|Scientific Name:||Geochelone Elegans|
Turtles are reptiles of the order Testudines characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield. The order Testudines includes both living and extinct species. The earliest known members of this group date from157 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians.
Turtles are found in all of the major oceans and smaller seas except the Arctic Circle. The bigger species of turtle are found in the Southern Hemisphere in the tropical, warmer waters.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Turtles have colour vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet to red. Some land turtles have very poor pursuit movement abilities, which are normally found only in predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads quickly to snap.
The upper shell of the turtle is called the carapace. The lower shell that encases the belly is called the plastron. The carapace and plastron are joined together on the turtle's sides by bony structures called bridges. The inner layer of a turtle's shell is made up of about 60 bones that include portions of the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes. Scutes are made up of the fibrous protein keratin that also makes up the scales of other reptiles.
Sea turtles are almost entirely aquatic and have flippers instead of feet. Sea turtles fly through the water, using the up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion, but may be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility on land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally never leave the sea. Females must come back onto land to lay eggs.