Turtle model

Turtles are reptiles of the order Testudines (or Chelonii[3]) characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield.[4] "Turtle" may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English).[5]

The order Testudines includes both extant (living) and extinct species. The earliest known members of this group date from 157 million years ago,[1] making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians. Of the 327 known species alive today, some are highly endangered.[6][7]

Turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded. However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.

Turtles are classified as amniotes, along with other reptiles, birds, and mammals. Lik