Alligators and crocodiles. Alligators are often mistaken for crocodiles but are different from them in some ways. The fourth tooth of the alligator's lower jaw fits into a pocket of the upper jaw. The same tooth in the crocodile fits into a groove in the side of the upper jaw, making it visible when the animal's mouth is closed. Another way to tell the American alligator from the American crocodile is that the American alligator has a much broader snout.
Alligators are also much less aggressive and active than crocodiles.
In the United States, alligators and crocodiles are found together only in the marshes at the southern tip of Florida. Both alligators and crocodiles belong to the great group of crocodilians. This group also includes caymans and gavials. Where alligators live. Alligators were once common in lakes, swamps, and rivers along the Gulf of Mexico and on the Atlantic Coast as far north as North Carolina.