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''Oryzomys nelsoni'' is an extinct rodent of María Madre Island, Nayarit, Mexico. Within the genus ''Oryzomys'' of the family Cricetidae, it may have been most closely related to the mainland species ''O. albiventer''. Since its first description in 1898, most authors have regarded it as a distinct species, but it has also been classified as a mere subspecies of the marsh rice rat (''O. palustris''). After its discovery in 1897, it has never been recorded again and it is now considered extinct; the presence of introduced black rats on María Madre may have contributed to its extinction. ''Oryzomys nelsoni'' was a large species, distinguished in particular by its long tail, robust skull, and large incisors. It was reddish to yellowish above and mostly white below. Its diet may have included plant material and small animals. ==Taxonomy== ''Oryzomys nelsoni'' was collected by Edward William Nelson and Edward Goldman in May 1897 and never found again.〔Carleton and Arroyo-Cabrales, 2009, p. 114; Nelson, 1899a, pp. 7–8〕 Their visit for the Biological Survey of the United States Department of Agriculture was one of the first scientific explorations of the islands.〔Nelson, 1899a, pp. 7–8; Merriam, 1899, p. 13〕 Clinton Hart Merriam identified the mammals they obtained, including four specimens of ''Oryzomys nelsoni'', which were deposited in the United States National Museum and remain there.〔Merriam, 1898, p. 13; Nelson, 1899a, p. 15; Carleton and Arroyo-Cabrales, 2009, p. 122〕 He named it as a species of the genus ''Oryzomys'', ''Oryzomys nelsoni''; the specific name honors Nelson.〔Merriam, 1898, p. 15; Álvarez-Castañeda and Méndez, 2003, p. 2〕 Investigators have generally retained it as a species distinct from other ''Oryzomys'',〔 but in 1971 Hershkovitz listed it as one of many subspecies of ''Oryzomys palustris'',〔 which he envisaged as a wide-ranging species encompassing what is now the marsh rice rat (''O. palustris'') of the southern and eastern United States, ''O. couesi'' of Central America, and several other species with more limited distributions.〔Musser and Carleton, 2005, pp. 1147, 1152–1153; Carleton and Arroyo-Cabrales, 2009, p. 116〕 In his 1918 revision of North American ''Oryzomys'', Goldman considered ''O. nelsoni'' to be most closely related to the nearest mainland subspecies of ''O. couesi'', ''O. couesi mexicanus''. In 2009, Michael Carleton and Joaquin Arroyo-Cabrales revised the ''Oryzomys'' of western Mexico and confirmed that ''O. nelsoni'' is a very distinct species. Their morphometrical analysis found some resemblance between the species and ''Oryzomys albiventer'' of interior mainland Mexico, and they suggested that although ''O. nelsoni'' likely represents an old, distinctive lineage, it may have derived from a common ancestor with ''O. albiventer''.〔Carleton and Arroyo-Cabrales, 2009, p. 110〕 ''Oryzomys nelsoni'' is one of about eight species in the genus ''Oryzomys'', which occurs from the eastern United States (''O. palustris'') into northwestern South America (''O. gorgasi'').〔Carleton and Arroyo-Cabrales, 2009, p. 106〕 ''O. nelsoni'' is further part of the ''O. couesi'' section, which is centered around the widespread Central American ''O. couesi'' and also includes various other species with more limited and peripheral distributions.〔Carleton and Arroyo-Cabrales, 2009, p. 117〕 Many aspects of the systematics of the ''O. couesi'' section remain unclear and it is likely that the current classification underestimates the true diversity of the group.〔Carleton and Arroyo-Cabrales, 2009, p. 107〕 ''Oryzomys'' previously included many other species, which were progressively removed in various studies culminating in a contribution by Marcelo Weksler and coworkers in 2006 that removed more than forty species from the genus.〔Weksler et al., 2006, table 1〕 All are classified in the tribe Oryzomyini ("rice rats"), a diverse assemblage of American rodents of over a hundred species,〔Weksler, 2006, p. 3〕 and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.〔Musser and Carleton, 2005〕 Common names proposed for this species include Nelson rice rat,〔Goldman, 1918, p. 46〕 Nelson's rice rat,〔Álvarez-Castañeda and Méndez, 2003, p. 1〕 Nelson's oryzomys,〔Musser and Carleton, 2005, p. 1152〕 and Tres Marias Island rice rat.〔 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「Oryzomys nelsoni」の詳細全文を読む スポンサード リンク
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