''Pseudoryzomys simplex'', also known as the Brazilian false rice rat
[ or false oryzomys, is a ]species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
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 ...
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 ...
from south-central 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 ...
. It is found in lowland palm savanna and thorn scrub habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s. It is a medium-sized species, weighing about , with gray–brown fur, long and narrow hindfeet, and a tail that is about as long as the head and body. The IUCN has assessed its conservation status as being of least concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
, although almost nothing is known about its diet or reproduction.
The only species in the genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Pseudoryzomys'', its closest living relatives are the large rats ''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' ...
'' and '' Lundomys'', which 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 much of their time in the water. The three genera share several characters
Character or Characters may refer to:
Arts, entertainment, and media Literature
* ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk
* ''Characters'' (Theophrastus), a classical Greek set of character sketches attributed to The ...
, including specializations towards a semiaquatic lifestyle, such as the presence of membranes between the digits ( interdigital webbing), and a reduction in the complexity of the molar crowns, both of which are at incipient stages in ''Pseudoryzomys''. Together, they form a unique assemblage within the oryzomyine tribe, a very diverse group including over one hundred species, mainly in South America. This tribe is part of the subfamily Sigmodontinae
The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
and 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 include many more species, mainly from Eurasia and the Americas. ''Pseudoryzomys simplex'' was independently described in 1888 on the basis of subfossil cave specimens from Brazil (as ''Hesperomys simplex''); and in 1921 on the basis of a live specimen from Paraguay (as ''Oryzomys wavrini''). This was confirmed in 1991 that both names pertained to the same species.
Taxonomy
Discovery and recognition
''Pseudoryzomys simplex'' has had a complex taxonomic history. It was first described in 1888 by Danish zoologist Herluf Winge
Adolf Herluf Winge (19 March 1857 – 10 November 1923) was a Danish zoologist.
Biography
As a young student, along with his brother Oluf, Winge was interested in small mammals, particularly moles, shrews and insectivora. He studied mammalian ...
, who reviewed the materials Peter Wilhem Lund had collected in the caves of Lagoa Santa, Minas Gerais
Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...
, Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. Winge described the species as ''Hesperomys simplex'', and placed it in the same genus ('' Hesperomys'') as the species now called ''Lundomys molitor
''Lundomys molitor'', also known as Lund's amphibious ratMusser and Carleton, 2005, p. 1124 or the greater marsh rat, is a semiaquatic rat species from southeastern South America.
Its distribution is now restricted to Uruguay and nearby Ri ...
'' and two species now placed in '' Calomys''. Like most other species Winge proposed, ''H. simplex'' was mostly ignored in the systematic literature, but from 1952 it was used briefly, in the combination "''Oecomys simplex''", for an ''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 ...
'' species from central Brazil. In his 1960 review of ''Oecomys'', Field Museum mammalogist Philip Hershkovitz denied any affinities between ''simplex'' and ''Oecomys'', noting that various features of the ''H. simplex'' skull illustrated by Winge instead suggested affinities to the phyllotine or sigmodont groups.
In 1921, renowned British mammalogist In zoology, mammalogy is the study of mammals – a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous system
In biology, the nervous system is the highly complex part ...
Oldfield Thomas described ''Oryzomys wavrini'' as a new species of '' Oryzomys'' from Paraguay. In the next decades, it was viewed as an aberrant species of ''Oryzomys'' (then used in a much broader sense than now),[ but it was moved to a separate genus, named ''Pseudoryzomys'', by Hershkovitz in 1959, who noted that although it is similar to '']Oryzomys palustris
The marsh rice rat (''Oryzomys palustris'') is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, fr ...
'' in appearance, other features suggest it is more closely related to '' Phyllotis''.[Hershkovitz, 1959, pp. 8–9] Thus, he viewed the animal as a member of the phyllotine group of rodents, which includes ''Calomys'' and ''Phyllotis'', not of the oryzomyine group, which includes ''Oryzomys'', and his opinion was mostly accepted in the next few decades. Scientific knowledge of the rare ''Pseudoryzomys wavrini''—only three specimens were known when Hershkovitz described the genus ''Pseudoryzomys'' in 1959—increased in the following years, and in 1975 the Bolivian population was named as a separate subspecies, ''Pseudoryzomys wavrini reigi'', because Bolivian animals are slightly larger and darker than those from Paraguay.[
In 1980, Argentinean zoologist Elio Massoia suggested that Winge's ''Hesperomys simplex'' and the living ''Pseudoryzomys wavrini'' are in fact the same species. In a 1991 study, American zoologists Voss and Myers confirmed this suggestion after re-examining Winge's material, finding no appreciable differences among specimens of ''H. simplex'' and ''P. wavrini''. Since then, the species has been known as ''Pseudoryzomys simplex'' (Winge, 1888), because ''simplex'' is the oldest specific name for the animal; ''Oryzomys wavrini'' Thomas, 1921, and ''Pseudoryzomys wavrini reigi'' Pine and Wetzel, 1975, are junior synonyms. Voss and Myers also re-evaluated the relationships of ''Pseudoryzomys''; they considered it closer to oryzomyines than to phyllotines, but declined to formally place it in Oryzomyini in the absence of explicit ]phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
justification for such a placement.[Voss and Myers, 1991, p. 423]
Oryzomyine relationships
When Voss and Carleton formally characterized Oryzomyini two years later, they did place ''Pseudoryzomys'' in the group, even though it lacks complete mesoloph(id)s. The mesoloph is an accessory crest on the upper molars and the mesolophid is the corresponding structure on the lower molars. Only a few other animals now considered oryzomyines lack complete mesoloph(id)s, but they are absent in various non-oryzomyines, some of which had previously been regarded as close relatives of the oryzomyines that lack them. Oryzomyines with and without complete mesoloph(id)s share various other characters, however, including presence 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, absence of a gall bladder, and some characters of the skull, suggesting that they form one natural, monophyletic group. Oryzomyini is now one of 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 ...
recognized within the subfamily Sigmodontinae
The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily 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 ...
, other members of which include 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, lemming
A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also includ ...
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, and deermice, all mainly from Eurasia and North America.
Several phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
studies published during the 1990s and 2000s supported a close relationship between ''Pseudoryzomys'' and two other oryzomyines with reduced or absent mesoloph(id)s, ''Lundomys'' and ''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' ...
''. The extinct genera ''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 ...
'', described in 1999 and 2008 respectively, were also recognized as members of the group. In 2006, a broad morphological and molecular phylogenetic study of Oryzomyini provided further support for the relationship between ''Holochilus'', ''Lundomys'', and ''Pseudoryzomys''. Within this group, morphological data supported a closer relationship between ''Holochilus'' and ''Lundomys'' to the exclusion of ''Pseudoryzomys'', but DNA sequence data favored a clustering between ''Holochilus'' and ''Pseudoryzomys'' to the exclusion of ''Lundomys''; among all oryzomyines, this was the only case where relationships which received strong support from morphological and DNA sequence data conflicted. Together, the three genera form part of a large group of oryzomyines (" clade D"), which contains tens of other species. Several of those display some adaptations to life in the water, being partially aquatic, as do ''Pseudoryzomys'' and its relatives. Morphological data indicate that the genus '' Oryzomys'' is the closest relative of the group that includes ''Pseudoryzomys'', but DNA sequence data from the nuclear IRBP gene did not support this relationship; convergent adaptations towards a semiaquatic lifestyle may explain the morphological support for a relation between ''Oryzomys'' and the other three genera.
Description
''Pseudoryzomys simplex'' is a nondescript, medium-sized rat with long, soft fur. The upperparts are gray–brown and the underparts are buff
Buff or BUFF may refer to:
People
* Buff (surname), a list of people
* Buff (nickname), a list of people
* Johnny Buff, ring name of American world champion boxer John Lisky (1888–1955)
* Buff Bagwell, a ring name of American professional ...
; the color changes gradually over the body. The small ears are covered with short hairs. The tail is as long as or slightly longer than the head and body, and is dark above and light below. Despite the presence of short hairs, the scales on the tail are clearly visible. The hairs on the feet are pale. The hindfeet are long and narrow and have five toes, the first and fifth of which are short.[Voss and Myers, 1991, p. 420] Webbing
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is present between the second, third, and fourth toes, but the membranes are not as large as in ''Lundomys'' or ''Holochilus''. The tufts of hair on the toes and several of the pads are reduced, other common characteristics of semiaquatic oryzomyines. The head-body length is , tail length , hindfeet length , ear length and body mass .
The female has four pairs of teat
A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...
s, including one on the chest and three on the belly, and the 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 ...
is absent, both important characters of Oryzomyini. As is characteristic of Sigmodontinae, ''Pseudoryzomys'' has a complex penis, with the baculum (penis bone) displaying large protuberances at the sides. In the cartilaginous
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...
part of the baculum, the central digit is smaller than those at the sides.
Skull
The skull, which is short at the front, shows some typical oryzomyine characters. The palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...
is long, extending past the molars and the maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
ry bones. The alisphenoid strut, which in some sigmodontines separates two (openings) in the skull, is absent. 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 lacks a suspensory process
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
contacting 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 ...
, the roof 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 front part is short.[Voss and Myers, 1991, p. 422]
The nasal bones end bluntly close to the hindmost extent of the premaxillary bones. The narrow interorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups.
In oryzomyine rodents, for example, the width, form, an ...
,[ located between the eyes, converges towards the front and is flanked by low beads. The interparietal bone, located in the roof of the skull on the braincase, is nearly as wide as the frontals, but does not reach the squamosals.
The ]incisive foramina
In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...
, which perforate the palate between the incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s and the molars
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
, are long and narrow, extending between the first molars. The back margins of the zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the ...
s, the flattened front portions of the zygomatic arch
In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...
es (cheekbones), are located before the first molars. Like its close relatives ''Lundomys'' and ''Holochilus'', ''Pseudoryzomys'' has spinous processes on its zygomatic plates. These genera also share relatively simple posterolateral palatal pits, perforations of the palate near the third molar. Unlike ''Holochilus'' and ''Lundomys'', however, ''Pseudoryzomys'' has a flat palate, lacking a ridge on the middle that extends along the length of the palate. The parapterygoid fossae, which are located behind the third molars, are excavated beyond the level of the palate, but not as deeply as in ''Holochilus'' and ''Lundomys''. The mastoid
The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, ...
skull bone contains a conspicuous opening, as in most oryzomyines.[Weksler, 2006, p. 41]
The mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
(lower jaw) is short and deep.[ The ]mental foramen
The mental foramen is one of two foramina (openings) located on the anterior surface of the mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels.
Structure
The ...
, an opening at the front of the mandible, just before the first molar, opens to the side.[ The capsular process of the lower incisor, a raising of the mandibular bone at the back end of the incisor, is well developed. The two masseteric ridges, to which some of the chewing muscles are attached, are entirely separate, joining only at their front edges, which are located below the first molar.
]
Molars
As in all oryzomyines except ''Holochilus'' and its close relatives, the molars are brachyodont
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 ...
, low-crowned, and bunodont
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 the cusps extending higher than the central parts of the molars. They are characterized by strong cusps and absence or reduction of accessory crests. The cusps of the upper molars are opposite, but in the lower molars the labial (outer) cusps are slightly further to the front than the lingual (inner) ones. On the upper first molar, one accessory ridge, the anteroloph, is lacking, but another, the mesoloph, is present. Unlike in most other oryzomyines, however, which have mesolophs reaching the labial margin of the molar, the mesolophs of ''Pseudoryzomys'' are short and protrude only slightly from the middle of the molar. The corresponding structure in the lower molars, the mesolophid, is completely absent.[ The hindmost valley between cusps on the lower first molar, the posteroflexid, is severely reduced, foreshadowing its loss in ''Lundomys'' and ''Holochilus''.][Weksler, 2006, p. 52] A number of molar traits support ''Pseudoryzomys''s relationship with ''Holochilus'' and ''Lundomys'', forming steps in the transition from the complex, low-crowned generalized oryzomyine molar pattern to the simpler, high-crowned pattern of ''Holochilus''.
As in all oryzomyines, the upper molars all have one root on the inner (lingual) side and two on the outer (labial) side; in addition, the first upper molar in ''Pseudoryzomys'' and some other species has another labial root. The first lower molar has large roots at the front and back of the tooth and two smaller ones in between, at the labial and lingual side. The second and third lowers molars have two roots at the front, one labial and one lingual, and another at the back.[
]
Postcranial skeleton
''Pseudoryzomys'' has 19 or 20 thoracic
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
(chest) and lumbar vertebrae
The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...
,[ 13 of which bear ribs, as is characteristic of oryzomyines. The first ribs contact both the ]seventh
Seventh is the ordinal form of the number seven.
Seventh may refer to:
* Seventh Amendment to the United States Constitution
* A fraction (mathematics), , equal to one of seven equal parts
Film and television
*"The Seventh", a second-season e ...
cervical (neck) vertebra and the first thoracic vertebra, an important character of the Sigmodontinae
The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
.[ Unlike in most sigmodontines, including ''Holochilus'' and ''Lundomys'', the fourth lumbar vertebra lacks the processes known as anapophyses.][Weksler, 2006, p. 53] There are three or four sacral
Sacral may refer to:
*Sacred
Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property ...
and about 29 caudal (tail) vertebrae.[ Between the second and third caudal vertebrae, separate bones called hemal arches are present. These display a spinous process at the back, as in both ''Holochilus'' and ''Lundomys''.][ On the humerus, the upper arm bone, the entepicondylar foramen is absent, as in all members of the ]Sigmodontinae
The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
; in some other cricetids, it perforates the far (distal) end of the humerus.
Karyotype
The karyotype generally includes 56 chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s with a total of 54 major arms (2n = 56, FN = 54) in specimens from both Bolivia and Brazil; a poorly prepared Paraguayan specimen seems to have a similar karyotype. In this karyotype, all autosomes (non-sex chromosomes) are acrocentric
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
(with one arm so short as to be almost invisible). However, in two specimens from the Brazilian states of Tocantins
Tocantins () is one of the 26 states of Brazil. It is the newest state, formed in 1988 and encompassing what had formerly been the northern two-fifths of the state of Goiás. Tocantins covers and had an estimated population of 1,496,880 in 20 ...
and São Paulo
São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the Ga ...
, one pair of autosomes contains both an acrocentric and a metacentric
Metacentric may refer to:
* Metacentric height
The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger ...
chromosome (with two equally long arms), yielding an FN of 55. One arm of the metacentric chromosome consists entirely of heterochromatin.[Moreira et al., 2013, p. 202] Apparently, a whole heterochromatic arm was added to this chromosome; cases of similar variation are known from the rodents ''Peromyscus
''Peromyscus'' is a genus of rodents. They are commonly referred to as deer mice or deermice, not to be confused with the chevrotain or "mouse deer". They are New World mice only distantly related to the common house and laboratory mouse, ''Mu ...
'', '' Clyomys'', and '' Thaptomys''.[Moreira et al., 2013, p. 204] Both sex chromosome
A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...
s are acrocentric, and X is larger than Y. In addition to heterochromatin near the centromere
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
, the Y chromosome contains two large blocks of heterochromatin on its long arm. The karyotype is closely similar to that of ''Holochilus brasiliensis
''Holochilus brasiliensis'', also known as the Brazilian marsh ratMusser, 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 refer ...
''.
Distribution, ecology, and variation
''Pseudoryzomys simplex'' is known from northeastern Argentina, probably south to about 30°S,[ northward through western ]Paraguay
Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...
to eastern Bolivia and from there eastward through Brazil in the states of Mato Grosso, Goiás
Goiás () is a Brazilian state located in the Center-West region. Goiás borders the Federal District and the states of (from north clockwise) Tocantins, Bahia, Minas Gerais, Mato Grosso do Sul and Mato Grosso. The state capital is Goi ...
, Tocantins, Minas Gerais
Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...
, São Paulo, Bahia
Bahia ( , , ; meaning "bay") is one of the 26 states of Brazil, located in the Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo, Minas Gerais, and Rio de Janeiro) and the 5th-largest b ...
, and far in the northeast, Alagoas
Alagoas (, ) is one of the 27 federative units of Brazil and is situated in the eastern part of the Northeast Region. It borders: Pernambuco (N and NW); Sergipe (S); Bahia (SW); and the Atlantic Ocean (E). Its capital is the city of Maceió. ...
and Pernambuco
Pernambuco () is a States of Brazil, state of Brazil, located in the Northeast Region, Brazil, Northeast region of the country. With an estimated population of 9.6 million people as of 2020, making it List of Brazilian states by population, sev ...
. Paraguayan animals are somewhat smaller than those from Bolivia and Brazil and those from Bolivia have darker fur than Paraguayan specimens, but these differences are not considered significant enough to recognize subspecies. Certain bat
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...
s show a similar pattern of variation: they are smaller and paler in the Chaco region, which includes much of Paraguay.[Voss and Myers, 1991, p. 424] Two specimens from Paraguay, collected apart, differed by 1.4% in the sequence of the cytochrome ''b'' gene,[D'Elia et al., 2008, p. 49] but nothing is known about genetic variation in other parts of the range. The species has long been rare in collections; in 1991, Voss and Myers could use less than 50 specimens for their study of the species, including Lund's fragmentary material from Lagoa Santa.
A fragmentary lower jaw of "''Pseudoryzomys'' aff. ''P. simplex''" (i.e., an unnamed species close to ''Pseudoryzomys simplex'') is known from a cave deposit in Cueva Tixi, Buenos Aires Province, Argentina, outside the current distribution of the species. It is dated from the first millennium CE. The jaw's 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 ...
agrees with that of ''P. simplex'', but the toothrow is relatively long (5.78 mm; 4.61 to 5.60 mm in three specimens of ''P. simplex'') and the first molar is relatively narrow (1.28 mm; 1.30 to 1.40 mm in five ''P. simplex'').
''P. simplex'' inhabits open, usually humid tropical and subtropical lowlands.[Voss and Myers, 1991, p. 425] In Argentina, it is mainly a species of the eastern Chaco[ and in Brazil it is found in the ]Cerrado
The ''Cerrado'' (, ) is a vast ecoregion of tropical savanna in eastern Brazil, particularly in the states of Goiás, Mato Grosso do Sul, Mato Grosso, Tocantins, Minas Gerais, and the Federal District. The core areas of the Cerrado biome are the ...
and Caatinga
Caatinga (, ) is a type of semi-arid tropical vegetation, and an ecoregion characterized by this vegetation in interior northeastern Brazil. The name "Caatinga" is a Tupi word meaning "white forest" or "white vegetation" (''caa'' = forest, v ...
.[Bonvicino et al., 2008, p. 54] Most specimens for which habitat data are known were caught on the ground in humid grassland, some in seasonally flooded areas; an Argentinean specimen was captured in dense swamp vegetation.[Pardiñas et al., 2004, p. 108] It is terrestrial and semiaquatic, living on the ground but also spending time in the water.
Nothing is known about behavior or diet. ''P. simplex'' has frequently been found in pellets of the barn owl (''Tyto alba'')[Pardiñas et al., 2004, p. 105] and also in those of the great horned owl
The great horned owl (''Bubo virginianus''), also known as the tiger owl (originally derived from early naturalists' description as the "winged tiger" or "tiger of the air"), or the hoot owl, is a large owl native to the Americas. It is an extre ...
(''Bubo virginianus''). It is a preferred prey of the maned wolf
The maned wolf (''Chrysocyon brachyurus'') is a large canine of South America. It is found in Argentina, Brazil, Bolivia, Peru, and Paraguay, and is almost extinct in Uruguay. Its markings resemble those of foxes, but it is neither a fox nor a w ...
(''Chrysocyon brachyurus'').
Conservation status
The species is not known to be threatened and its conservation status is classified as least concern
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
by the IUCN. It is a widely distributed species without substantial threats to its continued existence, but degradation of its habitat may endanger some populations.[ It was assessed as "potentially vulnerable" in Argentina.][Díaz and Ojeda, 2000]
Footnotes
References
Literature cited
*Belentani, S.C. da S., Motta-Junior, J.C. and Talamoni, S.A. 2005
Notes on the food habits and prey selection of the maned wolf (''Chrysocyon brachyurus'') (Mammalia, Canidae) in southeastern Brazil
''Biocièncias'' 13(1):95–98.
*Bonvicino, C.R., Lemos, B. and Weksler, M. 2005
Small mammals of Chapada dos Veadeiros National Park (Cerrado of Central Brazil): Ecologic, karyologic, and taxonomic considerations
''Brazilian Journal of Biology'' 65(3):395–406.
*Bonvicino, C.R., Oliveira, J.A. and D'Andrea, P.S. 2008. . Rio de Janeiro: Centro Pan-Americano de Febre Aftosa – OPAS/OMS, 120 pp. (in Portuguese).
*Carleton, M.D. and Olson, S.L. 1999
Amerigo Vespucci and the rat of Fernando de Noronha: a new genus and species of Rodentia (Muridae, Sigmodontinae) from a volcanic island off Brazil's continental shelf
''American Museum Novitates'' 3256:1–59.
*Chebez, J.C., Pereira, J., Massoia, E., Di Giacomo, A.G. and Fortabat, S.H. 2005
Mamíferos de la Reserva El Bagual
''Temas de Naturaleza y Conservación'' 4:467–499 (in Spanish).
*D'Elia, G., Mora, I., Myers, P. and Owen, R.D. 2008
New and noteworthy records of Rodentia (Erethizontidae, Sciuridae, and Cricetidae) from Paraguay
(subscription required for full paper). ''Zootaxa'' 1784:39–57.
*Díaz, G. and Ojeda, R. 2000. Libro Rojo de los mamíferos amenazados de la Argentina. Mendoza: Sociedad Argentina para el Estudio de los Mamíferos, 106 pp. (in Spanish).
*Hershkovitz, P.M. 1959. Two new genera of South American rodents (Cricetinae). ''Proceedings of the Biological Society of Washington'' 72:5–10.
*Hershkovitz, P.M. 1960
Mammals of northern Colombia, preliminary report no. 8: Arboreal rice rats, a systematic revision of the subgenus ''Oecomys'', genus ''Oryzomys''
''Proceedings of the United States National Museum'' 110:513–568.
*Hershkovitz, P. 1962
Evolution of Neotropical cricetine rodents (Muridae) with special reference to the phyllotine group
''Fieldiana Zoology'' 46:1–524.
*Moreira, C.N., Di-Nizo, C.B., Silva, M.J.d.J., Yonenaga-Yassuda, Y. and Ventura, K. 2013
A remarkable autosomal heteromorphism in ''Pseudoryzomys simplex'' 2n = 56; FN = 54-55 (Rodentia, Sigmodontinae)
(subscription required). ''Genetics and Molecular Biology'' 36(2):201–206.
*
*Pardiñas, U.F.J. 1995
Novedosos cricetidos (Mammalia, Rodentia) en el Holoceno de la Región Pampeana, Argentina
''Ameghiniana'' 32(2):197–203 (in Spanish).
*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., Cirignoli, S. and Galliari, C.A. 2004
Distribution of ''Pseudoryzomys simplex'' (Rodentia: Cricetidae) in Argentina
''Mastozoología Neotropical'' 11(1):105–108.
*
*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. 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.
*Wetzel, R.M. and Lovett, J.W. 1974. A collection of animals from the Chaco of Paraguay. ''University of Connecticut Occasional Papers'' 2(13):203–216.
*Winge, H. 1888
Jordfundne og nulevende Gnavere (Rodentia) fra Lagoa Santa, Minas Geraes, Brasilien
''E Museo Lundii'' 1(3):1–200.
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Oryzomyini
Monotypic rodent genera
Mammals of Argentina
Mammals of Bolivia
Mammals of Brazil
Mammals of Paraguay
Mammals described in 1888
Taxa named by Philip Hershkovitz