Class - Reptilia
Reptiles are a class of cold-blooded vertebrates - their body temperature varies with their environment. Reptiles include snakes, lizards, crocodiles, and turtles.
Reptiles have scaly skin, breathe air with lungs, and have a three-chambered heart.
Most reptiles lay eggs, although some produce eggs that hatch internally.
Order - Testudines
This order includes all turtles and tortoises. It is divided into three suborders: Pleurodira (side-necked turtles), Cryptodira (freshwater turtles, snapping turtles, tortoises, soft-shelled turtles, and sea turtles), and Amphichelydia (a suborder of turtles that is now extinct).
Most scientists recognize two families of sea turtles:
- Family Cheloniidae includes all sea turtles with scutes (horny plates) covering their shells.
- Family Dermochelyidae are scuteless turtles with only one modern species; the leatherback turtle. A leatherback turtle is covered with leathery skin. It is the only marine turtle whose backbone is not attached to the inside of its shell.
Most scientists recognize seven species and one subspecies of sea turtles:
green (Chelonia mydas); two subspecies the green (Chelonia mydas mydas) and the black or Eastern Pacific green turtle (Chelonia mydas agassizii)
loggerhead (Caretta caretta)
Kemp's ridley (Lepidochelys kempii)
olive ridley (Lepidochelys olivacea)
hawksbill (Eretmochelys imbricate)
flatback (Natator depressus)
leatherback (Dermochelys coriacea)
The first turtles appeared during the Triassic period, 245 to 209 million years ago.
The earliest known sea turtles appear in the fossil record in the Late Jurassic period, 208 to 144 million years ago. Scientists believe that modern sea turtles are derived from marsh-inhabiting ancestors that lived during the Late Triassic period.
Fossil records show that the now-extinct sea turtle Archelon ischyros, which lived 144 to 65 million years ago, was one of the largest turtles that ever lived. It reached a length of 3 to 4 m (9.8 to 13 ft.).
Together with saltwater crocodiles, sea snakes, and marine iguanas, sea turtles are the only surviving seawater-adapted reptiles.