Tuesday, April 10, 2012

Reptiles

The reptiles came into being about 300 million years ago; descending from some kind of amphibian ancestor that gained a scaly waterproof skin and the ability to lay shelled eggs that could survive on land. Most living reptiles still lay eggs, although some give birth to active young. They live on land in fresh water and in the sea, and between them they eat almost every kind of food. There are about 6000 living species, of which some 3000 are lizards and 2700 are snakes. Turtles, tortoises, crocodiles and alligators make up the rest of the class.
Reptiles are said to be cold blooded because they have no internal mechanism for maintaining a constant temperature like birds and mammals. Many however can adjust their body temperatures by varying their behaviors. They bask in the morning sun to warm up, hideaway in the midday heat and then come out again in the evening.
The lizard like tuatara is the only living member of a lineage more ancient than the dinosaurs, but it has hardly changed since its relatives died out of over 200 million years ago. It lives only on a few off shore islands of New Zealand, having been exterminated elsewhere in the country by introduced predators.