to be the most highly evolved of the living reptiles.

Crocodilians are amphibious animals, spending most of their time in water but emerging onto land to bask in the sun and lay their eggs. Their usual habitat is in warm tropical or subtropical waters. Most species occur in freshwater , with only the saltwater crocodile being partial to marine habitats. Fish are the typical food of most adult crocodilians, but the biggest species will also eat large mammals , including humans. Younger crocodilians eat invertebrates and small fish.

Crocodilians are economically important for their thick, attractive hide, which can be used to make fine leather for expensive consumer goods, such as shoes, handbags, and other luxury items. Wild crocodilians are hunted for their hide wherever they occur, and in some areas they are also raised on ranches for this purpose. Crocodilian meat is also eaten, often as a gourmet food.

Most populations of wild crocodilians have been greatly reduced in size because of overhunting and habitat loss, and numerous species are endangered.


Biology of crocodilians

Among the more distinctive characteristics of the crocodilians are their almost completely four-chambered heart , teeth that are set into sockets in the jaw, a palate that separates the mouth from the nasal chambers, and spongy lungs. These animals also have a protective covering of partially calcified, horny plates on their back. The plates are not connected with each other, and are set into the thick, scaly skin, allowing a great freedom of movement. Crocodilians have a heavy body with squat legs and a large, strong, scale-ridged tail.

Sinusoidal motions of the powerful tail are used to propel the animal while swimming. The tail is also a formidable weapon, used to subdue prey and also for defense. Although they appear to be ungainly and often spend most of their time lying about, crocodilians can actually move quite quickly. Some crocodilians can even lift their body fully above the ground, and run quickly using all four legs; a human cannot outrun a crocodile over a short distance on open land.

Crocodilians have numerous adaptations for living in water. They have webbed feet for swimming slowly and their nostrils, eyes, and ears are set high on the head so they can be exposed even while most of the body and head are below the surface. When a crocodilian is totally submerged, its eye is covered by a semi-transparent nictitating membrane , and flaps of skin seal its nostrils and ears against water inflow. Crocodilians often float motionless in the water, commonly with the body fully submerged and only the nostrils and eyes exposed. To accomplish this behavior , crocodilians regulate their body density by varying the amount of air held in the lungs. Also, the stomach of most adult crocodiles contain stones, to as much as 1% of the animal's total body weight. The stones are thought to be used as buoyancy-regulating ballast.

Crocodilians are poikilothermic, meaning they do not regulate their body temperature by producing and conserving metabolic heat . However, these animals are effective at warming themselves by basking in the sun, and they spend a great deal of time engaged in this activity. Crocodilians commonly bask through much of the day, often with their mouths held open to provide some cooling by the evaporation of water. Only when the day is hottest will these animals re-enter the water to cool down. Most species of crocodilians are nocturnal predators, although they will also hunt during the day if prey is available.

Stories exist of birds entering the open mouths of crocodiles to glean leeches and other parasites . This phenomenon has not been observed by scientists, although it is well known that crocodiles will tolerate certain species of birds picking external parasites from their skin, but not necessarily inside of their mouth.

Male crocodilians are territorial during the breeding season, and chase other males away from places that have good nesting, basking, and feeding habitat. The male animals proclaim their territory by roaring loudly, and sometimes by snapping their jaws together. Intruders are aggressively chased away, but evenly matched animals may engage in vicious fights. Territory-holding males do not actively assemble females into a harem. Rather, they focus on chasing other males away from a territory. Females will enter the defended territory if they consider it to be of high quality.

All crocodilians are predators, and they have large, strong jaws with numerous sharp teeth for gripping their prey. Crocodiles do not have cutting teeth. If they capture prey that is larger than they can eat in a single gulp, it is dismembered by gripping strongly with the teeth and rolling their body to tear the carcass. Some crocodiles will opportunistically cooperate to subdue a large mammal, and then to tear it into bits small enough to be swallowed. However, extremely large animals with tough skin, such as a dead hippopotamus, will be left to rot for some time until the carcass softens and can be torn apart by the crocodiles.

All crocodilians are oviparous , laying hard, white-shelled eggs. The nest may be a pit dug into a beach above high water, or it may be made of heaps of aquatic vegetation, which help to incubate the eggs through heat produced during decomposition . Often, a number of females will nest close to each other, but each builds a separate nest. The nesting grounds are used by the same females, year after year. In many species the female carefully guards and tends her nest. Fairly open, sandy beaches are generally preferred as sites upon which to build the nest or nest mound.

Typically, 20–40 eggs are laid at a time, but this varies with species and the size of the female. Incubation time varies with species and temperature, but ranges, in the case of the Nile crocodile, from 11 to 14 weeks. Predators as diverse as monitor lizards , mongooses , dogs, raccoons , and even ants seek out crocodile nests to eat the eggs and newly hatched young.

An infant crocodilian has a small, so-called "egg tooth" at the end of its snout, which helps it to break out of the shell when ready to hatch. All of the baby crocodilians hatch within a short time of each other, synchronized in part by the faint peeping noises they make during the later stages of incubation. In some crocodilians, the mother assists her babies in hatching, by gently taking eggs into her mouth and cracking them with her teeth. The mother also may guard her offspring for some time after hatching, often allowing them to climb onto her body and head. Female crocodiles are very aggressive against intruders while their eggs are hatching and newborn babies are nearby, and under these circumstances they will even emerge from the water to chase potential predators away. Nevertheless, young crocodilians are vulnerable to being eaten by many predators, and this is a high-risk stage of the life cycle.

Potentially, crocodilians are quite long-lived animals. Individuals in zoos have lived for more than 50 years, and the potential longevity of some species may be as great as a century.


Species of crocodilians

The gavial or gharial (family Gavialidae) is a single species, Gavialus gangeticus, which lives in a number of sluggish, tropical rivers in India, Bangladesh, and Indochina. Gavials have a long, slender snout, and are almost exclusively fish eaters, catching their prey with sideways sweeps of the open-mouthed head. Gavials can attain a length of about 20 ft (6 m). Gavials are considered holy in the Hindu religion, and this has afforded these animals a measure of protection in India. Unfortunately, this is not sufficiently the case anymore, and gavials have become severely endangered as a result of overhunting for their hide.

The true crocodiles (family Crocodylidae) include about 16 species that live in tropical waters. Crocodiles are large, stout animals, with a much heavier snout than that of the gavial. The main food of crocodiles is fish, but some species can catch and subdue large mammals that venture close to their aquatic habitat, or attempt to cross rivers in which the crocodiles are living. Perhaps the most famous species is the Nile crocodile (Crocodylus niloticus) of Africa , which can grow to a length of 23 ft (7 m). This crocodile can be a predator of unwary humans, although its reputation in this respect far exceeds the actual risks, except in certain places. This species used to be very abundant and widespread in Africa, but unregulated hunting and, to a lesser degree, habitat loss, have greatly reduced its population.

The most dangerous crocodilian to humans is the estuarine or salt-marsh crocodile (Crocodylus porosus), which lives in salt and brackish waters from northern Australia and New Guinea, through most of SoutheastAsia , to southern India. This species can achieve a length of more than 23 ft (7 m). Individuals of this crocodile species sometimes occur well out to sea.

Other species are the mugger crocodile (Crocodylus palustris) of India, Bangladesh, and Ceylon; the Australian crocodile (C. johnsoni) of northern Australia; and the New Guinea crocodile (C. novaeguineae) of New Guinea and parts of the Philippines.

The American crocodile (Crocodylus acutus) is a rare and endangered species of brackish estuaries in southern Florida, occurring more widely in central and northwestern South America and the Caribbean. This species can achieve a length of 20 ft (6 m). The Orinoco crocodile (C. intermedius) occurs in the Orinoco and Amazon Rivers of South America.

The false gavial (Tomistoma schlegelii) is a slender-snouted species of Southeast Asia.

The alligators and caimans (family Alligatoridae) are seven species that occur in fresh water, with a broader head and more rounded snout than crocodiles. The American alligator (Alligator mississipiensis) can achieve a length of 13 ft (4 m), and occurs in the southeastern United States as far north as South Carolina and Alabama. This species was endangered by unregulated hunting for its hide. However, strict conservation measures have allowed for a substantial recovery of the species, and it is now the subject of a regulated hunt.

The Chinese alligator (Alligator sinensis) occurs in the lower reaches of the Yangtze and Kiang Rivers in southern China, and it is the only member of its family to occur outside of the Americas. The Chinese alligator can grow as long as 6.5 ft (2 m).

Caimans are animals of freshwater habitat in South and Central America. The black caiman (Melanosuchus niger) can achieve a length of 16 ft (5 m). The spectacled caiman (Caiman crocodilus) and the broad-nosed caiman (C. latisrostris) of eastern Brazil can both grow somewhat longer than 6.5 ft (2 m). The dwarf caiman (Paleosuchus palpebrosus) and the smooth-fronted caiman (P. trigonatus) live in more swiftly flowing streams and rivers and are relatively small species that do not exceed about 5 ft (1.5 m) in length.


Crocodilians and people

The larger species of crocodilians are fierce predators. In particular, crocodiles have posed a long-standing risk to domestic livestock that try to drink from their aquatic habitat as well as to unwary humans. For this reason, crocodiles are commonly regarded as dangerous pests , and they are sometimes killed to reduce the risks associated with their presence.

Because some species of crocodilians are dangerous, they are greatly feared in many places. This fear is justified in some cases, at least in places where large human-eaters are abundant. In some cultures, the deep fear and revulsion that people have for dangerous crocodilians has transformed into an attitude of reverence. For example, a pool near Karachi, Pakistan, contains a number of large mugger crocodiles, which are venerated as priest-like entities and worshipped by pilgrims. In other places, human sacrifices have been made to crocodiles to pacify animist spirits.

The skins of crocodilians can be used to make a very tough and beautiful leather. This valuable product is widely sought for use in making expensive shoes, handbags, wallets, belts, suitcases, and other items. Crocodilians are readily hunted at night, when they can be found using searchlights that reflect brightly off their eyes. In almost all parts of the range of crocodilians, they have been hunted to endangerment or extirpation. Almost all species in the crocodile family are endangered to some degree.

In a few places, however, strict conservation regulations have allowed the populations of crocodilians to increase from historically depleted lows. This has been particularly true of the American alligator, which was considered to be an endangered species only a few decades ago, but has now recovered sufficiently to allow for a carefully regulated sport and market hunt.

Some species of crocodilians are also ranched, usually by capturing young animals in the wild and feeding them in confinement until they reach a large enough size to slaughter for their hide. The meat of crocodilians is also a saleable product, but it is secondary in importance to the hide.

Crocodilians are sometimes used to entertain people, and some species are kept as pets. The Romans, for example, sometimes displayed Nile crocodiles in their circuses. To amuse the masses of assembled people, the crocodiles would be killed by humans, or alternatively, humans would be killed by the crocodiles.

In more modern times, alligator wrestling has been popular in some places, for example, in parts of Florida. The key to successful alligator wrestling is to hold the jaws of the animal shut, which can be accomplished using only the hands (but watch out for the lashing tail!). Crocodilians have very powerful muscles for closing their jaws, but the muscles to open their mouth are quite weak.


Resources

books

Alderton, D. Crocodiles and Alligators of the World. U.K.: Blandford Press, 1991.

Cogger, H.G., and R.G. Zweifel. Encyclopedia of Reptiles andAmphibians. San Diego: Academic Press, 1998.

Dudley, K. Alligators and Crocodiles. Raintree/Steck Vaughan, 1998.

Dudley. K. Crocodiles and Alligators of the World. Sterling Publications, 1998.

Grenard, S. Handbook of Alligators and Crocodiles. New York: Krieger, 1991.

Halliday, T. R., and K. Adler. The Encyclopedia of Reptiles andAmphibians. New York: Facts on File, 1986.

Messel, H., F. W. King, and J. P. Ross, eds. Crocodiles: An ActionPlan for Their Conservation. Gland, Switzerland: International Union for the Conservation of Nature (IUCN), 1992.

Webb, G., S. Manolis, and P. Whitehead, eds. Crocodiles andAlligators. Australia: Surrey Beatty, 1988.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd ed. New York: Academic Press, 2001.


Bill Freedman

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Endangered

—Refers to species or populations of organisms that are so small that there is a likelihood of imminent local extirpation, or even global extinction over its entire range.

Extirpated

—The condition in which a species is eliminated from a specific geographic area of its habitat.

Nictitating membrane

—An inner eyelid.

Overhunting

—Hunting of an animal at a rate that exceeds its productivity, so that the population size decreases, often to the point of endangerment.

Oviparous

—This refers to an animal that lays eggs, from which the young hatch after a period of incubation.

Poikilotherm

—Refers to animals that have no physiological mechanism for the regulation of their internal body temperature. These animals are also known, less accurately, as "cold-blooded." In many cases, these animals bask in the sun or engage in other behaviors to regulate their body temperature.

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