Galapagos giant tortoise  (Geochelone spp.)

This enormous giant tortoise was once so numerous that Spanish explorers of this region named the archipelago after one of its more extraordinary inhabitants; 'Galapagos' means 'tortoise' in Spanish (7). These reptiles are the largest living tortoises and the heavy carapace can reach lengths of up to 150 centimetres (7); they have relatively heavy limbs and a long neck (2). These tortoises illustrate the principal of adaptive radiation that Darwin coined after insights in the Galapagos; populations isolated on islands or on parts of larger islands have adapted to different conditions and now have distinct appearances. Presently 11 species are recognised (5), relating to isolated populations on certain islands within the Galapagos chain (8). The species can be generally separated into those with 'domed' shells, which occur on the larger, wetter islands, and smaller tortoises with 'saddleback' carapaces that are found on smaller islands with dry vegetation (9). It is thought that the distinctive saddleback shell enables its bearer to reach taller vegetation; these tortoises also have longer limbs and necks (9).