Friday, January 24, 2014

Giaesnt Tortois

Giaesnt Tortois
Giaesnt tortois are characteristic reptiles of certain tropical islands. Often reaching enormous size-they can weigh as much as 300 kg  and can grow to be 1.3 m they live, or lived  in the Seychelles, the Mascarenes and the Galapagos. Today, the world's largest population inhabits Aldabra Atoll in Seychelles, where there are approximately 150,000 individuals. Although appearing similar, the tortoises represent separate branches of evolution. The Seychelles and Mascarenes tortoises derive from nearby Madagascar, while the Galapagos tortoises came from nearby Ecuador.

Galápagos tortoise, Giant Tortoise on Santa Cruz Island
Although often considered examples of island gigantism, prior to the arrival of Homo sapiens giant tortoises also occurred in non-island locales, as well as on a number of other, more accessible islands. During the Pleistocene, and mostly during the last 50,000 years, tortoises of the mainland of southern Asia  North and South America, Australia  Indonesia, Madagascar  and even the island of Malta became extinct. The giant tortoises formerly of Africa died out somewhat earlier, during the late Pliocene. While the timing of the disappearances of various extinct giant tortoise species seems to correlate with the arrival of humans, direct evidence for human involvement in these extinctions is usually lacking; however, such evidence has been obtained in the case of Meiolania damelipi in Vanuatu. One interesting relic is the shell of an extinct giant tortoise found in a submerged sinkhole in Florida with a wooden spear piercing it, carbon dated to 12,000 years ago.
These animals belong to an ancient group of reptiles, appearing about 250 million years ago. In the Upper Cretaceous, 70 or 80 million years ago some already became gigantic. About 1 million years ago tortoises reached the Galápagos Islands. Since 100,000 years ago most of the gigantic species began to disappear. Only 250 years ago there were at least 20 species and subspecies in islands of the Indian Ocean and 14 or 15 subspecies in the Galápagos Islands.


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