Turtles (Chelonia) are a unique group of reptiles that first appeared about 200 million years ago during the Late Triassic period. Since that time, turtles have changed little and it is quite possible that modern turtles closely resemble those that roamed the Earth during the time of the dinosaurs.
Turtles have a rather unique anatomy. They are best known for the hard shell (also called a 'carapace'), which is a modification of the animal's ribcage and vertebral column. The shell is entirely internal, it is part of the turtle's skeleton (a turtle cannot 'crawl out' of its shell). The shell is composed of two layers, an outer layer of thin plates (called 'scutes') and an inner layer of bone. The underside of the turtle's shell (which protects its belly) is referred to as the 'plastron'. Turtles do not have teeth, instead they possess a sharp beak that enables them to tear their food.
Several common names are used to describe the various groups of turtles. These include:
- tortoises - terrestrial turtles
- terrapins - freshwater turtles
- turtles - any member of the Order Chelonia (formerly, the term turtles was used to refer only to marine turtles but now it has taken on more general usage)
Diet: Many turtles are herbivores and feed primarily on plant matter. Since they are slow movers, turtles lack the ability to actively pursue prey. So a few aquatic species have developed an ambushing technique and instead wait for unsuspecting invertebrates, fish, or other small animals to cross their path. Most marine species feed primarily on seaweed but some species also eat invertebrates such as jellyfish.
