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The pygmy three-toed sloth (''Bradypus pygmaeus''), also known as a monk sloth or dwarf sloth, is a small three-toed sloth, endemic to Isla Escudo de Veraguas, a small island off the coast of Panama, which separated from the mainland nearly 8900 years ago. Only described as a separate species in 2001, they are thought to have originated from isolation of individuals of the mainland population of brown-throated three-toed sloths. The population became a distinct species through insular dwarfism on the island. Studies suggest an inverse, linear relationship between mean body sizes and age of the island for island populations of sloths in this region.〔 == Characteristics == Pygmy three-toed sloths have a tan face with a dark brown band across the brow and orange eye patches. The back can exhibit either uniform or blotchy color distribution, but is usually dark brown with an obvious dorsal stripe. Pygmy sloths are unique in that they have long hairs on the crown and the sides of the head, giving the distinct impression of a hood. Compared to the related brown-throated three-toed sloth, the pygmy species is, on average 40% smaller in body mass, weighing , and 15% smaller in body length. Adults measure , with a tail long. They have a relatively small skull, with a large external auditory meatus, narrow squamosal and mandibular processes, no foramina in the anterodorsal nasopharynx, a minuscule stylomastoid foramen, and usually lack foramina for the external carotid artery.〔 They have 18 teeth, 10 in the upper jaw and 8 in the lower. Two of the teeth in each jaw are incisor-like, although those in the upper jaw are small or may be absent. The incisor-like teeth in the lower jaw are compressed anteroposteriorly. Many of the features found in pygmy sloths are thought to be indicative of a relatively rapid evolution of a new species in an isolated, island habitat.〔 Pygmy sloths are also 12–16% smaller in cranial dimensions than the mainland species (length: ; width: .〔 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「Pygmy three-toed sloth」の詳細全文を読む スポンサード リンク
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