Turtles are reptilians of the Order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilaginous shell developed from their ribs. The Order Testudines includes both extant (living) and extinct species, the earliest known turtles being from around 215 million years ago,http://www.enchantedlearning.com/subjects/dinosaurs/dinos/Archelon.shtml making turtles one of the oldest reptile groups, and a much more ancient group than l