A crocodile (family Crocodylidae) 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 (both members of the family Alligatoridae), the gharial and false gharial (both members of the family Gavialidae) as well as other extinct taxa. This article uses "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 (croc.) 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, and existed, though and were forms in Medieval Latin. The Latin form is found as cocodrille the 13th century in the Old French work Li livres dou tresor, in which the croc. is jaune (yellow).
The earliest known source in the English language is within the work Kyng AlisaunderKing Alisaunder Weber edition (1810) from towards the beginning of the 14th century, a magical romance poetry work of rhyming couplets, where the word is found line 5720:
Forth went the kyng wondres sekynde : A griselich hest he gonne fynde; So mychel seigh he neuere, ne non swiche; Two heudes it had wel ferlich To a cokedrill that on was liche, That others the monoceros selcouthliche.
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 (Crocodylus niloticus), the Dwarf crocodile (Osteolaemus tetraspis), 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.
Subfamily Crocodylinae Genus Crocodylus Crocodylus acutus, American crocodile Crocodylus halli, Hall's New Guinea crocodile found South of the New Guinea Highlands Crocodylus intermedius, Orinoco crocodile Crocodylus johnsoni, freshwater crocodile, or Johnstone's crocodile Crocodylus mindorensis, Philippine crocodile Crocodylus moreletii, Morelet's crocodile or Mexican crocodile Crocodylus niloticus, Nile crocodile or African crocodile (the subspecies found in Madagascar is sometimes called the black crocodile) Crocodylus novaeguineae, New Guinea crocodile found North of the New Guinea Highlands Crocodylus raninus, the Borneo crocodile, is related to C. novaeguineae, but whether or not it is a distinct species remains unclear. Crocodylus palustris, mugger, marsh or Indian crocodile Crocodylus porosus, saltwater crocodile or estuarine crocodile Crocodylus rhombifer, Cuban crocodile Crocodylus siamensis, Siamese crocodile (may be extinct in the wild) Crocodylus suchus, West African crocodile, desert or sacred crocodile Crocodylus anthropophagus Crocodylus checchiai Crocodylus falconensis Crocodylus palaeindicus Crocodylus thorbjarnarsoni Genus Voay Voay robustus (formerly Crocodylus robustus) Subfamily Osteolaeminae Genus Osteolaemus Osteolaemus tetraspis, dwarf crocodile Osteolaemus osborni, Osborn's dwarf crocodile Recent (2009) DNA analysis indicate a third distinct species, currently unnamed. Genus Mecistops Mecistops cataphractus West African slender-snouted crocodile Mecistops leptorhynchus Central African slender-snouted crocodile Genus Brochuchus Brochuchus pigotti (formerly Crocodylus pigotti) Brochuchus parvidens Genus Euthecodon Euthecodon nitriae Euthecodon brumpti Euthecodon arambourgi Genus Rimasuchus Rimasuchus lloydi (formerly Crocodylus lloydi)
Phylogeny 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 (M. leptorhynchus, C. halli and the third Osteolaemus 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.