Tortoises () are a family, Testudinidae. Testudinidae is a Family under the order Testudines and suborder Cryptodira. There are fourteen extant families of the order Testudines, an order of reptile commonly known as turtles, tortoises, and terrapins. The suborder Cryptodira (Greek: hidden neck ) is a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pluerodia (side- neck turtles) in that they lower their necks and pull the heads straight back into the shells, instead of folding their necks sideways along the body under the shells' marginals.The testudines are some of the most ancient reptiles alive. Tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The carapace is fused to both the vertebrae and ribcage, and tortoises are unique among vertebrates in that the pectoral and pelvic girdles are inside the ribcage rather than outside. Tortoises can vary in size from a few centimeters to two meters. They are usually diurnal animals with tendencies to be crepuscular depending on the ambient temperatures.
