Crocodile

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For other uses, see Crocodile (disambiguation).

For differences between alligators and crocodiles, see Crocodilia#Differences between alligators and crocodiles.

Crocodiles Temporal range: 55–0Ma PreЄ Є O S D C P T J K Pg N Eocene – Recent
Nile crocodile (Crocodylus niloticus)
Estuarine crocodile (Crocodylus porosus)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Sauropsida
Clade:	Crocodylomorpha
Order:	Crocodylia
Family:	Crocodylidae
Subfamily:	Crocodylinae Cuvier, 1807
Type species
Crocodylus niloticus Laurenti, 1768
Genera
Crocodylus Osteolaemus Mecistops (proposed)

Crocodiles (subfamily Crocodylinae) or true crocodiles are large aquatic tetrapods that live throughout the tropics in Africa, Asia, the Americas and Australia. Crocodylinae, in which all its members are considered true crocodiles, is classified as a biological subfamily. A broader sense of the term crocodile, Crocodylidae, that includes the tomistoma, was excluded in this article since new genetic studies reveal the possibility of tomistoma as a close relative of the gharial.^[1] This article applies the term crocodile only to the species within the subfamily of Crocodylinae. The term is sometimes used even more loosely to include all extant members of the order Crocodilia: which includes all members of Crocodylidae, including the tomistoma, the alligators and caimans (family Alligatoridae) and the gharials (family Gavialidae), and the rest of Crocodylomorpha, which includes all of the prehistoric crocodile relatives and ancestors.
Although they appear to be similar to the untrained eye, crocodiles, alligators and the gharial belong to separate biological families. The gharial having a 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 the upper and lower jaws of the crocodiles are the same width, and 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 small depressions in the upper jaw where the lower teeth fit into. 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 family, the species belongs to.^[2] 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, are the much higher levels of aggression.^[3] All reptiles are all scaled diapsids, which are divided into two groups: crocodilians are archosaurs, along with birds and the extinct dinosaurs, while other reptiles are lepidosaurs.
Although all crocodiles are anatomically and biologically similar; their size, morphology, behavior and ecology somewhat differs between 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 first separated from other crocodilians during the Eocene epoch, about 55 million years ago.^[4] A lineage, including the rest of Crocodylomorpha, have been around for at least 225 million years, survived multiple mass extinctions, but today, due to habitat destruction and poaching, many species are at the risk of extinction, some being classified as critically endangered.

Contents

• 1 Etymology
• 2 Species
• 3 Characteristics
  • 3.1 Size
• 4 Biology and behavior
  • 4.1 Senses
    • 4.1.1 Vision
    • 4.1.2 Olfaction
    • 4.1.3 Hearing
    • 4.1.4 Touch
  • 4.2 Hunting and diet
    • 4.2.1 Bite
  • 4.3 Locomotion
  • 4.4 Longevity
  • 4.5 Social behavior and vocalization
  • 4.6 Reproduction
• 5 Relationship with humans
  • 5.1 Danger to humans
  • 5.2 Crocodile products
• 6 Taxonomy and phylogeny
  • 6.1 Phylogeny
• 7 See also
• 8 References
• 9 Further reading
• 10 External links

Etymology

The word "crocodile" comes from the Ancient Greek κροκόδιλος (crocodilos), "lizard," used in the phrase ho krokódilos tou potamoú, "the lizard of the (Nile) river". There are several variant Greek forms of the word attested, including the later form κροκόδειλος (crocodeilos)^[5] found cited in many English reference works.^[6] 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 krokè ("pebbles"), and drilos/dreilos ("worm"), although drilos is only attested as a colloquial term for "penis".^[6] It is ascribed to Herodotus, and supposedly describes the basking habits of the Egyptian crocodile.^[7]
The form crocodrillus is attested in Medieval Latin.^[6] 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).

Species

Distribution of crocodiles

A total of 14 extant species have been recognized. Further genetic study is needed for the confirmation of proposed species under the genus Osteolaemus, which is currently monotypic.