海龟科科

形态

与生活在陆地上的乌龟相比，海龟没有将头部缩回壳内的能力。海龟的胸骨是其下面的骨板，与其他龟类相比，海龟的胸骨更小，由胸骨板和腹骨板之间没有铰链的韧带连接到龟壳的顶部。七种海龟的大小从71厘米到213厘米不等；例如最小的龟科海龟品种坎普氏雷氏龟的壳只有大约75厘米和50公斤重。但是所有的物种都有一个独特的坚硬的外壳。

分类

现存物种

• 蠵龟属 Caretta
• 赤蠵龟 Caretta caretta
• 丽龟属 Lepidochelys
• 肯氏龟 Lepidochelys kempii
• 丽龟 Lepidochelys olivacea
• 海龟属 Chelonia
• 绿蠵龟 Chelonia mydas
• 玳瑁属 Eretmochelys
• 玳瑁 Eretmochelys imbricata
• 平背龟属 Natator
• 平背龟 Natator depressus

已灭绝物种

• †泥海龟属
• †Argillochelys africana
• †Argillochelys antiqua
• †Argillochelys athersuchi
• †Argillochelys cuneiceps
• †Carolinochelys
• †Carolinochelys wilsoni
• †巨型龟属
• †撒氏巨型龟 Gigantatypus salahi
• †Procolpochelys
• †Procolpochelys grandaeva

其他

一些旧有的亚科如 Cheloniinae 及 Carettinae 已过时。

Cheloniidae is a family of typically large marine turtles that are characterised by their common traits such as having a flat streamlined wide and rounded shell and almost paddle-like flippers for their forelimbs. They are the only sea turtles to have stronger front limbs than back limbs. The six living species that make up this family are the green sea turtle, loggerhead sea turtle, olive ridley sea turtle, hawksbill sea turtle, flatback sea turtle and the Kemp's ridley sea turtle.

Classification

Extant genera

• Subfamily Carettinae
• Genus Caretta
• Loggerhead sea turtle (Caretta caretta)
• Genus Lepidochelys
• Kemp's ridley sea turtle (Lepidochelys kempii)
• Olive ridley sea turtle (Lepidochelys olivacea)
• Subfamily Cheloniinae
• Genus Chelonia
• Green sea turtle (Chelonia mydas)
• Genus Eretmochelys
• Hawksbill sea turtle (Eretmochelys imbricata)
• Genus Natator
• Flatback sea turtle (Natator depressus) (previously in Chelonia)

Extinct genera

• †Allopleuron
• †Argillochelys
• †Cabindachelys
• †Carolinochelys
• †Catapleura
• †Erquelinnesia
• †Gigantatypus
• †Glyptochelone
• †Itilochelys
• †Lytoloma
• †Marocokatognathus
• †Osteopygis
• †Pampaemys
• †Peritresius
• †Porthochelys
• †Prionochelys
• †Procolpochelys
• †Retechelys
• †Syllomus
• †Tasbacka
• †Thinochelys
• †Miocaretta

Morphology

In contrast to their earth-bound relatives, tortoises, sea turtles do not have the ability to retract their heads into their shells. Their plastron, which is the bony plate making up the underside of a turtle or tortoise's shell, is comparably more reduced from other turtle species and is connected to the top part of the shell by ligaments without a hinge separating the pectoral and abdominal plates of the plastron. Sizes among the seven species of sea turtles range from 71 to 213 cm; for example, the smallest turtle species in the family Cheloniidae, the Kemp's ridley, only has a shell size of about 75 cm and a weight of 50 kg.

Reproduction and life cycle

Reproductive behaviors among the different species of sea turtles are similar, with slight differences in each of the species. The females come to shore and bury their clutch of eggs on beaches or sandy environments typically at night and well away from the high tide line of the shore. Most females nest only once every three to four years and most species have two to four egg laying time periods per nesting season, which is from spring to late fall. A common number of eggs laid in a nest is often about 100 eggs per clutch. The incubation period of some turtles can range anywhere from 50 to 60 days.

Habitat and ecology

The habitat range of sea turtles, in general, is known to be far reaching into warmer temperatures and the tropical and subtropical areas of the Pacific and Atlantic Oceans and is even also found in warmer seas such as the Mediterranean Sea. Within these temperamental biomes, sea turtles frequent near by the coastlines when nesting, and spend most of their lives swimming out in waters over the continental shelf when feeding. Travelling throughout the oceans has been reported in olive ridley sea turtles but more often than not, they tend to frequent bays and estuaries.

Climate change

Sea turtles are ectotherms, meaning their life history traits, behaviors, and physiology are impacted by environmental temperature, which determines sea turtle sex-ratio and hatching success. This sensitivity makes them highly vulnerable to increasing temperatures and events related to climate change. Temperature increases also drive processes like sea-level rise and cyclonic activity, both of which can alter nesting environments and increase the risk of embryo mortality.

Conservation status and significance to humans

The conservation status of each of the seven turtle species vary from endangered or threatened, to least concern or data deficient (Flatback). The green and Loggerhead sea turtles were both recategorized in late 2025 to least concern and vulnerable, respectively. Olive Ridley are classified as vulnerable, Kemp's Ridley, and Hawksbill sea turtles are critically endangered and the Flatback sea turtle does not have enough data to draw an accurate conclusion on conservation status.

Most do not reach sexual maturity before becoming prey to other organisms, or being caught by humans either intentionally or as bycatch by commercial fishing operations.