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''Carletonomys cailoi'' is an extinct rodent from the Pleistocene of Buenos Aires Province, Argentina. Although known only from a single maxilla (upper jaw) with the first molar, its features are so distinctive that it is placed in its own genus, ''Carletonomys''. Discovered in 1998 and formally described in 2008, it is part of a well-defined group of oryzomyine rodents that also includes ''Holochilus'', ''Noronhomys'', ''Lundomys'', and ''Pseudoryzomys''. This group is characterized by progressive semiaquatic specializations and a reduction in the complexity of molar morphology. The single known molar is high-crowned (hypsodont) and flat-crowned (planar) and is distinctive in lacking the ridge that connects the front to the middle part of the molar, the anterior mure, and in the configuration of another ridge, the mesoloph. ''Carletonomys'' was probably herbivorous and lived in a wet habitat. ==Taxonomy== ''Carletonomys cailoi'' was discovered in 1998 in a silt deposit in San Cayetano Partido, southeastern Buenos Aires Province. The stratigraphic context suggests this locality is slightly over 1 million years old (Ensenadan South American Land Mammal Age), making ''Carletonomys'' the oldest known oryzomyine.〔Pardiñas, 2008, p. 1276〕 The single known specimen is now in the collections of the Museo de La Plata. It was initially referred to the genus ''Noronhomys'', which is currently known only from the island of Fernando de Noronha off northeastern Brazil, but in 2008 Argentinean mammalogist Ulyses Pardiñas established it as the holotype of a new genus and species of rodent in a publication in the ''Journal of Mammalogy''. The generic name, ''Carletonomys'', combines the name of American mammalogist Michael Carleton with the Ancient Greek μυς ''mys'' "mouse"〔Pardiñas, 2008, p. 1271〕 and the specific name, ''cailoi'', honors Argentinean biologist Carlos "Cailo" Galliari.〔Pardiñas, 2008, p. 1272〕 The fossil has a number of features that suggest a relation to a group of oryzomyine rodents that includes the South American marsh rat ''Holochilus'', its living relatives ''Lundomys'' and ''Pseudoryzomys'', and the extinct ''Noronhomys'' and ''Holochilus primigenus''.〔Pardiñas, 2008, p. 1275〕 They share high-crowned (hypsodont) molars and several simplifications of molar morphology,〔Pardiñas, 2008, pp. 1273–1274; Weksler, 2006, p. 131〕 as well as other features that cannot be assessed in ''Carletonomys'', which indicate specializations towards a semiaquatic lifestyle.〔Weksler, 2006, p. 131〕 It shows the most similarity to ''Noronhomys'' and ''Holochilus'', so much so that Pardiñas considered placing it in either of these two genera, but its distinctive morphological features justify placement in a separate genus.〔Pardiñas, 2008, pp. 1274–1275〕 This group of genera encompasses only a small part of the diversity of the tribe Oryzomyini, a group of over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands and some of the Antilles. Oryzomyini is one of several tribes recognized within the subfamily Sigmodontinae, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae, other members of which include voles, lemmings, hamsters, and deermice, all mainly from Eurasia and North America.〔Musser and Carleton, 2005〕 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「Carletonomys」の詳細全文を読む スポンサード リンク
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