Crocodile (Crocodylidae) is a large aquatic tetrapod that lives throughout the tropics in Africa, Asia, the Americas and Australia. Lizards, snakes and crocodiles are all scaled diapsids, but crocodiles are archosaurs, which means they are genetically closer to birds and the extinct dinosaurs. Crocodylidae is classified as a biological family or subfamily.
The term can also be used more loosely to include all extant members of the order Crocodilia: which includes the crocodiles of Crocodylidae, the alligators and caimans (family Alligatoridae) and the gharials (family Gavialidae), and the rest of Crocodylomorpha, which includes prehistoric crocodile relatives and ancestors.
Crocodiles tend to congregate in freshwater habitats such as rivers, lakes, wetlands and sometimes in brackish water. They feed mostly on vertebrates – fish, reptiles, and mammals, and sometimes on invertebrates – molluscs and crustaceans, depending on species. They first appeared during the Eocene epoch, about 55 million years ago.
The word “crocodile” comes from the Ancient Greek (crocodilos), “lizard,” used in the phrase ho krokódilos tou potamoú, “the lizard of the (Nile) river”.
In the Koine Greek of Roman times, crocodilos and crocodeilos would have been pronounced identically, and either or both may be the source of the Latinized form crocodīlus used by the ancient Romans.
Crocodilos or crocodeilos is a compound of “pebbles”, and drilos/dreilos (“worm”). It is ascribed to Herodotus, supposedly to describe the basking habits of the Egyptian crocodile. However the word drilos is only attested as a colloquial term for “penis”. The meaning of krokè is explained as describing the skin texture of lizards (or crocodiles) in most sources, but is alternately claimed to refer to a supposed habit of (lizards or crocodiles) basking on pebbly ground.
The form crocodrillus is attested in Medieval Latin. It is not clear whether this is a medieval corruption or derives from alternate Greco-Latin forms (late Greek corcodrillos and corcodrillion are attested).
A (further) corrupted form cocodrille is found in Old French and was borrowed into Middle English as cocodril(le). The Modern English form crocodile was adapted directly from the Classical Latin crocodīlus 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).
Crocodiles are similar to alligators and caimans; for their common biology and differences between them, see Crocodilia.
Crocodiles, like dinosaurs, have the abdominal ribs modified into gastralia.
Crocodiles are among the more biologically complex reptiles despite their prehistoric look. Unlike other reptiles, a crocodile has a cerebral cortex, a four-chambered heart,and the functional equivalent of a diaphragm, by incorporating muscles used for aquatic locomotion into respiration (e.g. m. diaphragmaticus); Its external morphology, on the other hand, is a sign of its aquatic and predatory lifestyle.
A crocodile’s physical traits allow it to be a successful predator. Its streamlined body enables it to swim swiftly, it also tucks its feet to the side while swimming, which makes it faster by decreasing water resistance. Its webbed feet, though not used to propel the animal through the water, allow it to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallower water, where the animal sometimes moves around by walking.
Crocodiles have a palatal flap, a rigid tissue at the back of the mouth that blocks the entry of water. The palate has a special path from the nostril to the glottis that bypasses the mouth. The nostrils are closed during submergence. Like other archosaurs, crocodilians are diapsid, although their post-temporal fenestrae are reduced. The walls of the braincase are bony, but lack supratemporal and postfrontal bones. Their tongues are not free, but held in place by a membrane that limits movement; as a result, crocodiles are unable to stick out their tongues.
Crocodilian scales have pores believed to be sensory in function, analogous to the lateral line in fishes. They are particularly seen on their upper and lower jaws. Another possibility is that they are secretory, as they produce an oily substance, which appears to flush mud off.
Crocodiles are very fast over short distances, even out of water. Since they feed by grabbing and holding onto their prey, they have evolved sharp teeth for tearing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. These jaws can bite down with immense force, by far the strongest bite of any animal. The pressure of the crocodile’s bite is more than 5,000 pounds per square inch (30,000 kPa), compared to just 335 pounds per square inch (2,300 kPa) for a Rottweiler, 400 pounds per square inch (2,800 kPa) for a large great white shark, 800 pounds per square inch (6,000 kPa) to 1,000 pounds per square inch (7,000 kPa) for a hyena, or 2,000 pounds per square inch (10,000 kPa) for a large alligator. The jaws are opened, however, by a very weak set of muscles. Crocodiles can thus be subdued for study or transport by taping their jaws or holding their jaws shut with large rubber bands cut from automobile inner tubes. They have limited lateral (side-to-side) neck movement.