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Arnold's giant tortoise (''Aldabrachelys gigantea arnoldi''), also known as the Seychelles saddle-backed tortoise, is a tortoise subspecies of the Aldabra giant tortoise. It inhabited the granitic Seychelles islands until around 1840, when it was presumed to be extinct, along with the Seychelles giant tortoise; a species which shared the same islands. The Aldabran species has generally been assumed to have been the only one to survive over-exploitation. Occasionally, most recently in 1995, it has been suggested that some Seychelles granitic island tortoises survive in captivity. The report of oddly-shaped captive tortoises prompted the Nature Protection Trust of Seychelles to examine the identity of the living tortoises. Examination of museum specimens of the 'extinct' Seychelles species by Dr. Justin Gerlach and Laura Canning confirmed that some living tortoises do show characteristics of the supposedly extinct species.〔(【引用サイトリンク】url=http://islandbiodiversity.com/tortoise.htm )〕 Some recently published scientific papers on the genetics of the Seychelles and Indian Ocean tortoises provide conflicting results. Some studies suggest only one species was ever present in the islands, whilst others suggest three distinct, but closely related, species. These different views derive from studies of different genes. A synthesis of all available genetic data indicates Arnold's tortoise is genetically the most distinctive ''Aldabrachelys'' tortoise. This fits with the ecology and morphology of the species, as a highly distinctive tortoise adapted to feeding on low vegetation rather than the grazing habits of the Seychelles giant tortoise and Aldabra giant tortoise. Due to its unusual 'saddlebacked' shape, this is the only Seychelles tortoise species that regularly basks in the sun. The other species do so occasionally, but Arnold's tortoises rapidly lose heat from the skin of their exposed necks and need to heat up in the sun in the mornings. ==Description== The three Aldabra-Seychelles giant tortoise species can be distinguished based on carapace shape, but many captive animals may have distorted carapaces, so may be difficult to identify. Arnold's tortoise is flattened, smooth, and with a relatively high opening to the shell; it is usually black. This species usually has a depression on the suture between the first and second costal scutes, this may be a shallow depression or a distinctive pit. The plastron is less variable than the carapace and usually provides a good indication of the species.〔(【引用サイトリンク】url=http://islandbiodiversity.com/tortid.htm )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aldabrachelys gigantea arnoldi」の詳細全文を読む スポンサード リンク
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