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AquaFacts: Crocodilians

What are crocodilians?

Crocodiles, alligators, caiman, false gharials and gharials make up the crocodilian group, which has survived for about 200 million years. There are three families included in the crocodilians:

  • Alligatoridae: the American and Chinese alligators, South American caimans; 7 species
  • Crocodylidae: crocodiles and the false gharial; 14 species
    Gavialidae: the gharial; 1 species which is the Indian Gharial

Where do crocodilians live?

They are widely distributed throughout the tropical and subtropical regions of Africa, India, South-east Asia, Australia, North, Central and South America. They are found in habitats such as swamps, ponds, rivers, lakes and marshes.

What is the difference between a crocodile and an alligator?

The main difference is in the shape of the heads. Alligators have broad, rounded snouts whereas crocodiles have more narrow snouts that taper to a point. The other difference is with their teeth. Alligators have a wider upper jaw than lower jaw so when their mouth is closed the teeth in the lower jaw are almost completely hidden and fit into sockets of the upper jaw. In crocodiles, the upper and lower jaw are the same width and so teeth in the lower jaw fit outside when the mouth is closed. This makes them look like they have interlocking teeth. Another difference is the skin of a crocodile which is covered in sensory pits, whereas alligators only have these pits near their jaws.

Are crocodiles more dangerous than alligators?

Some crocodiles are more aggressive than alligators. There are probably more incidents of humans being attacked by crocodiles than alligators because there are more crocodiles in existence.

What do crocodiles and alligators eat?

Their diet is diverse. They prey on anything from dragonflies and bats to sharks, antelopes and even buffalo. Although attacks on humans have occurred, most species of crocodilian don't include humans as a food source. In fact, it has been suggested that a person bending down over a water source may resemble an antelope in the eyes of a crocodile and this is why the attacks occur. The species that habitually hunt humans are the Nile and Indo-Pacific crocodiles. The American crocodile, black caiman and the Indian mugger will on occasion kill humans for food or to defend their nests or territories.

Why don't crocodiles and alligators eat very often?

Crocodilians are extremely energy efficient. They are poikilotherms (cold-blooded), and so depend on external heat sources to regulate their body temperature. Because of this, they do not have to heat themselves using energy fueled by food as humans and other mammals do. Usually crocodilians need only eat once a week or less to maintain their energy levels.

Why do alligators and crocodiles often sit with their mouths open?

This behaviour is called gaping and it is done when the crocodile or alligator is basking in the sun. It is thought that this may act in cooling the crocodile, however, since they also do this during rain and at night it could suggest that gaping has a social function as well.

How are they adapted to an aquatic environment?

Crocodilians are well adapted to water, as well as land. They are excellent swimmers and can hold their posture in water. When submerging underwater they close their ear and nostril flaps. When feeding underwater the back of the tongue acts as a valve to stop water from going into their lungs. Crocodiles and alligators can dive for long periods of time due to their slow metabolic rate. Vibration sensors and touch receptors help them to feel movements of prey in the water. They have a third eyelid, called the nictitating membrane that protects their eyes underwater.

Why are many species of crocodilian endangered?

Some species are endangered due to habitat destruction such as the Nile crocodile whose nesting areas along the river are disrupted by boat traffic. Nearly all crocodilians live in the rainforests and wetlands of developing countries which are being destroyed by logging, development and other industries. Poaching also lowers the crocodilian population. A multi-million dollar business exists in the illegal trade of crocodilian hides. The common caiman is the most hunted crocodile, and makes up 60% - 80% of skins in the trade. However, their bony hides only receive a tenth of the price that is paid for alligator or crocodile skins. The American alligator was one of the first animals to receive protection under the United States Endangered Species Act, they are now no longer endangered but listed as 'threatened' instead. Steps are being taken to alleviate poaching and repopulate species of crocodilians by setting up crocodile farms.

How do crocodiles and alligators catch their prey?

Prey is seized using the element of surprise. Crocodiles sit camouflaged and motionless in the water waiting for prey to come to them. Their eyes and nostrils are high on their head so the rest of their body can be hidden under water. When prey is only a short distance away the crocodile quickly snaps its muscular jaws around the prey and drags it below the water to drown and consume it.

Where do they lay their eggs?

Females lay their eggs in holes they dig in the sand or in large nests made of vegetation and mud. The mother will guard the nest until she hears the cry of her babies, which break their shells with an "egg" tooth. Without the babies call of distress the hatchlings may never see light, since it is the mother who digs them out of the mound of mud. She then picks up her babies in her mouth and carries them to water, breaking the remaining shells and swallowing them. The smallest of the crocodilians may lay 10 to 15 eggs, but larger species like the Indo-Pacific crocodile may lay 50.

Are there any crocodilians at the Aquarium?

The Aquarium houses three caimans that were born in 1978 at Fort Worth, Texas. They were sent here in 1983 from the National Zoological Park in Washington, D.C. The Aquarium is the temporary home for the Golden Crocodiles until April 2000. While these rare and endangered crocs are with us, the caiman will be removed from the exhibit. The Golden Crocodiles, also known as the Indo-Pacific crocodiles, were born in Samutprakan Crocodile Farm in Thailand.

Do crocodilians make good pets?

No. Some people keep baby alligators and crocodiles, but when they grow to over 2 metres long and are difficult to house, they no longer make ideal pets and often have to be put down. They can be dangerous to keep as pets, potentially harming other pets or even people.

How long can they hold their breath underwater?

Usually they can hold their breath from 4 - 15 minutes but can remain underwater for 2 hours if needed and if they aren't stressed. The record time spent underwater is 8 hours in freezing conditions, this is because a colder crocodile uses less energy and oxygen and can hold its breath longer than a warmer one.

Did you know?

Crocodilians:

  • Shed their teeth regularly. No cavities, no dentists, they have it easy.
  • Can last months without feeding as long as their body temperature remains low.
  • Roar like lions. They also snort, jaw snap and tail slap to establish courtships, dominance, territory, and aggression. Crocodiles and alligators also communicate visually through body language and with sub-audible vibrations which are transmitted to animals both in the water and on the surface. These vibrations are created by contracting their trunk muscles.
  • Are only distantly related to the dinosaurs, while birds are the closest living relative to dinosaurs.
  • When the American alligator's swamp freezes over most of the reptiles will survive by maintaining a hole through the ice in which to breath.
  • Mothers respond to the distress call of juveniles and defend them against predators.
  • Are the only reptile to have a four-chambered heart (all other reptiles have a three-chambered heart).
  • Have a muscular gizzard similar to birds - which is used to grind up food prior to entering the stomach.
  • Incubation temperature will determine what sex the juvenile will be.

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