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Once this is accomplished, the lizard can emerge into the open again, positioning itself so that minimum surface area is exposed to the sun and reheating takes place slowly. Changing back to a pale, more reflective color also facilitates gradual heat absorption. Another example of reptile ingenuity is found in the habits of marine iguanas of the Galápagos Islands. They spend their morn- ings like statues, lined up together facing the same direction to absorb sunlight. They rest on black volcanic rocks, which provide them with abundant heat, and when warm enough, plunge into the cold Pacific Ocean to feed on seaweeds. They cannot tolerate this for long and soon emerge from the water to warm up once again, resuming their basking positions below the equatorial sun. There is great com- petition for the best basking sites, and the largest, dominant iguanas claim places where they can gain maximum exposure to the sun. With all of these methods of thermoregu- lation available to them, reptiles can live in many regions of the world, apart from the very cold polar regions and high, mountain- ous areas.

absorb the heat and then distribute it around the body, warming the muscles and internal organs. These same blood vessels will later constrict and route blood away from the skin when the air temperature falls in order to conserve heat. Some lizards can flatten their bodies in order to increase the surface area available for heat absorption; some can even alter their colorings and become darker in order to gain still more heat. Once a lizard’s body temperature has been raised sufficiently to allow normal activity it will search for food, usually in the form of insects. Most lizards can move very quickly, and their excellent eyesight helps them spot fast-moving insect prey. In a desert the tem- perature may rise to very high levels by the afternoon. At this time, the lizard faces over- heating. Retreating to the shade helps to reduce body heat and cut down on the absorp- tion of more heat from the sun. If there is no shade the lizard may climb into a shrub and expose itself to cooling breezes in order to dis- sipate heat. It may be necessary to retreat underground in order to stay within the acceptable body temperature limits.

Two species of land iguana are found on the Galápagos Islands. This one occurs on the island of Santa Fe and feeds on the succulent leaves of cactuslike plants. They are vulnerable to predation by the many rats, cats, and dogs introduced by man to the Galápagos.

Not the most appealing of lizards, the marine iguana is often coated with white powder. This substance is actually salt and forms from the concentrated salt water they expel from their

nostrils from time to time.

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