Turtle or Tortoise?

All of us have heard the story of the Rabbit and the Tortoise a number of times over our growing years. And as we grew old, there came Turtles. Turtles? Aren't they the same as the Tortoise? Or just the plural of Tortoise? Or a new species?

Long long back, the Chordates Phylum - animals having vertebrates or backbone, evolved and formed the Reptiles Class, who in turn evolved into Testudines Order. Both the Tortoise and the Turtles belong to the Testudines Order in the Animal Kingdom with 300 known species dating back to 250 million years ago - much older than evolution of lizards and snakes in the reptile family. So how do tortoise and turtle differ then?

In general, the Turtles are water dwelling - Marine Turtles whose primary habitat is the sea or ocean, and Aquatic Turtles whose habitat is fresh water bodies - river, lakes, ponds, etc. Then there are land dwelling testudines - the Tortoise. There's a third category called Terrapins, which are found in Brackish water. Turtles are also classified on the way they retract their necks - Cryptodira: those who draw their necks in under the spine, and Pleurodira: those who contract their necks to the side.

As all other reptiles, they are cold-blooded (ectotherms), they breath air and do not lay eggs under water. They come in all sizes - largest ones grow up to 6.6 feet in length with more than 900kg of weight, to smallest ones measuring 8cm in length weighing 140gms. Turtles and Tortoises are believed to have very large lifespans ranging from typical 50 - 60 years up to 150 years. There have been records and claims for longer lifespans too ranging up to 250 years. They have a color vision and are though to have excellent night vision too. They have rigid beaks with knife-sharp or serrated-edged ridges to cut and chew food. The tortoise have short sturdy feet to walk on land, amphibious turtles have webbed feet with claws, while sea turtles have flippers to help them move in the water. Turtles actually fly in the water - they use the front flippers like birds to generate the lift and the thrust, the rear flipper are used as pitch, yaw and roll. :)

References:

http://en.wikipedia.org/wiki/Turtle

http://en.wikipedia.org/wiki/Tortoise

http://en.wikipedia.org/wiki/Terrapin