Both crocodiles and alligators are large, predatory lizard-like reptiles that are closely related to each other. These large, semi aquatic reptiles belong to the order Crocodilia which includes the true crocodiles (Crocodylidae), the alligators and caimans (Alligatoridae), and the gharial and false gharial (Gavialidae).
Crocodiles and alligators belong to the sub group Eusuchia. This group appeared 100 million years ago during the late cretaceous period and includes three families, Gavialidae, Crocodylidae and Alligatoridae.
Both are found mainly throughout the tropics in Africa, Asia, the Americas and Australia. They have long flattened snouts lined with sharp teeth which deliver a powerful bite. Their eyes, ears and nostrils are located on top of the head, which enables them to see above water whilst submerged almost entirely by it. Confident swimmers, they are also capable of walking on land, and can in fact reach considerable speeds.
The skin on the back is toughened and armoured with embedded bony plates. Typically solitary and territorial animals they are largely carnivorous, feeding on the fish, snails and other invertebrates, birds, frogs, and mammals that come to the water's edge. They use their sharp teeth to seize and hold prey, swallowing small prey whole and shaking apart larger prey into manageable pieces
During the breeding season males stake out their territory, posturing and defining their area. Males will approach females and gently rub head to head, after which the female will either swim away or raise her body to encourage copulation to fertilise her eggs. Females dig the nest in sandy soil above the water line and deposit their eggs. They remain close to the nest until the eggs hatch.
The easiest way to distinguish an alligator from a crocodile is by looking at the teeth. The large fourth tooth in the lower jaw of an alligator fits into a socket in the upper jaw and is not visible when the mouth is closed. This does not happen in crocodiles whose fourth tooth on the bottom jaw of the is visible when its mouth is closed.
Crocodiles have a slimmer, pointed snout than the wider, 'u' shaped snouts of alligators. Their habitat differs too, with crocodiles living in salt water environments whilst alligators are found in freshwater marshes and lakes.
There are two living species of alligator, the American alligator and the Chinese alligator. In addition, several extinct species of alligator are known from fossil remains.
Alligators are usually found in freshwater, in slow-moving rivers as well as swamps, marshes and lakes. Because they do not have salt glands they can tolerate salt water for only brief periods.
Alligators grin is different from the crocodile as they hide all their teeth when they close their mouths. Alligators have between 74 and 80 teeth in their mouth at a time and they are replaced with new teeth as they wear down.
The average size for an adult female American alligator is 2.6 meters and the male is 3.4 meters. Large males can reach a weight of nearly half a ton or 1,000 pounds.
Alligators usually remain in a small area but this are is extended during the courting and breeding season. Unlike most other reptiles, alligators care for their hatched young. Young remain with their mother for several years before they are driven out by the group. Young can be distinguished from adults by the bright yellow stripes on the tail; adults have dark stripes on the tail.
Alligators undergo periods of dormancy when the weather is cold, excavating a gator hole in the muds which fills with water. These tunnels can be as long as 20 meters and provide protection during extreme hot or cold weather.
Crocodiles appeared 83.5 million years ago in the Late Cretaceous period. Strangely they are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria.
Crocodiles have toothy grin and unlike the alligator the fourth tooth on the bottom jaw of the American crocodile is visible when its mouth is closed.
They have long, slender snouts and are usually coloured grey-green or olive-green. With a lifespan of around 70 years crocodiles can reach up to 15 feet long and weigh 150-450 lbs.
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