A portrait of a Galápagos giant tortoise. They are the largest living species of tortoise and one of the heaviest reptilians. 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. With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. A captive individual lived at least 170 years. Shell size and shape vary between the islands, Charles Darwin’s observations of these differences on the second voyage of the Beaglein 1835, contributed to the development of his theory of evolution. All subspecies of Galápagos tortoises evolved from common ancestors that arrived from mainland South America by overwater dispersal. Genetic studies have shown that the Chaco tortoise of Argentina and Paraguay is their closest living relative. Survival on the 1000-km oceanic journey is accounted for because the tortoises are buoyant, can breathe by extending their necks above the water, and are able to survive months without food or fresh water. As they are poor swimmers, the journey was facilitated by the Humboldt Current, which diverts westwards towards the Galápagos Islands from the mainland. @RobertClarkphoto @Natgeo @thephotosociety @instituteartist.
by natgeo http://bit.ly/1MBxeOE

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