The first difference between a crocodile and an alligator is that they are from different families of crocodilians. Crocodiles are from the crocodylidae family, while alligators and caiman are from the alligatoridae family.

In terms of physical differences the easiest way to tell the difference between the two is that a crocodile has a very long, narrow, V-shaped snout, while the alligator's snout is wider and U-shaped. Because of the wide snout of the alligator it packs more crushing power to eat prey like turtles that constitute part of its diet. The narrow crocodile snout, although still very powerful, is not really suited for prey like turtles but is very versatile for fish and mammals.

Another physical difference between the crocodile and the alligator is that the crocodile's upper and lower jaws are nearly the same width, so the teeth are exposed all along the jaw line in an interlocking pattern, even when the mouth is closed. They also have an enormous 4th tooth on the lower jaw that is accommodated by depressions in the upper jaw just behind the nostrils.

An alligator, on the other hand, has a wider upper jaw, so when its mouth is closed the teeth in the lower jaw fit into sockets of the upper jaw, hidden from view. Only the teeth of the upper jaw are exposed along the lower jaw line. Even the enormous 4th tooth on the bottom jaw, which is exposed in a crocodile, is hidden in the alligator.

Another physical difference is that crocodiles have a lighter olive brown coloration, while alligators appear blackish. Alligators also prefer freshwater while crocodiles like brackish water and sometimes even ocean.

Speaking to this difference, while crocodiles and alligators both have glands on their tongues, crocodiles still use these glands to excrete excess salt. Alligators seem to have lost this ability, making their tolerance for salt water comparatively brief. Biologists believe this suggests that the crocodile is less removed from its oceanic ancestry.

Both crocodiles and alligators have dotted sensory pits along the upper and lower jaws that look almost like beard stubble. They detect slight changes in water pressure, thought to help the animals locate prey. These sensory pits were called Integumentary Sense Organs (ISOs) until they were renamed to Dermal Pressure Receptors (DPRs). While both animals have them along the jaws, the crocodile has one on every scale covering its entire body. Some researchers believe the crocodile's DPRs might be linked to detecting levels of salinity.

It is generally stated that alligators are docile compared to aggressive saltwater crocodiles, and that crocodiles grow larger. While true in general, there are exceptions to every rule among the many species. As an example, the average alligator grows to about 14 feet (4.3 meters), while crocodiles can reach 19 feet (5.8 meters) or more. That said there is one species of crocodile - the African dwarf - that barely reaches 5 feet (1.5 meters). Also, the Indian mugger crocodile has a decidedly U-shaped snout, breaking the V-shaped rule.

In terms of nesting, crocodiles lay their eggs in mud or sand nests near brackish water, while alligators make their nests out of mounds of vegetation surrounding freshwater.

In the United States crocodiles are only found around the southern tip of Florida, though they can also be found in the Caribbean, Central America and South America. Alligators are found in the southeastern United States, and South Florida is the only known place in the world where crocodiles and alligators cohabitate the same areas.

Crocodilians, which includes both crocodiles and alligators, are believed descended from archosauria which lived 250 million years ago at the end of the Paleozoic era when all the continents were joined together in a single mass known as Pangea. About 30 million years later in the Triassic period (220 million years ago) archosauria split into two lines of evolution, one being crocodilians and the other dinosaurs and birds. Scientists theorize that the Age of Reptiles, which lasted some 155 million years, ended about 65 million years ago when an asteroid struck Earth wiping out the dinosaurs. But while dinosaurs vanished crocodilians survived!

After surviving nearly unchanged for over 200 million years crocodiles and alligators were hunted to the brink of extinction between 1900 and 1967in a period as brief as a single man's life. Additionally their habitats continue to shrink. Today due to conservation efforts the American alligator is no longer on the endangered species list but many species of crocodiles remain at risk. Continued diligence is necessary if we are to preserve these incredible animals that open a door to the planet's early history and a window into an age of fantastic creatures that ruled the earth for tens of millions of years.