Several different scientific names are used for turtles including Chelonia, Chelonii, Testudines, and Testudinata.
The earliest fossils are from the beginning of the age of dinosaurs, in the late Triassic. The Testudines reached its greatest diversity by the end of the Cretaceous. Today only 260 species representing 13 families survive. Although turtles are abundant in the tropics, they also are quite diverse in temperate regions and have been recorded in Arctic waters.
Records from Olduvai Gorge indicate that people have eaten turtles for at least 2 million years. We have had a severe impact on turtles, causing the extinction of many forms, especially land tortoises. Today the problem is quite serious with many land tortoises, sea turtles and aquatic forms facing extinction. Loss and degradation of habitat and continued killing of reproductive females on the nesting beach and removal of their eggs are the biggest problems. Turtles (including tortoises and terrapins) are characterized by a shell that completely encloses both of the limb girdles. The shell is composed of a dorsal carapace of dermal bone that incorporates endochondral contributions from the vertebrae and ribs and a ventral plastron of clavicles and interclavicles anteriorly and abdominal ribs posteriorly. No turtles have teeth on their jaws, and all have the external ear supported by a large, semicircular quadrate.