Shells
The shells of tortoises are comprised of 59 to 61 bones that are covered by scutes, the shell's protective plates. The tortoise's shell tend to be a tall, rounded dome, which is fastened to its spine and rib cage. The visible upper half of the tortoise's shell is the carapace, while the plastron is the lower shell half that protects the tortoise's underbody.
Lifespan
Tortoises have long lifespans, routinely living 25 to 50 years in the wild. National Geographic notes that the Galapagos tortoise has a particularly long lifespan, with the oldest documented member of the species living 152 years. With proper care and feeding, pet tortoises can live for more than 20 years.
Diet
These reptiles subsist primarily on vegetarian diets, but younger tortoises are often omnivores, supplementing their diets with worms and insects for additional protein. A wild tortoise's diet consists largely of grasses, fruits and flowers, and while tortoises don't have teeth, their beaks have a hard edge that is sharp enough to allow them to chew their food.
Birth and Infancy
A pregnant tortoise will find a secluded spot to lay her clutch of eggs, bury them in the surrounding soil or plant detritus, then abandon them. A baby tortoise uses its egg tooth to crack its egg shell, and while infants are on their own in searching for food, they have yolk sacks on their bodies that supply nutrients for 3 to 7 days. The nest's temperature plays a large role in determining an infant tortoise's gender -- warmer nests are conducive to the births of females, while cooler nests yield more males.
Tortoises as Pets
Tortoise owners need to ensure that their pets have fresh drinking water and an adequate food supply available at all times. Hungry tortoises tend to get restless, but if they go too long without food, they sink into a deep lethargy and may not respond to the presence of food no matter how great their hunger. Pet tortoises are most comfortable in their habitats when they have a secluded spot for sleeping that offers privacy, so furnishing your tortoise's habitat with a manufactured house or a cluster of plants to use as a den will make your pet more comfortable.