Cheloniidae

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These are the only turtles whose front limbs are stronger than their back limbs.

The family Cheloniidae contains seven species within five genera. The sea turtles occur worldwide in all tropical oceans. They are truly marine, with females coming ashore only to nest.

Cheloniids are large turtles, ranging between 71 cm (Lepidochelys olivacea) and 213 cm (Caretta caretta) in maximum carapace length. The shell is oval or heart-shaped. The limbs are modified into flippers for swimming and cannot support the weight of the turtle on land. Sea turtles have lost the ability to retract the head within the shell. The lone unifying skeletal feature is the platycoelous articulation between the sixth and seventh cervical vertebrae.

Sea turtles are omnivorous and feed on a variety of sponges, cnidarians, mollusks, crustaceans, algae, plants, and fish. Adult turtles have relatively few natural predators, although sharks and saltwater crocodiles are known to consume adults, and nesting females are preyed upon by coyotes and other canids. Eggs and hatchlings are the most vulnerable, falling prey to insects, crustaceans, mollusks, small mammals, birds, other reptiles, and various fishes.

Courtship and mating usually occur in shallow offshore waters. Mating often involves the male and female pair floating near the surface, with the male's carapace protruding from the water. Females reproduce on multi-year cycles, but produce multiple clutches within a single season. Nesting occurs at night (except in Lepidochelys), and a range of seven to 238 eggs (averages vary across species) are deposited in a single clutch.

Most, if not all, Cheloniids are in need of conservation. Development has reduced nesting areas, so that the original range of some species will never be known. Turtles are harvested for food and/ or "tortoise shell" (Eretmochelys), and humans also take eggs as food. Many turtles are harmed by commercial shrimp boats and pollution.

It is relatively certain that the Cheloniidae form a monophyletic group with the D< ermochelyidae>, referred to as the Chelonioidea. The characters that unite these two families include elongation of digits III and IV, flattening of the carpals and tarsals, and articulation between the neural spine of the eighth cervical vertebra and the ventral surface of the nuchal bone.

The fossil record for Cheloniids places them among the oldest turtles. Six extinct genera, as well as the extant genera Caretta and Chelonia, date from the Upper Cretaceous of Europe and North America.

Ernst, C.H., and Barbour, R.W. 1989. Turtles of the World. Smithsonian Inst. Press, Washington, D.C.

Ernst, C.H., Lovich, J.E., and Barbour, R.W. 1994. Turtles of the United States and Canada. Smithsonian Inst. Press, Washington, D.C.

Pough, F.H., Andrews, R.M., Cadle, J.E., Crump, M.L., Savitzky, A.H., and Wells, K.D. 2000. Herpetology, 2nd ed. Prentice Hall, Upper Saddle River, NJ.

Contributors

Keith Pecor (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.