The Desert Tortoise


April 19, 1998


The desert tortoise (Gopherus agassizii) has many adaptations to a hot, dry environment. Tortoises are turtles that live only on land and are reptiles. Tortoises eat only plants. 

A tortoise has a strong, bony skull and jaws to give protection to the sense organs. The long neck helps them reach out to eat plants and withdraw into the shell to save water. 

A tortoise has a round bony upper shell (carapace) and a flat bony lower shell (plastron), which help conserve water and block predators. The top and bottom are united by bony bridges. The shell grows out of the backbone and ribs. 

1. Horny shields (scutes) cover the outside, just like the scales of other reptiles. The pattern of scutes is different in each tortoise, just like fingerprints in people. Desert tortoises do not shed their scutes, like some other turtles do.

Two large points stick out from the front of the plastron (gular horns) which help tortoises to push through the desert sand and to fight.

A tortoise has two eye lids. The upper is like our eyelid, and the lower (nictitating membrane) is transparent and keeps the eye from drying.

A tortoise has no teeth so it tears at desert plants, from which it gets most of its water.

The forelimbs and hindlimbs are alike with five toes, most with claws, to help them move on sand. The leg muscles are strong, and the front legs look like shovels to dig with. 

The skin is tough and dark, to help conserve water and radiate heat.

Tortoises live in burrows they dig, to stay out of the heat in summer and to conserve water. In summer, tortoises live in holes, where they rest during the hot part of the day (estivate), but in winter they dig a den to hibernate in. Tortoises are cold-blooded (ectothermic) like most reptiles.

Tortoises get most of their water from plants they eat. Some tortoises can store water in special places (cloacal bladders). 

Tortoises can live one hundred years. 

Tortoises lay leathery eggs in nests, so the eggs do not dry out.

References

Bare, C.S., The Durable Desert Tortoise. Dodd Mead, New York, 1979.

Fine, E.H. The Turtle and Tortoise. Crestwood House, Mankato MN, 1988.

Souza, D.M. What's Under the Shell? Carolrhoda, Minneapolis MN, 1992.

Ashley, L.M. The Laboratory Anatomy of the Turtle. Brown, Dubuque IA, 1962.