Dr Simon Pooley, Lambert Lecturer in Environment (Applied Herpetology) explains the differences between crocodiles and alligators. Crocodiles and alligators are members of different families of the order Crocodilia. There are currently 13 recognised species of crocodile in the family Crocodylidae. These are widely distributed across the tropics from the Americas, across parts of the Caribbean, Africa, South Asia, Malaysia, Indonesia and all the way down to Australia and the islands of Oceania. They range greatly in size from the small African Dwarf Crocodile (1.9m / 6ft) to the giant Saltwater (or Estuarine) Crocodile which is the largest living reptile and grows up to 6m (20ft) long.
In contrast, there are only two types of alligator, along with 6 caiman in the family Alligatoridae. The bigger and better-known of the two is the American Alligator, which lives on the Atlantic coastal plains of the south east coast of the USA. The other type is the Chinese Alligator, of which a few may still exist in the wild in the lower reaches of the Yantze River. Today, a 4m (14ft) alligator is considered large, although there are historical records of them reaching up to 5m (16ft).
Most crocodiles (not all) have a more triangular skull than the rounded, broad skulls alligators. A more reliable visual difference is the interlocking teeth of crocodiles, where upper and lower rows of teeth protrude when the jaws are closed, as opposed to the alligators where the bottom jaw (and teeth) fit inside the upper when the jaws are closed.
The two species of Gharial of the family Gavialidae (not shown) are clearly recognisable by their long, very narrow skulls designed for catching and eating fish.
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