The turtles (order Testudines) are a group of reptiles instantly recognisable thanks to their bowed legs, slow movements and, most striking of all, their shells. This unique structure, formed from the ribs and a few other bones, offers amazing protection against predators, even allowing the vulnerable head and neck to be retracted inside in the vast majority of species. Turtles proper evolved in the late Jurassic, and have since become extremely successful, found on every continent except Antarctica and coming in a wide variety of forms, including terrestrial herbivores, semi-aquatic omnivores, freshwater ambush-hunters and marine wanderers. However, the greater group that the turtles belong to, the Pantestudines, had their start in the Triassic (possibly even earlier, as a Permian reptile called Eunotosaurus is sometimes considered to be a turtle relative, but whether it actually is is unclear). Most of these animals would have looked very similar to modern turtles, differing only in a few minor anotomical traits, but the earliest forms would have more resembled lizards. Even so, these proto turtles already had the beginnings of a shell, in the form of their expanded ribs.
