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Brief Summary

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There are 23 living species of crocodilian. These include crocodiles, alligators, and caimans. This family’s closest living relatives are birds, not other reptiles. Crocodilians can walk on four legs or swim using their strong tails. They can also walk on their tails. The American crocodile can swim up to 20 miles per hour.
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Crocodylidae

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The crocodylian family Crocodylidae includes the true crocodiles, which are the members of the subfamily Crocodylinae, as well as potentially the false gharial, the only extant member of the subfamily Tomistominae. The latter is a subject of controversy as to whether it is a crocodile or actually belongs in the family Gavialidae.[1] Further genetic analysis has to be done to come to a final conclusion.

Taxonomy

A total of three extant genera are placed in the family Crocodylidae, including a total of 15 species, including the desert crocodile, which is now accepted as a true species rather than a subspecies of the Nile crocodile. Recent studies suggest the dwarf crocodile, Osteolaemus tetraspis, is not a single, but two or even three species, and that the slender-snouted crocodile is two species.[2][3] If so, the species count of extant crocodiles would be 18 or 19, putting the extant crocodylian species to a total of 28 or 29 instead of 25.

True crocodiles

The two extant genera of true crocodiles, Crocodylus and Osteolaemus, are in the subfamily Crocodylinae. Even according to traditional classification, the Tomistoma is not a true crocodile, though it is a member of the family Crocodylidae. Latest molecular evidence points to an even greater difference, creating the possibility that in fact Tomistoma is genetically closer to the gharial than true crocodiles. If proven, the species will be classified under the family Gavialidae.[1]

Their most obvious external differences from alligators are visible in the head. Crocodiles have narrower and longer heads, and more V-shaped than U-shaped snouts. The alligator's upper jaw is wider than its lower jaw, and the teeth in the lower jaw fit into small depressions in the upper jaw. 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. 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 a species.

Crocodylidae

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A skull of the extinct Voay robustus

Most species are grouped into the genus Crocodylus. The other extant genus, Osteolaemus, is monotypic (as is Mecistops, if recognized).

Phylogeny

The cladogram below follows the topology from a 2012 analysis of morphological traits by Christopher A. Brochu and Glenn W. Storrs. Many extinct species of Crocodylus might represent different genera. C. suchus was not included because its morphological codings were identical to those of C. niloticus. However, the authors suggested that it could be explained by their specimen sampling, and considered the two species to be distinct.[4]

References

  1. ^ a b Gatesy, Jorge; Amato, G.; Norell, M.; DeSalle, R.; Hayashi, C. (2003). "Combined support for wholesale taxic atavism in gavialine crocodylians" (PDF). Systematic Biology. 52 (3): 403–422. doi:10.1080/10635150309329.
  2. ^ Eaton, Mitchell J.; Andrew Martin; John Thorbjarnarson; George Amato (March 2009). "Species-level diversification of African dwarf crocodiles (Genus Osteolaemus): A geographic and phylogenetic perspective". Molecular Phylogenetics and Evolution. 50 (3): 496–506. doi:10.1016/j.ympev.2008.11.009. PMID 19056500.
  3. ^ SHIRLEY, MATTHEW H.; CARR, AMANDA N.; NESTLER, JENNIFER H.; VLIET, KENT A.; BROCHU, CHRISTOPHER A. (2018-10-24). "Systematic revision of the living African Slender-snouted Crocodiles ( Mecistops Gray, 1844)". Zootaxa. 4504 (2). ISSN 1175-5334.
  4. ^ Brochu, C. A.; Storrs, G. W. (2012). "A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of Crocodylus in Africa". Journal of Vertebrate Paleontology. 32 (3): 587. doi:10.1080/02724634.2012.652324.
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Crocodylidae: Brief Summary

provided by wikipedia EN

The crocodylian family Crocodylidae includes the true crocodiles, which are the members of the subfamily Crocodylinae, as well as potentially the false gharial, the only extant member of the subfamily Tomistominae. The latter is a subject of controversy as to whether it is a crocodile or actually belongs in the family Gavialidae. Further genetic analysis has to be done to come to a final conclusion.

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wikipedia EN