A crocodile is a semi-aquatic reptile in the order Crocodilia. Reptiles in this order are collectively known as crocodilians, and they include the true crocodiles, along with alligators, caimans, and the gharial, a very rare Indian reptile. Crocodilians can be found all over the world, typically near large deposits of salt or freshwater, with many species being considered threatened due to habitat pressure and hunting.
Several traits are common to all of the members of this order of reptiles. They are incredibly strong, with bodies built for predation, including powerful tapering jaws. A crocodile can take down prey much larger than it is, and multiple animals can be essentially unstoppable. They also have an extremely keen sense of hearing, and they communicate with a wide range of vocalizations, including grunts, coughs, and barks.
As a general rule, these reptiles are carnivores, and most are not picky about what they eat. Fish, small mammals, and larger prey like oxen are all fair game to a hungry croc, as are humans. Like other reptiles, they use basking to regulate their internal temperatures, preferring banks near their aquatic habitat so that they can slip underwater if threatened. Crocodiles tend to be more active at night, and some burrow into the bank to nest, with only their nostrils protruding.
Crocodiles are also covered in thick, scaly skin that acts like armor. Depending on the species, they can reach up to 16 feet (5 meters) in length, and some individuals may live to be well over 100 years old. These animals are also quite intelligent, able to work in groups when necessary and to patiently lie in wait for prey.
One interesting trait of animals in this order is the habit of swallowing stones. The stones may act as ballast, allowing the animals to dive, and they may also play a role in digestion. Researchers who focus on crocodilians have found that the reptiles can “make change” with their ballast stones when presented with an assortment of stones to swallow; they will disgorge stones if necessary to make the right weight. This habit is referenced in the animal's name, which comes from the Greek kroke, which means “pebble,” and drilos, or “worm.”
As a general rule, crocodiles are found in tropical and semitropical regions of Africa, Asia, and the Americas. Many people use the term specifically to refer to the true crocodiles, differentiating these crocodilians from their cousins, the alligators and caimans. Crocodilians are physically fairly similar, although true crocodiles have distinctive protruding lower teeth that are visible even when their jaws are closed, making it easy to distinguish between these animals and alligators.