Crocodilians are reptiles.
The crocodilian family is divided into 3 groups: 

• crocodiles

• alligators and caimans

• gharials, or gavials.

There are about 23 species, or kinds, of crocodilians.  

Crocodilians are reptiles. They live in hot, tropical places of the world. They keep their body temperature steady by basking in the sun when the weather is cool, and by resting in the shade when it is hot.

Crocodiles

Crocodiles have longer, narrower snouts than alligators, with a V shape nose,  and the 4th tooth of the lower jaw is outside when the mouth is closed.  Some kinds of crocodile live in salt water and others live in fresh water.

Unlike other reptiles, crocodiles have four sections in their hearts, like mammals and birds have.  

Their movement in the water is powered by their tail.Their long, flattened tail moves from side to side and propels them through the water, with their legs by their sides.  This movement is helped by two ridges of upright scales along the tail.  

Crocodiles have an incredible ability to leap straight up into the air from the water. They need to see their prey before they leap, so they start the leap while stationary at the surface of the water. They can judge the distance very accurately, and uses powerful movements of its tail to push itself upwards out of the water. It takes just seconds to lift itself several metres into the air.

A crocodile’s legs are short, with webbed toes, five on the front legs and four on the back legs. On land, crocodiles can run very quickly, lifting their bodies up off the ground.  

The eyes and nostrils are on the top part of the head so that they can lie in the water almost completely hidden from view while watching for prey.

Communication

Crocodiles communicate with each other with sounds that they make by forcing air through a voice box in the throat. The young call to the adults when they are in danger and make lots of noise while they are being fed. Adults make loud, low roars to each other. If they are threatened, adult crocodiles hiss and growl.

When a male and a female mate, they purr softly. They also use poses and movements to communicate. Raising the jaw off the ground is one such movement.

Listen to alligator warning hisses. Crocodiles also hiss!

Feeding

Crocodiles have very strong jaws, so strong that when they bite down to grab food, there is a loud sound. They do not chew their food. They swallow it in large chunks. In the stomach the food is broken down. They feed on a large variety of prey such as small mammals, birds and even domestic livestock, such as sheep and goats. Crocodiles grab their prey and roll over in the water to drown the animal. They can leap high out of the water to reach their prey if necessary.

Life Cycle

After mating with a male, the female crocodile lays about 50-80 eggs in a nest she makes near a river bank. She covers the nest with leaves and other vegetation. The rotting vegetation keeps the eggs warm and the nest moist.

The temperature inside the nest of several kinds of crocodilians decides the sex of the young : if the nest temperature is 30ºC, mostly females will hatch from all the eggs, and if the temperature is above 34ºC, there will be mostly males. If the temperature is in between, there will be young of both sexes. 

The female stays nearby and guards the nest for 90 days until the eggs hatch. The hatching babies call out and their mother opens up the nest and carries the babies to the water, where they immediately start feeding on crabs, small frogs, shrimps and insects. About half will not survive the first year.

Crocodile Fun Fact

The oldest known crocodile was 115 years old when it died in a Russian zoo in 1997.

Some of the world's crocodile species: 

Nile crocodile

• 4-5 metres long

• central & southern Africa, Madagascar

• freshwater

• Known to attack people, & will attack boats

Estuarine crocodile

• 4-7 metres

• northern Australia, southeast Asia

• saltwater, but survives in freshwater rivers far from the sea

• The most dangerous and heaviest of the crocodiles

American crocodile

• up to 7 metres

• central America, Mexico, Colombia, Ecuador, parts of Florida

• freshwater

• Not known to attack people, but still dangerous

Johnson's crocodile

• up to 3 metres

• only in northern Australia

• freshwater

• Not known to attack people but still regarded as dangerous

Marsh crocodile

• up to 4 metres

• India & Sri Lanka

• freshwater

• Known to attack people, but most commonly feeds on small mammals

Alligators and Caimans 

Alligators and caimans are both in the same group of the crocodilian family. They have a broader head than crocodiles, and a 'U' shaped nose.

Caimans have a slightly narrower head than alligators.   

Alligators and caimans show their front teeth when their mouths are closed.

Alligators and caimans live in fresh water. They have little black bumps called dermal pressure receptors on their lower jaw. These detect small pressure changes in the water, helping the animal find and capture prey. 

Gharials (also called gavials) 

Gharials can grow to a length of 4-5 metres long. The body looks almost exactly like that of an alligator, with its greenish skin, long pointed tail, and short stubby legs. However, the nose, or snout, is elongated and flattened, and has upper and lower jaws that are studded with sharp-edged teeth close together.
 

They are found in the calm water of deep rivers in northern India, Bangladesh, Pakistan, Bhutan, Nepal and Burma (Myanmar) in freshwater rivers. They eat mostly fish, but do feed on any dead animals they find floating in the river.

Crocodilian Conservation Status and Threats

All 23 species of crocodilian are protected. Five crocodilian species are critically endangered, and are, in order: the Chinese alligator, Philippine crocodile, Siamese crocodile, tomistoma (SE Asia) and Orinoco crocodile.  Gharials are the most critically endangered of the crocodilians. 

Their major threat is from humans as they expand their living areas and fish the rivers heavily.

 
Watch a video about saltwater crocodiles:

https://www.youtube.com/watch?v=qyTNzTYFqlw

Read about crocodiles :

https://www.livescience.com/28306-crocodiles.html

Read about alligators:

http://www.sciencekids.co.nz/sciencefacts/animals/alligator.html

Read the kidcyber pages:

• Crocodile farming

• Reptiles and amphibians