The measured sizes of
turtles varies from a few centimetres (forest/jungle species)
to up to two meters (the leatherback and the galapagos tortoises).
All turtles have a protective shell around their bodies. The top
part of their case is called the carapace, the underside is the
plastron, and the two are connected by the bridge. Turtles generally
live a long time; some individuals are known to have lived longer
than 150 years. The first turtles already existed in the era of
the dinosaurs, some 200 million years ago. Turtles are the only
surviving branch of the even more ancient clade Anapsida, which
includes groups such as the procolophonoids, millerettids and
pareiasaurs. All anapsid skulls lack a temporal opening. All other
extant amniotes have temporal openings (although in mammals the
hole has become the zygoid arch). Most of the anapsids became
extinct in the late Permian period, with the exception of the
procolophonoids and the precursors of the testudines (turtles).