Sea Turtle - Taxonomy and Evolution

Taxonomy and Evolution

Sea turtles, along with other turtles and tortoises, are part of the order Testudines.

The seven living species of sea turtles are: flatback sea turtle, green sea turtle, hawksbill sea turtle, Kemp's ridley sea turtle, leatherback sea turtle, loggerhead sea turtle and olive ridley sea turtle. All species except the leatherback are in the family Cheloniidae. The leatherback belongs to the family Dermochelyidae and is its only member.

The species are primarily distinguished by their anatomy: for instance, the prefrontal scales on the head, the number of and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron. The leatherback is the only sea turtle that does not have a hard shell; instead, it bears a mosaic of bony plates beneath its leathery skin. It is the largest sea turtle, measuring 6 to 7 feet (1.8 to 2.1 m) in length at maturity, and 3 to 5 feet (0.91 to 1.5 m) in width, weighing up to 1,300 pounds (590 kg). Other species are smaller, being mostly 2 to 4 feet (0.61 to 1.2 m) and proportionally narrower.

Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago.

From SWOT Report, vol. 1:

• Family Cheloniidae
  • Chelonia mydas or green sea turtle
  • Eretmochelys imbricata or hawksbill sea turtle
  • Natator depressus or flatback sea turtle
  • Caretta caretta or Loggerhead sea turtle
  • Lepidochelys kempii or Kemp's ridley sea turtle
  • Lepidochelys olivacea or olive ridley sea turtle
• Family Dermochelyidae
  • Dermochelys coriacea or leatherback sea turtle