The desert tortoise, Xerobates agassizi (formerly Gopherus agassizi), is an ancient animal, thought to have originated 50 million years ago. Evolution has created an animal ideally suited to the harsh, dry climate of our southwestern desert. It has been designated as the California state reptile, though it is also found in parts of Utah, Nevada, Arizona and Mexico.
The Desert Tortoise as a Pet: Many people seem to have an inexplicable affinity for tortoises. These reptiles have been kept as pets for centuries. Some find it extremely difficult to avoid the temptation of removing one of these animals from its natural habitat and taking it home, in spite of the legal ramifications. Fortunately, desert tortoises readily breed in captivity, creating a supply of hatchlings that may be kept as pets.
The age of young desert tortoises can be estimated by their size and rate of growth, though the high-protein diets frequently fed to captive tortoises can result in freakish overgrowth and development. Counting scute rings is meaningless. Plastron (bottom shell) differentiation usually occurs at 10-15 years of age, and maturity is reached at 25-30 years of age. Once a desert tortoise has reached maturity, it is virtually impossible to determine its exact age. However, shell patterns change and the shell becomes flattened and concave as a tortoise ages. As a result, experienced biologists can "guestimate" the age of an older tortoise with reasonable accuracy. Tortoises theoretically grow for life, and giants are occasionally found. The life span of desert tortoises is thought to exceed 130-150 years!