Sea turtles are reptiles remarkably suited to life in the sea. Their hydrodynamic shape, large size, and powerful front flippers allow them to dive to great depths and swim long distances. These front flippers are long, narrow, and winglike, while their hind flippers are shorter. Although sea turtles can remain submerged for hours at a time while resting or sleeping, they typically surface several times each hour to breathe.
Sea turtles are among the oldest creatures on Earth and have remained essentially unchanged for 110 million years. In most sea turtles, the top shell—or carapace—is composed of many bones covered with horny scales, or scutes. Unlike their terrestrial relatives, they cannot retract their heads into their shells. The smallest of the sea turtles are the two species of ridleys, weighing in at 85 to 100 pounds (38 to 45 kilograms) as adults. Leatherbacks are the biggest and can grow to 2,000 pounds (900 kilograms). Most sea turtles grow slowly and have a lifespan of many decades.
All sea turtles are threatened or endangered. They face an uncertain future due to threats of many kinds, including pollution and the encroachment of coastal development on their nesting beaches. They are also susceptible to accidental drowning in fishing gear and are at risk from the international trade in turtle meat and shell products.
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