Alligators and crocodiles are both crocodilians; but from different families. There are three separate families of crocodilians: Aligatoridae include alligators and caimans, Crocodylidae include crocodiles and Gavialidae include only the gharial. This is only the difference in classification; there are many physical differences between the two animals.
Alligators are found in only two places in the world; the southeastern United States and in China. The Chinese alligator is classified as Critically Endangered by the IUCN. It is found in small bodies of water on the lower Yangtze River. Habitat destruction is the biggest culprit as more and more Chinese land is converted for agricultural uses – we really are insatiable in the West aren’t we? There is hope for them; there are over 10,000 Chinese alligators in zoos and sanctuaries. This is probably enough to maintain genetic diversity. Crocodiles are found in Africa, Asia, North and South America and Australia.
Alligators, in general have a more pointed and stronger jaw that assists them in crunching through the hard shells of turtles that are plentiful in their habitat in the United States. Crocodiles have a weaker jaw. Their jaws are also different. Only the top teeth are visible on an alligator with a closed mouth; their top jaw completely covers their lower jaw whereas crocodiles have jaws that allow their teeth to fit nicely between each other; meaning top and bottom teeth are both visible.
Two more interesting features distinguish alligator from crocodile. Small sensory organs on the skin of both animals are thought to detect changes in pressure, allowing them to locate prey easier. Alligators only have them in the area around their head, whereas crocodiles have them covering most of their body. The second feature is salivary like glands in the tongue that secrete salt. Both alligators and crocodiles have these organs, but they are only active in crocodiles. This is why crocodiles are able to live in ocean and fresh water while alligators live only in fresh water.
As with many things in life, there are exceptions to the rule. The Indian Mugger crocodile actually has a snout resembling an alligator, but is a crocodile in all other ways.