Pet Turtle : Turtle World

Turtles are a group of vertebrate animals belonging to the order Testudines. Together with snakes, lizards, crocodilians, and the tuatara, they form the reptiles (Class Reptilia). Turtles are the oldest living group of reptiles, first appearing about 200 million years ago. Like the other orders of reptiles, turtles are cold-blooded (ectotherms), have scaly skin, and lay eggs with a yolk and tough outer covering (amniote egg).

The study of reptiles and amphibians is called Herpetology. Herp is from a Greek word, herpeton, which is loosely translated into "things which creep and crawl on their bellies."

Among the differences between turtles and other reptiles, the most exceptional is the presence of shells. The turtle's shell is a covering that encloses the turtle's body. Within this armor, the turtle's soft body parts are protected. From the shell project the turtle's head, legs, and tail. The shell of the turtle is divided into two parts, the upper carapace and the lower plastron. The two are connected on the sides by the bridge. A turtle can not walk out of its shell, the carapace is fused with the ribs of the turtle. It even has nerve endings in the shell…so don't mistake the shell to be equivalent to your nails!

The attributes of the turtle's shell can varygreatly, from hard and bony to flexible and leathery. Some turtles have shells with bright markings or unusual shapes.

Instead of teeth, they have horny beaks. The beak of a turtle is adapted for it's primary diet. Carnivorous species have sharp hooked beaks to grasp and slice animal prey. Vegetarian turtles and those that eat mollusks have beaks with flat, broad crushing surfaces.

Turtles can be found on every continent except Antarctica. They have adapted to a wide range of habitats, including deserts, rainforests, mountains, and rivers. Marine turtles occur in tropical and temperate seas throughout the world. Many of the terrestrial turtles are referred to as tortoises. In the United Kingdom and many other countries, freshwater turtles are called terrapins. In the United States, this name is used for a species that lives in brackish water.

Varying greatly in size turtles range in size from diminutive mud turtles maturing at 4.5 inches (11.2 cm) to the monstrous leatherback sea turtle that reaches lengths of 8 feet (244 cm) and weighs 1,600 pounds (726 kg). Infact fossilized remains of extinct turtles species have measured in excess if 13 feet!
Having evolved & survived way before mankind, turtles are highly adapted & specialized to their habitats. You need to carefully consider whether you can recreate a similar habitat for it, before you go in for a turtle as a pet!