Alligators and crocodiles are in the same reptile subgroup. They mostly live in tropical or semitropical regions. Alligators are mostly found in the southern United States and the crocodiles in Africa, India, South America, and southern United States. They are among the largest reptiles. Their bodies are covered with scales and they have webbed toes. They live in swamps and along the banks of rivers.
Two species of crocodilians are native to the United States - the American alligator (Alligator mississippiensis) and the American crocodile (Crocodylus acutus). American alligators are restricted to the southeastern United States, while the highly endangered American crocodile is found only in the southern tip of Florida.
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Some of the similarities between alligators and crocodiles are that they are both fierce and have a long tail, bumpy backs, sharp teeth, short legs, intelligent, cold-blooded, love to swim, and have webbed feet. They have vertical pupils that open wide in low light, which allows them to be impressive nocturnal hunters. Their throat (gular) pouch blocks water so that they can eat prey under water as well as on land. They are also large, lizard-shaped reptiles with four, short legs and a long, muscular tail. Their hide is rough and scaled. Both the alligator and crocodile eat fish and nearby land animals. They can also attack man.
While alligators (and caimans) are often confused with crocodiles, they belong to two quite separate taxonomic families.
The most obvious external differences are visible in the head—alligators and caimans have wider and shorter heads, and a more U-shaped than V-shaped snout. The alligator's upper jaw is wider than its lower jaw, and the teeth in the lower jaw fit into small depressions in the upper jaw. The upper and lower jaws of the crocodiles are the same width and teeth in the lower jaw fall along the edge or outside the upper jaw when the mouth is closed. When the crocodile's mouth is closed, the large fourth tooth in the lower jaw fits into a constriction in the upper jaw. For hard-to-distinguish specimens, the protruding tooth is the most reliable feature to define a species. However, in captivity, alligators and caimans may show jaw deformities which result in lower teeth protruding.
Alligators lack the jagged fringe which appears on the hind legs and feet of the crocodile and have the toes of the hind feet webbed, not more than halfway to the tips. Alligators strongly prefer, while crocodiles can better tolerate due to specialized glands for filtering out salt. However, both can survive in either.
Both species of alligator also tend to be darker in color than crocodiles—often nearly black—but color is very dependent on water quality. Algae-laden waters produce greener skin, while from overhanging trees can produce often darker skin.
When cleaning alligator pools, some zookeepers can tread on alligators without eliciting a response, though crocodiles almost invariably react aggressively and are for the most part more aggressive in their natural habitat.
The difference between alligators and crocodiles is often easy to spot once you get the hang of it. Alligators are dark colored with a broad, rounded snout and are usually found in fresh water. Crocodiles are grayish-green and prefer coastal, brackish and salt-water habitats. They have a narrow, tapered, triangular snout. Also, the fourth tooth on either side of the lower jaw of an alligator fits into an internal socket in the upper jaw so that these teeth are hidden when the mouth is closed. In a crocodile, the fourth tooth is always exposed. The crocodile spends more time in the water than the alligator. Crocodiles are more active than alligators.