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{{Short description|Family of large reptilian carnivores}} | |||
{{otheruses}} | |||
{{Other uses}} | |||
{{Taxobox | |||
{{Pp|small=yes}} | |||
| | |||
{{Use British English|date=June 2016}} | |||
| name = Crocodile | |||
{{Use dmy dates|date=February 2022}} | |||
| fossil_range = ] - Recent | |||
{{Automatic taxobox | |||
| image = NileCrocodile.jpg | |||
| name = Crocodiles | |||
| image_caption = ] | |||
| fossil_range = ]–], {{Geological range|46|0}} | |||
| regnum = ]ia | |||
| image = Nile crocodile head.jpg | |||
| phylum = ] | |||
| image_caption = ] (''Crocodylus niloticus'') | |||
| classis = ] | |||
| image2 = Pangil Crocodile Park Davao City.jpg | |||
| ordo = ] | |||
| image2_caption = ] (''Crocodylus porosus'') | |||
| familia = '''Crocodylidae''' | |||
| taxon = Crocodylidae | |||
| familia_authority = ], 1807 | |||
| authority = ], 1807 | |||
| subdivision_ranks = Genera | |||
| type_genus = '']'' | |||
| subdivision = | |||
| type_genus_authority = ], 1768 | |||
* '']'' | |||
| range_map = | |||
* '']'' | |||
| range_map_caption = | |||
'''See ].''' | |||
| subdivision_ranks = Subfamilies | |||
| subdivision = | |||
*] | |||
*] | |||
}} | }} | ||
A '''crocodile''' is any ] belonging to the ] '''Crocodylidae''' (sometimes classified instead as the ] '''Crocodylinae'''). The term can also be used more loosely to include all members of the ] ]: i.e. the true crocodiles, the ]s and ]s (family ]) and the ]s (family ]), or even the ] which includes prehistoric crocodile relatives and ancestors. Crocodiles are large aquatic ]s that live throughout the ] in ], ], the ] and ]. Crocodiles tend to congregate in freshwater habitats like ]s, ]s, ]s and sometimes in ] water. They feed mostly on ]s like ], ]s, and ]s, sometimes on ]s like ]s and ]s, depending on species. They are an ancient lineage, and are believed to have changed little since the time of the dinosaurs. They are believed to be 200 million years old whereas dinosaurs became extinct 65 million years ago; crocodiles survived great extinction events.<ref name=ausfauna>Grigg, Gordon and Gans, Carl (1993) Morphology And Physiology Of The Crocodylia, in Fauna of Australia Vol 2A Amphibia and Reptilia, chapter 40, pages 326-336. Australian Government Publishing Service, Canberra. </ref> | |||
'''Crocodiles''' (] '''Crocodylidae''') or '''true crocodiles''' are large, ] ]s that live throughout the tropics in ], ], the ] and ]. The term “crocodile” is sometimes used more loosely to include all ] members of the ] ], which includes the ]s and ]s (both members of the family ]), the ] and ] (both members of the family ]) as well as other, extinct, taxa. | |||
Although crocodiles, alligators, and the gharial are similar in appearance, they belong to separate ]. The gharial, with its narrow ], is easier to distinguish, while ] 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 ] 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 ]' ].<ref>{{cite web |url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q1.htm |title=Crocodilian Biology Database – FAQ – What's the difference between a crocodile and an alligator |publisher=Flmnh.ufl.edu |access-date=5 April 2009}}</ref> Crocodiles have more ] on the toes of the hind ] and can better tolerate ] due to specialized ]s 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 ].<ref name="Guggisberg">{{cite book | author = Guggisberg, C. A. W. | title = Crocodiles: Their Natural History, Folklore, and Conservation| year = 1972 | page = 195 | isbn = 978-0-7153-5272-4 | publisher = David & Charles | location = Newton Abbot, England}}</ref> | |||
Crocodile ], ], ] and ] differ somewhat among ]. However, they have many similarities in these areas as well. All crocodiles are ] and tend to congregate in ] habitats such as ]s, ]s, ]s and sometimes in ] water and ]. They are ] animals, feeding mostly on ]s such as ], ]s, ]s and ]s, and sometimes on ]s such as ]s and ]s, depending on species and age. All crocodiles are ] species that, unlike alligators, are very sensitive to ]. They separated from other ]ns during the ] epoch, about 55 million years ago.<ref name=kambara>{{cite journal | last1 = Buchanan | first1 = L.A. | year = 2009 | title = Kambara taraina sp. nov (Crocodylia, Crocodyloidea), a new Eocene mekosuchine from Queensland, Australia, and a revision of the genus | journal = Journal of Vertebrate Paleontology | volume = 29 | issue = 2| pages = 473–486 | doi=10.1671/039.029.0220| bibcode = 2009JVPal..29..473B | s2cid = 86254159 }}</ref> Many species are at the risk of ], some being classified as ]. | |||
==Etymology== | ==Etymology== | ||
The word ''crocodile'' comes {{ety|grc|''{{wikt-lang|grc|κροκόδιλος}}'' (krokódilos)|lizard}}, used in the phrase {{lang|grc-Latn|ho krokódilos tou potamoú}}, {{gloss|the lizard of the (]) river}}. There are several variant Greek forms of the word attested, including the later form {{lang|grc-Latn|krokódeilos}} ({{wikt-lang|grc|κροκόδειλος}})<ref>{{Cite web |url=http://perseus.mpiwg-berlin.mpg.de/cgi-bin/vor?lookup=krokodeilos&lang=greek |title=Perseus Lookup Tool |access-date=30 July 2008 |archive-url=https://web.archive.org/web/20160303205859/http://perseus.mpiwg-berlin.mpg.de/cgi-bin/vor?lookup=krokodeilos&lang=greek |archive-date=3 March 2016 |url-status=dead}}</ref> found cited in many English reference works.<ref name=dictionary.com /> In the ] of ] times, {{lang|grc-Latn|krokodilos}} and {{lang|grc-Latn|krokodeilos}} would have been pronounced identically, and either or both may be the source of the ] form {{lang|la|crocodīlus}} used by the ancient Romans. It has been suggested, but it is not certain that the word {{lang|grc-Latn|crocodilos}} or {{lang|grc-Latn|crocodeilos}} is a compound of {{lang|grc-Latn|krokè}} ({{gloss|pebbles}}), and {{lang|grc-Latn|drilos/dreilos}} ({{gloss|worm}}), although {{lang|grc-Latn|drilos}} is only attested as a colloquial term for {{gloss|penis}}.<ref name=dictionary.com>{{cite web|url=http://dictionary.reference.com/browse/crocodile |title=Crocodile | Define Crocodile at Dictionary.com |publisher=Dictionary.reference.com |access-date=26 April 2013}}</ref> It is ascribed to ], and supposedly describes the basking habits of the Egyptian crocodile.<ref name=etymonline>{{cite web|url=http://etymonline.com/index.php?search=crocodile |title=Online Etymology Dictionary |publisher=Etymonline.com |access-date=16 March 2010}}</ref> | |||
{{wiktionary}} | |||
The word ''crocodile'' comes from the ] κροκόδιλος (''crocodilos''), "lizard," used in the phrase ''ho crocodilos ho potamós'', "the lizard of the ] river." | |||
The form {{lang|la|crocodrillus}} is attested in ].<ref name="dictionary.com" /> It is not clear whether this is a medieval corruption or derives from alternative Greco-Latin forms (late Greek {{lang|grc-Latn|corcodrillos}} and {{lang|grc-Latn|corcodrillion}} are attested). A (further) corrupted form {{lang|fro|cocodrille}} is found in ] and was borrowed into ] as {{lang|enm|cocodril(le)}}. The ] form ''crocodile'' was adapted directly from the Classical Latin {{lang|la|crocodīlus}} in the 16th century, replacing the earlier form. The use of ''-y-'' in the scientific name '']'' (and forms derived from it) is a corruption introduced by ] (1768). | |||
There are several variant Greek forms of the word attested, including the later form κροκόδειλος (''crocodeilos'')<ref>http://perseus.mpiwg-berlin.mpg.de/cgi-bin/vor?lookup=krokodeilos&lang=greek</ref> found cited in many English reference works.<ref>{{cite web|url=http://dictionary.reference.com/browse/crocodile |title=Crocodile | Define Crocodile at Dictionary.com |publisher=Dictionary.reference.com |date= |accessdate=2010-03-16}}</ref> In the ] of ] times, ''crocodilos'' and ''crocodeilos'' would have been pronounced identically, and either or both may be the source of the ] form ''crocodīlus'' used by the ancient ]. | |||
==Taxonomy and phylogeny== | |||
''Crocodilos/crocodeilos'' itself is described in reference sources as a corruption of ''crocè'' ("pebbly"), and ''drilos/dreilos'' supposedly meaning "worm" although attested only as "(man with circumcized) penis".<ref name="dictionary.com">{{cite web|url=http://dictionary.com/browse/crocodile |title=Crocodile | Define Crocodile at |publisher=Dictionary.com |date= |accessdate=2010-03-16}}</ref> It is unclear how well supported this analysis is. The meaning of ''crocè'' 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.<ref>{{cite web|url=http://etymonline.com/index.php?search=crocodile |title=Online Etymology Dictionary |publisher=Etymonline.com |date= |accessdate=2010-03-16}}</ref> | |||
{{See also|List of crocodilians}} | |||
Crocodylidae was named as a ] by ] in 1807. It belongs to the larger ] ], which also includes additional extinct crocodile relatives. These all belong to the ] ], which also includes ] and ]. | |||
Crocodylidae is ]ally defined as a ] composed of the ] of the ] (''Crocodylus niloticus''), the ] (''Osteolaemus tetraspis''), and all of its descendants.<ref name="Rio2021">{{cite journal |last1=Rio |first1=Jonathan P. |last2=Mannion |first2=Philip D. |date=6 September 2021 |title=Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem |journal=] |volume=9 |pages=e12094 |doi=10.7717/peerj.12094 |pmid=34567843 |pmc=8428266 |doi-access=free}}</ref> It contains two ]: ] and ].<ref name="Hekkala2021">{{Cite journal|last1=Hekkala |first1=E. |last2=Gatesy |first2=J. |last3=Narechania |first3=A. |last4=Meredith |first4=R. |last5=Russello |first5=M. |last6=Aardema |first6=M. L. |last7=Jensen |first7=E. |last8=Montanari |first8=S. |last9=Brochu |first9=C. |last10=Norell |first10=M. |last11=Amato |first11=G. |date=27 April 2021 |title=Paleogenomics illuminates the evolutionary history of the extinct Holocene "horned" crocodile of Madagascar, Voay robustus |journal=Communications Biology |language=en |volume=4 |issue=1 |page=505 |doi=10.1038/s42003-021-02017-0 |pmid=33907305 |pmc=8079395 |issn=2399-3642 |doi-access=free}}</ref> Crocodylinae contains 13-14 living species, as well as 6 ] species. Osteolaeminae was named by Christopher Brochu in 2003 as a subfamily of Crocodylidae separate from Crocodylinae,<ref name=C.thorbjarnarsoni>{{Cite journal | last1 = Brochu | first1 = C. A. | last2 = Storrs | first2 = G. W. | doi = 10.1080/02724634.2012.652324 | title = A giant crocodile from the Plio-Pleistocene of Kenya, the phylogenetic relationships of Neogene African crocodylines, and the antiquity of ''Crocodylus'' in Africa | journal = Journal of Vertebrate Paleontology | volume = 32 | issue = 3 | pages = 587–602 | year = 2012 | bibcode = 2012JVPal..32..587B | s2cid = 85103427 }}</ref> and contains the two ] ] '']'' and '']'', along with several extinct genera. The number of extant species within Osteolaeminae is currently in question.<ref name="Eaton"/> | |||
The form ''crocodrillus'' is attested in ].<ref name="dictionary.com"/> It is not clear whether this is a medieval corruption or derives from alternate Greco-Latin forms (late Greek ''corcodrillos'' and ''corcodrillion'' are attested). | |||
]ing in Australia]] | |||
]]] | |||
] at ]]] | |||
]'']] | |||
* '''Subfamily ]''' | |||
** Genus '']'' | |||
***'']'', ] | |||
***'']'', ] found South of the ]<ref name="MurrayRussoZorrillaMcMahan2019">{{cite journal | last1 = Murray | first1 = Christopher M. | last2 = Russo | first2 = Peter | last3 = Zorrilla | first3 = Alexander | last4 = McMahan | first4 = Caleb D. | year = 2019 | title = Divergent Morphology among Populations of the New Guinea Crocodile, Crocodylus novaeguineae (Schmidt, 1928) Diagnosis of An Independent Lineage and Description of A New Species. | journal = Copeia | volume = 107 | issue = 3| pages = 517–523 | doi = 10.1643/CG-19-240 | doi-access = free }}</ref> | |||
***'']'', ] | |||
***'']'', ], or Johnstone's crocodile | |||
***'']'', ] | |||
***'']'', ] or Mexican crocodile | |||
***'']'', ] or African crocodile (the subspecies found in Madagascar is sometimes called the black crocodile) | |||
***'']'', ] found North of the ] | |||
***'']'', ], marsh or Indian crocodile | |||
***'']'', ] or estuarine crocodile | |||
****'']'', the ], is currently considered to be a synonym of ''Crocodylus porosus''; whether or not it is a distinct species remains unclear.<ref>{{Cite web|url=http://reptile-database.reptarium.cz/species?genus=Crocodylus&species=raninus|title = Species | the Reptile Database}}</ref> | |||
***'']'', ] | |||
***'']'', ] (may be extinct in the wild) | |||
***'']'', ], desert or sacred crocodile | |||
***'']''{{extinct}} | |||
***'']''{{extinct}} | |||
***'']''{{extinct}} | |||
***'']''{{extinct}} | |||
***'']''{{extinct}} | |||
** Genus '']''{{extinct}} | |||
***'']''{{extinct}} (formerly ''Crocodylus robustus'') | |||
* '''Subfamily ]''' | |||
** Genus '']'' | |||
*** '']'', ] (There has been controversy as to whether or not this is actually two species; recent (2010) DNA analysis indicate three distinct species: ''O. tetraspis'', ''O. osborni'' and a third, currently unnamed.) | |||
** Genus '']'' | |||
***'']'' ] | |||
*** '']'' ] | |||
** Genus '']''{{extinct}} | |||
*** '']''{{extinct}} (formerly ''Crocodylus pigotti'') | |||
*** '']''{{extinct}} | |||
** Genus '']''{{extinct}} | |||
*** '']''{{extinct}} | |||
*** '']''{{extinct}} | |||
*** '']''{{extinct}} | |||
** Genus '']''{{extinct}} | |||
*** '']''{{extinct}} (formerly ''Crocodylus lloydi'') | |||
===Phylogeny=== | |||
A (further) corrupted form ''cocodrille'' is found in ] and was borrowed into ] as ''cocodril(le)''. The ] form ''crocodile'' was adapted directly from the Classical Latin ''crocodīlus'' in the 16th Century, replacing the earlier form. | |||
Recent molecular studies using ] have shown crocodiles to be more closely related to the ]s rather than to ]s, contrary to prior theories based on ] studies alone.<ref name="Harshman2003">{{cite journal |pmid=12775527 |year=2003 |last1=Harshman |first1=J. |title=True and false gharials: A nuclear gene phylogeny of crocodylia |journal=Systematic Biology |volume=52|issue=3|pages=386–402|last2=Huddleston|first2=C. J. |last3=Bollback |first3=J. P. |last4=Parsons|first4=T. J.|last5=Braun|first5=M. J.|doi=10.1080/10635150309323 |url=http://si-pddr.si.edu/bitstream/handle/10088/6275/2003C_Harshman_et_al.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://si-pddr.si.edu/bitstream/handle/10088/6275/2003C_Harshman_et_al.pdf |archive-date=2022-10-09 |url-status=live|doi-access=free }}</ref><ref name="Gatesy2008">{{cite journal|last1=Gatesy |first1=J. |last2=Amato |first2=G. |year=2008 |title=The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships |journal=]|volume=48 |issue=3 |pages=1232–1237 |doi=10.1016/j.ympev.2008.02.009|pmid=18372192|bibcode=2008MolPE..48.1232G }}</ref><ref name=bite>{{cite journal| author=Erickson, G. M.| author2=Gignac, P. M.| author3=Steppan, S. J.| author4=Lappin, A. K.| author5=Vliet, K. A.| author6=Brueggen, J. A.| author7=Inouye, B. D.| author8=Kledzik, D.| author9=Webb, G. J. W. | year=2012 | title=Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation | journal=PLOS ONE | volume=7 |issue=3 |page=e31781 |doi=10.1371/journal.pone.0031781|editor1-last=Claessens|editor1-first=Leon|bibcode = 2012PLoSO...731781E | pmid=22431965 | pmc=3303775| doi-access=free}}</ref><ref name="LeeYates2018">{{cite journal | author=Michael S. Y. Lee |author2=Adam M. Yates |date=27 June 2018 |title=Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil |journal=] |volume=285 |issue=1881 |doi=10.1098/rspb.2018.1071 |pmid=30051855 |pmc=6030529 |doi-access=free}}</ref><ref name="Hekkala2021"/> | |||
Below is a ] showing the relationships of the major ] crocodile groups based on molecular studies, excluding separate extinct taxa: | |||
The use of -y- in the scientific name '']'' (and forms derived from it) is a corruption introduced by ] (1768). | |||
{{clade| style=font-size:85%;line-height:85% | |||
|label1=''']''' | |||
|1={{clade | |||
|label1=] | |||
|1={{clade | |||
|label1=] | |||
|1={{clade | |||
|1={{clade | |||
|1='']'' ] | |||
|2='']'' ] }} | |||
|2='']'' ] }} | |||
|label2=] | |||
|2='']'' ] }} | |||
|label2=] | |||
|2={{clade | |||
|label1='''Crocodylidae''' | |||
|1={{clade | |||
|1='']'' ] | |||
|2={{clade | |||
|1='']'' ] | |||
|2='']'' ] }} }} | |||
|label2=] | |||
|2={{clade | |||
|1='']'' ] | |||
|2='']'' ] | |||
}} }} }} }} | |||
Below is a more detailed cladogram of Crocodylidae, based on a 2021 study using ] that extracted DNA from the extinct '']''.<ref name="Hekkala2021"/> | |||
==Description== | |||
{{clade| style=font-size:85%;line-height:85% | |||
:''Crocodiles are similar to alligators and caiman; for their common biology and differences between them, see ].'' | |||
|label1='''Crocodylidae''' | |||
|sublabel1=(]) | |||
|1={{clade | |||
|label1=] | |||
|1={{clade | |||
|1={{clade | |||
|1=''Mecistops cataphractus'' ] | |||
|2='']''{{extinct}} }} | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|2={{clade | |||
|1=''Osteolaemus osborni'' ] | |||
|2=''Osteolaemus tetraspis'' ] }} }} }} }} | |||
|label2=] | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|label2='']'' | |||
|2={{clade | |||
|1={{clade | |||
|1={{clade | |||
|1='']''{{extinct}} | |||
|2='']''{{extinct}} }} | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|2=''Crocodylus'' Tirari Desert{{extinct}} }} }} | |||
|2={{clade | |||
|1={{clade | |||
|1={{clade | |||
|1=''Crocodylus johnstoni'' ] | |||
|2={{clade | |||
|1=''Crocodylus novaeguineae'' ] | |||
|2=''Crocodylus mindorensis'' ] }} }} | |||
|2={{clade | |||
|1=''Crocodylus porosus'' ] | |||
|2={{clade | |||
|1=''Crocodylus siamensis'' ] | |||
|2=''Crocodylus palustris'' ] }} }} }} | |||
|2={{clade | |||
|1={{clade | |||
|1='']''{{extinct}} | |||
|2='']''{{extinct}} }} | |||
|2={{clade | |||
|1=''Crocodylus suchus'' ] | |||
|2={{clade | |||
|1=''Crocodylus niloticus'' ] | |||
|2={{clade | |||
|1={{clade | |||
|1=''Crocodylus moreletii'' ] | |||
|2=''Crocodylus rhombifer'' ] }} | |||
|2={{clade | |||
|1=''Crocodylus intermedius'' ] | |||
|2=''Crocodylus acutus'' ] }} }} }} }} }} }} }} }} }} }} | |||
Alternatively, some ] studies have recovered '']'' as a ] member of ], more closely related to '']'' than to '']'' and the other members of ],<ref name="Rio2021"/><ref name="Azzara2021">{{cite journal |last1=Azarra |first1=Beatrice |last2=Boschian |first2=Giovanni |last3=Brochu |first3=Christopher |last4=Delfino |first4=Massimo |last5=Iurino |first5=Dawid Adam |last6=Kimambo |first6=Jackson Stanley |last7=Manzi |first7=Giorgio |last8=Masao |first8=Fidelis T. |last9=Menconero |first9=Sofia |last10=Njau |first10=Jackson K |last11=Cherin |first11=Marco |year=2021 |title=A new cranium of Crocodylus anthropophagus from Olduvai Gorge, northern Tanzania |journal=Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy) |volume=127 |issue=2 |pages=275–295 |url=https://www.researchgate.net/publication/352560805 |doi=10.13130/2039-4942/15771 |s2cid=237962496 }}</ref> as shown in the cladogram below.<ref name="Azzara2021"/> | |||
]''.]] | |||
{{clade| style=font-size:85%;line-height:85% | |||
Crocodiles are among the more biologically complex reptiles despite their prehistoric look. Unlike other reptiles, they have a ]; a four-chambered ]; and the functional equivalent of a diaphragm, by incorporating muscles used for aquatic locomotion into respiration (e.g. ''M. diaphragmaticus'');<ref name="Uriona & Farmer, 2008">Uriona TJ, Farmer CG. 2008. Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (''Alligator mississippiensis''). ''Journal of Experimental Biology'' '''211''': 1141-1147.</ref> Their external morphology on the other hand is a sign of their aquatic and predatory lifestyle. A crocodile’s physical traits allow it to be a successful ]. They have a streamlined body that enables them to swim swiftly. Crocodiles also tuck their feet to their sides while swimming, which makes them faster by decreasing water resistance. They have webbed feet which, although 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 animals sometimes move around by walking. | |||
|grouplabel1={{clade labels |width=10em; |label1='''Paleoafrican ''Crocodylus''''' |top1=40% |color1=red |label2='''Neotropical ''Crocodylus''''' |top2=60% |color2=black |style2=background-color:#ffffee; |label3='''Indo-Pacific ''Crocodylus''''' |top3=85% |color3=green}} | |||
|label1='''Crocodylidae''' | |||
|1={{clade | |||
|label1=''']''' | |||
|1={{clade | |||
|1='']''{{extinct}} | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|2={{clade | |||
|1=''Osteolaemus osborni'' ] | |||
|2=''Osteolaemus tetraspis'' ] }} }} | |||
|3={{clade | |||
|1='']''{{extinct}} | |||
|2={{clade | |||
|1={{clade | |||
|1='']''{{extinct}} | |||
|2='']''{{extinct}} }} | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|2='']''{{extinct}} }} }} }} }} | |||
|label2=''']''' | |||
|2={{clade | |||
|1='''''Mecistops''' cataphractus'' ] | |||
|2={{clade | |||
|style1=background-color:#ffdddd; | |||
|1={{clade | |||
|1='']''{{extinct}} |barbegin1=red | |||
|2='']''{{extinct}} |barend2=red }} | |||
|2={{clade | |||
|1=''Crocodylus niloticus'' ] | |||
|2={{clade | |||
|1='']''{{extinct}} | |||
|style2=background-color:#ffffee; | |||
|2=''Crocodylus moreletii'' ] |barbegin2=yellow | |||
|style3=background-color:#ffffee; | |||
|3=''Crocodylus intermedius'' ] |bar3=yellow | |||
|style4=background-color:#ffffee; | |||
|4=''Crocodylus acutus'' ] |bar4=yellow | |||
|style5=background-color:#ffffee; | |||
|5=''Crocodylus rhombifer'' ] |barend5=yellow }} | |||
|style3=background-color:#ddffdd; | |||
|3='']''{{extinct}} |barbegin3=lightgreen |barend3=lightgreen | |||
|style4=background-color:#ccffcc; | |||
|4={{clade | |||
|1=''Crocodylus palustris'' ] |barbegin1=green | |||
|2={{clade | |||
|1={{clade | |||
|1='']''{{extinct}} |bar1=green | |||
|2=''Crocodylus siamensis'' ] |bar2=green }} | |||
|2={{clade | |||
|1=''Crocodylus mindorensis'' ] |bar1=green | |||
|2=''Crocodylus johnstoni'' ] |bar2=green | |||
|3=''Crocodylus porosus'' ] |bar3=green | |||
|4={{clade | |||
|1=''Crocodylus raninus'' ] |bar1=green | |||
|2=''Crocodylus novaeguineae'' ] |barend2=green }} }} }} }} }} }} }} }} }} | |||
==Species== | |||
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 ]s, crocodilians are ], although their post-temporal ] are reduced. The walls of the braincase are bony but they lack supratemporal and postfrontal bones.<ref name=ausfauna/> Their tongues are not free but held in place by a membrane which limits movement; as a result, crocodiles are unable to stick out their tongues.<ref>{{cite book | last = Huchzermeyer | first = Fritz | year = 2003 | title = Crocodiles: Biology, Husbandry and Diseases | publisher = CABI Publishing | isbn =9780851996561 | url = http://books.google.co.uk/books?id=4Arv-IUFnuoC&printsec=frontcover#PPA13,M1 | page = 13 | accessdate = 2000-01-07}}</ref> | |||
]{{Clear}} | |||
A total of 18 ] species have been recognized. Further ] is needed for the confirmation of proposed species under the genus '']''. | |||
{| class="wikitable" | |||
Crocodilian scales have pores that are believed to be sensory, analogous to the ] 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 that appears to flush mud off.<ref name=ausfauna/> | |||
|- | |||
!Species name!! Image !! Distribution!! Description/Comments | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus acutus''}}) | |||
|] | |||
| valign="top" | Throughout the ], including many of the ]s and ]. | |||
| valign="top" | A larger sized species, with a greyish colour and a prominent V-shaped snout. Prefers ] water, but also inhabits lower stretches of ]s and true ] environments. This is one of the rare species that exhibits regular sea-going behaviour, which explains the great distribution throughout the ]. It is also found in ]s such as ], in the ], which has one of the largest populations of this species.<ref name="nationalgeographic1">{{cite web|url=http://animals.nationalgeographic.com/animals/reptiles/american-crocodile/ |archive-url=https://web.archive.org/web/20100117092839/http://animals.nationalgeographic.com/animals/reptiles/american-crocodile |url-status=dead |archive-date=17 January 2010 |title=American Crocodiles, American Crocodile Pictures, American Crocodile Facts – National Geographic |publisher=Animals.nationalgeographic.com |date=15 April 2013 |access-date=25 April 2013}}</ref> Diet consists mostly of aquatic and terrestrial vertebrates. Classified as ], but certain local populations under greater threat. | |||
|- | |||
|] (''Crocodylus halli'') | |||
| | |||
|The island of ], south of the ] | |||
|A smaller species that closely resembles and was long classified under the ], 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 ] and enlarged ]l elements. Cranial elements can still widely vary within the species, with populations from ] having much wider heads than those from the ].<ref>{{Cite journal|last1=Murray|first1=Christopher M.|last2=Russo|first2=Peter|last3=Zorrilla|first3=Alexander|last4=McMahan|first4=Caleb D.|date=September 2019|title=Divergent Morphology among Populations of the New Guinea Crocodile, Crocodylus novaeguineae (Schmidt, 1928): Diagnosis of an Independent Lineage and Description of a New Species|journal=Copeia|volume=107|issue=3|pages=517–523|doi=10.1643/CG-19-240|issn=0045-8511|doi-access=free}}</ref> | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus intermedius''}}) | |||
|] | |||
| valign="top" | ] and ] | |||
| valign="top" | This is a large species with a relatively elongated snout and a pale tan coloration with scattered dark brown markings. Lives primarily in the ]. Despite having a rather narrow snout, preys on a wide variety of vertebrates, including large mammals. It is a ] species. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus johnstoni''}}) | |||
|] | |||
| valign="top" | ] | |||
| valign="top" | A smaller species with a narrow and elongated snout. It has light brown coloration with darker bands on body and tail. Lives in ]s with considerable distance from the sea, to avoid confrontations with saltwater crocodiles. Feeds mostly on ] and other small vertebrates. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus mindorensis''}}) | |||
|] | |||
| valign="top" | ] to the ] | |||
| valign="top" | This 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 ] habitats and feeds on a variety of small to medium sized vertebrates. This species is ] and the most severely threatened species of crocodile.<ref>(2011-09-06). . National Geographic Daily News.</ref> | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus moreletii''}}) | |||
| ] | |||
| valign="top" | Atlantic regions of ], ] and ] | |||
| valign="top" | A small to medium sized crocodile with a rather broad snout. It has a dark greyish-brown colour and is found in mostly various ] habitats. Feeds on mammals, birds and reptiles. It is listed as ]. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus niloticus''}}) | |||
| ] | |||
| valign="top" | ] | |||
| valign="top" | A 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 ] that is capable of taking a wide array of ]n vertebrates, including large ungulates and other predators.<ref>{{cite web |url=http://crocodilian.com/cnhc/csp_cnil.htm |title=IUCN-SSC Crocodile Specialist Group |publisher=Crocodilian.com |access-date=25 April 2013 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025183255/http://crocodilian.com/cnhc/csp_cnil.htm |url-status=dead }}</ref> This species is listed as ]. | |||
|- | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus novaeguineae'')}} | |||
| ] | |||
| valign="top" | The island of ], north of the ] | |||
| valign="top" | A smaller species of crocodile with a grey-brown colour and dark brown to black markings on the tail. The young have a narrower V-shaped snout that becomes wider as the animal matures. Prefers ] habitats, even though is tolerant to salt water, in order to avoid competition and predation by the saltwater crocodile. This species feeds on small to mid-sized vertebrates. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus palustris''}}) | |||
|] | |||
| valign="top" | The ] and surrounding countries | |||
| valign="top" | This 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 ]s, ]s and ]s. It can also be found in ] swamps but avoids areas populated by saltwater crocodiles.<ref> {{Webarchive|url=https://web.archive.org/web/20130123063953/http://crocodilian.com/cnhc/cst_cpal_dh_map.htm|date=23 January 2013}}. Crocodile Species List. Retrieved on 13 April 2013.</ref> Feeds on a wide array of vertebrates. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus porosus''}}) | |||
|] | |||
| valign="top" | Throughout {{nowrap|]}}, ] and surrounding waters | |||
| valign="top" | The largest 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 ] and ] environments as well as lower stretches of ]s. This species has the greatest distribution of all crocodiles. Tagged specimens showed long-distance marine travelling behaviour. It is the ] throughout its range and preys on virtually any animal within its reach. It is classified as ] but with several populations under greater risk.<ref name=IUCN>{{Cite iucn | author = Crocodile Specialist Group | title = ''Crocodylus porosus'' | volume = 1996 | page = e.T5668A11503588 | date = 1996 | doi = 10.2305/IUCN.UK.1996.RLTS.T5668A11503588.en }}</ref> | |||
|- | |||
|] (''Crocodylus raninus'') | |||
| | |||
|Island of Borneo in ] | |||
|A freshwater species of crocodile that has been considered a synonym of the ]. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus rhombifer''}}) | |||
|] | |||
| valign="top" | Found only in the ] and ] of ] | |||
| valign="top" | It is a small but extremely aggressive species of crocodile that prefers ] ].<ref>{{cite web|url=http://www.markoshea.info/reptileworld_zone2-4.php|title=Mark O'Shea – The Official Website}}</ref> 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 ] 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.<ref name = "Alexander">{{Cite journal| last = Alexander | first = Marc | title = Last of the Cuban crocodile? | journal = Americas (English Edition)| date = 1 January 2006| url = http://www.thefreelibrary.com/_/print/PrintArticle.aspx?id=141091822| issn = 0379-0940 | access-date = 9 July 2010}}</ref> Today most prey are small to medium sized vertebrates. It is ], and the remaining wild population is under threat of hybridization.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2011/06/110624-cuban-american-crocodile-animals-hybrids-science/|archive-url=https://web.archive.org/web/20110626155943/http://news.nationalgeographic.com/news/2011/06/110624-cuban-american-crocodile-animals-hybrids-science/|url-status=dead|archive-date=26 June 2011|title=Hybrid Cuban-American Crocodiles on the Rise|date=26 June 2011}}</ref> | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus siamensis''}}) | |||
|] | |||
| valign="top" | ], ], ] and southern ] | |||
| valign="top" | A fairly small crocodile that prefers ] 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 ], but might be already extinct in the wild; status is unknown.<ref name=Bezuijen>{{cite journal|last=Simpson |first=Boyd |author2=Bezuijen |title=Siamese Crocodile Crocodylus Siamensis |journal=Crocodiles |year=2010 |volume=Third Edition |url=http://www.iucncsg.org/365_docs/attachments/protarea/20_C-637b6a34.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.iucncsg.org/365_docs/attachments/protarea/20_C-637b6a34.pdf |archive-date=2022-10-09 |url-status=live |access-date=13 January 2018 }}</ref> | |||
|- | |||
| valign="top" | ] ({{nowrap|''Crocodylus suchus''}}) | |||
|] | |||
| valign="top" | ] and ] | |||
| valign="top" | Recent studies revealed that this is distinct species from the larger Nile crocodile.<ref>, Nature.com</ref><ref name = "schmitz">{{cite journal|author1=Schmitz, A. |author2=Mausfeld, P. |author3=Hekkala, E. |author4=Shine, T. |author5=Nickel, H. |author6=Amato, G. |author7= Böhme, W. |name-list-style=amp |year=2003|title=Molecular evidence for species level divergence in African Nile crocodiles ''Crocodylus niloticus'' (Laurenti, 1786)|journal=Comptes Rendus Palevol|volume=2|issue=8 |pages=703–12|doi=10.1016/j.crpv.2003.07.002|bibcode=2003CRPal...2..703S }}</ref> It has a slightly narrower snout and is much smaller compared to its larger cousin. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Osteolaemus osborni''}}) | |||
|] | |||
| valign="top" | ] | |||
| valign="top" | 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. | |||
|- | |||
| valign="top" | ] ({{nowrap|''Osteolaemus tetraspis''}}) | |||
|] | |||
| valign="top" | ] | |||
| valign="top" | It belongs to its own ] ]; however, new studies indicate there might be two or even three distinct species.<ref name="Eaton">{{cite journal|last=Eaton|first=Mitchell J.|author2=Andrew Martin |author3=John Thorbjarnarson |author4=George Amato |title=Species-level diversification of African dwarf crocodiles (Genus Osteolaemus): A geographic and phylogenetic perspective|journal=Molecular Phylogenetics and Evolution|date=March 2009|volume=50|issue=3|pages=496–506|doi=10.1016/j.ympev.2008.11.009 |pmid=19056500|bibcode=2009MolPE..50..496E }}</ref> 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 ]. | |||
|- | |||
|] ({{nowrap|''Mecistops cataphractus''}}) | |||
|] | |||
|] | |||
|A medium sized species with a narrow and elongated snout. Lives in ] habitats within tropical forests of the continent. Feeds mostly on ] but also other small to medium sized vertebrates. It is a ] species. | |||
|- | |||
|] (''Mecistops leptorhynchus'') | |||
|] | |||
|] | |||
|A medium sized species found in watery areas in dense rainforest. Feeds largely on fish. Insufficient conservation data, but was classified as ] when lumped with ''M. cataphractus'', although ''M. leptorhynchus'' is doing better in its home range. | |||
|} | |||
{{For|information on Tomistoma or false gharial, that is recently not considered as a true crocodile|False gharial}} | |||
Crocodiles are very fast over short distances, even out of water. Since crocodiles feed by grabbing and holding onto their prey, they have ] sharp teeth for tearing and holding onto flesh, and powerful muscles that close the jaws and hold them shut. These jaws can bite down with immense force, by far the strongest bite of any animal. The crocodile's bite force is more than {{convert|5000|psi|atm}},<ref>National Geographic documentary; "Bite Force", Brady Barr.</ref> compared to just {{convert|335|psi|atm}} for a ], {{convert|400|psi|atm}} for a large ], or {{convert|800|psi|atm}} to {{convert|1000|psi|atm}} for a ]. The jaws are opened, however, by a very weak set of muscles. Crocodiles can thus be subdued for study or transport by ] their jaws or holding their jaws shut with large ]s cut from automobile ]s. They have limited lateral (side-to-side) movement in their neck. | |||
==Characteristics== | |||
{{Hatnote|Crocodiles are similar to alligators and caimans; for their common characteristics and differences among them, see ].}} | |||
], ] and ]s, with post-occipital scutes highlighted in red, nuchal shield in blue and dorsal scutes in green]] | |||
]''.]] | |||
A crocodile's physical traits allow it to be a successful ]. Its external ] is a sign of its ] and ] lifestyle. Its ] body enables it to swim swiftly; it also tucks its feet to the side while swimming, making it faster by decreasing water resistance. Crocodiles have ] which, though not used to propel them through the water, allow them to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallow water, where the animals sometimes move around by walking. Crocodiles have a ] flap, a rigid tissue at the back of the mouth that blocks the entry of water. The palate has a special path from the ] to the ] that bypasses the mouth. The nostrils are closed during submergence. | |||
Like other ]s, crocodilians are ], although their ]e are reduced. The walls of the braincase are bony but lack supratemporal and postfrontal bones.<ref name=ausfauna>Grigg, Gordon and Gans, Carl (1993) {{webarchive|url=https://web.archive.org/web/20050720011236/http://eprint.uq.edu.au/archive/00002011/02/croc.pdf |date=20 July 2005 }}, in Fauna of Australia Vol 2A Amphibia and Reptilia, chapter 40, pp. 326–336. Australian Government Publishing Service, Canberra.</ref> Their ]s are not free, but held in place by a membrane that limits movement; as a result, crocodiles are unable to stick out their tongues.<ref>{{cite book | last = Huchzermeyer | first = Fritz | year = 2003 | title = Crocodiles: Biology, Husbandry and Diseases | publisher = CABI Publishing | isbn =978-0-85199-656-1 | url = https://books.google.com/books?id=4Arv-IUFnuoC| page = 13 }}</ref> Crocodiles have smooth skin on their bellies and sides, while their dorsal surfaces are armoured with large ]. The armoured skin has scales and is thick and rugged, providing some protection. They are still able to absorb heat through this armour, as a network of small ] allows blood through the scales to absorb heat. The osteoderms are highly vascularised and aid in calcium balance, both to neutralize acids while the animal cannot breathe underwater<ref>{{Cite web|last=Wednesday|first=25 April 2012 Anna SallehABC|date=25 April 2012|title=Antacid armour key to tetrapod survival|url=http://www.abc.net.au/science/articles/2012/04/25/3488040.htm|access-date=26 July 2020|website=www.abc.net.au|language=en-AU}}</ref> and to provide calcium for eggshell formation.<ref name=":0">{{Cite journal|last1=Dacke|first1=C.|last2=Elsey|first2=R.|last3=Trosclair|first3=P.|last4=Sugiyama|first4=T.|last5=Nevarez|first5=Javier|last6=Schweitzer|first6=Mary|date=1 September 2015|title=Alligator osteoderms as a source of labile calcium for eggshell formation|url=https://www.researchgate.net/publication/280973901|journal=Journal of Zoology|volume=297|issue=4|pages=255–264|doi=10.1111/jzo.12272}}</ref> Crocodilian tegument have pores believed to be sensory in function, analogous to the ] 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.<ref name=ausfauna /> | |||
===Size=== | |||
] in captivity]] | |||
Size greatly varies among species, from the ] to the ]. Species of the dwarf crocodile ''Osteolaemus'' grow to an adult size of just {{convert|1.5|to|1.9|m|ft|abbr=on}},<ref>. Crocodilian Species List. Retrieved on 14 April 2012</ref> whereas the saltwater crocodile can grow to sizes over {{convert|6|m|ft|abbr=on}} and weigh over {{convert|1000|kg|lb|abbr=on}}.<ref>Guinness Book of World Records. Retrieved on 8 April 2013.</ref> Several other large species can reach over {{convert|5.2|m|ft|abbr=on}} long and weigh over {{convert|900|kg|lb|abbr=on}}. Crocodilians show pronounced ], with males growing much larger and more rapidly than females.<ref name=ausfauna /> Despite their large adult sizes, crocodiles start their lives at around {{convert|20|cm|in|abbr=on}} long. The largest species of crocodile is the saltwater crocodile, found in eastern India, northern Australia, throughout ], and in the surrounding waters. | |||
The brain volume of two adult crocodiles was 5.6 cm<sup>3</sup> for a ] and 8.5 cm<sup>3</sup> for a larger ].<ref>{{Cite journal | doi=10.1371/journal.pone.0178491| pmid=28614349| pmc=5470673|bibcode = 2017PLoSO..1278491J|title = Volume of the crocodilian brain and endocast during ontogeny| journal=PLOS ONE| volume=12| issue=6| pages=e0178491|last1 = Jirak|first1 = Daniel| last2=Janacek| first2=Jiri| year=2017| doi-access=free}}</ref> | |||
The largest crocodile ever held in captivity is a saltwater–Siamese hybrid named Yai ({{langx|th|ใหญ่}}, meaning big; born 10 June 1972) at the ], ]. This animal measures {{convert|6|m|abbr=on}} in length and weighs {{convert|1200|kg|abbr=on}}.<ref> {{Webarchive|url=https://web.archive.org/web/20101105124058/http://www.worldcrocodile.com/centerfarm.swf |date=5 November 2010 }}, Worldcrocodile.com</ref> | |||
The longest crocodile captured alive was ], a saltwater crocodile which was measured at {{convert|6.17|m|ft|abbr=on}} and weighed at {{convert|1075|kg|abbr=on}} by a National Geographic team in Agusan del Sur Province, Philippines.<ref>{{cite web|last=Britton|first=Adam|title=Lolong officially the world's largest crocodile in captivity|url=http://crocodilian.blogspot.com/2012/06/lolong-officially-worlds-largest.html|publisher=Crocodilian.com|access-date=12 July 2012|date=23 June 2012}}</ref><ref>{{cite news|title=Displaced Species|url=http://www.philstar.com/Article.aspx?articleId=824855&publicationSubCategoryId=64|archive-url=https://archive.today/20130131170445/http://www.philstar.com/Article.aspx?articleId=824855&publicationSubCategoryId=64|url-status=dead|archive-date=31 January 2013|newspaper=PhilStar|access-date=12 July 2012}}</ref><ref>{{cite web|author=GMA News with Ben Serrano|author2=Paterno Esmaquel|name-list-style=amp|title=NatGeo team confirms Lolong the croc is world's longest|url=http://www.gmanews.tv/story/237992/nation/natgeo-team-confirms-lolong-the-croc-is-worlds-longest|work=GMA News Online Top Stories|date=9 November 2011 |publisher=GMA Network Inc.|access-date=15 November 2011}}</ref> | |||
===Teeth=== | |||
Crocodiles are ]s; they are able to replace each of their 80 teeth up to 50 times in their 35- to 75-year lifespan.<ref>{{cite web|url=http://blogs.smithsonianmag.com/science/2013/05/solving-an-alligator-mystery-may-help-humans-regrow-lost-teeth/#ixzz2jeiA3qon|title=Solving an Alligator Mystery May Help Humans Regrow Lost Teeth|first=Rachel|last=Nuwer|author-link=Rachel Nuwer |access-date=4 November 2013|archive-date=25 June 2013|archive-url=https://web.archive.org/web/20130625153648/http://blogs.smithsonianmag.com/science/2013/05/solving-an-alligator-mystery-may-help-humans-regrow-lost-teeth/#ixzz2jeiA3qon|url-status=dead}}</ref><ref>{{cite journal|title=Specialized stem cell niche enables repetitive renewal of alligator teeth|first1=Ping|last1=Wu|first2=Xiaoshan|last2=Wu|first3=Ting-Xin|last3=Jiang|first4=Ruth M.|last4=Elsey|first5=Bradley L.|last5=Temple|first6=Stephen J.|last6=Divers|first7=Travis C.|last7=Glenn|first8=Kuo|last8=Yuan|first9=Min-Huey|last9=Chen|first10=Randall B.|last10=Widelitz|first11=Cheng-Ming|last11=Chuong|author-link11=Cheng-Ming Chuong|date=28 May 2013|journal=PNAS|volume=110|issue=22|pages=E2009–E2018|doi=10.1073/pnas.1213202110|pmid=23671090|pmc=3670376|bibcode=2013PNAS..110E2009W|doi-access=free}}</ref> Next to each full-grown tooth, there is a small replacement tooth and an ] ] in the ] in standby that can be activated if required.<ref> {{webarchive |url=https://web.archive.org/web/20131104212952/http://www-hsc.usc.edu/~cmchuong/2013AllTooth.pdf |date=4 November 2013 }}</ref> | |||
==Biology and behaviour== | ==Biology and behaviour== | ||
Crocodiles are ambush hunters, waiting for little jewish girls, then rushing out to attack. As cold-blooded predators, they have a very slow ], and thus can survive long periods without food. Despite their appearance of being slow, crocodiles are top predators in their environment, and various species have been observed attacking and killing muslim boys.<ref name = NGeographicCroc>{{cite web|url=http://animals.nationalgeographic.com/animals/reptiles/saltwater-crocodile.html?nav=A-Z |title=Saltwater Crocodile, Saltwater Crocodile Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News - National Geographic |publisher=Animals.nationalgeographic.com |date= |accessdate=2010-03-16}}</ref> A famous exception is the ] which is said to enjoy a ] relationship with the crocodile. According to unauthenticated reports, the plover feeds on parasites that infest the crocodile's mouth and the reptile will open its jaws and allow the bird to enter to clean out the mouth.<ref>{{cite book | author = Richford, Andrew S., and Christopher J. Mead | year = 2003 | title = Firefly Encyclopedia of Birds | chapter = Pratincoles and Coursers | editor = ] (Ed.) | pages = 252–253 | publisher = Firefly Books | isbn = 1-55297-777-3}}</ref> | |||
Crocodilians are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three families being included in the group ] ('ruling reptiles'). Despite their prehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles, a crocodile has a ] and a four-chambered ]. Crocodilians also have the functional equivalent of a diaphragm by incorporating muscles used for aquatic locomotion into respiration.<ref name="Uriona & Farmer, 2008">{{cite journal|vauthors=Uriona TJ, Farmer CG |year=2008|title=Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (''Alligator mississippiensis'') |journal=Journal of Experimental Biology|volume=211|pages=1141–1147|pmid=18344489|doi=10.1242/jeb.015339|issue=Pt 7|doi-access=free}}</ref> ]s are present in the tongues of crocodiles and they have a pore opening on the surface of the tongue, a trait that separates them from alligators. Salt glands are dysfunctional in Alligatoridae.<ref name=ausfauna /> Their function appears to be similar to that of salt glands in ]s. Crocodiles do not have sweat glands and release heat through their mouths. They often sleep with their mouths open and may pant like a dog.<ref>{{cite web | author= Anitai, Stefan | title = 14 Amazing Facts About Crocodiles – Living dinosaurs | date = 3 November 2007 | url=http://news.softpedia.com/news/14-Amazing-Facts-About-Crocodiles-69931.shtml | publisher= Softpedia | access-date = 1 April 2008}}</ref> Four species of freshwater crocodile climb trees to bask in areas lacking a shoreline.<ref>{{cite journal | url=http://www.herpetologynotes.seh-herpetology.org/Volume7_PDFs/Dinets_HerpetologyNotes_volume7_pages3-7.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.herpetologynotes.seh-herpetology.org/Volume7_PDFs/Dinets_HerpetologyNotes_volume7_pages3-7.pdf |archive-date=2022-10-09 |url-status=live | title=Climbing behaviour in extant crocodilians |author1=Dinets, Vladimir |author2=Britton, Adam |author3=Shirley, Matthew | journal=Herpetology Notes | year=2013 | volume=7 | pages=3–7}}</ref> | |||
Many large crocodilians swallow stones (called gastroliths or stomach stones) which may act as ballast to balance their body or assist in crushing food,<ref name=ausfauna/> similar to grit in birds. | |||
===Senses=== | |||
]s are present in the tongues of most crocodylids and they have a pore opening on the surface of the tongue. They appear to be similar to those in marine turtles; they seem to be absent in Alligatoridae.<ref name=ausfauna/> | |||
] | |||
Crocodiles have acute senses, an evolutionary advantage that makes them successful predators. The eyes, ears and nostrils are located on top of the head, allowing the crocodile to lie low in the water, almost totally submerged and hidden from prey. | |||
====Vision==== | |||
Crocodilians can produce sounds during distress and in aggressive displays. They can also hear well and the tympanic membranes are concealed by flat flaps that may be raised or lowered by muscles.<ref name=ausfauna/> | |||
Crocodiles have very good night vision, and are mostly ] hunters. They use the disadvantage of most prey animals' poor nocturnal vision to their advantage. The light receptors in crocodilians' eyes include ] and numerous ], so it is assumed all crocodilians can see colours.<ref>{{cite web|url=http://wikis.evergreen.edu/m2o1112/index.php/Reptiles|title=Reptiles|author=evergreen|access-date=29 April 2013|archive-url=https://web.archive.org/web/20130615152003/http://wikis.evergreen.edu/m2o1112/index.php/Reptiles|archive-date=15 June 2013|url-status=dead}}</ref> Crocodiles have vertical-slit shaped pupils, similar to those of domestic cats. One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight.<ref name="Land, (2006)">{{cite journal | last1 = Land | first1 = M.F. | year = 2006 | title = Visual optics: the shapes of pupils | journal = Current Biology | volume = 16 | issue = 5| pages = R167–R168 | doi=10.1016/j.cub.2006.02.046 | pmid=16527734| doi-access = free | bibcode = 2006CBio...16.R167L }}</ref> On the rear wall of the eye is a ], which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage. In addition to the protection of the upper and lower eyelids, crocodiles have a ] (sometimes called a "third eye-lid") that can be drawn over the eye from the inner corner while the lids are open. The eyeball surface is thus protected under the water while a certain degree of vision is still possible.<ref name="Encyclopædia Britannica">{{cite web|url=https://www.britannica.com/EBchecked/topic/143679/crocodile/38424/Form-and-function|title=Crocodile|author=Encyclopædia Britannica|access-date=29 April 2013}}</ref> | |||
====Olfaction==== | |||
]]] | |||
Crocodilian ] is also very well developed, aiding them to detect prey or animal carcasses that are either on land or in water, from far away. It is possible that crocodiles use olfaction in the egg prior to hatching.<ref name="Encyclopædia Britannica" /> | |||
Crocodiles eat fish, birds, mammals and occasionally smaller crocodiles. | |||
] in crocodiles is especially interesting because they hunt in both terrestrial and aquatic surroundings. Crocodiles have only one olfactory chamber and the ] is absent in the adults<ref>{{cite journal | last1 = Hansen | first1 = A | year = 2007 | title = Olfactory and solitary chemosensory cells: two different chemosensory systems in the nasal cavity of the American alligator, Alligator mississippiensis | journal = BMC Neuroscience | volume = 8 | page = 64 | doi = 10.1186/1471-2202-8-64 | pmid = 17683564 | pmc = 1950884 | doi-access = free }}</ref> indicating all olfactory perception is limited to the olfactory system. Behavioural and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. When above water, crocodiles enhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of the floor of the pharynx.<ref>{{cite journal | last1 = Gans | first1 = C. | last2 = Clark | first2 = B. | year = 1976 | title = Studies on ventilation of Caiman crocodilus (Crocodilia: Reptilia) | url =https://deepblue.lib.umich.edu/bitstream/2027.42/21779/1/0000173.pdf | journal = Respir. Physiol | volume = 26 | issue = 3| pages = 285–301 | doi=10.1016/0034-5687(76)90001-3| pmid = 951534 | hdl = 2027.42/21779 | hdl-access = free }}</ref><ref>{{cite journal | last1 = Putterill | first1 = J.F. | last2 = Soley | first2 = J.T. | year = 2006 | title = Morphology of the gular valve of the Nile crocodile, Crocodylus niloticus (Laurenti, 1768) | journal = J. Morphol. | volume = 267 | issue = 8| pages = 924–939 | doi=10.1002/jmor.10448| pmid = 16634086 | s2cid = 21995436 }}</ref> Crocodiles close their nostrils when submerged, so olfaction underwater is unlikely. Underwater food detection is presumably gustatory and tactile.<ref>Schwenk, K. (2008). Comparative anatomy and physiology of chemical senses in nonavian aquatic reptiles. In, ''Sensory Evolution on the Threshold: Adaptations in Secondarily Aquatic Vertebrates''. J.G.M ] and S. Nummels (Eds). University of California Press, Berkeley. pp. 65–81</ref> | |||
Crocodiles are protected in many parts of the world, but they also are farmed commercially. Their hide is tanned and used to make leather goods such as shoes and ]s, whilst crocodile meat is also considered a delicacy. The most commonly farmed species are the Saltwater and Nile crocodiles, while a hybrid of the Saltwater and the rare ] is also bred in Asian farms. Farming has resulted in an increase in the Saltwater crocodile population in ], as eggs are usually harvested from the wild, so landowners have an incentive to conserve crocodile habitat. | |||
====Hearing==== | |||
Crocodiles are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three being included in the group ] ('ruling reptiles'). See ] for more information. | |||
Crocodiles can hear well; their ] are concealed by flat flaps that may be raised or lowered by muscles.<ref name=ausfauna /> | |||
====Touch==== | |||
Crocodile embryos do not have sex chromosomes, and unlike humans sex is not determined genetically. ], with males produced at around {{convert|31.6|°C|0|abbr=on}}, and females produced at slightly lower and higher temperatures. The average incubation period is around 80 days, and also is dependent upon temperature.<ref>Britton, Adam. . ''Crocodilians: Natural History Conservation: Crocodiles, Caimans, Alligators, Gharials.'.' Retrieved 4 January 2007.</ref> | |||
The touch sensors, concentrated in crocodile skin, can be thicker than those in human fingerprints.<ref>{{Cite web|date=9 November 2012|title=Croc Jaws More Sensitive Than Human Fingertips|url=https://www.nationalgeographic.com/animals/article/121108-nile-crocodile-duncan-leitch-science-human-sensitive-touch|archive-url=https://web.archive.org/web/20210325143141/https://www.nationalgeographic.com/animals/article/121108-nile-crocodile-duncan-leitch-science-human-sensitive-touch|url-status=dead|archive-date=25 March 2021|access-date=31 January 2022|website=Animals|language=en}}</ref> Crocodiles can feel the touch on their skin.<ref>{{Cite web|date=14 October 2021|title=Do Crocodiles Feel Pain? (Surprising Answer) {{!}}|url=https://wildexplained.com/do-crocodiles-feel-pain/|access-date=31 January 2022|language=en-us}}</ref> | |||
'''Cranial''': The upper and lower jaws are covered with sensory pits, visible as small, black speckles on the skin, the crocodilian version of the ] organs seen in fish and many amphibians, though arising from a completely different origin. These pigmented nodules encase bundles of ] innervated beneath by branches of the trigeminal nerve. They respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes as small as a single drop.<ref>{{cite news|url=https://www.cbc.ca/news/science/alligators-detect-silent-ripples-when-hunting-1.320458|title=Alligators detect silent ripples when hunting|author=CBCnews|year=2002|access-date=29 April 2013|work=CBC News}}</ref> This makes it possible for crocodiles to detect prey, danger and intruders, even in total darkness. These sense organs are known as domed pressure receptors (DPRs).<ref name="Jackson and Brooks">{{cite journal | last1 = Jackson | first1 = K. | last2 = Brooks | first2 = D.R. | year = 2007 | title = Do crocodiles co-opt their sense of "touch" to "taste"? A possible new type of vertebrate sensory organ | url = http://people.whitman.edu/~jacksok/AMRE2447.pdf | journal = Amphibia-Reptilia | volume = 28 | issue = 2 | pages = 277–285 | doi = 10.1163/156853807780202486 | access-date = 29 April 2013 | archive-url = https://web.archive.org/web/20130730091857/http://people.whitman.edu/~jacksok/AMRE2447.pdf | archive-date = 30 July 2013 | url-status = dead }}</ref> | |||
Crocodiles may possess a form of ]. Three rogue saltwater crocodiles were relocated 400 kilometres by ] in northern ] but had returned to their original locations within three weeks, based on data obtained from tracking devices attached to the reptiles.<ref>Read MA, Grigg GC, Irwin SR, Shanahan D, Franklin CE (2007) Satellite Tracking Reveals Long Distance Coastal Travel and Homing by Translocated Estuarine Crocodiles, ''Crocodylus porosus''. PLoS ONE 2(9): e949. doi:10.1371/journal.pone.0000949</ref> | |||
'''Post-Cranial''': While alligators and caimans have DPRs only on their jaws, crocodiles have similar organs on almost every scale on their bodies. The function of the DPRs on the jaws is clear; to catch prey, but it is still not clear what the function is of the organs on the rest of the body. The receptors flatten when exposed to increased osmotic pressure, such as that experienced when swimming in sea water ] to the body fluids. When contact between the integument and the surrounding sea water solution is blocked, crocodiles are found to lose their ability to discriminate salinities. It has been proposed that the flattening of the sensory organ in hyperosmotic sea water is sensed by the animal as "touch", but interpreted as chemical information about its surroundings.<ref name="Jackson and Brooks" /> This might be why in alligators they are absent on the rest of the body.<ref>{{cite web|url=http://crocodilian.com/cnhc/cbd-gb1.htm |title=Crocodilian Biology Database – Integumentary Sense Organs |publisher=Crocodilian.com |access-date=26 April 2013}}</ref> | |||
The ] record for a crocodile is 17 km/h (11 mph) measured in a galloping ].<ref>{{cite web | |||
| last = Britton | |||
| first = Adam | |||
| title = Crocodilian Biology Database FAQ, "How fast can a crocodile run?" | |||
| url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q4.htm | |||
| accessdate = 2008-02-02 }} | |||
</ref> Maximum speed varies from species to species. Certain types of crocodiles can indeed gallop, including Cuban crocodiles, New Guinea crocodiles, ], and even small ]. The fastest means by which most species can move is a kind of "belly run", where the body moves in a snake-like fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of 10 or 11 km/h (around 7 mph) when they "belly run", and often faster if they're slipping down muddy riverbanks. Another form of locomotion is the "high walk" where the body is raised clear off the ground. | |||
===Hunting and diet=== | |||
] sleeping with its mouth open to pant]] | |||
] | |||
Crocodiles do not have sweat glands and release heat through their mouths. They often sleep with their mouths open and may even pant like a dog.<ref>{{cite web | |||
] | |||
| last = Anitai | |||
] | |||
| first = Stefan | |||
Crocodiles are ]s, waiting for fish or land animals to come close, then rushing out to attack. Crocodiles mostly eat ], ]s, ]s, ]s, ]s, ]s, and ]s, and they occasionally ] smaller crocodiles. What a crocodile eats varies greatly with species, size and age. From the mostly fish-eating species, like the ] and ]s, to the larger species like the ] and the ] that prey on large mammals, such as ], ] and ], diet shows great diversity. Diet is also greatly affected by the size and age of the individual within the same species. All young crocodiles hunt mostly ] and small ], gradually moving on to larger prey. Being ]ic (cold-blooded) predators, they have a very slow ], so they can survive long periods without food. Despite their appearance of being slow, crocodiles have a very fast strike and are top ]s in their environment, and various species have been observed attacking and killing other ]s such as ]s and ]s.<ref name = NGeographicCroc>{{cite web|url=https://www.nationalgeographic.com/animals/?nav=A-Z |title=Saltwater Crocodile, Saltwater Crocodile Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News – National Geographic |publisher=Animals.nationalgeographic.com |access-date=16 March 2010}}</ref><ref>{{cite web |url=http://crocodilian.com/cnhc/csp_cnil.htm |title=Crocodilian Species – Nile Crocodile (Crocodylus niloticus) |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025183255/http://crocodilian.com/cnhc/csp_cnil.htm |url-status=dead }}</ref> Crocodiles are also known to be aggressive ]s who feed upon ] and steal from other predators.<ref>{{cite web|url=http://www.australiananimallearningzone.com/saltwater-crocodile-crocodylus-porosus.htm|title=Saltwater Crocodile Profile|work=Australian Animal|date=22 December 2012 }}</ref> Evidence suggests that crocodiles also feed upon fruits, based on the discovery of seeds in stools and stomachs from many subjects as well as accounts of them feeding.<ref>{{cite magazine|url=http://www.popsci.com/article/science/are-crocodiles-secret-fruit-lovers|title=ARE CROCODILES SECRET FRUIT-LOVERS?|magazine=]|author=Jon Tennant}} 13 November 2013</ref><ref>{{cite web|url=http://www.livescience.com/39198-crocodiles-alligators-eat-fruit.html?li_source=LI&li_medium=more-from-livescience|title=Crikey! Crocodiles and Alligators Snack on Fruit|work=]|author=Charles Q. Choi|date=27 August 2013}} 27 August 2013</ref> | |||
| title = 14 Amazing Facts About Crocodiles - Living dinosaurs | |||
| url=http://news.softpedia.com/news/14-Amazing-Facts-About-Crocodiles-69931.shtml | |||
| publisher= Softpedia | |||
| accessdate = 2008-04-01}}</ref> | |||
Crocodiles have the most acidic stomach of any vertebrate. They can easily digest bones, hooves and horns. The ]<ref>BBC channel 1 program ''Inside The Perfect Predator'', Thursday 25 March 2010</ref> reported that a ] that has lurked a long time underwater to catch prey builds up a large ]. When it has caught and eaten that prey, it closes its right ] and uses its left aortic arch to flush blood loaded with ] from its muscles directly to its stomach; the resulting excess acidity in its blood supply makes it much easier for the stomach lining to secrete more ] to quickly dissolve bulks of swallowed prey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomach stones), which may act as ballast to balance their bodies or assist in crushing food,<ref name=ausfauna /> similar to grit ingested by birds. ] claimed that Nile crocodiles had a ] with certain birds, such as the ], which enter the crocodile's mouth and pick ]es feeding on the crocodile's blood; with no evidence of this interaction actually occurring in any crocodile species, it is most likely mythical or allegorical fiction.<ref>{{cite web|author=Adam Britton |url=http://crocodilian.blogspot.com/2009/09/crocodile-myths-1-curious-trochilus.html |title=Croc Blog: Crocodile myths #1 – the curious trochilus |publisher=Crocodilian.blogspot.com |date=6 September 2009 |access-date=26 April 2013}}</ref> | |||
=== |
====Bite==== | ||
] in ], South Africa]] | |||
] in captivity in Australia]] | |||
Since they feed by grabbing and holding onto their prey, they have ] sharp teeth for piercing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. The teeth are not well-suited to tearing flesh off of large prey items as are the dentition and claws of many mammalian carnivores, the hooked bills and talons of ], or the serrated teeth of sharks. However, this is an advantage rather than a disadvantage to the crocodile since the properties of the teeth allow it to hold onto prey with the least possibility of the prey animal escaping. Cutting teeth, combined with the exceptionally high ], would pass through flesh easily enough to leave an escape opportunity for prey. The jaws can bite down with immense force, by far the strongest bite of any animal. The force of a large crocodile's bite is more than {{convert|5000|lbf|N|abbr=on}}, which was measured in a {{convert|5.5|m|ft|abbr=on}} ], in the field;<ref>National Geographic documentary; "Bite Force", Brady Barr.</ref> comparing to {{convert|335|lbf|N|abbr=on}} for a ], {{convert|800|lbf|N|abbr=on}} for a ], {{convert|2200|lbf|N|abbr=on}} for an ],<ref>{{cite web|url=http://dogfacts.wordpress.com/2008/02/03/national-geographics-dr-brady-barrs-bite-pressure-tests/ |title=National Geographic's Dr. Brady Barr's Bite Pressure Tests | Dog Facts |publisher=Dogfacts.wordpress.com |access-date=26 April 2013|date=3 February 2008 }}</ref>{{failed verification|date=October 2014}} and {{convert|4095|lbf|N|abbr=on}} for the largest confirmed ].<ref name="GWB">{{cite journal|last=Wroe|first=S.|author2=Huber, D. R.|author3=Lowry, M.|author4=McHenry, C.|author5=Moreno, K.|author6=Clausen, P.|author7=Ferrara, T. L.|author8=Cunningham, E.|author9=Dean, M. N. |author10= Summers, A. P.|title=Three-dimensional computer analysis of white shark jaw mechanics: how hard can a great white bite?|url=http://www.bio-nica.info/Biblioteca/Wroe2008GreatWhiteSharkBiteForce.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.bio-nica.info/Biblioteca/Wroe2008GreatWhiteSharkBiteForce.pdf |archive-date=2022-10-09 |url-status=live|journal=Journal of Zoology|volume=276|issue=4|pages=336–342|year= 2008|doi=10.1111/j.1469-7998.2008.00494.x}}</ref> | |||
Size greatly varies between species, from the ] to the ]. Species of ''Palaeosuchus'' and ''Osteolaemus'' grow to an adult size of just {{convert|1|m|ft}} to {{convert|1.5|m|ft}}. Larger species can reach over {{convert|4.85|m|ft}} long and weigh well over {{convert|1200|kg|lb}}. Crocodilians show pronounced ] with males growing much larger and more rapidly than females.<ref name=ausfauna/> Despite their large adult size, crocodiles start their life at around {{convert|20|cm|in}} long. The largest species of crocodile is the ], found in northern Australia, throughout ], and in the surrounding waters. | |||
A {{convert|5.2|m|ft|abbr=on}} long saltwater crocodile has been confirmed as having the strongest ] ever recorded for an animal in a laboratory setting. It was able to apply a bite force value of {{convert|3700|lbf|N|abbr=on}}, and thus surpassed the previous record of {{convert|2125|lbf|N|abbr=on}} made by a {{convert|3.9|m|ft|abbr=on}} long ].<ref name="lappin">{{cite journal|title=The ontogeny of bite-force performance in American alligator (Alligator mississippiensis)|journal=]|volume=260|issue=3|pages=317–327|url=http://www.alligatorfarm.us/images/Research/Erickson%20et%20al.%202003.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.alligatorfarm.us/images/Research/Erickson%20et%20al.%202003.pdf |archive-date=2022-10-09 |url-status=live|doi=10.1017/S0952836903003819|year=2003|last1=Erickson|first1=Gregory M.|last2=Lappin|first2=A. Kristopher|last3=Vliet|first3=Kent A.}}</ref><ref>{{cite journal|url=https://www.sciencedaily.com/releases/2012/03/120316093427.htm|title=Australian saltwater crocodiles are world's most powerful biters |journal=PLOS ONE |volume=7 |issue=3 |pages=e31781 |doi=10.1371/journal.pone.0031781 |pmid=22431965 |pmc=3303775 |date=16 March 2012 |access-date=26 April 2013|bibcode=2012PLoSO...731781E|last1=Erickson |first1=Gregory M. |last2=Gignac |first2=Paul M. |last3=Steppan |first3=Scott J. |last4=Lappin |first4=A. Kristopher |last5=Vliet |first5=Kent A. |last6=Brueggen |first6=John D. |last7=Inouye |first7=Brian D. |last8=Kledzik |first8=David |last9=Webb |first9=Grahame J. W. |doi-access=free }}</ref> Taking the measurements of several {{convert|5.2|m|ft|abbr=on}} crocodiles as reference, the bite forces of 6-m individuals were estimated at {{convert|7700|lbf|N|abbr=on}}.<ref name=autogenerated1>{{cite web|url=http://news.nationalgeographic.com/news/2012/03/120315-crocodiles-bite-force-erickson-science-plos-one-strongest/ |archive-url=https://web.archive.org/web/20120317064400/http://news.nationalgeographic.com/news/2012/03/120315-crocodiles-bite-force-erickson-science-plos-one-strongest/ |url-status=dead |archive-date=17 March 2012 |title=Crocodiles Have Strongest Bite Ever Measured, Hands-on Tests Show |publisher=News.nationalgeographic.com |date=15 March 2012 |access-date=26 April 2013}}</ref> The study, led by Dr. ], also shed light on the larger, ] species of ]s. Since crocodile ] has changed only slightly over the last 80 million years, current data on modern crocodilians can be used to estimate the bite force of extinct species. An {{convert|11|to(-)|12|m|ft|adj=on}} ] would apply a force of {{convert|23100|lbf|N|abbr=on}}, nearly twice that of the latest, higher bite force estimations of ] ({{convert|12814|lbf|N|abbr=on}}).<ref name="nationalgeographic1" /><ref name="FalkinghamBatesBiteforce2012">{{cite web|url=http://www.smithsonianmag.com/science-nature/The-Tyrannosaurus-Rexs-Dangerous-and-Deadly-Bite-37252918/|title=The Tyrannosaurus Rex's Dangerous and Deadly Bite|website=]|date=October 2012|first=Riley|last=Black|access-date=6 June 2021}}</ref><ref name="BatesFalkingham2012">{{Cite journal|last1=Bates|first1=K. T.|last2=Falkingham|first2=P.L.|date=29 February 2012|title=Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics|journal=Biological Letters|volume=8|issue=4|pages=660–664|doi=10.1098/rsbl.2012.0056|pmid=22378742|pmc=3391458}}</ref><ref>Crispian Scully, (2002) ''Oxford Handbook of Applied Dental Sciences'', Oxford University Press –{{ISBN|978-0-19-851096-3}} P156</ref> The extraordinary bite of crocodilians is a result of their ]. The space for the jaw muscle in the ] is very large, which is easily visible from the outside as a bulge at each side. The ] is so stiff, it is almost as hard as bone to touch, as if it were the continuum of the skull. Another trait is that most of the muscle in a crocodile's jaw is arranged for clamping down. Despite the strong muscles to close the jaw, crocodiles have extremely small and weak muscles to open the jaw. Crocodiles can thus be subdued for study or transport by ] their jaws or holding their jaws shut with large ]s cut from automobile ]s. | |||
Two larger certifiable records are both of {{convert|6.2|m|ft}} crocodiles. The first crocodile was shot in the ] in the ] of ] in 1974 by poachers and measured by wildlife rangers.{{Citation needed|date=September 2008}} The second crocodile was killed in 1983 in the ], ]. In the case of the second crocodile it was actually the skin that was measured by zoologist Jerome Montague, and as skins are known to underestimate the size of the actual animal, it is possible this crocodile was at least another 10 cm longer.{{Citation needed|date=September 2008}} | |||
<!-- Deleted image removed: ], a large saltwater crocodile that attacked boats {{deletable image-caption|Friday, 14 August 2009}}]] --> | |||
===Locomotion=== | |||
The largest crocodile ever held in captivity is an Estuarine–Siamese hybrid named Yai ({{lang-th|ใหญ่}}, meaning ''big'') (born 10 June 1972) at the famous ], ]. This animal measures {{convert|6|m|2|abbr=on|lk=out}} (19 ft 8 in) in length and weighs 1114.27 kg. | |||
] | |||
Crocodiles can move quickly over short distances, even out of water. The ] record for a crocodile is {{convert|17|km/h|0|abbr=on}} measured in a galloping ].<ref>{{cite web | last = Britton | first = Adam | title = Crocodilian Biology Database FAQ, "How fast can a crocodile run?" | url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q4.htm | access-date = 2 February 2008}}</ref> Maximum speed varies between species. Some species can gallop, including Cuban crocodiles, Johnston's crocodiles, New Guinea crocodiles, ], and even small ]. The fastest means by which most species can move is a "belly run", in which the body moves in a snake-like (sinusoidal) fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of {{convert|10|-|11|km/h|0|abbr=on}} when they "belly run", and often faster if slipping down muddy riverbanks. When a crocodile walks quickly, it holds its legs in a straighter and more upright position under its body, which is called the "high walk". This walk allows a speed of up to 5 km/h.<ref>{{cite book|last1=Walters|first1=Martin|last2=Johnson|first2=Jinny|title=Encyclopedia of Animals|publisher=Marks and Spencer p.l.c|isbn=978-1-84273-964-8|page=145}}</ref> | |||
Crocodiles may possess a ]. In northern Australia, three rogue saltwater crocodiles were relocated {{convert|400|km|0|abbr=on}} by ], but returned to their original locations within three weeks, based on data obtained from tracking devices attached to them.<ref>{{cite journal|author=Read M. A.|author2=Grigg G. C.|author3=Irwin S. R.|author4=Shanahan D.|author5=Franklin C. E. |year=2007 |title=Satellite Tracking Reveals Long Distance Coastal Travel and Homing by Translocated Estuarine Crocodiles, ''Crocodylus porosus'' |journal= PLOS ONE |volume=2 |issue=9 |page=e949 |doi=10.1371/journal.pone.0000949 |editor1-last=Lusseau |editor1-first=David |pmid=17895990 |pmc=1978533|bibcode=2007PLoSO...2..949R|doi-access=free}}</ref> | |||
The largest captive crocodile alive in the US is located in South Carolina. In June 2002, Alligator Adventure introduced Utan. At {{convert|20|ft|m}} long and weighing in at more than a ton, "Utan", the largest crocodile to ever be exhibited in the United States, made his new home in Myrtle Beach.<ref>http://www.worldcrocodile.com/centerfarm.swf</ref> | |||
===Longevity=== | |||
Wildlife experts, however, argue that the largest crocodile so far found in the Bhitarkanika was almost {{convert|23|ft|m}} long, which could be traced from the skull preserved by the Kanika Royal Family. The crocodile was shot near Dhamara in 1926 and later its skull was preserved by the then Kanika King. Crocodile experts estimate the animal was between {{convert|20|ft|m}} and {{convert|23|ft|m}} long, as the size of the skull was measured one ninth of the total length of the body.{{Citation needed|date=March 2009}} | |||
Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons.<ref>{{cite web|url=http://www.flmnh.ufl.edu/cnhc/cbd-faq-q3.htm |title=Crocodilian Biology Database, FAQ. "How long do crocodiles live for?" |publisher=Flmnh.ufl.edu |access-date=26 April 2013}}</ref> Bearing these inaccuracies in mind, it can be safely said that all crocodile species have an average lifespan of at least 30–40 years, and in the case of larger species an average of 60–70 years. The oldest crocodiles appear to be the largest species. ] is estimated to live around 70 years on average, with limited evidence of some individuals exceeding 100 years.<ref>{{cite web |url=http://crocodilian.com/cnhc/cbd-faq-q3.htm |title=Crocodilian Biology Database – FAQ – How long do crocodiles live for? |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=21 March 2015 |archive-url=https://web.archive.org/web/20150321151949/http://crocodilian.com/cnhc/cbd-faq-q3.htm |url-status=dead }}</ref> | |||
In captivity, some individuals are claimed to have lived for over a century. A male crocodile lived to an estimated age of 110–115 years in a Russian zoo in ].<ref name=yeka /> Named Kolya, he joined the zoo around 1913 to 1915, fully grown, after touring in an animal show, and lived until 1995.<ref name=yeka>{{cite news | agency=Associated Press | title=Crocodile at Russian zoo dies; on display since czars | date=16 February 1995 | work=The News–Journal | location=Daytona Beach, Florida | volume=70 | issue=47 | publisher=News–Journal Corporation | url=https://news.google.com/newspapers?nid=1901&dat=19950216&id=MqgtAAAAIBAJ&pg=2827,36264 }}</ref> A male freshwater crocodile lived to an estimated age of 120–140 years at the ].<ref name=campbell2010>{{cite news | title=Freshie the croc dies at age 140 | first=Kieran | last=Campbell | date=24 March 2010 | url=http://www.sunshinecoastdaily.com.au/news/freshie-the-croc-dies-at-age-140/494141/ | work=Sunshine Coast Daily }}</ref> Known affectionately as "Mr. Freshie", he was rescued around 1970 by ] and ], after being shot twice by hunters and losing an eye as a result, and lived until 2010.<ref name=campbell2010 /> Crocworld Conservation Centre, in ], South Africa, claims to have a male ] that was born in 1900. Named Henry, the crocodile is said to have lived in ] along the ], according to centre director Martin Rodrigues.<ref>{{cite web|url=http://ibnlive.in.com/news/johannesburg-worlds-oldest-crocodile-turns-114/518422-2.html |archive-url=https://web.archive.org/web/20141217215908/http://ibnlive.in.com/news/johannesburg-worlds-oldest-crocodile-turns-114/518422-2.html |url-status=dead |archive-date=17 December 2014 |title=Johannesburg: World's oldest crocodile turns 114 |publisher=IBN Live |date=16 December 2014| access-date=19 December 2014}}</ref><ref>{{cite news |url=http://www.elnuevodia.com/celebrancumpleanosdelcocodrilomaslongevodelmundo-1911287.html |title=Celebran cumpleaños del cocodrilo más longevo del mundo |newspaper=] |date=16 December 2014 |access-date=19 December 2014 |archive-date=21 December 2014 |archive-url=https://web.archive.org/web/20141221220518/http://www.elnuevodia.com/celebrancumpleanosdelcocodrilomaslongevodelmundo-1911287.html |url-status=dead }}</ref> | |||
] treading on a crocodile (], ])]] | |||
===Social behaviour and vocalization=== | |||
===Age=== | |||
] | |||
There is no reliable way of measuring crocodile age, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons.<ref>Britton Adam. . Retrieved 9/11/2006.</ref> Bearing these inaccuracies in mind, the oldest crocodilians appear to be the largest species. ''C. porosus'' is estimated to live around 70 years on average, and there is limited evidence that some individuals may exceed 100 years. One of the oldest crocodiles recorded died in a zoo in Russia. A male freshwater crocodile at the ] is estimated to be 130 years old. He was rescued from the wild by ] and ] after being shot twice by hunters. As a result of the shootings, this crocodile (known affectionately as "Mr. Freshy") has lost his right eye.<ref>. Retrieved 1 February 2007.</ref> | |||
Crocodiles are the most social of reptiles. Even though they do not form social groups, many species congregate in certain sections of ]s, tolerating each other at times of ] and ]. Most species are not highly territorial, with the exception of the saltwater crocodile, which is a highly ] and aggressive species: a mature, male saltwater crocodile will not tolerate any other males at any time of the year, but most other species are more flexible. There is a certain form of ] in crocodiles: the largest and heaviest males are at the top, having access to the best basking site, while females are priority during a group feeding of a big kill or carcass. A good example of the hierarchy in crocodiles would be the case of the ]. This species clearly displays all of these behaviours. Studies in this area are not thorough, however, and many species are yet to be studied in greater detail.<ref>{{cite web |url=http://crocodilian.com/cnhc/csp_cnil.htm |title=Crocodilian Species List |publisher=Crocodilian.com |access-date=26 April 2013 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025183255/http://crocodilian.com/cnhc/csp_cnil.htm |url-status=dead }}</ref> ]s are also known to show toleration in group feedings and tend to congregate in certain areas. However, males of all species are aggressive towards each other during mating season, to gain access to females. | |||
Crocodiles are also the most vocal of all reptiles, producing a wide variety of sounds during various situations and conditions, depending on species, age, size and sex. Depending on the context, some species can communicate over 20 different messages through ] alone.<ref>{{cite web|url=http://crocodilian.com/cnhc/croccomm.html |title=Crocodilian Communication |publisher=Crocodilian.com |access-date=29 April 2013}}</ref> Some of these vocalizations are made during social communication, especially during ] displays towards the same sex and ] with the opposite sex; the common concern being ]. Therefore most ] vocalization is made during the ], with the exception being year-round ] in some species and quarrels during feeding. Crocodiles also produce different distress calls and in aggressive displays to their own kind and other animals; notably other predators during ] predatory confrontations over carcasses and terrestrial kills. | |||
===Skin=== | |||
Crocodiles have smooth skin on their belly and side, while their dorsal surface is armoured with large ]. The armoured skin has scales and is thick and rugged, providing some protection. They are still able to absorb heat through this thick, rugged armour as a network of small ] push blood through the scales to absorb heat. | |||
Specific vocalisations include — | |||
==Taxonomy of the Crocodylidae== | |||
]]] | |||
] | |||
] at ]]] | |||
] | |||
Most species are grouped into the ] ''Crocodylus''. The other ] genus, '']'', is ] (as is '']'', if recognized). | |||
* Family Crocodylidae | |||
** '''Subfamily †]''' (extinct) | |||
** '''Subfamily Crocodylinae''' | |||
*** Genus '']'' | |||
**** '']'', ] | |||
**** '']'', ] (studies in ] and ] suggest that this species may be more ] than '']'', and therefore belongs in its own genus, '']'')<ref>McAliley, Willis, Ray, White, Brochu & Densmore (2006). ''Are crocodiles really monophyletic?—Evidence for subdivisions from sequence and morphological data.'' Molecular Phylogenetics and Evolution 39:16-32.</ref> | |||
**** '']'', ] | |||
**** '']'', ] | |||
**** '']'', ] | |||
**** '']'', ] or Mexican Crocodile | |||
**** '']'', ] or African Crocodile (the subspecies found in Madagascar is sometimes called the ]) | |||
**** '']'', ] | |||
**** '']'', ], Marsh Crocodile, or Indian Crocodile | |||
**** '']'', ] or Estuarine Crocodile | |||
**** '']'', ] | |||
**** '']'', ] | |||
*** Genus '']'' | |||
**** '']'', ] (there has been controversy whether or not this is actually two species; current thinking is that there is one species with 2 subspecies: ''O. tetraspis tetraspis'' & ''O. t. osborni'') | |||
*** Genus †'']'' | |||
*** Genus †'']'' (formerly ''Crocodylus lloydi'') | |||
*** Genus †'']'' <small>Brochu, 2007</small> (formerly ''Crocodylus robustus'')<!-- ZoolJLinnSoc150:835. --> | |||
* '''Chirp''': When about to hatch, the young make a "peeping" noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female<ref>{{cite web|url=http://www.arkive.org/nile-crocodile/crocodylus-niloticus/|archive-url=https://web.archive.org/web/20090123041108/http://www.arkive.org/nile-crocodile/crocodylus-niloticus/|url-status=dead|archive-date=23 January 2009|author=Arkive|title=Nile crocodile (''Crocodylus niloticus'')|access-date=29 April 2013}}</ref> | |||
Some of the extinct relatives of true crocodiles, members of the larger group ], were herbivorous. | |||
* '''Distress call''': A high-pitched call used mostly by younger animals to alert other crocodiles to imminent danger or an animal being attacked. | |||
* '''Threat call''': A hissing sound that has also been described as a coughing noise. | |||
* '''Hatching call''': Emitted by a female when breeding to alert other crocodiles that she has laid eggs in her nest. | |||
* '''Bellowing''': Male crocodiles are especially vociferous. Bellowing choruses occur most often in the spring when breeding groups congregate, but can occur at any time of year. To bellow, males noticeably inflate as they raise the tail and head out of water, slowly waving the tail back and forth. They then puff out the throat and with a closed mouth, begin to vibrate air. Just before bellowing, males project an ] signal at about 10 Hz through the water, which vibrates the ground and nearby objects. These low-frequency vibrations travel great distances through both air and water to advertise the male's presence and are so powerful they result in the water's appearing to "dance".<ref>{{cite web |url=http://factsanddetails.com/Asian.php?itemid=2435&subcatid=434 |archive-url=https://archive.today/20130629045148/http://factsanddetails.com/Asian.php?itemid=2435&subcatid=434 |url-status=dead |archive-date=29 June 2013 |author=Hays, J. |title=Crocodiles: Their history, characteristics and behavior |year=2008 |access-date=31 May 2013 }}</ref> | |||
===Reproduction=== | |||
==Crocodiles and Humans== | |||
] | |||
Crocodiles lay ]s, which are laid in either holes or mound ]s, depending on species. A hole nest is usually excavated in sand and a mound nest is usually constructed out of vegetation. ]ing periods range from a few weeks up to six months. ] takes place in a series of behavioural interactions that include a variety of snout rubbing and submissive display that can take a long time. Mating always takes place in water, where the pair can be observed mating several times. Females can build or dig several trial nests which appear incomplete and abandoned later. Egg-laying usually takes place at night and about 30–40 minutes.<ref name="autogenerated2000">{{cite book |author1=K. Richardson |author2=G. Webb |author3=C. Manolis |title = Crocodiles: Inside and Out |year = 2000}}</ref> Females are highly protective of their nests and young. The eggs are hard shelled, but translucent at the time of egg-laying. Depending on the species of crocodile, 7 to 95 eggs are laid. Crocodile ]s do not have sex chromosomes, and unlike humans, sex is not determined genetically. ], where at {{convert|30|°C|0|abbr=on}} or less most hatchlings are females and at {{convert|31|°C|0|abbr=on}}, offspring are of both sexes. A temperature of {{convert|32|to|33|°C|0|abbr=on}} gives mostly males whereas above {{convert|33|°C|0|abbr=on}} in some species continues to give males, but in other species resulting in females, which are sometimes called high-temperature females.<ref>{{cite book |author1=G. Webb |author2=C. Manolis |title = Crocodiles of Australia |year = 1989}}</ref> Temperature also affects growth and survival rate of the young, which may explain the ] in crocodiles. The average ] is around 80 days, and also is dependent on temperature and species that usually ranges from 65 to 95 days. The eggshell structure is very conservative through evolution but there are enough changes to tell different species apart by their eggshell microstructure.<ref>{{cite journal | last1 = Marzola | first1 = M. | last2 = Russo | first2 = J. | last3 = Mateus | first3 = O. | year = 2015 | title = Identification and comparison of modern and fossil crocodilian eggs and eggshell structures | journal = Historical Biology | volume = 27 | issue = 1| pages = 115–133 | doi=10.1080/08912963.2013.871009| bibcode = 2015HBio...27..115M | s2cid = 85685470 }}</ref> Scutes may play a role in calcium storage for eggshell formation.<ref name=":0" /> | |||
At the time of hatching, the young start calling within the eggs. They have an ] at the tip of their snouts, which is developed from the skin, and that helps them pierce out of the shell. Hearing the calls, the female usually excavates the nest and sometimes takes the unhatched eggs in her mouth, slowly rolling the eggs to help the process. The young is usually carried to the water in the mouth. She would then introduce her hatchlings to the water and even feed them.<ref>{{cite web|url=http://scienceblogs.com/tetrapodzoology/2008/11/08/crocs-feed-their-babies/|title=Do crocodilians (sometimes) feed their young?|publisher=Science Blogs|author=Darren Naish}} 8 November 2008</ref> The mother would then take care of her young for over a year before the next mating season. In the absence of the mother crocodile, the father would act in her place to take care of the young.<ref>{{cite web|url=http://oddstuffmagazine.com/10-delightful-baby-animals-that-grow-up-to-be-fatal-predators.html|title=10 Delightful Baby Animals that Grow up to Be Fatal Predators|date=3 February 2012|publisher=Odd Stuff}} 3 February 2012</ref> However, even with a sophisticated ], young crocodiles have a very high mortality rate due to their vulnerability to predation.<ref>{{cite web|url=http://animals.mom.me/life-cycle-alligators-crocodiles-8058.html|title=THE LIFE CYCLE OF ALLIGATORS AND CROCODILES|publisher=Demand Media|author= Jasey Kelly}}</ref> A group of ]s is called a pod or ] and may be protected for months.<ref name="autogenerated2000" /> | |||
===Cognition=== | |||
Crocodiles possess some advanced cognitive abilities.<ref name="LA">{{cite news|url=https://www.latimes.com/science/sciencenow/la-sci-sn-clever-crocodiles-alligators-sticks-twigs-birds-lure-prey-20131206-story.html|title=Scary smart! Clever crocodiles, alligators use sticks to lure prey|author=Amina Khan|newspaper=Los Angeles Times|date=6 December 2013}} 6 December 2013</ref><ref name="Wash">{{cite news|url=https://www.washingtonpost.com/national/health-science/crocodiles-and-their-ilk-may-be-smarter-than-they-look/2013/12/06/1084cf28-5d2c-11e3-bc56-c6ca94801fac_story.html|title=Crocodiles and their ilk may be smarter than they look|newspaper=]|author=Jason G. Goldman}} 9 December 2013</ref><ref name="Phy">{{cite web|url=http://phys.org/news/2014-10-crocodiles-sophisticated-hunters.html|title=Scary smart! Clever crocodiles, alligators use sticks to lure prey|publisher=Phys Org}} 13 October 2014</ref> They can observe and use patterns of prey behaviour, such as when prey come to the river to drink at the same time each day. ] of the ], observed that crocodiles use ] for birds looking for nesting material.<ref>{{cite web|url=https://www.sciencedaily.com/releases/2013/12/131204182433.htm|title=Crocodiles are cleverer than previously thought: Some crocodiles use lures to hunt their prey|website=ScienceDaily|date=4 December 2013|access-date=8 December 2013}}</ref> They place sticks on their snouts and partly submerge themselves. When the birds swooped in to get the sticks, the crocodiles then catch the birds. Crocodiles only do this in spring nesting seasons of the birds, when there is high demand for sticks to be used for building nests. Vladimir also discovered other similar observations from various scientists, some dating back to the 19th century.<ref name="LA" /><ref name="Phy" /> Aside from using sticks, crocodiles are also capable of ].<ref name="Phy" /><ref name="One">{{cite web|url=http://www.oneworldmagazine.org/tales/crocs/smart.html|archive-url=https://web.archive.org/web/20000930224445/http://www.oneworldmagazine.org/tales/crocs/smart.html|url-status=dead|archive-date=30 September 2000|title=The Crocodile Files|work=One World Magazine}}</ref> Large numbers of crocodiles swim in circles to trap fish and take turns snatching them. In hunting larger prey, crocodiles swarm in, with one holding the prey down as the others rip it apart. | |||
According to a 2015 study, crocodiles engage in all three main types of play behaviour recorded in animals: locomotor play, play with objects and social play. Play with objects is reported most often, but locomotor play such as repeatedly sliding down slopes, and social play such as riding on the backs of other crocodiles is also reported. This behaviour was exhibited with conspecifics and mammals and is apparently not uncommon, though has been difficult to observe and interpret in the past due to obvious dangers of interacting with large carnivores.<ref>{{Cite web|title=Crocodiles just wanna have fun, too|url=https://www.sciencedaily.com/releases/2015/02/150210212044.htm|access-date=26 July 2020|website=ScienceDaily|language=en}}</ref> | |||
==Relationship with humans== | |||
===Danger to humans=== | ===Danger to humans=== | ||
{{Citations missing|section|date=June 2008}} | |||
{{Main|Crocodile attacks}} | {{Main|Crocodile attacks}} | ||
], Australia]] | |||
The larger ] of crocodiles are very dangerous to humans. The main danger that crocodiles pose is not their ability to run after a person but their ability to strike before the person can react. The ] and ]s are the most dangerous, killing hundreds of people each year in parts of ] and ]. ]s and possibly the endangered ] are also very dangerous to humans. ]s are less aggressive and rarely assault humans without provocation. | |||
The larger species of crocodiles are very dangerous to humans, mainly because of their ability to strike before the person can react.<ref name=iucncsg>{{cite web|title=Crocodilian Attacks|url=http://www.iucncsg.org/pages/Crocodilian-Attacks.html|publisher=IUCN Crocodile Specialist Group (iucncsg.org)|access-date=3 February 2013}}</ref> The ] and ] are the most dangerous, killing hundreds of people each year in parts of Southeast Asia and Africa. The ] and ] are also dangerous to humans.{{citation needed|date=August 2023}} | |||
The most deaths in a single crocodile attack incident may have occurred during the ], on February 19, 1945, in ]. Nine hundred soldiers of an ] unit, in an attempt to retreat from the ] and rejoin a larger battalion of the Japanese ], crossed through {{convert|16|km|mi}} of ]s which contained Saltwater Crocodiles. Twenty Japanese soldiers were captured alive by the ], and almost five hundred are known to have escaped Ramree. Many of the remainder may have been eaten by the crocodiles, although gunfire from the British troops was undoubtedly a contributory factor.{{Citation needed|date=December 2008}}. | |||
===Crocodile products=== | ===Crocodile products=== | ||
{{ |
{{Further|Crocodile farm|Crocodile skin}} | ||
] | ] crocodile farm]] | ||
] in ], Finland]] | |||
Crocodiles are protected in many parts of the world, but are also farmed commercially. Their hides are tanned and used to make leather goods such as shoes and ]s; crocodile meat is also considered a delicacy.<ref>{{cite news |url=https://www.nytimes.com/1998/11/30/us/anahuac-journal-alligator-farmer-feeds-demand-for-all-the-parts.html |title=Anahuac Journal; Alligator Farmer Feeds Demand for All the Parts |work=The New York Times |date=30 November 1998 |last=Lyman |first=Rick |access-date=13 November 2013}}</ref> The most commonly farmed species are the saltwater and Nile crocodiles, while a hybrid of the saltwater and the rare ] is also bred in Asian farms. Farming has resulted in an increase in the saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve their habitat. Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags, belts, hats, and shoes. ] has been used for various purposes.<ref>{{cite book|author=Elisabeth Janos|title=Country Folk Medicine: Tales of Skunk Oil, Sassafras Tea and Other Old-Time Remedies|url=https://books.google.com/books?id=FUaaDBFsYFEC&pg=PA56|year=2004|publisher=Globe Pequot Press|isbn=978-1-59228-178-7|page=56}}</ref> ] while they were taboo and off limits for Chinese. Vietnamese women who married Chinese men adopted the Chinese taboo.<ref name="Peters2012">{{cite book |author=Erica J. Peters |title=Appetites and Aspirations in Vietnam: Food and Drink in the Long Nineteenth Century |url=https://books.google.com/books?id=o_P1ig12re4C&pg=PA142 |year=2012 |publisher=Rowman Altamira |isbn=978-0-7591-2075-4 |pages=142–}}</ref> | |||
Crocodile meat is consumed in some countries, such as Australia, ], Thailand, South Africa, China, and Cuba (in pickled form). It is also occasionally eaten as an "exotic" delicacy in the western world.<ref>{{cite news| last1=Armstrong| first1=Hilary|title=Best exotic restaurants in London|url=https://www.standard.co.uk/goingout/restaurants/best-exotic-restaurants-in-london-6863561.html|newspaper=]|access-date=4 September 2016|date=8 April 2009}}</ref> Cuts of meat include backstrap and tail fillet.{{citation needed|date=August 2023}} | |||
Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags, belts, hats, and shoes. | |||
Due to high demand for crocodile products, ] states that 1,418,487 Nile Crocodile skins were exported from Africa between 2006 and 2015.<ref>{{Cite web|url=https://www.traffic.org/what-we-do/species/reptiles-and-amphibians/|title=Reptiles and amphibians – Species we work with at TRAFFIC|website=www.traffic.org|access-date=10 January 2019}}</ref> | |||
Crocodile meat is consumed in some countries, such as Australia, Ethiopia, Thailand, South Africa and also Cuba (in pickled form); it can also be found in specialty restaurants in some parts of the United States. The meat is white and its nutritional composition compares favourably with that of other meats{{Citation needed|date=August 2008}}. It tends to have a slightly higher cholesterol level than other meats{{Citation needed|date=August 2008}}. Crocodile meat has a delicate flavour; some describe it as a cross between chicken and crab{{Citation needed|date=August 2008}}. Cuts of meat include backstrap and tail fillet. | |||
==={{anchor|hunting}}<!---redirect targets this anchor - do not remove--->Crocodile hunting and conservation=== | |||
] harvested eggs and hunted crocodiles in a sustainable way for many thousands of years. The ] (aka Marrithiyal) of the ] in the ] (NT) used ]s and ], and even their own hands to capture crocodiles for food.<ref name=mash>{{cite web | last=Ryall | first=Jenni | title=Incredible video shows how crocodiles were hunted in Australia in 1949 |format=text + video, 10m.| website=] | date=29 October 2021 | url=https://mashable.com/article/crocodile-hunters-australia | access-date=29 August 2023}}</ref> After settlement of northern Australia, in the late-19th and early 20th centuries, non-] people killed individual crocodiles, mostly by locals to protect the population, or novelty-seeking visitors, or just opportunistically, so numbers were not noticeably reduced. From the 1930s, commercial hunting began, with Aboriginal people often employed to kill the crocodiles using traditional methods. From the 1940s to the 1960s, hunting began on a larger scale using ]s.<ref name=qha>{{cite web | title=Crocodile hunting | website=Queensland Historical Atlas | date=21 August 2013 | url=https://www.qhatlas.com.au/crocodile-hunting | access-date=29 August 2023}}</ref> They were hunted for leather, with the skins shipped to plants in capital cities.<ref name=mash/> ] banned hunting freshwater crocodiles in 1962 and saltwater crocodiles in 1970, while NT bans were brought in 1964 and 1971; ] did not pass such legislation. The federal government later banned the export of crocodile skins, which brought commercial hunting to an end in Queensland.<ref name=qha/> They have been a ] since the 1970s, when numbers were down to approximately 3,000 in the NT at the lowest estimate. In 2021, after several attacks on humans by the "salties" and an estimated population of around 200,000 had been reached, Queensland politician ] called for the reintroduction of hunting.<ref name= vidler2021>{{cite web | last=Vidler | first=Adam | title=With more big crocs than ever, should hunting be allowed? | website=] | date=29 March 2021 | url=https://www.9news.com.au/national/crocodile-populations-rising-protected-hunting-bob-katter/023d28c2-ee46-436c-a790-a5c952efe160 | access-date=29 August 2023}}</ref> | |||
===In religion and mythology=== | |||
{{Further|Crocodilia#Cultural depictions}} | |||
] from the mortuary temple of ] {{circa}} 1810 BC. ], Oxford.]] | |||
] | |||
Crocodiles have appeared in various forms in religions across the world. ] had ], the crocodile-headed god, with his cult-city ], as well as ], the goddess of childbirth and fertility, with the back and tail of a crocodile.<ref>{{cite web|url=http://www.touregypt.net/featurestories/sobek.htm|title=Egypt: The Crocodile God, Sobek|publisher=Tour Egypt|author=Catherine C. Harris}}</ref> The ], Nigeria is dedicated to crocodiles in thanks for their aid during migration.<ref>{{cite news|url=http://allafrica.com/stories/200906240052.html|title=Nigeria: How Giant Crocodiles Guided Jukun to Kwararafa|work=All Africa|author=Fidelis Mac-Leva}} 24 June 2009</ref> In ] various peoples such as the ] and ] see crocodiles as ancestor spirits and under local '']'' often offer them food;<ref name="Campbell, Gwyn 2012">Campbell, Gwyn (2012). David Griffiths and the Missionary "History of Madagascar". Leiden, The Netherlands: Brill. {{ISBN|978-90-04-19518-9}}.</ref><ref>Marty Crump, Livros no Google Play | |||
Eye of Newt and Toe of Frog, Adder's Fork and Lizard's Leg: The Lore and Mythology of Amphibians and Reptiles, University of Chicago Press, 16 November 2015</ref> in the case of the latter at least a crocodile features prominently as an ancestor deity.<ref name="Campbell, Gwyn 2012"/><ref>An '']'' article of a specific crocodile deity named textually as "Jacaret", but less biased sources do not mention this theonym in any capacity.</ref> | |||
Crocodiles appear in different forms in ]. ], a ] and Hindu god, rides a part-crocodile ]; his consort ] rides a crocodile.<ref name="One" /> Similarly the goddess personifications of the ] and ] rivers are often depicted as riding crocodiles.<ref>{{cite web | title = Holy Rivers, Lakes, and Oceans | work = Heart of Hinduism | publisher = ISKCON Educational Services | year = 2004 | url = http://hinduism.iskcon.org/practice/504.htm | quote = Most rivers are considered female and are personified as goddesses. Ganga, who features in the Mahabharata, is usually shown riding on a crocodile (see right). | access-date = 16 September 2014 | archive-url = https://web.archive.org/web/20141014184216/http://hinduism.iskcon.org/practice/504.htm | archive-date = 14 October 2014 | url-status = dead}}</ref><ref>{{cite web | title = Ganga The River Goddess – Tales in Art and Mythology | date = August 2003 | first = Nitin | last = Kumar | url = http://www.exoticindiaart.com/article/ganga/ | quote = The second distinguishing aspect of Ganga's iconography is her animal mount, which is often shown serving as a pedestal for her. This is the makara, a hybrid creature having the body of a crocodile and the tail of a fish. The makara in Hindu thought corresponds to the star sign of Capricorn in western astrology. The crocodile is a unique animal in that it can live on both land and sea. It thus denotes the wisdom of both the earth and waters.}}</ref><ref>{{cite web | title = Hindu gods and their holy mounts | publisher = Sri.Venkateswara Zoological Park | url = http://svzoo.org/html/anicult2.htm | quote = The river goddesses, Ganga and Yamuna, were appropriately mounted on a tortoise and a crocodile respectively. | url-status = dead | archive-url = https://web.archive.org/web/20140623165912/http://svzoo.org/html/anicult2.htm | archive-date = 23 June 2014}}</ref> Also in India, in ], crocodile worship is practised, including the annual ''Mannge Thapnee'' ceremony.<ref>{{cite journal |author=<!--unclear. possibly L. Rattanani because blurb may be except from India Today Magazine, 15 January 1995, page 23--> |title=The Crocodile is God in Goa |journal=Crocodile Specialist Group Newsletter |date=January–March 1995 |volume=14 |issue=1 |page=8 |url=http://www.iucncsg.org/365_docs/attachments/protarea/CSG%20-96e3654b.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.iucncsg.org/365_docs/attachments/protarea/CSG%20-96e3654b.pdf |archive-date=2022-10-09 |url-status=live }}</ref> | |||
] warriors known as ] also have connections with crocodiles. ''Nihang'' may come from the Persian word for a mythical sea creature ({{langx|fa|نهنگ}}).<ref>{{cite book | last=Taba| first= David| year=2011| title= Iranian Character of The Armenian Language | page=9}}</ref> The term owes its origin to ] historians, who compared the ferocity of the Akali with that of crocodiles.<ref>{{cite web | title=Explainer Nihang Sikh sect in spotlight again after Singhu killing | website=The Federal | date=15 October 2021 | url=https://thefederal.com/videos/explainers/explainer-nihang-sikh-sect-in-spotlight-again-after-singhu-killing/ | access-date=29 August 2023}}</ref><ref>{{cite web | title=The Nihang | website=Sikh Heritage | url=http://www.sikh-heritage.co.uk/movements/Nihangs/Nihangs.htm | access-date=29 August 2023}}</ref> The meaning of Akali in ] however, is the immortal army of Akal (god).<ref>{{cite book | last=Singh | first=Khushwant | year=1999 | title=A History of the Sikhs Voghzlume I:1469–1839 | publisher=Oxford University Press | location=India | isbn = 0-19-562643-5 | page=215}}</ref> | |||
In Latin America, ] was the giant earth crocodile of the ] and other ].{{citation needed|date=September 2021}} | |||
] | |||
The name of ], Indonesia, is locally believed to be derived from the words "''suro"'' (]) and "''boyo"'' (crocodile), two creatures which, in a local ], fought each other in order to gain the title of "the strongest and most powerful animal" in the area. It was said that the two powerful animals agreed for a truce and set boundaries; that the shark's domain would be in the sea while the crocodile's domain would be on the land. However one day the shark swam into the river estuary to hunt, this angered the crocodile, who declared it his territory. The Shark argued that the river was a water-realm which meant that it was shark territory, while the crocodile argued that the river flowed deep inland, so it was therefore crocodile territory. A ferocious fight resumed as the two animals bit each other. Finally the shark was badly bitten and fled to the open sea, and the crocodile finally ruled the estuarine area that today is the city.<ref name="Irwan Rouf & Shenia Ananda 60">{{cite book|author1=Irwan Rouf|author2=Shenia Ananda|title=Rangkuman 100 Cerita Rakyat Indonesia: Dari Sabang Sampai Merauke|url=https://books.google.com/books?id=cPJqcwuSOUkC&pg=PA64| year=2013| publisher=AnakKita |isbn=978-602-9003-82-6 |page=60}}</ref> Another source alludes to a ] prophecy—a 12th-century psychic king of ]—as he foresaw a fight between a giant ] and a giant white crocodile taking place in the area, which is sometimes interpreted as a foretelling of the ], a major conflict between the forces of the ], ] ruler of ], and those of ]'s ] in 1293.<ref name="EastJava">{{cite web|title=Welcome to Surabaya City, East Java|publisher=Surabaya Tourism, EastJava.com| url=http://www.eastjava.com/tourism/surabaya/|access-date=17 November 2014}}</ref> The two animals are now used as the city's symbol, with the two facing and circling each other, as depicted in a statue appropriately located near the entrance to the ] (see photo on the ] page).{{citation needed|date=August 2023}} | |||
===In language and as symbols=== | |||
] depicting Roman Catholic bishops as crocodiles attacking public schools, with the connivance of Irish Catholic politicians]] | |||
{{Main|Crocodile tears}} | |||
The term "]" (and equivalents in other languages) refers to a false, insincere display of emotion, such as a ] crying fake tears of ]. It is derived from an ancient anecdote that crocodiles weep in order to lure their prey, or that they ] for the victims they are eating, first told in the '']'' by ].<ref>{{cite book |title=Bibliothèque. Tome VIII : Codices 257–280. |last=PHOTIUS |others=Texte établi et traduit par R. Henry. |year=1977 |publisher=Les Belles Lettres |location=Paris |language=fr, grc |isbn=978-2-251-32227-8 |page=93 }}</ref> The story is repeated in bestiaries such as ]. This tale was first spread widely in English in the stories of the ''Travels of ]'' in the 14th century, and appears in several of ]'s plays.<ref>{{cite book |url=https://books.google.com/books?id=8-KxOZWvNdgC&pg=PT185 |title=Curious creatures in zoology |author=John Ashton |isbn=978-1-4092-3184-4 |year=2009}}</ref> In fact, crocodiles can and do generate tears, but they do not actually cry.<ref> ''Crocodilian Biology Database''. Retrieved 13 March 2006 from the Crocodile Specialist Group, Crocodile Species List, FAQ.</ref> | |||
In the UK, a row of ] walking in pairs, or two by two is known as "crocodile".<ref>Martin H. Manser, Turton and Nigel D. Turton {{Google books|DXHJ1ylVHnYC|Advanced Learner's Dictionary|page=164}}</ref><ref>Angela Brazil {{Google books|mmtGAgAAQBAJ|The Nicest Girl in the School|page=50}}</ref> | |||
===Fashion logos=== | |||
The French clothing company ] features a crocodile in its ]. The American shoe company ] also uses this imagery in its logo.<ref>{{Cite web |last=Sandu |first=Bogdan |date=2023-09-25 |title=The Crocs Logo History, Colors, Font, and Meaning |url=https://www.designyourway.net/blog/crocs-logo/ |access-date=2024-10-29 |website=Design Your Way |language=en-US}}</ref> | |||
==See also== | ==See also== | ||
{{Portal|Reptiles}} | |||
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*] | *] | ||
*'']'' <!--scope here for a section on Crocodiles in film & literature in the relations with humans section--><!--more at ]--> | |||
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*] – an ancient Egyptian deity associated with the Nile crocodile | |||
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==References== | ==References== | ||
{{ |
{{Reflist|30em}} | ||
==Further reading== | ==Further reading== | ||
* Iskandar, DT (2000). ''Turtles and Crocodiles of Insular Southeast Asia and New Guinea''. ITB, Bandung. | * Iskandar, DT (2000). ''Turtles and Crocodiles of Insular Southeast Asia and New Guinea''. ITB, Bandung. | ||
* Crocodilian Biology Database, FAQ. {{sic}} Adam Britton. | * Crocodilian Biology Database, FAQ. , "How long do crocodiles live for?" {{sic}} Adam Britton. | ||
* Crocodilian Biology Database, FAQ. Adam Britton. | * Crocodilian Biology Database, FAQ. , "How fast can a crocodile run?" Adam Britton. | ||
==External links== | ==External links== | ||
{{wiktionary}} | |||
{{Wikispecies|Crocodilia}} | |||
{{Wikispecies|Crocodylidae}} | |||
{{commons|Crocodilia}} | |||
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* {{Webarchive|url=https://web.archive.org/web/20110708204615/http://www.crocodilian.com/ |date=8 July 2011 }} | |||
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Latest revision as of 11:23, 24 December 2024
Family of large reptilian carnivores For other uses, see Crocodile (disambiguation).
Crocodiles Temporal range: Eocene–Holocene, 46–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N | |
---|---|
Nile crocodile (Crocodylus niloticus) | |
Saltwater crocodile (Crocodylus porosus) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha |
Clade: | Archosauriformes |
Order: | Crocodilia |
Superfamily: | Crocodyloidea |
Family: | Crocodylidae Cuvier, 1807 |
Type genus | |
Crocodylus Laurenti, 1768 | |
Subfamilies | |
Crocodiles (family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live 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.
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.
Crocodile size, morphology, behaviour and ecology differ somewhat 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. They separated from other crocodilians during the Eocene epoch, about 55 million years ago. Many species are at the risk of extinction, some being classified as critically endangered.
Etymology
The word crocodile comes from Ancient Greek κροκόδιλος (krokódilos) '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 krokódeilos (κροκόδειλος) found cited in many English reference works. In the Koine Greek of Roman times, krokodilos and krokodeilos would have been pronounced identically, and either or both may be the source of the Latinized form crocodīlus used by the ancient Romans. It has been suggested, but it is not certain that the word crocodilos or crocodeilos is a compound of krokè ('pebbles'), and drilos/dreilos ('worm'), although drilos is only attested as a colloquial term for 'penis'. It is ascribed to Herodotus, and supposedly describes the basking habits of the Egyptian crocodile.
The form crocodrillus is attested in Medieval Latin. It is not clear whether this is a medieval corruption or derives from alternative 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).
Taxonomy and phylogeny
See also: List of crocodiliansCrocodylidae 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.
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 palustris, mugger, marsh or Indian crocodile
- Crocodylus porosus, saltwater crocodile or estuarine crocodile
- Crocodylus raninus, the Borneo crocodile, is currently considered to be a synonym of Crocodylus porosus; whether or not it is a distinct species remains unclear.
- 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)
- Genus Crocodylus
- Subfamily Osteolaeminae
- Genus Osteolaemus
- Osteolaemus tetraspis, dwarf crocodile (There has been controversy as to whether or not this is actually two species; recent (2010) DNA analysis indicate three distinct species: O. tetraspis, O. osborni and a third, currently unnamed.)
- Genus Mecistops
- Genus Brochuchus†
- Brochuchus pigotti† (formerly Crocodylus pigotti)
- Brochuchus parvidens†
- Genus Euthecodon†
- Genus Rimasuchus†
- Rimasuchus lloydi† (formerly Crocodylus lloydi)
- Genus Osteolaemus
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:
Crocodilia |
| ||||||||||||||||||||||||||||||||||||||||||||||||
Below is a more detailed cladogram of Crocodylidae, based on a 2021 study using paleogenomics that extracted DNA from the extinct Voay.
Crocodylidae |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
(crown group) |
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.
Crocodylidae |
|
Paleoafrican CrocodylusNeotropical CrocodylusIndo-Pacific Crocodylus | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 name | Image | Distribution | Description/Comments |
---|---|---|---|
American crocodile (Crocodylus acutus) | 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 (Crocodylus halli) | The island of New Guinea, south of the New Guinea Highlands | A 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 (Crocodylus intermedius) | Colombia and Venezuela | This 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 (Crocodylus johnstoni) | Northern Australia | A 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 (Crocodylus mindorensis) | Endemic to the Philippines | This 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 (Crocodylus moreletii) | Atlantic regions of Mexico, Belize and Guatemala | A 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 (Crocodylus niloticus) | Sub-saharan Africa | A 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 (Crocodylus novaeguineae) | The island of New Guinea, north of the New Guinea Highlands | A smaller species of crocodile with a grey-brown colour and dark brown to black markings on the tail. The young have a narrower V-shaped snout that becomes wider as the animal matures. Prefers freshwater habitats, even though is tolerant to salt water, in order to avoid competition and predation by the saltwater crocodile. This species feeds on small to mid-sized vertebrates. | |
Mugger crocodile (Crocodylus palustris) | The Indian subcontinent and surrounding countries | This 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 (Crocodylus porosus) | Throughout Southeast Asia, Northern Australia and surrounding waters | The largest 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 (Crocodylus raninus) | Island of Borneo in Southeast Asia | A freshwater species of crocodile that has been considered a synonym of the saltwater crocodile. | |
Cuban crocodile (Crocodylus rhombifer) | Found only in the Zapata Swamp and Isle of Youth of Cuba | It 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 (Crocodylus siamensis) | Indonesia, Brunei, East Malaysia and southern Indochina | A 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 (Crocodylus suchus) | Western and Central Africa | Recent 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 (Osteolaemus osborni) | Western Africa | 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. | |
Dwarf crocodile (Osteolaemus tetraspis) | Western Africa | It 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 (Mecistops cataphractus) | Western Africa | A 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 (Mecistops leptorhynchus) | Central Africa | A 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. |
Characteristics
Crocodiles are similar to alligators and caimans; for their common characteristics and differences among them, see Crocodilia.A crocodile's physical traits allow it to be a successful predator. Its external morphology is a sign of its aquatic and predatory lifestyle. Its streamlined body enables it to swim swiftly; it also tucks its feet to the side while swimming, making it faster by decreasing water resistance. Crocodiles have webbed feet which, though not used to propel them through the water, allow them to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallow water, where the animals sometimes move 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. Crocodiles have smooth skin on their bellies and sides, while their dorsal surfaces are armoured with large osteoderms. The armoured skin has scales and is thick and rugged, providing some protection. They are still able to absorb heat through this armour, as a network of small capillaries allows blood through the scales to absorb heat. The osteoderms are highly vascularised and aid in calcium balance, both to neutralize acids while the animal cannot breathe underwater and to provide calcium for eggshell formation. Crocodilian tegument 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.
Size
Size greatly varies among species, from the dwarf crocodile to the saltwater crocodile. Species of the dwarf crocodile Osteolaemus grow to an adult size of just 1.5 to 1.9 m (4.9 to 6.2 ft), whereas the saltwater crocodile can grow to sizes over 6 m (20 ft) and weigh over 1,000 kg (2,200 lb). Several other large species can reach over 5.2 m (17 ft) long and weigh over 900 kg (2,000 lb). Crocodilians show pronounced sexual dimorphism, with males growing much larger and more rapidly than females. Despite their large adult sizes, crocodiles start their lives at around 20 cm (7.9 in) long. The largest species of crocodile is the saltwater crocodile, found in eastern India, northern Australia, throughout South-east Asia, and in the surrounding waters.
The brain volume of two adult crocodiles was 5.6 cm for a spectacled caiman and 8.5 cm for a larger Nile crocodile.
The largest crocodile ever held in captivity is a saltwater–Siamese hybrid named Yai (Thai: ใหญ่, meaning big; born 10 June 1972) at the Samutprakarn Crocodile Farm and Zoo, Thailand. This animal measures 6 m (20 ft) in length and weighs 1,200 kg (2,600 lb).
The longest crocodile captured alive was Lolong, a saltwater crocodile which was measured at 6.17 m (20.2 ft) and weighed at 1,075 kg (2,370 lb) by a National Geographic team in Agusan del Sur Province, Philippines.
Teeth
Crocodiles are polyphyodonts; they are able to replace each of their 80 teeth up to 50 times in their 35- to 75-year lifespan. Next to each full-grown tooth, there is a small replacement tooth and an odontogenic stem cell in the dental lamina in standby that can be activated if required.
Biology and behaviour
Crocodilians are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three families being included in the group Archosauria ('ruling reptiles'). Despite their prehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles, a crocodile has a cerebral cortex and a four-chambered heart. Crocodilians also have the functional equivalent of a diaphragm by incorporating muscles used for aquatic locomotion into respiration. Salt glands are present in the tongues of crocodiles and they have a pore opening on the surface of the tongue, a trait that separates them from alligators. Salt glands are dysfunctional in Alligatoridae. Their function appears to be similar to that of salt glands in marine turtles. Crocodiles do not have sweat glands and release heat through their mouths. They often sleep with their mouths open and may pant like a dog. Four species of freshwater crocodile climb trees to bask in areas lacking a shoreline.
Senses
Crocodiles have acute senses, an evolutionary advantage that makes them successful predators. The eyes, ears and nostrils are located on top of the head, allowing the crocodile to lie low in the water, almost totally submerged and hidden from prey.
Vision
Crocodiles have very good night vision, and are mostly nocturnal hunters. They use the disadvantage of most prey animals' poor nocturnal vision to their advantage. The light receptors in crocodilians' eyes include cones and numerous rods, so it is assumed all crocodilians can see colours. Crocodiles have vertical-slit shaped pupils, similar to those of domestic cats. One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight. On the rear wall of the eye is a tapetum lucidum, which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage. In addition to the protection of the upper and lower eyelids, crocodiles have a nictitating membrane (sometimes called a "third eye-lid") that can be drawn over the eye from the inner corner while the lids are open. The eyeball surface is thus protected under the water while a certain degree of vision is still possible.
Olfaction
Crocodilian sense of smell is also very well developed, aiding them to detect prey or animal carcasses that are either on land or in water, from far away. It is possible that crocodiles use olfaction in the egg prior to hatching.
Chemoreception in crocodiles is especially interesting because they hunt in both terrestrial and aquatic surroundings. Crocodiles have only one olfactory chamber and the vomeronasal organ is absent in the adults indicating all olfactory perception is limited to the olfactory system. Behavioural and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. When above water, crocodiles enhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of the floor of the pharynx. Crocodiles close their nostrils when submerged, so olfaction underwater is unlikely. Underwater food detection is presumably gustatory and tactile.
Hearing
Crocodiles can hear well; their tympanic membranes are concealed by flat flaps that may be raised or lowered by muscles.
Touch
The touch sensors, concentrated in crocodile skin, can be thicker than those in human fingerprints. Crocodiles can feel the touch on their skin.
Cranial: The upper and lower jaws are covered with sensory pits, visible as small, black speckles on the skin, the crocodilian version of the lateral line organs seen in fish and many amphibians, though arising from a completely different origin. These pigmented nodules encase bundles of nerve fibers innervated beneath by branches of the trigeminal nerve. They respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes as small as a single drop. This makes it possible for crocodiles to detect prey, danger and intruders, even in total darkness. These sense organs are known as domed pressure receptors (DPRs).
Post-Cranial: While alligators and caimans have DPRs only on their jaws, crocodiles have similar organs on almost every scale on their bodies. The function of the DPRs on the jaws is clear; to catch prey, but it is still not clear what the function is of the organs on the rest of the body. The receptors flatten when exposed to increased osmotic pressure, such as that experienced when swimming in sea water hyperosmotic to the body fluids. When contact between the integument and the surrounding sea water solution is blocked, crocodiles are found to lose their ability to discriminate salinities. It has been proposed that the flattening of the sensory organ in hyperosmotic sea water is sensed by the animal as "touch", but interpreted as chemical information about its surroundings. This might be why in alligators they are absent on the rest of the body.
Hunting and diet
Crocodiles are ambush predators, waiting for fish or land animals to come close, then rushing out to attack. Crocodiles mostly eat fish, amphibians, crustaceans, molluscs, birds, reptiles, and mammals, and they occasionally cannibalize smaller crocodiles. What a crocodile eats varies greatly with species, size and age. From the mostly fish-eating species, like the slender-snouted and freshwater crocodiles, to the larger species like the Nile crocodile and the saltwater crocodile that prey on large mammals, such as buffalo, deer and wild boar, diet shows great diversity. Diet is also greatly affected by the size and age of the individual within the same species. All young crocodiles hunt mostly invertebrates and small fish, gradually moving on to larger prey. Being ectothermic (cold-blooded) predators, they have a very slow metabolism, so they can survive long periods without food. Despite their appearance of being slow, crocodiles have a very fast strike and are top predators in their environment, and various species have been observed attacking and killing other predators such as sharks and big cats. Crocodiles are also known to be aggressive scavengers who feed upon carrion and steal from other predators. Evidence suggests that crocodiles also feed upon fruits, based on the discovery of seeds in stools and stomachs from many subjects as well as accounts of them feeding.
Crocodiles have the most acidic stomach of any vertebrate. They can easily digest bones, hooves and horns. The BBC TV reported that a Nile crocodile that has lurked a long time underwater to catch prey builds up a large oxygen debt. When it has caught and eaten that prey, it closes its right aortic arch and uses its left aortic arch to flush blood loaded with carbon dioxide from its muscles directly to its stomach; the resulting excess acidity in its blood supply makes it much easier for the stomach lining to secrete more stomach acid to quickly dissolve bulks of swallowed prey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomach stones), which may act as ballast to balance their bodies or assist in crushing food, similar to grit ingested by birds. Herodotus claimed that Nile crocodiles had a symbiotic relationship with certain birds, such as the Egyptian plover, which enter the crocodile's mouth and pick leeches feeding on the crocodile's blood; with no evidence of this interaction actually occurring in any crocodile species, it is most likely mythical or allegorical fiction.
Bite
Since they feed by grabbing and holding onto their prey, they have evolved sharp teeth for piercing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. The teeth are not well-suited to tearing flesh off of large prey items as are the dentition and claws of many mammalian carnivores, the hooked bills and talons of raptorial birds, or the serrated teeth of sharks. However, this is an advantage rather than a disadvantage to the crocodile since the properties of the teeth allow it to hold onto prey with the least possibility of the prey animal escaping. Cutting teeth, combined with the exceptionally high bite force, would pass through flesh easily enough to leave an escape opportunity for prey. The jaws can bite down with immense force, by far the strongest bite of any animal. The force of a large crocodile's bite is more than 5,000 lbf (22,000 N), which was measured in a 5.5 m (18 ft) Nile crocodile, in the field; comparing to 335 lbf (1,490 N) for a Rottweiler, 800 lbf (3,600 N) for a hyena, 2,200 lbf (9,800 N) for an American alligator, and 4,095 lbf (18,220 N) for the largest confirmed great white shark.
A 5.2 m (17 ft) long saltwater crocodile has been confirmed as having the strongest bite force ever recorded for an animal in a laboratory setting. It was able to apply a bite force value of 3,700 lbf (16,000 N), and thus surpassed the previous record of 2,125 lbf (9,450 N) made by a 3.9 m (13 ft) long American alligator. Taking the measurements of several 5.2 m (17 ft) crocodiles as reference, the bite forces of 6-m individuals were estimated at 7,700 lbf (34,000 N). The study, led by Dr. Gregory M. Erickson, also shed light on the larger, extinct species of crocodilians. Since crocodile anatomy has changed only slightly over the last 80 million years, current data on modern crocodilians can be used to estimate the bite force of extinct species. An 11-to-12-metre (36–39 ft) Deinosuchus would apply a force of 23,100 lbf (103,000 N), nearly twice that of the latest, higher bite force estimations of Tyrannosaurus (12,814 lbf (57,000 N)). The extraordinary bite of crocodilians is a result of their anatomy. The space for the jaw muscle in the skull is very large, which is easily visible from the outside as a bulge at each side. The muscle is so stiff, it is almost as hard as bone to touch, as if it were the continuum of the skull. Another trait is that most of the muscle in a crocodile's jaw is arranged for clamping down. Despite the strong muscles to close the jaw, crocodiles have extremely small and weak muscles to open the jaw. 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.
Locomotion
Crocodiles can move quickly over short distances, even out of water. The land speed record for a crocodile is 17 km/h (11 mph) measured in a galloping Australian freshwater crocodile. Maximum speed varies between species. Some species can gallop, including Cuban crocodiles, Johnston's crocodiles, New Guinea crocodiles, African dwarf crocodiles, and even small Nile crocodiles. The fastest means by which most species can move is a "belly run", in which the body moves in a snake-like (sinusoidal) fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of 10–11 km/h (6–7 mph) when they "belly run", and often faster if slipping down muddy riverbanks. When a crocodile walks quickly, it holds its legs in a straighter and more upright position under its body, which is called the "high walk". This walk allows a speed of up to 5 km/h.
Crocodiles may possess a homing instinct. In northern Australia, three rogue saltwater crocodiles were relocated 400 km (249 mi) by helicopter, but returned to their original locations within three weeks, based on data obtained from tracking devices attached to them.
Longevity
Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons. Bearing these inaccuracies in mind, it can be safely said that all crocodile species have an average lifespan of at least 30–40 years, and in the case of larger species an average of 60–70 years. The oldest crocodiles appear to be the largest species. C. porosus is estimated to live around 70 years on average, with limited evidence of some individuals exceeding 100 years.
In captivity, some individuals are claimed to have lived for over a century. A male crocodile lived to an estimated age of 110–115 years in a Russian zoo in Yekaterinburg. Named Kolya, he joined the zoo around 1913 to 1915, fully grown, after touring in an animal show, and lived until 1995. A male freshwater crocodile lived to an estimated age of 120–140 years at the Australia Zoo. Known affectionately as "Mr. Freshie", he was rescued around 1970 by Bob Irwin and Steve Irwin, after being shot twice by hunters and losing an eye as a result, and lived until 2010. Crocworld Conservation Centre, in Scottburgh, South Africa, claims to have a male Nile crocodile that was born in 1900. Named Henry, the crocodile is said to have lived in Botswana along the Okavango River, according to centre director Martin Rodrigues.
Social behaviour and vocalization
Crocodiles are the most social of reptiles. Even though they do not form social groups, many species congregate in certain sections of rivers, tolerating each other at times of feeding and basking. Most species are not highly territorial, with the exception of the saltwater crocodile, which is a highly territorial and aggressive species: a mature, male saltwater crocodile will not tolerate any other males at any time of the year, but most other species are more flexible. There is a certain form of hierarchy in crocodiles: the largest and heaviest males are at the top, having access to the best basking site, while females are priority during a group feeding of a big kill or carcass. A good example of the hierarchy in crocodiles would be the case of the Nile crocodile. This species clearly displays all of these behaviours. Studies in this area are not thorough, however, and many species are yet to be studied in greater detail. Mugger crocodiles are also known to show toleration in group feedings and tend to congregate in certain areas. However, males of all species are aggressive towards each other during mating season, to gain access to females.
Crocodiles are also the most vocal of all reptiles, producing a wide variety of sounds during various situations and conditions, depending on species, age, size and sex. Depending on the context, some species can communicate over 20 different messages through vocalizations alone. Some of these vocalizations are made during social communication, especially during territorial displays towards the same sex and courtship with the opposite sex; the common concern being reproduction. Therefore most conspecific vocalization is made during the breeding season, with the exception being year-round territorial behaviour in some species and quarrels during feeding. Crocodiles also produce different distress calls and in aggressive displays to their own kind and other animals; notably other predators during interspecific predatory confrontations over carcasses and terrestrial kills.
Specific vocalisations include —
- Chirp: When about to hatch, the young make a "peeping" noise, which encourages the female to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female
- Distress call: A high-pitched call used mostly by younger animals to alert other crocodiles to imminent danger or an animal being attacked.
- Threat call: A hissing sound that has also been described as a coughing noise.
- Hatching call: Emitted by a female when breeding to alert other crocodiles that she has laid eggs in her nest.
- Bellowing: Male crocodiles are especially vociferous. Bellowing choruses occur most often in the spring when breeding groups congregate, but can occur at any time of year. To bellow, males noticeably inflate as they raise the tail and head out of water, slowly waving the tail back and forth. They then puff out the throat and with a closed mouth, begin to vibrate air. Just before bellowing, males project an infrasonic signal at about 10 Hz through the water, which vibrates the ground and nearby objects. These low-frequency vibrations travel great distances through both air and water to advertise the male's presence and are so powerful they result in the water's appearing to "dance".
Reproduction
Crocodiles lay eggs, which are laid in either holes or mound nests, depending on species. A hole nest is usually excavated in sand and a mound nest is usually constructed out of vegetation. Nesting periods range from a few weeks up to six months. Courtship takes place in a series of behavioural interactions that include a variety of snout rubbing and submissive display that can take a long time. Mating always takes place in water, where the pair can be observed mating several times. Females can build or dig several trial nests which appear incomplete and abandoned later. Egg-laying usually takes place at night and about 30–40 minutes. Females are highly protective of their nests and young. The eggs are hard shelled, but translucent at the time of egg-laying. Depending on the species of crocodile, 7 to 95 eggs are laid. Crocodile embryos do not have sex chromosomes, and unlike humans, sex is not determined genetically. Sex is determined by temperature, where at 30 °C (86 °F) or less most hatchlings are females and at 31 °C (88 °F), offspring are of both sexes. A temperature of 32 to 33 °C (90 to 91 °F) gives mostly males whereas above 33 °C (91 °F) in some species continues to give males, but in other species resulting in females, which are sometimes called high-temperature females. Temperature also affects growth and survival rate of the young, which may explain the sexual dimorphism in crocodiles. The average incubation period is around 80 days, and also is dependent on temperature and species that usually ranges from 65 to 95 days. The eggshell structure is very conservative through evolution but there are enough changes to tell different species apart by their eggshell microstructure. Scutes may play a role in calcium storage for eggshell formation.
At the time of hatching, the young start calling within the eggs. They have an egg-tooth at the tip of their snouts, which is developed from the skin, and that helps them pierce out of the shell. Hearing the calls, the female usually excavates the nest and sometimes takes the unhatched eggs in her mouth, slowly rolling the eggs to help the process. The young is usually carried to the water in the mouth. She would then introduce her hatchlings to the water and even feed them. The mother would then take care of her young for over a year before the next mating season. In the absence of the mother crocodile, the father would act in her place to take care of the young. However, even with a sophisticated parental nurturing, young crocodiles have a very high mortality rate due to their vulnerability to predation. A group of hatchlings is called a pod or crèche and may be protected for months.
Cognition
Crocodiles possess some advanced cognitive abilities. They can observe and use patterns of prey behaviour, such as when prey come to the river to drink at the same time each day. Vladimir Dinets of the University of Tennessee, observed that crocodiles use twigs as bait for birds looking for nesting material. They place sticks on their snouts and partly submerge themselves. When the birds swooped in to get the sticks, the crocodiles then catch the birds. Crocodiles only do this in spring nesting seasons of the birds, when there is high demand for sticks to be used for building nests. Vladimir also discovered other similar observations from various scientists, some dating back to the 19th century. Aside from using sticks, crocodiles are also capable of cooperative hunting. Large numbers of crocodiles swim in circles to trap fish and take turns snatching them. In hunting larger prey, crocodiles swarm in, with one holding the prey down as the others rip it apart.
According to a 2015 study, crocodiles engage in all three main types of play behaviour recorded in animals: locomotor play, play with objects and social play. Play with objects is reported most often, but locomotor play such as repeatedly sliding down slopes, and social play such as riding on the backs of other crocodiles is also reported. This behaviour was exhibited with conspecifics and mammals and is apparently not uncommon, though has been difficult to observe and interpret in the past due to obvious dangers of interacting with large carnivores.
Relationship with humans
Danger to humans
Main article: Crocodile attacksThe larger species of crocodiles are very dangerous to humans, mainly because of their ability to strike before the person can react. The saltwater crocodile and Nile crocodile are the most dangerous, killing hundreds of people each year in parts of Southeast Asia and Africa. The mugger crocodile and American crocodile are also dangerous to humans.
Crocodile products
Further information: Crocodile farm and Crocodile skinCrocodiles are protected in many parts of the world, but are also farmed commercially. Their hides are tanned and used to make leather goods such as shoes and handbags; crocodile meat is also considered a delicacy. The most commonly farmed species are the saltwater and Nile crocodiles, while a hybrid of the saltwater and the rare Siamese crocodile is also bred in Asian farms. Farming has resulted in an increase in the saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve their habitat. Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags, belts, hats, and shoes. Crocodile oil has been used for various purposes. Crocodiles were eaten by Vietnamese while they were taboo and off limits for Chinese. Vietnamese women who married Chinese men adopted the Chinese taboo.
Crocodile meat is consumed in some countries, such as Australia, Ethiopia, Thailand, South Africa, China, and Cuba (in pickled form). It is also occasionally eaten as an "exotic" delicacy in the western world. Cuts of meat include backstrap and tail fillet.
Due to high demand for crocodile products, TRAFFIC states that 1,418,487 Nile Crocodile skins were exported from Africa between 2006 and 2015.
Crocodile hunting and conservation
Aboriginal Australians harvested eggs and hunted crocodiles in a sustainable way for many thousands of years. The Brinkin people (aka Marrithiyal) of the Daly River in the Northern Territory (NT) used harpoons and bamboo, and even their own hands to capture crocodiles for food. After settlement of northern Australia, in the late-19th and early 20th centuries, non-Indigenous people killed individual crocodiles, mostly by locals to protect the population, or novelty-seeking visitors, or just opportunistically, so numbers were not noticeably reduced. From the 1930s, commercial hunting began, with Aboriginal people often employed to kill the crocodiles using traditional methods. From the 1940s to the 1960s, hunting began on a larger scale using .303 rifles. They were hunted for leather, with the skins shipped to plants in capital cities. Western Australia banned hunting freshwater crocodiles in 1962 and saltwater crocodiles in 1970, while NT bans were brought in 1964 and 1971; Queensland did not pass such legislation. The federal government later banned the export of crocodile skins, which brought commercial hunting to an end in Queensland. They have been a protected species since the 1970s, when numbers were down to approximately 3,000 in the NT at the lowest estimate. In 2021, after several attacks on humans by the "salties" and an estimated population of around 200,000 had been reached, Queensland politician Bob Katter called for the reintroduction of hunting.
In religion and mythology
Further information: Crocodilia § Cultural depictionsCrocodiles have appeared in various forms in religions across the world. Ancient Egypt had Sobek, the crocodile-headed god, with his cult-city Crocodilopolis, as well as Taweret, the goddess of childbirth and fertility, with the back and tail of a crocodile. The Jukun shrine in the Wukari Federation, Nigeria is dedicated to crocodiles in thanks for their aid during migration. In Madagascar various peoples such as the Sakalava and Antandroy see crocodiles as ancestor spirits and under local fady often offer them food; in the case of the latter at least a crocodile features prominently as an ancestor deity.
Crocodiles appear in different forms in Hinduism. Varuna, a Vedic and Hindu god, rides a part-crocodile makara; his consort Varuni rides a crocodile. Similarly the goddess personifications of the Ganga and Yamuna rivers are often depicted as riding crocodiles. Also in India, in Goa, crocodile worship is practised, including the annual Mannge Thapnee ceremony.
Sikh warriors known as nihang also have connections with crocodiles. Nihang may come from the Persian word for a mythical sea creature (Persian: نهنگ). The term owes its origin to Mughal historians, who compared the ferocity of the Akali with that of crocodiles. The meaning of Akali in Sikhism however, is the immortal army of Akal (god).
In Latin America, Cipactli was the giant earth crocodile of the Aztec and other Nahua peoples.
The name of Surabaya, Indonesia, is locally believed to be derived from the words "suro" (shark) and "boyo" (crocodile), two creatures which, in a local myth, fought each other in order to gain the title of "the strongest and most powerful animal" in the area. It was said that the two powerful animals agreed for a truce and set boundaries; that the shark's domain would be in the sea while the crocodile's domain would be on the land. However one day the shark swam into the river estuary to hunt, this angered the crocodile, who declared it his territory. The Shark argued that the river was a water-realm which meant that it was shark territory, while the crocodile argued that the river flowed deep inland, so it was therefore crocodile territory. A ferocious fight resumed as the two animals bit each other. Finally the shark was badly bitten and fled to the open sea, and the crocodile finally ruled the estuarine area that today is the city. Another source alludes to a Jayabaya prophecy—a 12th-century psychic king of Kediri Kingdom—as he foresaw a fight between a giant white shark and a giant white crocodile taking place in the area, which is sometimes interpreted as a foretelling of the Mongol invasion of Java, a major conflict between the forces of the Kublai Khan, Mongol ruler of China, and those of Raden Wijaya's Majapahit in 1293. The two animals are now used as the city's symbol, with the two facing and circling each other, as depicted in a statue appropriately located near the entrance to the city zoo (see photo on the Surabaya page).
In language and as symbols
Main article: Crocodile tearsThe term "crocodile tears" (and equivalents in other languages) refers to a false, insincere display of emotion, such as a hypocrite crying fake tears of grief. It is derived from an ancient anecdote that crocodiles weep in order to lure their prey, or that they cry for the victims they are eating, first told in the Bibliotheca by Photios I of Constantinople. The story is repeated in bestiaries such as De bestiis et aliis rebus. This tale was first spread widely in English in the stories of the Travels of Sir John Mandeville in the 14th century, and appears in several of Shakespeare's plays. In fact, crocodiles can and do generate tears, but they do not actually cry.
In the UK, a row of schoolchildren walking in pairs, or two by two is known as "crocodile".
Fashion logos
The French clothing company Lacoste features a crocodile in its logo. The American shoe company Crocs also uses this imagery in its logo.
See also
- Alligator meat
- The Crocodile Hunter
- Crocodilian armor
- Game (hunting)
- Sewer alligator
- Sobek – an ancient Egyptian deity associated with the Nile crocodile
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- An Athenæum article makes a claim of a specific crocodile deity named textually as "Jacaret", but less biased sources do not mention this theonym in any capacity.
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Most rivers are considered female and are personified as goddesses. Ganga, who features in the Mahabharata, is usually shown riding on a crocodile (see right).
- Kumar, Nitin (August 2003). "Ganga The River Goddess – Tales in Art and Mythology".
The second distinguishing aspect of Ganga's iconography is her animal mount, which is often shown serving as a pedestal for her. This is the makara, a hybrid creature having the body of a crocodile and the tail of a fish. The makara in Hindu thought corresponds to the star sign of Capricorn in western astrology. The crocodile is a unique animal in that it can live on both land and sea. It thus denotes the wisdom of both the earth and waters.
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The river goddesses, Ganga and Yamuna, were appropriately mounted on a tortoise and a crocodile respectively.
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Further reading
- Iskandar, DT (2000). Turtles and Crocodiles of Insular Southeast Asia and New Guinea. ITB, Bandung.
- Crocodilian Biology Database, FAQ. FLMNH.ufl.edu, "How long do crocodiles live for?" [sic] Adam Britton.
- Crocodilian Biology Database, FAQ. FLMNH.ufl.edu, "How fast can a crocodile run?" Adam Britton.
External links
- Media related to Crocodile at Wikimedia Commons
- Crocodilian Online Archived 8 July 2011 at the Wayback Machine
- Crocodilian Biology Database
- Crocodile Attacks in Australia
- BBC news finds powerful agent in crocodile blood
- World's most expensive handbag sells in Hong Kong for over US$377,000 – a Hermès white crocodile (31 May 2017), South China Morning Post
- 292 New Guinea crocodiles massacred in West Papua, Indonesia
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