Tortoises (Testudinidae) are a family of land-dwelling reptiles in the order Testudines. Like their marine cousins, the sea turtles, 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 tortoise has an endoskeleton with an adaptation of having an external shell fused to the ribcage. Tortoises can vary in size from a few centimeters to two meters. Tortoises are usually diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are generally reclusive animals. Although the word is used by biologists in reference to the family Testudinidae only, in colloquial usage it is often used to describe many land-dwelling Testudines. The inclusiveness of the term depends on the variety of English being used. Female tortoises dig nesting burrows in which they lay from one to thirty eggs.
Contributions by Joyous!, Mwng, and Arpingstone.