oryzomyines
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Oryzomyini is a
tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...
of
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 ...
s in the subfamily Sigmodontinae of the 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 ...
. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 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 ...
to the southernmost parts of
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 ...
, including many offshore islands. It is part of the clade Oryzomyalia, which includes most of the South American Sigmodontinae. The name ''Oryzomyini'' derives from that of its
type genus In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearing type of a nominal ...
, '' Oryzomys'', which means "rice rat" or "rice mouse". Many species are also known as rice rats.


Taxonomy


Contents of Oryzomyini

An oryzomyine group was first envisaged by Oldfield Thomas in the early 20th century. He defined it to include pentalophodont species, which have a mesoloph(id) on the upper and lower
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 ...
, with a long
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 ...
(extending past the third molars). Thomas included '' Oligoryzomys'', ''
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 Trinidad i ...
'', and '' Oryzomys'' (which included many species now in other genera), as well as '' Rhagomys'', which is currently classified in the related tribe Thomasomyini instead. In 1944, Hershkovitz proposed a more extended definition of the group, excluding ''Rhagomys'', but including ''
Nectomys ''Nectomys'' is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Musser and Carleton, 2005. It is closely related to '' Amphinectomys'' and was formerly considered congeneric with ''Sigmodontomys''. It consists of five species, whic ...
'' (then including '' Sigmodontomys''), ''
Neacomys The genus ''Neacomys'', also known as bristly mice because of their spiny fur, includes several species of rodents in the tribe Oryzomyini of family Cricetidae. It is most closely related to ''Oligoryzomys'', ''Oreoryzomys'', and ''Microryzomys'' ...
'', and '' Scolomys''. Some subsequent authors did not separate the oryzomyines from the thomasomyines, which were distinguished from them by having a short palate, including Vorontsov, who in 1959 was the first to use Oryzomyini as a formal family-group name. He included most current oryzomyines as well as the thomasomyines and tylomyines, which are now known to be more distantly related.Weksler, 2006, p. 4 The genera ''
Holochilus ''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus' ...
'' (including '' Lundomys'' at the time), '' Pseudoryzomys'', and '' Zygodontomys'' were not included at the time because of their tetralophodont molars (lacking complete mesoloph(id)s); instead, ''Holochilus'' was considered to be a sigmodont, related to '' Sigmodon'' and '' Reithrodon'', and ''Pseudoryzomys'' and ''Zygodontomys'' were considered to be members of Phyllotini, another large South American tribe. Although lacking mesoloph(id)s, these genera share other characters with oryzomyines, and a series of papers by Robert Voss and coworkers in the early 1990s established their membership in Oryzomyini.Weksler, 2006, p. 5 In a 1993 paper, Voss and Carleton proposed the first
cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...
diagnosis of Oryzomyini. They included twelve genera and proposed five synapomorphies for the tribe: presence of a pair of
mammae A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primat ...
on the chest; a long palate marked by posterolateral palatal pits, perforations near the third molar; absence of an alisphenoid strut, which in some sigmodontines separates two
foramina In anatomy and osteology, a foramen (;Entry "foramen"
in
(openings) in the skull; absence of a suspensory process of the
squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...
bone attached to the roof of the
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...
, the
tegmen tympani The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditor ...
; and absence of a
gall bladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...
.Voss and Carleton, 1993, p. 31 Some of these have been reversed in some oryzomyines; for example, an alisphenoid strut is present in several oryzomyines, including '' Eremoryzomys''.Weksler, 2006, p. 38 The contents of Oryzomyini have been largely stable since, but the allocation of some animals has been contentious. '' Megaoryzomys'', an extinct giant rat from the
Galápagos Islands The Galápagos Islands (Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
, has been allocated to both Oryzomyini and Thomasomyini, but its correct classification currently remains unclear.Musser and Carleton, 2005 The genus '' Scolomys'' has been excluded from Oryzomyini on the basis of studies of the mitochondrial cytochrome ''b'' gene, but the nuclear IRBP gene provides evidence for its membership in Oryzomyini.Weksler, 2006, p. 124 '' Handleyomys fuscatus'' was placed in the thomasomyine genus ''
Aepeomys ''Aepeomys'' is a small genus of rodents in the family Cricetidae. The species in this genus are found in Ecuador (''A. lugens'') and Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Boli ...
'' before its close relationship to '' H. intectus'' was recognized in 2002. '' Microakodontomys transitorius'' was described as a transitional form between oryzomyines and akodontines, but later allied with Oryzomyini and even summarily dismissed as an anomalous '' Oligoryzomys''. In the early 2000s, the advent of
molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
has led to progress in the understanding of the relationships of oryzomyines. They are currently classified in the 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 ...
, which includes the
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of lo ...
s,
hamster Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera.Fox, Sue. 2006. ''Hamsters''. T.F.H. Publications Inc. They have become established as popular small pets. The ...
s, deermice, and many other species, chiefly in the Americas and Eurasia. Within this family, they are part of the subfamily Sigmodontinae, which is mainly distributed in South America but also extends into southern North America. Sigmodontinae includes several
tribes The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...
, most of which cluster into a clade now known as Oryzomyalia, which includes Oryzomyini, Akodontini, Phyllotini, Thomasomyini, and other, smaller groups, but not the
cotton rat A cotton rat is any member of the rodent genus ''Sigmodon''. Their name derives from their damaging effects on cotton as well as other plantation crops, such as sugarcane, corn, peanut and rice. Cotton rats have small ears and dark coats, and a ...
s (''Sigmodon'') and the Ichthyomyini.


Internal classification

The relationships among the oryzomyine genera have long been obscure, although several studies provided insights into the relations of some genera.Weksler, 2006, p. 7 The single most significant problem in oryzomyine taxonomy has been the definition of the
type genus In biological taxonomy, the type genus is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearing type of a nominal ...
, '' Oryzomys'',Weksler, 2006, p. 10 which in one classification included all animals then recognized as oryzomyines. Many groups were later excluded from the genus, but even so it included forty species that did not form a monophyletic group. In the 2000s, Marcelo Weksler published several studies in which he used evidence from IRBP, a nuclear gene, and
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
to assess the relationships among the members of Oryzomyini. He provided support for several intergeneric relationships and clarified the scale of the ''Oryzomys'' problem, as species of ''Oryzomys'' appeared in about ten separate clades.Weksler, 2006, figs. 34–39 In a 2006 publication, he and coworkers described ten new genera for species previously placed in ''Oryzomys'' and transferred some others to ''Handleyomys'', leaving only about six species in ''Oryzomys''. Weksler's analyses suggested that oryzomyines fall into four major clades, which were largely congruent across his analyses of morphology and IRBP, but support for all of those was limited and the placement of some genera remained unclear. He dubbed these clades "clade A" through "clade D". Some analyses supported a relationship between clades C and D, which in turn were related to clade B, with clade A at a basal position, but other analyses could not resolve the relationships among the major clades. The four clades are as follows: *Clade A includes only '' Scolomys'' and '' Zygodontomys'', but support for a relationship between those morphologically and
ecologically Ecology () is the study of the relationships between living organisms, including humans, and their biophysical environment, physical environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosy ...
dissimilar genera was not strong.Weksler, 2006, p. 75 *Clade B includes at least ''
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 Trinidad i ...
'', '' Handleyomys'', '' Euryoryzomys'', '' Transandinomys'', '' Hylaeamys'', and '' Nephelomys'', the latter four of which were included in ''Oryzomys'' until 2006.Weksler et al., 2006 '' Amphinectomys'' and '' Mindomys'' were also recovered in the clade in some analyses, but the former, for which most morphological characters are unknown, is more likely related to ''Nectomys'' within clade DWeksler, 2006, p. 133 and the relations of the latter, a poorly known yet unique animal, are obscure as some analyses suggest it is a basal member of Oryzomyini.Weksler et al., 2006, p. 17 There is little support for all intergeneric relationships within the clade. *Clade C includes '' Oligoryzomys'', ''
Neacomys The genus ''Neacomys'', also known as bristly mice because of their spiny fur, includes several species of rodents in the tribe Oryzomyini of family Cricetidae. It is most closely related to ''Oligoryzomys'', ''Oreoryzomys'', and ''Microryzomys'' ...
'', '' Microryzomys'', and '' Oreoryzomys'', which was placed in ''Oryzomys'' until 2006. No intergeneric relationships within this clade received substantial support. *Clade D includes '' Drymoreomys'',Percequillo et al., 2011, p. 372 '' Eremoryzomys'', '' Cerradomys'', '' Sooretamys'', '' Oryzomys'', '' Lundomys'', '' Pseudoryzomys'', ''
Holochilus ''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus' ...
'', '' Aegialomys'', '' Nesoryzomys'', '' Melanomys'', '' Sigmodontomys'', ''
Nectomys ''Nectomys'' is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Musser and Carleton, 2005. It is closely related to '' Amphinectomys'' and was formerly considered congeneric with ''Sigmodontomys''. It consists of five species, whic ...
'', most likely '' Amphinectomys'', and the extinct ''
Megalomys ''Megalomys'' is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains five large rodents from various Caribbean islands, of which two are known to have survived into modern times, but all of which are now ex ...
'',Weksler et al., 2006, p. 18 '' Agathaeromys'', and '' Pennatomys''. ''Eremoryzomys'', ''Cerradomys'', ''Sooretamys'', and ''Aegialomys'' were included in ''Oryzomys'' before 2006. There is some support for a basal placement of ''Eremoryzomys'' within this clade and for two major groups of related genera, one including ''Holochilus'', ''Lundomys'', and ''Pseudoryzomys'' and the other ''Nectomys'', ''Amphinectomys'', ''Sigmodontomys'', ''Melanomys'', ''Aegialomys'', and ''Nesoryzomys'',Weksler, 2006, figs. 37–39 with the extinct ''Megalomys'' and ''Pennatomys''. The ''Holochilus''–''Lundomys''–''Pseudoryzomys'' group also includes the extinct ''
Noronhomys ''Noronhomys vespuccii'', also known as Vespucci's rodent, is an extinct rat species from the islands of Fernando de Noronha off northeastern Brazil. Italian explorer Amerigo Vespucci may have seen it on a visit to Fernando de Noronha in 1503, ...
'' and ''
Carletonomys ''Carletonomys cailoi'' is an extinction, extinct rodent from the Pleistocene (Ensenadan) of Buenos Aires Province, Argentina. Although known only from a single maxilla (upper jaw) with the first molar (tooth), molar, its features are so distinct ...
''. ''Oryzomys'' may be its closest relative, but it is possible that this arrangement is the result of a convergent development of adaptations to a life in the water in the two groups.Weksler, 2006, p. 131 Within the group of ''Nectomys'' and related genera, there is some support for a core group that excludes ''Aegialomys'' and ''Nesoryzomys'' and for two subclades within the core group, one including ''Nectomys'' and ''Amphinectomys'' and the other ''Melanomys'' and ''Sigmodontomys''. The affinities of some species remain unclear. Many oryzomyines are known from the
Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...
, including "''
Ekbletomys hypenemus "''Ekbletomys hypenemus''" is an extinct oryzomyine rodent from the islands of Antigua and Barbuda, Lesser Antilles. It was described as the only species of the subgenus "''Ekbletomys''" of genus ''Oryzomys'' in a 1962 Ph.D. thesis, but that nam ...
''" and species of ''Megalomys'' and ''Oligoryzomys'', but most remain undescribed.


Description

Most oryzomyines are nondescript rodents that look like common
house mice The house mouse (''Mus musculus'') is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus ''Mus''. Although ...
and
rats Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...
, but the tribe also includes some spectacularly specialized forms. The smallest members, mainly in clade C, may have a head-body length of as little as and mass of , but the largest living oryzomyine, ''Nectomys'', reaches head and body lengths over and mass of about ; ''Lundomys'' and ''Holochilus'' are only a little smaller. Some of the extinct species from the Lesser Antilles, such as "''Ekbletomys hypenemus''" and '' Megalomys desmarestii'', were even larger.


Distribution and ecology

Oryzomyines range from
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
in the north, where the Marsh Rice Rat (''Oryzomys palustris'') is found, to
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...
in the south, where '' Oligoryzomys magellanicus'' occurs. Extinct species are known from
Jamaica Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of His ...
('' Oryzomys antillarum''), the
Galápagos Islands The Galápagos Islands (Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
(''Nesoryzomys'' and '' Aegialomys galapagoensis''),
Fernando de Noronha Fernando de Noronha () is an archipelago in the Atlantic Ocean, part of the State of Pernambuco, Brazil, and located off the Brazilian coast. It consists of 21 islands and islets, extending over an area of . Only the eponymous main island is in ...
(''Noronhomys''), and the
Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...
north to
Anguilla Anguilla ( ) is a British Overseas Territory in the Caribbean. It is one of the most northerly of the Leeward Islands in the Lesser Antilles, lying east of Puerto Rico and the Virgin Islands and directly north of Saint Martin. The terr ...
(''Megalomys'', '' Oligoryzomys victus'', and several unidentified genera). They are abundant in many environments, from rainforest to grassland.Weksler, 2006, p. 3 Most live in the forest, but ''Zygodontomys'', ''Lundomys'', ''Pseudoryzomys'', ''Aegialomys'', and ''Nesoryzomys'' live exclusively in open vegetation and some other genera include both forest and non-forest forms. Most oryzomyines are relatively unspecialized animals that live on the ground, but ''Oecomys'' is specialized to live in trees and various members of clade D, including ''Holochilus'', ''Oryzomys'', and ''Nectomys'', are
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...
, spending at least some of their time in the water.Weksler, 2006, pp. 78–79


References


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.  *Pardiñas, U.F.J. 2008
A new genus of oryzomyine rodent (Cricetidae: Sigmodontinae) from the Pleistocene of Argentina
(subscription required). ''Journal of Mammalogy'' 89(5):1270–1278. *Pardiñas, U.F.J., D'Elía, G. and Ortiz, P.E. 2002
Sigmodontinos fósiles (Rodentia, Muroidea, Sigmodontinae) de América del sur: Estado actual de su conocimiento y prospectiva
''Mastozoología Neotropical'' 9(2):209–252 (in Spanish). *Percequillo, A.R., Weksler, M., and Costa, L.P. 2011
A new genus and species of rodent from the Brazilian Atlantic Forest (Rodentia: Cricetidae: Sigmodontinae: Oryzomyini), with comments on oryzomyine biogeography
(subscription required). ''Zooilogical Journal of the Linnean Society'' 161(2):357–390. *Ray, C.E. 1962. The Oryzomyine Rodents of the Antillean Subregion. Doctor of Philosophy thesis, Harvard University, 211 pp. *Turvey, S.T. 2009. Holocene Extinctions. Oxford University Press US, 359 pp.  *Turvey, S.T., Weksler, M., Morris, E.L., and Nokkert, M. 2010
Taxonomy, phylogeny, and diversity of the extinct Lesser Antillean rice rats (Sigmodontinae: Oryzomyini), with description of a new genus and species
(subscription required). ''Zoological Journal of the Linnean Society'' 160:748–772. *Voss, R.S. and Carleton, M.D. 1993
A new genus for ''Hesperomys molitor'' Winge and ''Holochilus magnus'' Hershkovitz (Mammalia, Muridae) with an analysis of its phylogenetic relationships
''American Museum Novitates'' 3085:1–39. *Voss, R.S., Gómez-Laverde, M. and Pacheco, V. 2002
A new genus for ''Aepeomys fuscatus'' Allen, 1912, and ''Oryzomys intectus'' Thomas, 1921: Enigmatic murid rodents from Andean cloud forests
''American Museum Novitates'' 3373:1–42. *Voss, R.S. and Myers, P. 1991
''Pseudoryzomys simplex'' (Rodentia: Muridae) and the significance of Lund's collections from the caves of Lagoa Santa, Brazil
''Bulletin of the American Museum of Natural History'' 206:414–432. *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. *Zijlstra, J.S., Madern, P.A. and Hoek Ostende, L.W. van den. 2010
New genus and two new species of Pleistocene oryzomyines (Cricetidae: Sigmodontinae) from Bonaire, Netherlands Antilles
(subscription required). ''Journal of Mammalogy'' 91(4):860–873. {{Taxonbar, from=Q2410209 Sigmodontinae Stored-product pests Mammal tribes