Turtles belong to the order of Testudines, also known as Chelonii, which is divided into two suborders: Cryptodira and Pleurodira. The former group is formed of the turtles which retract their head between the scapulae within the shell, so that the neck forms an “S”-shaped curve on a vertical plane (Fig. 1). The Pleurodira, on the other hand, have a longer neck and in order to “hide” their head within the shell, they fold it to the side, forming the “S” on the horizontal plane. The widely present domestic species in Italy all belong to the suborder Cryptodira, with the most common belonging to the families Testudinidae (land-dwelling turtles) and Emydidae (semi-aquatic turtles). Another well-known family is that of the Cheloniidae, whose most representative species is the sea turtle Caretta caretta.
Turtles have managed to colonise all the continents except Antarctica, extending into almost all environments: in fact, there are terrestrial, semi-aquatic and aquatic turtles. The earliest fossils of chelonians currently known go back to about 220-210 million years ago to the Triassic era close to the time of the dinosaurs. However, unlike the dinosaurs, turtles are not extinct and have maintained their anatomical and physiological characteristics almost unaltered, which is a major evolutionary success. The first “paleo-turtles” seemed to live in the sea and have only a plastron, but then evolved to have a complete shell that protects the whole body.