''Oryzomys albiventer'' is a

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

in the genus ''

Oryzomys ''Oryzomys'' is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat (''O. palustris'') of the United States and ...

'' of family

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and h ...

from interior western

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

, in the states of Jalisco, Guanajuato, and Michoacán. First described in 1901 as a separate species, it was later lumped under '' O. couesi'' and the

marsh rice rat The marsh rice rat (''Oryzomys palustris'') is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, fr ...

(''O. palustris'') until it was reinstated as a species in 2009. It differs from neighboring ''Oryzomys'' populations in size and measurements and is a large, brightly colored species with a long tail and robust skull and molars. Its range has been much impacted by agricultural development, but isolated populations are thought to persist.

Taxonomy

''Oryzomys albiventer'' was first described by C.H. Merriam in 1901 on the basis of ten specimens from Ameca, Jalisco.Merriam, 1901, pp. 279–280 He named the animal ''albiventer'' after the white color of its underpartsCarleton and Arroyo-Cabrales, 2009, p. 118 and considered it most closely related to ''Oryzomys aquaticus'' (currently included in '' Oryzomys couesi'').Carleton and Arroyo-Cabrales, 2006, p. 116 Two years later, D.G. Eliot described ''Oryzomys molestus'' on the basis of a single individual from Ocotlán, Jalisco; the name ''molestus'' means "troublesome, irksome". Eliot considered ''Oryzomys fulgens'', another current synonym of ''O. couesi'', as the closest relative of his new species.Eliot, 1903, p. 145 In his 1918 review of North American ''

'', E.A. Goldman assessed the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

of ''O. molestus'', an old male, as merely a large example of ''albiventer'', and reduced ''albiventer'' to one of many subspecies of ''O. couesi''. He considered it closely related to three other highland Mexican forms.Goldman, 1918, p. 37 In 1960, E.R. Hall argued that ''O. couesi'' was the same species as the

(''O. palustris'') of the United States, and listed ''albiventer'' as a subspecies of the latter. Later, ''O. couesi'' was again accepted as separate from the marsh rice rat, but ''O. albiventer'' was still classified under ''O. couesi''.Carleton and Arroyo-Cabrales, 2009, p. 95 In a 2009 revision of the ''Oryzomys'' of western Mexico, M.D. Carleton and J. Arroyo-Cabrales noted substantial differences in coloration and measurements between highland populations (''albiventer'') and lowland populations (''mexicanus'') in Jalisco.Carleton and Arroyo-Cabrales, 2009, p. 99 On the basis of these differences, they recognized ''O. albiventer'' as a species separate from the lowland populations, which they classified under ''O. couesi''. They confirmed that Eliot's ''molestus'' was based on a large example of ''O. abiventer'', but left the status of the three forms Goldman had associated with ''albiventer''—''crinitus'', ''aztecus'', and ''regillus''—open, noting that there was no convincing evidence that these represented the same species as ''O. albiventer''.Carleton and Arroyo-Cabrales, 2009, p. 113 The identity and exact provenance of ''fulgens'' (supposed to be from the

Valley of Mexico The Valley of Mexico ( es, Valle de México) is a highlands plateau in central Mexico roughly coterminous with present-day Mexico City and the eastern half of the State of Mexico. Surrounded by mountains and volcanoes, the Valley of Mexico w ...

), and consequently its relationship to ''O. albiventer'', remain unknown.Carleton and Arroyo-Cabrales, 2009, p. 115 ''O. albiventer'' is part of the genus ''

'', which currently includes about eight species distributed from the eastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

(''O. palustris'') into northwestern

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

('' O. gorgasi'').Carleton and Arroyo-Cabrales, 2009, p. 106 ''O. albiventer'' is further part of the ''O. couesi'' section, which is centered on 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.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. All are classified in the tribe

Oryzomyini Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of ...

("rice rats"), a diverse assemblage of American rodents of over a hundred species, and on higher taxonomic levels in the subfamily

Sigmodontinae The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...

of family

, along with hundreds of other species of mainly small rodents.Musser and Carleton, 2005 In 1904, Eliot used the common name "white-bellied rice rat" for ''O. albiventer''Eliot, 1904, p. 236 and "Ocotlan rice rat" for ''O. molestus''. In 1918, Goldman also used "white-bellied rice rat" for ''O. albiventer''.

Description

''Oryzomys albiventer'' is a large and long-tailed ''Oryzomys''. The upperparts are brightly ochraceous, becoming grayer toward the front. The hairs on the underparts are pale gray near the bases and white in the outer half, so that the underparts appear pale grayish according to Carleton and Arroyo-Cabrales (not white as claimed by Merriman). The tail is dark above and light below. The skull and

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

are relatively robust. ''O. albiventer'' has broad

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...

es (cheekbones), long

incisive foramina In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...

(perforations of the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...

between the

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s and the molars), and long nasal bones that extend behind the premaxillary bones. Compared to its lowland relative ''O. couesi mexicanus'', ''O. albiventer'' is larger and more brightly colored and has larger molars but narrower incisive foramina.Carleton and Arroyo-Cabrales, 2009, pp. 101–102 In twelve specimens, total length is , averaging ; head and body length is , averaging ; tail length is , averaging ; hindfoot length is , averaging ; and skull length ( occipitonasal length) is , averaging .Carleton and Arroyo-Cabrales, 2009, table 2

Distribution and conservation

''O. albiventer'' occurs at about elevation in northern Michoacán, southern Guanajuato, and central and eastern Jalisco, mostly in the area around

Lake Chapala Lake Chapala ( es, Lago de Chapala, ) is Mexico's largest freshwater lake. It lies in the municipalities of Ocotlán, Chapala, Jocotepec, Poncitlán, and Jamay, in Jalisco, and in Venustiano Carranza and Cojumatlán de Régules, in Mich ...

. Its range has seen massive agricultural development and although populations may survive, the current distribution of the species is certainly highly fragmented. More survey work is needed to assess the distribution and status of ''O. albiventer''.

References

Literature cited

*Carleton, M.D. and Arroyo-Cabrales, J. 2009
Review of the ''Oryzomys couesi'' complex (Rodentia: Cricetidae: Sigmodontinae) in western Mexico
''Bulletin of the American Museum of Natural History'' 331:94–127. *Eliot, D.G. 1903
A list of a collection of Mexican mammals with descriptions of some apparently new forms
Field Columbian Museum, Zoological Series 3(8):141–149. *Eliot, D.G. 1904
The land and sea mammals of Middle America and the West Indies
Field Columbian Museum, Zoölogical Series 4(1):i–xxi, 1–439. *Goldman, E.A. 1918
The rice rats of North America
''North American Fauna'' 43:1–100. *Hall, E.R. 1960
''Oryzomys couesi'' only subspecifically different from the marsh rice rat, ''Oryzomys palustris''
(subscription required). ''The Southwestern Naturalist'' 5(3):171–173. *Merriam, C.H. 1901
Synopsis of the rice rats (genus ''Oryzomys'') of the United States and Mexico
''Proceedings of the Washington Academy of Sciences'' 3:273–295. *Musser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)
''Mammal Species of the World: a taxonomic and geographic reference''. 3rd ed
Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. *Weksler, M. 2006
Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data
''Bulletin of the American Museum of Natural History'' 296:1–149. *Weksler, M., Percequillo, A.R. and Voss, R.S. 2006
Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae)
''American Museum Novitates'' 3537:1–29. {{Good article Oryzomys Endemic mammals of Mexico Fauna of the Trans-Mexican Volcanic Belt Rodents of North America Natural history of Jalisco Natural history of Guanajuato Natural history of Michoacán Mammals described in 1901 Taxa named by Clinton Hart Merriam