Crocodilians - Alligators & Crocodiles
Modified: 30-11--0001 00:00:00
What are crocodilians?
Crocodiles, alligators, caiman, false gharials and gharials make up the crocodilian group, which has existed on earth for over 200 million years. There are three families included in the crocodilians:
Alligatoridae: inlcuding American and Chinese alligators, South American caimans; 7 species
Crocodylidae: crocodiles and the false gharial; 14 species
Gavialidae: the gharial; including 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. Crocodiles are subtropical, but alligators live in temperate zone. Alligators can tolerate frozen ponds as long as they have access to a hole in the ice through which to breathe.
What is the difference between an alligator and a crocodile?
Head
The main difference is in the shape of the heads. Alligators have broad, rounded snouts whilst crocodiles have more narrowed snouts tapering to a point.
Jaw 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.
Skin
The crocodile has skin which is covered in sensory pits, whereas alligators only have these pits near their jaws.
Are crocodiles more dangerous than alligators?
Generally, yes, crocodiles are more aggressive than alligators and they include species which grow much bigger than the biggest alligators. There are more incidents of humans being attacked by crocodiles than alligators, and more of these attacks are fatal.
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.
Crocodilians can not chew their food, instead tearing it into bite size chunks and swallowing these chunks whole.Some species will catch their prey, then leave it under an underwater tree to rot for a few days, so it is easier to tear apart.
Why don't crocodiles and alligators eat very often?
Crocodilians are extremely energy efficient. They are cold blooded and 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 and it covers their eye at the moment of attack.
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.
The Australian Saltwater Crocodile was hunted almost to extinction for its skin, meat, and to protect domestic herds, but since being protected some 30 years ago, has made a huge resurgence, with plague proportions being reported in areas such as Darwin.
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.
A saltwater crocodile can throw its body half its own length out of the water, so if you are sitting in a tree branch, 2 and a half meters above the water, you are a target for a 5 meter crocodile!
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.
Temperature of the nest determines the sex of the babies. Temperatures below 31.7 degrees Celsius produce females. Any temperature above that, in other words, above 31.7, right up until 34.5 degrees Celsius, produce males and then temperatures above 34.5 degrees produce female hatchlings once again.
Global warming thus, has the potential to wipe out crocodiles even though they are cold blooded and would seemingly benefit from a hotter planet, as at some point, too few males will be born to continue the species. Since period of warming have occurred on earth before, it is likely crocodiles migrated North/South of the equator depending on changes in the earth?s temperature. This is not likely to be as successful in future, as mankind has now developed the planet to the point where it would be difficult for crocodiles to be so mobile.
Do crocodilians make good pets?
Um?No. Some people keep alligators and crocodiles, but when they grow to over 2 metres long they are difficult to house, they no longer make ideal pets and often have to be put down. They can be dangerous to keep, potentially harming other pets or even people. You really don't want a pet, that sees you as dinner, and taking a 4 metre saltwater crocodile to school on pet day, the other pets are not going to have a good time.
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.
Further Information
Crocodilians:
- Shed their teeth regularly. No rotting teeth for these fellows, they simply replace them.
- 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 breathe.
- 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.
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