The Galapagos tortoise (or giant Galápagos tortoise), Geochelone nigra, is the largest living tortoise. It can weigh over 225 kg (500 pounds) and measure 1.8 m (6 feet) from head to tail. It is a very slow-moving animal, moving only 0.25 km/h (0.16 miles per hour). It is a herbivore, eating grasses, plant leaves, cactus and fruits. 

The Galapagos tortoise has a very large shell (or carapace) made of bone. The shape of the carapace and other morphological features are indicative of the terrain the animal inhabits. Highland areas with lush vegetation near the ground are normally home to tortoises with domed shells; these animals have restricted upward head movement due to shorter necks, and tend to have shorter limbs as well (see photo). Tortoises with saddleback shells inhabit coastal regions that have less vegetation at ground level; their extended necks and limbs help them to reach food higher off the ground. Shells can also be of intermediate type, with characteristics between domed and saddleback types. These features played an important role in the development of Charles Darwin's theory of evolution. 

The Galapagos tortoise is found on the Galapagos Islands just west of Ecuador in South America. Because of the 250,000 tortoises that inhabited the island, Spanish explorers named the islands Galápagos for the giant tortoises. Today only 15,000 are left, mainly due to action of whalers and pirates that killed them for food during the 18th. and 19th. Centuries. 

Research has shown that there were probably fourteen subspecies of Geochelone elephantopus. Now only eleven subspecies remain, five in each of the five volcanoes of Isabela island, and the other six at Santiago, Santa Cruz, San Cristobal, Pinzón, Española and Pinta. The Pinta subspecie is due to become extinct as only one single male, known as Lonesome George, is known to be alive. 

One of the oldest living specimens is a giant Galápagos tortoise named Harriet in the Australia Zoo at Beerwah, Queensland, Australia. Its estimated date of birth is 1830.