Marine Reptiles

Present-day diversity of marine reptiles in the seas is low. One reason for this appears to be that modern reptilian kidneys cannot tolerate high salinities and thus the only reptiles that have adapted to marine environments are those which have developed specialised salt-excreting glands. The most thoroughly marine reptiles are undoubtedly the sea snakes in the subfamily Hydrophiinae. These spend their entire lives in the sea, giving birth to live young there. Although largely air-breathing like other reptiles, they can also absorb some oxygen directly from sea water and are thus able to remain submerged for long periods. Around 50 species are known, widely distributed in tropical parts of the Indo-Pacific region.

Five species of sea krait are also largely marine, feeding mainly on eels. However they return to land to breed, generally on small Indo-Pacific tropical islands. One species of lizard, the Galapagos marine iguana Amblyrhynchus cristatus (family Iguanidae), feeds underwater on marine algae but spends a considerable proportion of time on land. Several other reptile species regularly enter sea water, most notably a number of mangrove snakes and the estuarine crocodile Crocodylus porosus.

Undoubtedly the most prominent group of marine reptiles is the sea turtles, comprising the leathery turtle Dermochelys coriacea in the family Dermochelyidae and six members of the family Cheloniidae. All species are large ranging from 70cm in length in Lepidochelys kempii to, exceptionally, 250 cm in Dermochelys coriacea, and most are widely distributed in tropical and subtropical waters. Sea turtles are almost completely marine: only the females emerge to nest on land, mostly within the tropics. One species, the loggerhead Caretta caretta, nests largely in temperate areas of the northern hemisphere.