What Makes Reptiles Cold Blooded?
Most species of animal are cold-blooded---or at least are some variation of that phenomenon. Full warm-blooded homeostasis is a recent evolutionary innovation endemic to most mammals and birds. As a cold-blooded animal, reptiles cannot actively regulate their metabolism, so they have adapted certain strategies to stay warm.
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Cold-Blooded
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The term cold-blooded is a slight misnomer. Organisms that are cold-blooded only have cold blood when the environment is cold. This occurs because cold-blooded creatures cannot regulate their internal body temperature, so it fluctuates with the ambient temperature of the surrounding area. According to Biology Online, organisms that maintain this phenomenon are also known as ectotherms, which is actually Greek for "outside" and "hot".
Homeostasis
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The key to internal body temperature is metabolism, which is the process that maintains energy and the other material substances of the cell. Warm-blooded animals such as mammals donate much of their energy to maintaining an active homeostasis. They generate heat in cool environments and cool themselves in hot environments.
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Reptile Metabolism
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Cold-blooded creatures, on the other hand, do not use their metabolism to regulate temperature, so they must rely upon the temperature of the atmosphere. The California Institute of Technology states that their metabolism rises and falls naturally with the ambient temperature. This is why reptiles are found so often in warm environments: they are attempting to keep warm.
Adaptations
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Because their metabolism is so highly variable, reptiles are well-suited to deal with periods of low metabolism. They can languor for long periods of time and lack many high cost organs or structure such as energy-intensive brains that warm-blooded animals can maintain. They also have different sets of enzymes---proteins that facilitate chemical reactions---that are used for changing levels of temperature.
Strategies
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Being cold-blooded may cost less energy, and it bestows upon an organism the ability to convert energy into body mass quickly, but reptiles must adapt specific strategies to deal with changing temperatures. Most reptiles bask in the sun, staying perpendicular to the direction of its rays to maximize the amount of sunlight they absorb. They can also expand their rib cage to increase surface area and darken their skin. If they get too cold, then they can lie parallel to the sun, open the mouth wide, burrow into soil, lighten the skin or seek out shade.
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References
- Photo Credit REPTILE image by sylvie BRELOT-FORMENTO from Fotolia.com
