The Galápagos tortoise or Galápagos giant tortoise (Chelonoidis nigra) is the largest living species of tortoise and the 13th-heaviest living reptile. Modern giant tortoises can weigh up to 250 kg; even larger versions, now extinct, roamed every continent except Antarctic and Australia into the Pleistocene (<1.8 million years ago). With life spans in the wild of over 100 years, it is one of the longest-lived vertebrates. A captive individual lived at least 170 years.
Today, they exist only on two remote archipelagos: the Galápagos 1000 km due west of Ecuador, and Aldabra in the Indian Ocean, 700 km east of Tanzania. The tortoise is native to seven of the Galápagos Islands, a volcanic archipelago about 1,000 km (620 mi) west of the Ecuadorian mainland. Tortoises are not likely to migrate as they are too big and hold an extremely slow metabolism. Spanish explorers, who discovered the islands in the 16th century, named them after the Spanish galápago, meaning tortoise. Tortoises also live very uncomplicated lives, and can nap up to 16 hours a day.
Shell size and shape vary between populations. On islands with humid highlands, the tortoises are larger, with domed shells and short necks - on islands with dry lowlands, the tortoises are smaller, with “saddleback” shells and long necks. Charles Darwin’s observations of these differences on the second voyage of the Beagle in 1835, contributed to the development of his theory of evolution. Darwin was highly impressed by these giants, although he referred to them as “antediluvian” and “giant monsters”, less than affectionate terms.