Newly hatched alligatorNewly hatched alligator Reptiles are cold-blooded animals with scaly skins. They include snakes, lizards, turtles and crocodiles. Most reptiles lay eggs, either soft and leathery or hard-shelled, but some give birth to live young. A few reptiles guard their eggs until they hatch. Apart from the crocodilians, most reptiles abandon their young after hatching or birth. Land-living reptiles must bask in the sun to warm up before going in search of food.

Reptile skin

A snake shedding its skinA snake shedding its skinReptiles have dry, scaly skins—not slimy. The scales form one continuous sheet, not individual scales like fish. Water cannot pass out through their skins, unlike those of amphibians. This means that reptiles do not need to keep their skins moist. Some reptiles moult regularly, shedding their skins when new ones have grown underneath.

A collared lizard basking on a rockA collared lizard basking on a rock

Warming up

Because they are cold-blooded animals, reptiles need to bask in the sun to raise their body temperature before they are able to move about in search of food. However, they do not need to eat as much food as the warm-blooded birds and mammals, so are able to survive more easily in harsh desert environments.



Hylonomus, one of the first reptilesHylonomus, one of the first reptiles

Rise of the reptiles

Reptiles are descended from the early amphibians. The first reptiles were probably small, lizard-like creatures that inhabited the Carboniferous swamps about 320 million years ago. Unlike the amphibians, they did not have to stay close to water to keep moist and lay their eggs. They were able to live more easily on land. The lizards, turtles and tortoises and the crocodilians (crocodiles and alligators) appeared during the Triassic Period, about 250 million years ago. Snakes evolved later, about 135 million years ago. Some modern-day reptiles have hardly changed since the time of the dinosaurs.

Some reptiles of the Amazon rainforestSome reptiles of the Amazon rainforest


 Chris Jarvis

See also in Earth

See also in Prehistoric

Reptiles' teeth keep growing throughout their lives.

Although, like all reptiles, leatherback turtles are cold-blooded, they can build up a high body temperature in cold water by vigorous exercise—constant swimming.

Leatherbacks are the fastest-moving reptiles, capable of speeds of more than 35 km/h (22 mph), and the deepest-diving ones, known to dive to at least 1300 m (4200 ft).

Reptiles range in size from the dwarf gecko, just 1.6 cm (0.6 inches) long, to the saltwater crocodile and Nile crocodile, both of which can grow to about 7 m (23 ft) long.

The horned toad is not a toad at all, but a lizard—one with a particularly rounded body. To deter predators, it can squirt streams of blood from the corners of its eyes up to 1.5 m (5 ft).

The viviparous lizard, whose range extends north of the Arctic Circle in Scandinavia and Finland, lives farther north than any other reptile.

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