The three basic carapace types -- domed , saddle-backed, and intermediate -- have evolved as adaptations to certain island environments. For instance, the saddle-backed types have especially long necks and limbs and a raised carapace. This helps them reach the taller vegetation typically found on the lower, drier islands where the saddle-backs roam. This is the oldest resident of the islands, a centenarian giant tortoise known as Lonesome George.