Turtles and Tortoises, common name for reptiles that are recognized by a hard shell that encloses the internal organs of the body. They are ancient life forms: the earliest recognized fossils date from the Triassic period, about 200 million years ago; thus, turtles and tortoises were in existence before the emergence of the great dinosaur groups. Unlike dinosaurs, however, turtles and tortoises have continued to adapt and flourish.

Turtles and tortoises make up the order Chelonia. The suborder comprising species that pull their heads into the shell by a telescoping movement of the neck is Cryptodira; the suborder comprising freshwater species that hide their heads by bending the neck sideways is Pleurodira. The family of freshwater and wood turtles which makes up about half the species of the order is Emydidae. The soft-shelled turtles make up the family Trionychidae. The American family of snapping turtles in which the plastron consists merely of two narrow, crossed bands is Chelydridae. The green, loggerhead, hawksbill, and ridley turtles belong to the family Cheloniidae, and the huge leatherback turtle to the family Dermochelyidae. Tortoises make up the family Testudinidae.

The order to which they belong is divided into two suborders: the first comprises species that pull their heads into the shell by a telescoping movement of the neck; the second comprises freshwater species that hide their heads by bending the neck sideways.

A total of about 250 species are grouped into 9 families; they are found only in the temperate or tropical zones. Most species are adapted to a freshwater or terrestrial habitat, and a small group to sea life.
In Britain the term turtle is restricted to aquatic species, while tortoise is applied to the terrestrial members of the order. In American usage, the term turtle is more widely applied; tortoise is used additionally for certain terrestrial species belonging to the first suborder.

Although few species of turtles and tortoises can be considered strictly carnivorous or herbivorous, some land-dwelling species prefer vegetation, and aquatic species are mostly carnivorous. All species lay eggs, which they bury in holes. Turtles and tortoises are generally long-lived; some species live for more than 100 years.

"Turtles and Tortoises," Microsoft(R) Encarta(R) 97 Encyclopedia. (c) 1993-1996 Microsoft Corporation. All rights reserved.