Crocodile


A crocodile or true crocodile is a large, semiaquatic reptile that lives throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include all extant members of the order Crocodilia, which includes the alligators and caimans, the gharial and false gharial as well as other extinct taxa. This article will use "crocodile" or "true crocodile" to refer only to the species taxonomically included in the Crocodylidae family, extant or extinct.
Crocodile size, morphology, behaviour and ecology differ 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. Many species are at the risk of extinction, some being classified as critically endangered.

Etymology

The word crocodile was derived during the Middle English period from the transliteration krokódilos of a Greek word which translates as "stones worm". Through Ancient Greece the English language word has developed from Grecian origination in Anatolia.
A very early extant Ancient Greek source is an Aesop's Fable named Ἀλώπηξ καὶ κροκόδειλος of the sixth century BC. Herodotus a century after in consideration of the Greek word thought it was from the Ionic period.
The Latin language word crocodilus existed in first century AD in the work Naturalis Historia of Pliny the Elder. Examples in writing in the sixth and seventh century AD, crocodillorum and crocodili existed, though corcodrillus and cocodrillus were forms in Medieval Latin. The Latin form is found as cocodrille c. the 13th century in the Old French work Li livres dou tresor, in which the croc. is jaune.
The earliest known source in the English language is within the work Kyng Alisaunder from towards the beginning of the 14th century, a magical romance poetry work of rhyming couplets, where the word is found line 5720:
Writing sometime after 1483 on his visit to the Holy Lands Felix Fabri in German and Latin mentions the Cocodrillen and cocodrillos respectively. By 1538 the exact same form of the modern word as the current English is found in French; croc. is within a poem of Edmund Spenser, thought written in 1579–80, and in the works of William Shakespeare, who died in 1616. The similitude of the English word formation to a Latin source was caused at least by the transmission of a relevant ancient science from the influx of the publication of translations of Pliny the Elder some time towards the end of fourteenth and, or, beginning of fifteenth century. The publication of concrete realization in the anatomical work of Andreas Vesalius during 1543 inspired the creation of monographs and books of animals contributing to new science in zoology.

Taxonomy and phylogeny

Crocodylidae was named as a family by Georges Cuvier in 1807. It belongs to the larger superfamily Crocodyloidea, which also includes additional extinct crocodile relatives. These all belong to the order Crocodilia, which also includes alligators and gharials.
Although crocodiles, alligators, and the gharial are similar in appearance, they 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.
Crocodylidae is cladistically defined as a crown group composed of the last common ancestor of the Nile crocodile, the Dwarf crocodile, and all of its descendants. It contains two subfamilies: Crocodylinae and Osteolaeminae. Crocodylinae contains 13–14 living species, as well as 6 extinct species. Osteolaeminae was named by Christopher Brochu in 2003 as a subfamily of Crocodylidae separate from Crocodylinae, and contains the two extant genera Osteolaemus and Mecistops, along with several extinct genera. The number of extant species within Osteolaeminae is currently in question.
File:Crocodylus acutus mexico 01.jpg|thumb|right|American crocodile at La Manzanilla, Jalisco, Mexico
Recent molecular studies using DNA sequencing have shown crocodiles to be more closely related to the gavialids rather than to alligators, contrary to prior theories based on morphological studies alone.
Below is a cladogram showing the relationships of the major extant crocodile groups based on molecular studies, excluding separate extinct taxa:
Below is a more detailed cladogram of Crocodylidae, based on a 2021 study using paleogenomics that extracted DNA from the extinct Voay. Recently recognised species placed according to 2023 study by Sales-Oliveira et al.
Alternatively, some morphological studies have recovered Mecistops as a basal member of Crocodylinae, more closely related to Crocodylus than to Osteolaemus and the other members of Osteolaeminae, as shown in the cladogram below.

Species

A total of 18 extant species have been recognized. Further genetic study is needed for the confirmation of proposed species under the genus Osteolaemus.
Species nameImageDistributionDescription/Comments
American crocodile Throughout the Caribbean Basin, including many of the Caribbean islands and South Florida.A larger sized species, with a greyish colour and a prominent V-shaped snout. Prefers brackish water, but also inhabits lower stretches of rivers and true marine environments. This is one of the rare species that exhibits regular sea-going behaviour, which explains the great distribution throughout the Caribbean. It is also found in hypersaline lakes such as Lago Enriquillo, in the Dominican Republic, which has one of the largest populations of this species. Diet consists mostly of aquatic and terrestrial vertebrates. Classified as Vulnerable, but certain local populations under greater threat.
Hall's New Guinea crocodile The island of New Guinea, south of the New Guinea HighlandsA smaller species that closely resembles and was long classified under the New Guinea crocodile, which it is now considered to be genetically distinct from. It lives south of the mountain barrier that divides the two species' ranges. It can be physically distinguished from the New Guinea crocodile by its shorter maxilla and enlarged postcranial elements. Cranial elements can still widely vary within the species, with populations from Lake Murray having much wider heads than those from the Aramia River.
Orinoco crocodile Colombia and VenezuelaThis is a large species with a relatively elongated snout and a pale tan coloration with scattered dark brown markings. Lives primarily in the Orinoco Basin. Despite having a rather narrow snout, preys on a wide variety of vertebrates, including large mammals. It is a Critically Endangered species.
Freshwater crocodile Northern AustraliaA smaller species with a narrow and elongated snout. It has light brown coloration with darker bands on body and tail. Lives in rivers with considerable distance from the sea, to avoid confrontations with saltwater crocodiles. Feeds mostly on fish and other small vertebrates.
Philippine crocodile Endemic to the PhilippinesThis is a relatively small species with a rather broader snout. It has heavy dorsal armour and a golden-brown colour that darkens as the animal matures. Prefers freshwater habitats and feeds on a variety of small to medium sized vertebrates. This species is Critically Endangered and the most severely threatened species of crocodile.
Morelet's crocodile Atlantic regions of Mexico, Belize and GuatemalaA small to medium sized crocodile with a rather broad snout. It has a dark greyish-brown colour and is found in mostly various freshwater habitats. Feeds on mammals, birds and reptiles. It is listed as Least Concern.
Nile crocodile Sub-Saharan AfricaA large and aggressive species with a broad snout, especially in older animals. It has a dark bronze coloration and darkens as the animal matures. Lives in a variety of freshwater habitats but is also found in brackish water. It is an apex predator that is capable of taking a wide array of African vertebrates, including large ungulates and other predators. This species is listed as Least Concern.
New Guinea crocodile The Indian subcontinent and surrounding countriesThis is a modest sized crocodile with a very broad snout and an alligator-like appearance. It has dark-grey to brown coloration. Enlarged scutes around the neck make it a heavily armoured species. Prefers slow moving rivers, swamps and lakes. It can also be found in coastal swamps but avoids areas populated by saltwater crocodiles. Feeds on a wide array of vertebrates.
Saltwater crocodile Throughout, Northern Australia and surrounding watersThe largest on average living reptile and most aggressive of all crocodiles. It is a big-headed species and has a relatively broad snout, especially when older. The coloration is pale yellow with black stripes when young but dark greenish-drab coloured as adults. Lives in brackish and marine environments as well as lower stretches of rivers. This species has the greatest distribution of all crocodiles. Tagged specimens showed long-distance marine travelling behaviour. It is the apex predator throughout its range and preys on virtually any animal within its reach. It is classified as Least Concern but with several populations under greater risk.
Borneo crocodile Island of Borneo in Southeast AsiaA freshwater species of crocodile that has been considered a synonym of the saltwater crocodile.
Cuban crocodile Found only in the Zapata Swamp and Isle of Youth of CubaIt is a small but extremely aggressive species of crocodile that prefers freshwater swamps. The coloration is vibrant even as adults and the scales have a "pebbled" appearance. It is a relatively terrestrial species with agile locomotion on land, and sometimes displays terrestrial hunting. The snout is broad with a thick upper-jaw and large teeth. The unique characteristics and fossil record indicates a rather specialized diet in the past, preying on megafauna such as the giant sloth. This species sometimes displays pack-hunting behaviour, which might have been the key to hunting large species in the past, despite its small size. Today most prey are small to medium sized vertebrates. It is Critically Endangered, and the remaining wild population is under threat of hybridization.
Siamese crocodile Indonesia, Brunei, East Malaysia and southern IndochinaA fairly small crocodile that prefers freshwater habitats. It has a relatively broad snout and olive-green to dark green coloration. It feeds on a variety of small to mid-sized vertebrates. Listed as Critically Endangered, but might be already extinct in the wild; status is unknown.
West African crocodile Western and Central AfricaRecent studies revealed that this is distinct species from the larger Nile crocodile. It has a slightly narrower snout and is much smaller compared to its larger cousin.
Osborn's dwarf crocodile Western AfricaIt is a heavily armoured species with uniform black coloration in adults, while juveniles have a lighter brown banding. Lives in the tropical forests of Western Africa. Feeds on small vertebrates and large aquatic invertebrates. It is a fairly terrestrial species and exhibits terrestrial hunting, especially at night.
Dwarf crocodile Western AfricaIt belongs to its own monotypic genus; however, new studies indicate there might be two or even three distinct species. It is a heavily armoured species with uniform black coloration in adults, while juveniles have a lighter brown banding. Lives in the tropical forests of Western Africa. Feeds on small vertebrates and large aquatic invertebrates. It is a fairly terrestrial species and exhibits terrestrial hunting, especially at night. This species is classified as Vulnerable.
West African slender-snouted crocodile Western AfricaA medium sized species with a narrow and elongated snout. Lives in freshwater habitats within tropical forests of the continent. Feeds mostly on fish but also other small to medium sized vertebrates. It is a Critically Endangered species.
Central African slender-snouted crocodile Central AfricaA medium sized species found in watery areas in dense rainforest. Feeds largely on fish. Insufficient conservation data, but was classified as Critically Endangered when lumped with M. cataphractus, although M. leptorhynchus is doing better in its home range.