Reptiles that live in the sea:
 • Saltwater crocodile (top left)
 • Sea turtle (top right)
 • Marine iguana (bottom left)
 • Sea snake (bottom right)

Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment.

The earliest marine reptile was Mesosaurus (not to be confused with Mosasaurus), which arose in the Permian period of the Paleozoic era.[1] During the Mesozoic era, many groups of reptiles became adapted to life in the seas, including such familiar clades as the ichthyosaurs, plesiosaurs (these two orders were once thought united in the group "Enaliosauria",[2] a classification now cladistically obsolete), mosasaurs, nothosaurs, placodonts, sea turtles, thalattosaurs and thalattosuchians. Most marine reptile groups became extinct at the end of the Cretaceous period, but some still existed during the Cenozoic, most importantly the sea turtles. Other Cenozoic marine reptiles included the bothremydids,[3] palaeophiid snakes, a few choristoderes such as Simoedosaurus and dyrosaurid crocodylomorphs. Various types of marine gavialid crocodilians remained widespread as recently as the Late Miocene.[4]

Currently, of the approximately 12,000 extant reptile species and subspecies, only about 100 are classed as marine reptiles: extant marine reptiles include marine iguanas, sea snakes, sea turtles and saltwater crocodiles.[5]

Some marine reptiles, such as ichthyosaurs, plesiosaurs, metriorhynchid thalattosuchians, and mosasaurs became so well adapted to a marine lifestyle that they were incapable of venturing onto land and gave birth in the water. Others, such as sea turtles and saltwater crocodiles, return to shore to lay their eggs. Some marine reptiles also occasionally rest and bask on land.

Extant (living) varieties

Hawksbill sea turtle (Eretmochelys imbricata)

Extinct groups

Fossil of Ophthalmosaurus icenius, a species of ichthyosaur

Adaptation to the marine environment

See also: Physiology of underwater diving § Aquatic reptiles

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Most species of marine reptiles are considered endangered to some degree. All but one species of sea turtles are endangered due to destruction of nesting habitats on coastal lands, exploitation, and marine fishing;[6] many species of sea snakes are threatened or endangered due to commercial exploitation (sale of skins) and pollution especially in Asia; marine iguanas are threatened due to their very limited habitation range.[5] Saltwater crocodiles are at low risk for extinction.[9]

See also


  1. ^ Piñeiro, Graciela; Ferigolo, Jorge; Ramos, Alejandro; Laurin, Michel (1 July 2012). "Cranial morphology of the Early Permian mesosaurid Mesosaurus tenuidens and the evolution of the lower temporal fenestration reassessed". Comptes Rendus Palevol. 11 (5): 379–391. doi:10.1016/j.crpv.2012.02.001.
  2. ^ Williston SW (1914) Water Reptiles of the Past and Present University of Chicago Press (reprint 2002). ISBN 1-4021-4677-9
  3. ^ Carvalho, Anny Rafaela De Araújo; Ghilardi, Aline Marcele; Barreto, Alcina Magnólia Franca (21 June 2016). "A new side-neck turtle (Pelomedusoides: Bothremydidae) from the Early Paleocene (Danian) Maria Farinha Formation, Paraíba Basin, Brazil". Zootaxa. 4126 (4): 491–513. doi:10.11646/zootaxa.4126.4.3. PMID 27395602.
  4. ^ Langston, Wann; Gasparini, Z. (1997). "Crocodilians, Gryposuchus, and the South American gavials". In Kay, Richard F; Madden, Richard H; Cifelli, Richard L; Flynn, John J. (eds.). Vertebrate paleontology in the neotropics: the Miocene fauna of La Venta, Colombia. Smithsonian Institution Press. pp. 113–154. ISBN 978-1-56098-418-4.
  5. ^ a b c d e f Rasmussen, Arne Redsted; Murphy, John C.; Ompi, Medy; Gibbons, J. Whitfield; Uetz, Peter (2011-11-08). "Marine Reptiles". PLOS ONE. 6 (11): e27373. doi:10.1371/journal.pone.0027373. PMC 3210815. PMID 22087300.
  6. ^ a b Zug, George R. "Sea Turtle". Encyclopædia Britannica Online. Retrieved December 8, 2015.
  7. ^ "Sea Snake". Encyclopædia Britannica Online. Retrieved December 8, 2015.
  8. ^ "Marine Iguanas". National Geographic. Archived from the original on May 21, 2011. Retrieved December 8, 2015.
  9. ^ a b "Saltwater crocodile". National Geographic. Archived from the original on February 4, 2010. Retrieved December 8, 2015.
  10. ^ Ellis, T. M. (1981). "Tolerance of Sea Water by the American Crocodile, Crocodylus acutus". Journal of Herpetology. 15 (2): 187–192. doi:10.2307/1563379. JSTOR 1563379.