St. Vincent Pygmy Rice Rat
Encyclopedia
Oligoryzomys victus, also known as the St. Vincent Colilargo or St. Vincent Pygmy Rice Rat, is a species of rodent
in the genus Oligoryzomys
of the oryzomyine
tribe. Only one specimen is known, which was collected on Saint Vincent
in the Lesser Antilles
in about 1892, and it is now presumed extinct.
The only known specimen was collected by H. H. Smith at an unknown location on Saint Vincent and later presented to the British Museum of Natural History, where it was registered as specimen BMNH 97.12.26.1. In 1898, Oldfield Thomas
described the specimen as the holotype
of a new species of Oryzomys
which he named Oryzomys victus. Although Thomas placed it close to species now placed in Oligoryzomys
, later compilators considered the affinities of O. victus as unknown; one study placed it in the Oryzomys tectus group (more or less = Oecomys
). In his 1962 study of Antillean oryzomyines, however, American paleontologist Clayton Ray reaffirmed its affinities with Oligoryzomys, but he was unable to resolve its relation within the genus. On the one hand, he saw closer morphological similarities to small Oligoryzomys such as O. fulvescens and O. delicatus, but on the other hand larger species such as O. longicaudatus are closer in size. Ray also considered the possibility that the St. Vincent population was in fact introduced from a still unknown mainland species, but considered this unlikely; no such species has since been found.
The holotype, a fluid-preserved adult female with the skull extracted, was described in Thomas' original description and in Ray's 1962 restudy. It is a relatively large Oligoryzomys and has the pelage dark reddish above and buffy white below. The short ears are brown in color. The tail nearly lacks hairs and is brown above and somewhat paler below. Like most oryzomyines, it has eight mammae, including a pectoral pair. The head and body length is 96 mm, the tail length 121 mm, the hind foot length (without claws) 25 mm, the ear length 14 mm, the greatest length of the skull 27.2 mm, the length of the upper molars is 3.9 mm, and the length of the lower molars is 4.0 mm.
Little is known about the habits or the ecology of O. victus; in fact, the only direct information is a collector's note which calls it a "forest rat". Its morphology suggests that it was not arboreal or fossorial
.
The extinction of O. victus may be associated with the introduction of the Small Asian Mongoose to St. Vincent in the 1870s. Ray suggests that the rice rat was an easier prey for the mongoose than introduced Rattus, which may have become partly arboreal, thus creating a competitive disadvantage for the rice rat. Any remaining populations may have been wiped out when the Soufrière
erupted in 1902, destroying the pristine vegetation on its slopes.
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....
in the genus Oligoryzomys
Oligoryzomys
Oligoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos...
of the oryzomyine
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...
tribe. Only one specimen is known, which was collected on Saint Vincent
Saint Vincent (island)
Saint Vincent is a volcanic island in the Caribbean. It is the largest island of the chain called Saint Vincent and the Grenadines. It is located in the Caribbean Sea, between Saint Lucia and Grenada. It is composed of partially submerged volcanic mountains...
in the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
in about 1892, and it is now presumed extinct.
The only known specimen was collected by H. H. Smith at an unknown location on Saint Vincent and later presented to the British Museum of Natural History, where it was registered as specimen BMNH 97.12.26.1. In 1898, Oldfield Thomas
Oldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
described the specimen as the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of a new species of 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...
which he named Oryzomys victus. Although Thomas placed it close to species now placed in Oligoryzomys
Oligoryzomys
Oligoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos...
, later compilators considered the affinities of O. victus as unknown; one study placed it in the Oryzomys tectus group (more or less = Oecomys
Oecomys
Oecomys is a genus of rodent within the tribe Oryzomyini of family Cricetidae. It contains about 17 species, which live in trees and are distributed across forested parts of South America, extending into Panama and Trinidad.-Literature cited:...
). In his 1962 study of Antillean oryzomyines, however, American paleontologist Clayton Ray reaffirmed its affinities with Oligoryzomys, but he was unable to resolve its relation within the genus. On the one hand, he saw closer morphological similarities to small Oligoryzomys such as O. fulvescens and O. delicatus, but on the other hand larger species such as O. longicaudatus are closer in size. Ray also considered the possibility that the St. Vincent population was in fact introduced from a still unknown mainland species, but considered this unlikely; no such species has since been found.
The holotype, a fluid-preserved adult female with the skull extracted, was described in Thomas' original description and in Ray's 1962 restudy. It is a relatively large Oligoryzomys and has the pelage dark reddish above and buffy white below. The short ears are brown in color. The tail nearly lacks hairs and is brown above and somewhat paler below. Like most oryzomyines, it has eight mammae, including a pectoral pair. The head and body length is 96 mm, the tail length 121 mm, the hind foot length (without claws) 25 mm, the ear length 14 mm, the greatest length of the skull 27.2 mm, the length of the upper molars is 3.9 mm, and the length of the lower molars is 4.0 mm.
Little is known about the habits or the ecology of O. victus; in fact, the only direct information is a collector's note which calls it a "forest rat". Its morphology suggests that it was not arboreal or fossorial
Fossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...
.
The extinction of O. victus may be associated with the introduction of the Small Asian Mongoose to St. Vincent in the 1870s. Ray suggests that the rice rat was an easier prey for the mongoose than introduced Rattus, which may have become partly arboreal, thus creating a competitive disadvantage for the rice rat. Any remaining populations may have been wiped out when the Soufrière
Soufrière (volcano)
La Soufrière [The Sulfurer] or Soufrière Saint Vincent is an active volcano on the island of Saint Vincent in the Windward Islands of the Caribbean.- Geography and structure :...
erupted in 1902, destroying the pristine vegetation on its slopes.
Literature cited
- 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 978-0-8018-8221-0Category:Extinct mammals
- Ray, C.E. 1962. The Oryzomyine Rodents of the Antillean Subregion. Doctor of Philosophy thesis, Harvard University, 211 pp.
- Turvey, S. and Dávalos, L. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on November 28, 2009.