Skin Prevents Water Loss

close up photograph of a beige and black crocodile's face

Biological Strategy

Crocodiles and alligators

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Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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The skin of crocodiles and alligators protects against water loss via bony scales called scutes.

“Crocodiles and alligators have rather different scales from those of other reptiles. Called ‘scutes’, they are bony and quite massive, but are not fused together joined to the underlying skeleton, so flexible fast movement is still possible. Each scute develops on its own, and is replaced by layers from below. The scutes are particularly massive on the back, perhaps because this is the area most exposed to the sun and most at risk of drying out…where the scutes are largest, the area of less waterproof skin between is smallest, so large scutes provide a good seal against water loss. Areas of small scutes occur on the sides and around the shoulders and hips, where greater flexibility is needed during movement.” (Foy and Oxford Scientific Films 1982:93)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.

Last Updated August 18, 2016

References

Book

The grand design: Form and colour in animals

BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London | 26/02/1983 | Sally Foy

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