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Habitat and Body Temperature A desert-dwelling lizard begins its day by creeping slowly from its nighttime hiding place in a burrow or under a stone. At this time, it is unable to make any rapid movements or capture food, but will just be able to maneu- ver its body into a position where it can be warmed by the sun. By lining up the maxi- mum surface area of its body to face the sun, this animal can start to absorb radiant heat; it will also gain heat from the warm rocks it is basking on and the warm desert air. Blood vessels close to the skin then dilate to

not require as much food to sustain them as mammals of the same body size, so they are able to inhabit regions which would be quite unsuitable for mammals. Deserts, for exam- ple, are ideal places for reptiles, as there is usually plenty of sunlight to warm them up and enough food to sustain them. Once they have had a meal, they can digest it at their leisure; some of the largest species can sur- vive for several months between meals. A large mammal could not survive with such infrequent food. Consequently, the deserts are left to the reptiles.

A full-grown land iguana basks in the warmth of the morning sun. These large inhabitants of the Galápagos Islands can reach a length of 1 meter(3.3 feet), but are completely harmless to man.

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