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Snakes are reptiles. They are part of the order Squamata. They are carnivores, with long narrow bodies and no legs. There are at least 20 families, about 500 genera and 3,400 species of snake.

The earliest known fossils are from the Jurassic period. This was between 143 and 167 million years ago.

Their long, slender body has some special features. They have overlapping scales which protect them, and help them move and climb trees. The scales have colours which may be camouflage or warning colours.

Many species have skulls with more joints than the skulls of their lizard ancestors. This allows the snakes to swallow prey much larger than their heads. In their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side. Most have only one working lung. Some species have kept a pelvic girdle with a pair of vestigial claws on either side of the cloaca. They have no eyelids or external ears. They can hiss, but otherwise make no vocal sounds.