Oryzomys Nelsoni - Taxonomy

Taxonomy

Oryzomys nelsoni was collected by Edward William Nelson and Edward Goldman in May 1897 and never found again. Their visit for the Biological Survey of the United States Department of Agriculture was one of the first scientific explorations of the islands. 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. He named it as a species of the genus Oryzomys, Oryzomys nelsoni; the specific name honors Nelson. 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.

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.

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). 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. 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. 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. All are classified in the tribe Oryzomyini ("rice rats"), a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.

Common names proposed for this species include Nelson rice rat, Nelson's rice rat, Nelson's oryzomys, and Tres Marias Island rice rat.