Turtles are diapsids of the order Testudines. The earliest known members of this group date from the Middle Jurassic,[1] making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians.
Turtles are ectotherms—animals commonly called cold-blooded—meaning that their internal temperature varies according to the ambient environment. However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.
The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which reaches a shell length of 200 cm (6.6 ft) and can reach a weight of over 900 kg (2,000 lb).
Turtles are divided into two groups, according to how they retract their necks into their shells (something the ancestral Proganochelys could not do).
The upper shell of the turtle is called the carapace. The lower shell that encases the belly is called the plastron. The carapace and plastron are joined together on the turtle's sides by bony structures called bridges.
A turtle's diet varies greatly depending on the environment in which it lives.
The text for this page taken from Wikipedia.