crocodile

Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant members of the order Crocodilia, which includes the alligators and caimans (family Alligatoridae), the gharial and false gharial (family Gavialidae) among other extinct taxa.

Although they appear similar, crocodiles, alligators and the gharial belong to separate biological families. The gharial, with its narrow snout, is easier to distinguish, while morphological differences are more difficult to spot in crocodiles and alligators. The most obvious external differences are visible in the head, with crocodiles having narrower and longer heads, with a more V-shaped than a U-shaped snout compared to alligators and caimans. Another obvious trait is that the upper and lower jaws of the crocodiles are the same width, and the teeth in the lower jaw fall along the edge or outside the upper jaw when the mouth is closed; therefore, all teeth are visible, unlike an alligator, which possesses in the upper jaw small depressions into which the lower teeth fit. Also, when the crocodile's mouth is closed, the large fourth tooth in the lower jaw fits into a constriction in the upper jaw. For hard-to-distinguish specimens, the protruding tooth is the most reliable feature to define the species' family. Crocodiles have more webbing on the toes of the hind feet and can better tolerate saltwater due to specialized salt glands for filtering out salt, which are present, but non-functioning, in alligators. Another trait that separates crocodiles from other crocodilians is their much higher levels of aggression.

Crocodile size, morphology, behaviour and ecology differ somewhat among species. However, they have many similarities in these areas as well. All crocodiles are semiaquatic and tend to congregate in freshwater habitats such as rivers, lakes, wetlands and sometimes in brackish water and saltwater. They are carnivorous animals, feeding mostly on vertebrates such as fish, reptiles, birds and mammals, and sometimes on invertebrates such as molluscs and crustaceans, depending on species and age. All crocodiles are tropical species that, unlike alligators, are very sensitive to cold. They separated from other crocodilians during the Eocene epoch, about 55 million years ago. Many species are at the risk of extinction, some being classified as critically endangered.

Etymology

The word ''crocodile'' comes from the Ancient Greek () meaning 'lizard', used in the phrase , "the lizard of the (Nile) river". There are several variant Greek forms of the word attested, including the later form () found cited in many English reference works. In the Koine Greek of Roman times, and would have been pronounced identically, and either or both may be the source of the Latinized form used by the ancient Romans. It has been suggested, but it is not certain that the word or is a compound of ('pebbles'), and ('worm'), although is only attested as a colloquial term for 'penis'. It is ascribed to Herodotus, and supposedly describes the basking habits of the Egyptian crocodile.

The form is attested in Medieval Latin. It is not clear whether this is a medieval corruption or derives from alternative Greco-Latin forms (late Greek and are attested). A (further) corrupted form is found in Old French and was borrowed into Middle English as . The Modern English form ''crocodile'' was adapted directly from the Classical Latin in the 16th century, replacing the earlier form. The use of ''-y-'' in the scientific name '' Crocodylus'' (and forms derived from it) is a corruption introduced by Laurenti (1768).

Species

A total of 18 extant species have been recognized. Further