Oryzomyini
Encyclopedia
Oryzomyini is a tribe of rodent
s 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. 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
, Oryzomys
, which means "rice rat/mouse". Many species are also known as rice rats.
in the early 20th century. He defined it to include pentalophodont species, which have a mesoloph(id) on the upper and lower molars
, with a long palate
(extending past the third molars). Thomas included Oligoryzomys
, Oecomys
, 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
(then including Sigmodontomys
), Neacomys
, 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.
The genera Holochilus
(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.
In a 1993 paper, Voss and Carleton proposed the first cladistic
diagnosis of Oryzomyini. They included twelve genera and proposed five synapomorphies
for the tribe: presence of a pair of mammae 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 (openings) in the skull; absence of a suspensory process of the squamosal
bone attached to the roof of the tympanic cavity
, the tegmen tympani; and absence of a gall bladder. Some of these have been reversed in some oryzomyines; for example, an alisphenoid strut is present in several oryzomyines, including Eremoryzomys.
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
, has been allocated to both Oryzomyini and Thomasomyini, but its correct classification currently remains unclear. 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. Handleyomys fuscatus was placed in the thomasomyine genus Aepeomys
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 has led to progress in the understanding of the relationships of oryzomyines. They are currently classified in the family Cricetidae
, which includes the vole
s, hamster
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, 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
s (Sigmodon) and the Ichthyomyini
.
, Oryzomys
, 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
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 clade
s. 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:
The affinities of some species remain unclear. The identity of Oryzomys anoblepas
, described from cave material in Lagoa Santa, eastern Brazil, is uncertain and many oryzomyines are known from the Lesser Antilles
, including "Ekbletomys hypenemus" and species of Megalomys and Oligoryzomys, but most remain undescribed.
and rats, 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 65 millimetres (2.6 in) and mass of 10 gram (0.35273962105112 oz), but the largest living oryzomyine, Nectomys, reaches head and body lengths over 250 millimetres (9.8 in) and mass of about 300 grams (10.6 oz); 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.
in the north, where the Marsh Rice Rat
(Oryzomys palustris) is found, to Tierra del Fuego
in the south, where Oligoryzomys magellanicus occurs. Extinct species are known from Jamaica
(Oryzomys antillarum), the Galápagos Islands
(Nesoryzomys and Aegialomys galapagoensis), Fernando de Noronha
(Noronhomys), and the Lesser Antilles
north to Anguilla
(Megalomys, Oligoryzomys victus, and several unidentified genera). They are abundant in many environments, from rainforest to grassland. 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, spending at least some of their time in the water.
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....
s 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...
. 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. It is part of the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Oryzomyalia, which includes most of the South American Sigmodontinae.
The name "Oryzomyini" derives from that of its type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
, 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 means "rice rat/mouse". Many species are also known as rice rats.
Contents of Oryzomyini
An oryzomyine group was first envisaged by Oldfield ThomasOldfield 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...
in the early 20th century. He defined it to include pentalophodont species, which have a mesoloph(id) on the upper and lower 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"....
, with a long 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...
(extending past the third molars). Thomas included 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...
, 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:...
, and 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 included many species now in other genera), as well as Rhagomys
Rhagomys
Rhagomys is a genus of South American rodents in the tribe Thomasomyini of family Cricetidae. Two species are known, found in Bolivia, southeast Peru and the Atlantic Forest of southeast Brazil. They are as follows:...
, 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
Nectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...
(then including Sigmodontomys
Sigmodontomys
Sigmodontomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is related to Nectomys and Melanomys and was previously included in Nectomys. It includes two species, Sigmodontomys alfari and the much rarer Sigmodontomys aphrastus, but whether these are indeed each other's...
), Neacomys
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. Neacomys species are mainly found in Amazonia, but N. pictus occurs...
, and Scolomys
Scolomys
Scolomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Some evidence suggests that it is related to Zygodontomys. It is characterized, among other traits, by spiny fur. It contains two species, Scolomys melanops and Scolomys ucayalensis.-Literature cited:*Musser, G.G. and...
. 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
Tylomyinae
The subfamily Tylomyinae consists of several species of New World rats and mice including the vesper and climbing rats. They are not as well known as their relatives in the subfamilies Sigmodontinae and Neotominae...
, which are now known to be more distantly related.
The genera Holochilus
Holochilus
Holochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
(including Lundomys at the time), Pseudoryzomys, and Zygodontomys
Zygodontomys
Zygodontomys is a genus of rodent in the tribe Oryzomyini of the family Cricetidae. Its closest relative may be Scolomys. It ranges from Central America east to the Guianas. It contains two species: Zygodontomys brunneus and Zygodontomys brevicauda....
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
Reithrodon
Reithrodon is a genus of rodent in the family Cricetidae.It contains the following species:* Bunny Rat * Naked-soled Conyrat...
, 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.
In a 1993 paper, Voss and Carleton proposed the first cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
diagnosis of Oryzomyini. They included twelve genera and proposed five synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
for the tribe: presence of a pair of mammae on the chest; a long palate marked by posterolateral palatal pits
Posterolateral palatal pits
In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...
, perforations near the third molar; absence of an alisphenoid strut
Alisphenoid strut
In some rodents, the alisphenoid strut is an extension of the alisphenoid bone that separates two foramina in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius...
, which in some sigmodontines separates two foramina (openings) in the skull; absence of a suspensory process of the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
bone attached to the roof of the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
, the tegmen tympani; and absence of a gall bladder. Some of these have been reversed in some oryzomyines; for example, an alisphenoid strut is present in several oryzomyines, including Eremoryzomys.
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
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, has been allocated to both Oryzomyini and Thomasomyini, but its correct classification currently remains unclear. The genus Scolomys
Scolomys
Scolomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Some evidence suggests that it is related to Zygodontomys. It is characterized, among other traits, by spiny fur. It contains two species, Scolomys melanops and Scolomys ucayalensis.-Literature cited:*Musser, G.G. and...
has been excluded from Oryzomyini on the basis of studies of the mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
gene, but the nuclear
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
IRBP
RBP3
Retinol-binding protein 3, interstitial , also known as IRBP is a protein that in humans is encoded by the RBP3 gene. RBP3 orthologs have been identified in most eutherians except tenrecs and armadillos.- Function :...
gene provides evidence for its membership in Oryzomyini. Handleyomys fuscatus was placed in the thomasomyine genus Aepeomys
Aepeomys
Aepeomys is a genus of rodent in the family Cricetidae.It contains the following species:* Olive Montane Mouse * Reig's Montane Mouse...
before its close relationship to H. intectus was recognized in 2002. Microakodontomys transitorius was described as a transitional form between oryzomyines and akodontines
Akodontini
Akodontini is the second most speciose tribe of the subfamily Sigmodontinae. It includes at least 106 living species in 19 genera and is distributed mainly in the southern half of South America, with only two genera extending into Guyana and Venezuela . It also includes genera previously placed in...
, but later allied with Oryzomyini and even summarily dismissed as an anomalous 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...
.
In the early 2000s, the advent of molecular phylogenetics has led to progress in the understanding of the relationships of oryzomyines. They are currently classified in 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...
, which includes the vole
Vole
A vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars . There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
s, hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s, deermice, and many other species, chiefly in the Americas and Eurasia. Within this family, they are part of 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...
, which is mainly distributed in South America but also extends into southern North America. Sigmodontinae includes several tribes, most of which cluster into a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
now known as Oryzomyalia, which includes Oryzomyini, Akodontini, Phyllotini, Thomasomyini, and other, smaller groups, but not the cotton rat
Cotton rat
A cotton rat is any member of the rodent genus Sigmodon. They are called cotton rats because they build their nests out of cotton, and can damage cotton crops. Cotton rats have small ears and dark coats, and are found in North and South America....
s (Sigmodon) and the Ichthyomyini
Ichthyomyini
Ichthyomyini is a tribe of New World rats and mice in the subfamily Sigmodontinae. The species within this tribe share the characteristic of all being fish-eating rodents.*Anotomys - Ecuadorian Fish-eating Rat*Chibchanomys - Chibchan Water Mouse...
.
Internal classification
The relationships among the oryzomyine genera have long been obscure, although several studies provided insights into the relations of some genera. The single most significant problem in oryzomyine taxonomy has been the definition of the type genusType genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
, 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 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
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
group.
In the 2000s, Marcelo Weksler published several studies in which he used evidence from IRBP, a nuclear gene, and morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
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 clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s. 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
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
position, but other analyses could not resolve the relationships among the major clades. The four clades are as follows:
- Clade A includes only ScolomysScolomysScolomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Some evidence suggests that it is related to Zygodontomys. It is characterized, among other traits, by spiny fur. It contains two species, Scolomys melanops and Scolomys ucayalensis.-Literature cited:*Musser, G.G. and...
and ZygodontomysZygodontomysZygodontomys is a genus of rodent in the tribe Oryzomyini of the family Cricetidae. Its closest relative may be Scolomys. It ranges from Central America east to the Guianas. It contains two species: Zygodontomys brunneus and Zygodontomys brevicauda....
, but support for a relationship between those morphologically and ecologicallyEcologyEcology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
dissimilar genera was not strong. - Clade B includes at least OecomysOecomysOecomys 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:...
, HandleyomysHandleyomysHandleyomys is a genus of Central and South American rodents in the tribe Oryzomyini of family Cricetidae. It was first described in 2002 to include two species from the Colombian Andes which were previously included in distinct and unrelated genera, Aepeomys and Oryzomys, but which turned out to...
, EuryoryzomysEuryoryzomysEuryoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes six species, which are distributed in South America. Until 2006, its members were included in the genus Oryzomys, but they are not closely related to the type species of that genus, and therefore they were...
, TransandinomysTransandinomysTransandinomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—T. bolivaris and T. talamancae—found in forests from Honduras in Central America south and east to southwestern Ecuador and northwestern Venezuela in northern South America...
, HylaeamysHylaeamysHylaeamys is a genus of South American oryzomyine rodents found principally in humid forested areas east of the Andes. The species in this genus have historically been placed in Oryzomys. They are most closely related to Euryoryzomys, Transandinomys, Nephelomys, Oecomys, and Handleyomys, and most...
, and NephelomysNephelomysNephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica...
, the latter four of which were included in Oryzomys until 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 D 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. There is little support for all intergeneric relationships within the clade. - Clade C includes OligoryzomysOligoryzomysOligoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos...
, NeacomysNeacomysThe 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. Neacomys species are mainly found in Amazonia, but N. pictus occurs...
, MicroryzomysMicroryzomysMicroryzomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Oreoryzomys, Oligoryzomys, and Neacomys. It contains two species, both restricted to the Andes: Microryzomys altissimus and Microryzomys minutus.-Literature cited:*Musser, G.G. and Carleton,...
, and Oreoryzomys, which was placed in Oryzomys until 2006. No intergeneric relationships within this clade received substantial support. - Clade D includes DrymoreomysDrymoreomysDrymoreomys is a genus of rodents in the tribe Oryzomyini, from the Atlantic Forest of Brazil. The single species, D. albimaculatus, is known only from the states of São Paulo and Santa Catarina and was not named until 2011. It lives in the humid forest on the eastern slopes of the Serra do...
, Eremoryzomys, CerradomysCerradomysCerradomys is a genus of oryzomyine rodents from eastern Bolivia, Paraguay, and central Brazil found in cerrado, Caatinga and Gran Chaco habitats. The species in this genus have historically been placed in Oryzomys, but according to cladistic research, they are not more closely related to the type...
, Sooretamys, OryzomysOryzomysOryzomys 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...
, Lundomys, Pseudoryzomys, HolochilusHolochilusHolochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
, AegialomysAegialomysAegialomys is a genus of oryzomyine rodents from the lowlands and mountains of western Peru and Ecuador, including the Galápagos Islands. The species in this genus have historically been placed in Oryzomys, but according to cladistic research, the genus is more closely related to a group...
, NesoryzomysNesoryzomysNesoryzomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae, endemic to the Galápagos Islands. Other rodents restricted to the Galápagos include Megaoryzomys curioi and Aegialomys galapagoensis.-References:...
, MelanomysMelanomysMelanomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae, which is distributed in northern South America and adjacent Central America. It contains three species, two of which—Melanomys robustulus and Melanomys zunigae—have limited distributions...
, SigmodontomysSigmodontomysSigmodontomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is related to Nectomys and Melanomys and was previously included in Nectomys. It includes two species, Sigmodontomys alfari and the much rarer Sigmodontomys aphrastus, but whether these are indeed each other's...
, NectomysNectomysNectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...
, most likely Amphinectomys, and the extinct MegalomysMegalomysMegalomys is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains four large rodents from various Caribbean islands, all of which are now extinct. The last species to survive was M...
, AgathaeromysAgathaeromysAgathaeromys is an extinct genus of oryzomyine rodents from the Pleistocene of Bonaire, West Indies. Two species are known, which differ in size and some details of tooth morphology. The larger A. donovani, the type species, is known from hundreds of teeth, found in four localities that are...
, and PennatomysPennatomysPennatomys nivalis is an extinct oryzomyine rodent from the islands of Sint Eustatius, Saint Kitts, and Nevis in the Lesser Antilles. The only species in the genus Pennatomys, it is known from skeletal remains found in Amerindian archeological sites on all three islands, with dates ranging from...
. 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, with the extinct Megalomys and Pennatomys. The Holochilus–Lundomys–Pseudoryzomys group also includes the extinct Noronhomys and CarletonomysCarletonomysCarletonomys cailoi is an extinct rodent from the Pleistocene of Buenos Aires Province, Argentina. Although known only from a single maxilla with the first molar, its features are so distinctive that it is placed in its own genus, Carletonomys...
. Oryzomys may be its closest relative, but it is possible that this arrangement is the result of a convergentConvergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
development of adaptations to a life in the water in the two groups. 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. The identity of Oryzomys anoblepas
Oryzomys anoblepas
Juliomys anoblepas is a rodent in the genus Juliomys of the subfamily Sigmodontinae known from a single broken skull. The specimen was collected by Peter Wilhelm Lund in the caves of Lagoa Santa in Minas Gerais, Brazil, in the first half of the 19th century and described by Herluf Winge in 1887 as...
, described from cave material in Lagoa Santa, eastern Brazil, is uncertain and many oryzomyines are known from 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...
, including "Ekbletomys hypenemus" and species of Megalomys and Oligoryzomys, but most remain undescribed.
Description
Most oryzomyines are nondescript rodents that look like common house miceHouse mouse
The house mouse is a small rodent, a mouse, one of the most numerous species of the genus Mus.As a wild animal the house mouse mainly lives associated with humans, causing damage to crops and stored food....
and rats, 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 65 millimetres (2.6 in) and mass of 10 gram (0.35273962105112 oz), but the largest living oryzomyine, Nectomys, reaches head and body lengths over 250 millimetres (9.8 in) and mass of about 300 grams (10.6 oz); 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 JerseyNew Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
in the north, where 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...
(Oryzomys palustris) is found, to Tierra del Fuego
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of a main island Isla Grande de Tierra del Fuego divided between Chile and Argentina with an area of , and a group of smaller islands including Cape...
in the south, where Oligoryzomys magellanicus occurs. Extinct species are known from Jamaica
Jamaica
Jamaica is an island nation of the Greater Antilles, in length, up to in width and 10,990 square kilometres in area. It is situated in the Caribbean Sea, about south of Cuba, and west of Hispaniola, the island harbouring the nation-states Haiti and the Dominican Republic...
(Oryzomys antillarum), the Galápagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
(Nesoryzomys and Aegialomys galapagoensis), Fernando de Noronha
Fernando de Noronha
Fernando de Noronha is an archipelago of 21 islands and islets in the Atlantic Ocean, offshore from the Brazilian coast. The main island has an area of and had a population of 3,012 in the year 2010...
(Noronhomys), and 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...
north to Anguilla
Anguilla
Anguilla is a British overseas territory and overseas territory of the European Union 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...
(Megalomys, Oligoryzomys victus, and several unidentified genera). They are abundant in many environments, from rainforest to grassland. 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, spending at least some of their time in the water.
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 978-0-8018-8221-0
- 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). Zoological 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. ISBN 978-0-19-953509-5
- 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.