Turtles are reptiles of the order Chelonii. Therefore they are also called chelonians by researchers and conservationists. Chelonians are charaterized by the special bony shell or carapace, which is developed from their ribs and acts as a shield. They are an old group with the very first proto-turtles having evolved over 220 milliom years ago in the Triassic Era. The order of Chelonii, also known as the Testudines, have three members in the group; turtles, tortoises and terrapins.