Nelson's Rice Rat - AbsoluteAstronomy.com

Oryzomys nelsoni is an extinct

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

of María Madre Island

Islas Marías

The Islas Marías are an archipelago of four islands that belong to Mexico. They are located in the Pacific Ocean, some off the coast of the state of Nayarit. They are part of the municipality of San Blas, Nayarit...

, Nayarit

Nayarit

Nayarit officially Estado Libre y Soberano de Nayarit is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 20 municipalities and its capital city is Tepic.It is located in Western Mexico...

, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. Within the genus Oryzomys
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 of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...

of the family Cricetidae

Cricetidae

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...

, it may have been most closely related to the mainland species O. albiventer
Oryzomys albiventer
Oryzomys albiventer is a rodent in the genus Oryzomys of family Cricetidae from interior western Mexico, 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 until it was reinstated as a...

. 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

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

of the marsh rice rat

Marsh Rice Rat

The marsh rice rat is a semiaquatic North American rodent in the family Cricetidae. It is found mostly in the eastern and southern United States, from New Jersey and Kansas south to Florida and northeasternmost Tamaulipas, Mexico; its range previously extended further west and north, where it may...

(O. palustris).

After its discovery in 1897, it has never been recorded again and it is now considered extinct; the presence of introduced

Introduced species

An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

black rat

Black Rat

The black rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae . The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.-Taxonomy:The black rat was...

s 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 incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

s. 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

Edward William Nelson

Edward William Nelson was an American naturalist and ethnologist. He was born in Manchester, New Hampshire. In 1871 together with his family, he became homeless due to the Chicago Fire....

and Edward Goldman in May 1897 and never found again. Their visit for the Biological Survey of the United States Department of Agriculture

United States Department of Agriculture

The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...

was one of the first scientific explorations of the islands. Clinton Hart Merriam

Clinton Hart Merriam

Clinton Hart Merriam was an American zoologist, ornithologist, entomologist and ethnographer.Known as "Hart" to his friends, Dr. Clinton Hart Merriam was born in New York City in 1855. His father, Clinton Levi Merriam, was a U.S. congressman. He studied biology and anatomy at Yale University and...

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

Philip Hershkovitz

Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...

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

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

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

Morphometrics

Morphometrics refers to the quantitative analysis of form, a concept that encompasses size and shape. Morphometric analyses are commonly performed on organisms, and are useful in analyzing their fossil record, the impact of mutations on shape, developmental changes in form, covariances between...

analysis found some resemblance between the species and Oryzomys albiventer
Oryzomys albiventer
Oryzomys albiventer is a rodent in the genus Oryzomys of family Cricetidae from interior western Mexico, 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 until it was reinstated as a...

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
Oryzomys gorgasi
Oryzomys gorgasi, also known as Gorgas's Oryzomys or Gorgas's Rice Rat, is a rodent in the genus Oryzomys of family Cricetidae. First collected as a living animal in 1967, it is known from only a few localities, including a freshwater swamp in the lowlands of northwestern Colombia and a mangrove...

). 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

Systematics

Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...

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

Oryzomyini

Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...

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

Sigmodontinae

The subfamily Sigmodontinae is one of the most diverse groups of mammals. It 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 species count...

of family Cricetidae

Cricetidae

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...

, along with hundreds of other species of mainly small rodents.

Common name

Common name

A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

s proposed for this species include Nelson Rice Rat, Nelson's Rice Rat, Nelson's Oryzomys, and Tres Marias Island Rice Rat.

Description

Oryzomys nelsoni was a large and long-tailed Oryzomys; its tail was longer than that of any other western Mexican Oryzomys. The upperparts were ochraceous to buff, most richly so on the rump, and paler further to the front and low on the flanks. On the head and the back, blackish hairs somewhat darkened the overall color. The underparts were white, with lead-colored underfur that was visible in some places. The ears were covered on both sides with scanty grayish hairs. The large hindfeet were sparsely covered with pale hairs. The tail was largely dark, but the underside of the basal one third to one half was light yellow.

Oryzomys nelsoni was distinctive in its large skull with broad, well-developed incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

s and a strong front part (rostrum) that is strongly curved downwards. In O. albiventer, the rostrum and incisors were not as massive, but the molars are larger. The interparietal bone, part of the roof of the braincase, was broad and the incisive foramina

Incisive foramen

The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...

, which perforated the palate

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 separate. The palate is divided into two parts, the anterior...

between the incisors and the molars

Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

, were relatively short.

Total length in the four known specimens is 282 to 344 mm (11.1 to 13.5 in), averaging 322 mm (12.7 in); head and body length is 122 to 153 mm (4.8 to 6.0 in), averaging 140.5 mm (5.53 in); tail length is 160 to 191 mm (6.3 to 7.5 in), averaging 181.5 mm (7.15 in); and hindfoot length is 35 to 39 mm (1.4 to 1.5 in), averaging 37.3 mm (1.47 in).

Ecology and extinction

Nelson and Goldman found the species only in a damp, herbaceous site now known as the "Sacatal" near a spring high on María Madre Island, the largest of the Islas Marías

Islas Marías

off the coast of Nayarit

Nayarit

, western Mexico, and Nelson wrote that it was rare. He gave the elevation of this place as 1800 ft, which Álvarez-Castañeda and Méndez converted to 550 m, but in his 1918 paper, Goldman gave 800 ft instead, which Carleton and Arroyo-Cabrales in 2009 converted to 245 m. The next survey of small mammals on the island took place in March 1976 by a team led by Don E. Wilson. They failed to collect O. nelsoni and instead found only the introduced

Introduced species

black rat

Black Rat

(Rattus rattus) at the locality where Nelson and Goldman had collected O. nelsoni; this species may have contributed to the decline of the indigenous rodent.

The species is now considered extinct, although as late as 2002 the Mexican government listed it as "threatened". Another Islas Marías endemic, the deermouse Peromyscus madrensis, still occurred on María Madre in 1976. Oryzomys nelsoni is thought to have fed on plant material such as weeds, fruit, and seeds, and more rarely on animals such as fish and invertebrates.

Literature cited

Álvarez-Castañeda, S.T. and Méndez, L. 2003. Oryzomys nelsoni. Mammalian Species 735:1–2.
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.
Goldman, E.A. 1918. The rice rats of North America. North American Fauna 43:1–100.
Merriam, C.H. 1898. Mammals from the Tres Marias Islands, off western Mexico. Proceedings of the Biological Society of Washington 12:13–19.
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. ISBN 978-0-8018-8221-0
Nelson, E.W. 1899a. General description of the Tres Marias Islands, Mexico. North American Fauna 14:7–14.
Nelson, E.W. 1899b. Mammals of the Tres Marias Islands. North American Fauna 14:15–20.
Timm, R., Álvarez-Castañeda, S.T. and Lacher, T. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on November 30, 2009.
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.
Wilson, D.E. 1991. Mammals of the Tres Marías Islands. Bulletin of the American Museum of Natural History 206:214–250.

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