The earliest known  turtles fossils, which are more than 200 million years old, show that ancient chelonians different little from today's turtles and tortoises. This evolutionary stability may be the result of the continuous benefit of the basic turtle design-a body covered by a shell. The shell consist of fused bony plates. The carapace is the top, or dorsal, part of the shell, and the plastron is the lower, or ventral, portion. In most species, the vertebrae and ribs are fused to the inner surface of the carapace. Turtles are also distinctive in that the pelvic and pectoral girdles lie within the ribs instead of outside the ribs, as they do in all other terrestrial vertebrates. Unlike other reptiles, turtle have a sharp beak instead of teeth.

     Turtles and tortoises live in a variety of habitats. Some species are permanently terrestrial, and some spend time both on land and in the water. The differing demands of these habitats are reflected in the shells and limbs of turtles. For example, water-dwelling turtles usually have a stream-lined, disk-shaped shell that permits rapids turning in water, and carapace into which they can retract their head, legs, and tail as a means of protection from predators. The limbs of marine turtles, which spend their entire lives in the ocean, have evolved into flippers for swimming and maneuvering.

      All turtles and tortoises lay eggs. The female selects an appropriate site on land, scoops out a hole with her hind limbs, deposits the eggs, and cover the nest. She provides no further care for the eggs or the hatchling. Marine turtles often migrates long distances to lay their eggs on the same beach where they hatched. For example, Atlantic green sea turtles travel from their feeding grounds of the coast of Brazil to Ascension Island in the South Atlantic- a distance of more than 2,000 km (1242 mi). These turtles probably rely on several environmental cues, possibly even the Earth's magnetic  field and the direction of currents, to find this tiny island.

For any questions email Mr. Reilly at biosnake@aol.com