Vol 5 World of Reptiles ... Introduction ... What are reptiles?
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Introduction

What are reptiles?

Reptiles are one of the oldest groups of backboned animals on our planet!
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Reptiles are modern-day animals related to the dinosaurs and other prehistoric animals. Because they rely on external heat sources rather than body chemistry to warm themselves, these animals do not need to eat as much food as the warm-blooded mammals and birds, so reptiles can live in regions largely uninhabitable to other groups of animals. It has been estimated that mammals need 30-50 times more food than reptiles of similar size.

Reptiles are also characterised by their dry, horny skin made up of a number of thickenings called scales. Reptiles often lay shelled eggs in nests, although some give birth to live young.

Other reptile characteristics include two pairs of five-toed limbs (absent in a few lizards and most snakes), young that resemble adults when hatched, respiration using lungs (not gills), and an incomplete, four-chambered heart.

The main groups of reptiles are the turtles, lizards, snakes and crocodilians. Less numerous groups are the worm lizards and the tuatara, a strange reptile that is placed in an order all of its own. The relationships between these reptile groups is discussed in the 'Groups' chapter of this Nature Explorer guide.