HISTORY- Fossil records show that the first sea turtles appeared with the dinosaurs during the Triassic period, 245 to 208 million years ago (seaworld.org). Although sea turtles have been dated as far back as the dinosaurs, scientists have little evidence to tell us how, when, and why one early reptilian group shortened their bodies by fusing their vertebrae, and developed a hard armour shell covered by scutes. Even though their bodies were shortened, ancient sea turtles were still massive creatures, and could be twice as big as thier biggest modern relative the leatherback (Euro Turtle). Like modern sea turtles, the head, tail, and limbs could not be withdrawn into the body, therefore, protection was probably gained by the addition of spines. Along with a dangerous outer covering, fossil records also indicate that early sea trutles had teeth, which could have been another important means of protection. From the Triassic and into the Cretaceous period, sea turtles showed various modifications and exhibited several lines of evolution. Presumably to save on weight and possibly because of a lack in enemies, scales and teeth were being discarded, and there was a reduction in the bony shell, bringing the 13 families of sea turtles of the Late Cretaceous (144 to 65 million years ago) much closer to modern forms (Euro Turtle). Today, eight species of sea turtles remain and they are divided into two families: Dermochelyidae and Cheloniidae. The lone extant speices in the Dermochelyidae family is the leatherback, and it has many unique qualities that make it stand out from the rest of its sea turlte relatives. (seaworld.org)
| Kingdom: Animalia |
| Phylum: Chordata |
| Class: Reptilia |
| Order: Testudines |
| Family: Dermochelyidae |
| Genus: Dermochelyes |
| Species: Coriacea |
Picture of Leatherback, courtsey of funkandwagnalls.
Giant Cretaceous Sea Turtle (Archelon ischyros). Courtesy of Black Hills Institute of Geological Research, Inc
Leatherback size and jaw features, modified from pictures on seaworld.org.
DESCRIPTION- The largest of all turtles species, and the largest marine reptile on the planet is the leatherback sea turtle. Mature leatherback's reach about four to six feet in length and can weigh anywhere from 450 to 2,000 pounds. The leatherback acquired its name from it's brown or black leathery textured skin which makes it unique from all other sea turtle species.While all other species exhibit scales and a bony caprice or shell composed of broadened, fused ribs, the leatherback's caprice is formed from seven logitudingal ridges of raised cartilage, with thousands of small dermal bones lying beneath the leathery skin (Rhodin et al., 1981). This thick layer of oil-suffused skin, which covers several inches of subcutaneous blubber is an ideal insulator and along with their big body mass, and counter current heat exchange allows the leatherback to venture into extremely cold waters where other species of turtle cannot survive. This design is also advantageous becuase it makes a leatherback's body more streamline than the rest of its turtle relatives, allwoing it to slide gracefully through the water. Another distinguishing feature about leatherback's is that that they are the only sea turtle species that lack claws on their flippers (seaworld.org).
Leatherback's have a relatively small head as compared to their bodies. Their jaws are weak and ideally shaped for eating jellyfish which make up the majority of their diet. Their throats also have spines which aid in keeping slippery prey such as jellyfish from sliding out. Although Leatherback's survive mostly on jellyfish, they must rely on other small marine invertebrates too, because jellyfish are composed mainly of water making them poor sources of nutrients and energy, requiring leatherbacks to consume up to twice their body weight in jellyfish daily (Eckert et al., 1989).
HABITAT- All sea turtles are well adapted for life in the water. For example, their limbs are held out to the sides more than downwards, which is ideal for swimming, but makes them awkward and vulnerable on land. Also, their forelimbs or front flippers are elongated and paddle-like to give them powerful propulsive force in the water. Although all species of sea turtle are designed to be great swimmers, they are all tied to land or at least coastal waters to breed and nest. All species of sea turtles nest in either tropical or subtropical beaches, and the only species of turtle found outside of the tropical or subtropical waters is the leatherback. The leatherback's big body mass and ability to regulate its temperature through counter current heat exchange, insulation, and metabolic heat, enable it to spread to the cold waters of the artic. These thermoregulatory capabilities also allow the leatherback to be the most pelagic species of sea turtle and male members may never leave the water. Some studies have shown that leatherbacks can migrate over 10,000 kilometers in a single year (Spotila et al., 1991). Due to their morphological and thermoregulatroy adaptations, leatherbacks are circumglobal and can be found in waters all over the world. However, due to commercialisation of tropical beaches, accidental capture by fishing activities, pollution, and human predation, leatherback populations have been decimated, and they are now considered an ENDANGERED SPECIES (Euro Turtle).
This website was created as a project for Animal Physiology at Davidson College.
If you have any questions or comments, email me at rycrawford@davidson.edu.
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Leatherback distribution, modified from diagram at mbgnet.
GENERAL INFORMATION
