Gray Rice Rat
Encyclopedia
Eremoryzomys polius, also known as the Gray Rice Rat or the Marañon Oryzomys, is a rodent
in the tribe Oryzomyini
of the family Cricetidae
. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in Oryzomys
and named Oryzomys polius. In 2006, a cladistic
analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus
, Eremoryzomys. The Brazilian genus Drymoreomys
, named in 2011, is likely the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River
in central Peru, but may yet contain more than one species.
A large, long-tailed rice rat, with head and body length of 138 to 164 mm (5.4 to 6.5 in), Eremoryzomys polius has gray fur and short ears. There are well-developed ungual tufts of hair on the hindfeet. Females have eight mammae. The rostrum (front part of the skull) is long and robust and the braincase is rounded. The bony palate
is relatively short. The IUCN assesses the conservation status
of the species as "Data Deficient
"; it is poorly known but may be threatened by habitat destruction
.
, Oryzomys polius. Osgood wrote that he was unable to find any species closely related to O. polius and compared it with O. xanthaeolus (currently Aegialomys xanthaeolus) "for convenience". Its relationships remained obscure ever afterward and it was never assigned to any of the several groups of species recognized within Oryzomys.
In 2006, Marcelo Weksler published a large-scale cladistic
analysis of Oryzomyini
("rice rats"), the tribe to which O. polius belongs. He used both morphological data and molecular characters from the IRBP
gene. In all of his analyses, O. polius was found to be part of clade D, one of four large groups within Oryzomyini, as the sister group to a clade containing all the other species of clade D. Clade D was supported by two shared derived (synapomorphic
) molecular characters and by seven morphological synapomorphies—the tail has a different color above and below; the parietal bone
extends to the side of the skull; the incisive foramina
(openings in the palate
) extend back between the first molars; the posterolateral palatal pits
(perforations of the palate near the third molars) are complex; the sphenopalatine vacuities
(openings in the mesopterygoid fossa, the gap behind the end of the palate) are large; the pattern of the arterial circulation in the head is derived
; and the posteroloph (a crest at the back) is present on the third upper molar. Two other molecular synapomorphies supported the clade of all members of clade D except O. polius, coupled with three morphological traits—in these species, but not in O. polius, the first upper molar has an additional small root at the outer (labial) side; the first lower molar has additional small roots; and the second upper molar has the mesoflexus (one of the valleys between the cusps and crests) divided in two.
In Weksler's analysis, species placed in Oryzomys did not form a coherent (monophyletic
) group, but instead were found at various positions across the oryzomyine tree, and he suggested that most of these species, including O. polius, should be placed in new genera. Later in 2006, Weksler and others described ten new genera for species formerly placed in Oryzomys, including Eremoryzomys for polius; thus, the species is now known as Eremoryzomys polius. In reference to its "isolated distribution", they incorporated the Greek word eremia "lonely place" into the generic name. The 2008 IUCN Red List
, citing Pacheco, commented that Eremoryzomys may in fact include more than one species. In 2011, a new oryzomyine, Drymoreomys albimaculatus, was described from southeastern Brazil, and phylogenetic analysis of morphological and molecular data suggested that this animal is the closest known relative of Eremoryzomys.
Eremoryzomys is now one of about 28 genera in the tribe Oryzomyini, which includes well over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands
and some of the Antilles
. Oryzomyini is one of several tribes recognized within the subfamily Sigmodontinae
, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae
, other members of which include vole
s, lemming
s, hamster
s, and deermice
, all mainly from Eurasia and North America.
s (patches of hair) along the plantar margins and between all of the digits, a character shared only with Sooretamys angouya among oryzomyines. The squamae
, small structures resembling scales that cover the soles of the hindfeet in many oryzomyines, are well developed. The claw of the first digit extends nearly to the end of the first phalanx of the second toe and the claw of the fifth toe extends slightly beyond the first phalanx of the fourth toe. As in most oryzomyines, the female has eight mammae. Head and body length is 138 to 164 mm (5.4 to 6.5 in). In Osgood's original two specimens, an old female and an adult female, tail length is 188 and 180 mm (7.4 and 7.1 in), respectively; hindfoot length is 30 and 30 mm (1.2 and 1.2 in); and greatest skull length is 37 and 34.7 mm (1.5 and 1.37 in). Eremoryzomys polius has 12 thoracic, 7 or 8 lumbar, and 35 or 36 caudal vertebrae; the presence of 12 thoracic vertebrae is a putative synapomorphy of Oryzomyini.
In the skull
, the rostrum (front part) is long and robust. The nasal bone
s are short, not extending further back than the lacrimals
, and the premaxillaries extend about as far back as the nasals. The zygomatic notch, an extension at the front of the zygomatic plate
, is present. The plate's back margin is level with the front of the first upper molar. A strong jugal bone is present in the zygomatic arch
(cheekbone), so that the maxillary and squamosal bones, which form the front and back parts of the arch, respectively, do not overlap when seen from the side.Weksler et al., 2006, p. 10; Percequillo et al., 2011, p. 388. Weksler, 2006, table 5, scores Eremoryzomys (as Oryzomys polius) as having overlapping squamosals and maxillaries (see character state definitions for character 30, p. 32). The narrowest part of the interorbital region
(located between the eyes) is to the front and the region's margins exhibit strong beading. Various crests develop on the rounded braincase, especially in old animals. The parietal bones form part of the roof of the braincase and, unlike in some other rice rats, also extend to the sides of the braincase. The interparietal bone at the back of the braincase is narrow and wedge-shaped, so that the parietal and occipital
bones meet extensively.
The incisive foramina are very long, extending well between the molars. The posterolateral palatal pits are well-developed and recessed into a fossa (depression). The bony palate is relatively short, with the mesopterygoid fossa extending forward to the end of the molar row or even between the third molars. The roof of the fossa is perforated by large sphenopalatine vacuities
. Usually, an alisphenoid strut
is present; this extension of the alisphenoid bone separates two foramina
(openings) in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. The condition of various grooves and foramina of the skull indicates that the pattern of the arterial circulation of the head is derived. The subsquamosal fenestra
, an opening at the back of the skull determined by the shape of the squamosal bone, is large and the mastoid bone is perforated by a fenestra (opening). The squamosal lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
, a defining character of oryzomyines.
In the mandible, the mental foramen
, an opening in the mandible just before the first molar, opens to the outside, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, usually join into a single crest at a point below the first molar and do not extend forward beyond the molar. There is no distinct capsular process
of the lower incisor, a trait Eremoryzomys shares with only a few other oryzomyines.
are bunodont (with the cusps higher than the connecting crests) and brachydont
(low-crowned). On the upper first and second molar, the outer and inner valleys between the cusps and crests do not interpenetrate. Many accessory crests are present, including the mesolophs and mesolophids. The anterocone and anteroconid, the front cusps on the upper and lower first molar, are not divided into smaller outer and inner cusps. Small accessory roots are absent from the molars, so that each of the three upper molars has two roots on the outer side and one on the inner side and each of the lower molars has one root at the front and one at the back.
, east of the main mountain range of the Andes. The biogeographical
pattern indicated by the relationship between Eremoryzomys and the Brazilian Drymoreomys is unusual. While there are some similar cases of relationships between Andean and Atlantic Forest animals, these involve inhabitants of humid forests in the Andes; Eremoryzomys, in contrast, lives in an arid area. Because E. polius is so poorly known, the 2008 IUCN Red List assesses it as "Data Deficient
". It is threatened by habitat destruction
for cattle pasture and is not known from any protected area
s.
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
in the tribe Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
of the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in 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...
and named Oryzomys polius. In 2006, a 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...
analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, Eremoryzomys. The Brazilian genus Drymoreomys
Drymoreomys
Drymoreomys 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...
, named in 2011, is likely the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River
Marañón River
The Marañón River rises about 160 km to the northeast of Lima, Peru, flows through a deeply-eroded Andean valley in a northwesterly direction, along the eastern base of the Cordillera of the Andes, as far as 5 degrees 36' southern latitude; then it makes a great bend to the northeast, and...
in central Peru, but may yet contain more than one species.
A large, long-tailed rice rat, with head and body length of 138 to 164 mm (5.4 to 6.5 in), Eremoryzomys polius has gray fur and short ears. There are well-developed ungual tufts of hair on the hindfeet. Females have eight mammae. The rostrum (front part of the skull) is long and robust and the braincase is rounded. The bony 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...
is relatively short. The IUCN assesses the conservation status
Conservation status
The conservation status of a group of organisms indicates whether the group is still extant and how likely the group is to become extinct in the near future...
of the species as "Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
"; it is poorly known but may be threatened by habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
.
Taxonomy
The first two specimens of Eremoryzomys polius were collected by Wilfred Osgood and M.P. Anderson in 1912. The next year, Osgood described these animals as a new species in the genus OryzomysOryzomys
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...
, Oryzomys polius. Osgood wrote that he was unable to find any species closely related to O. polius and compared it with O. xanthaeolus (currently Aegialomys xanthaeolus) "for convenience". Its relationships remained obscure ever afterward and it was never assigned to any of the several groups of species recognized within Oryzomys.
In 2006, Marcelo Weksler published a large-scale 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...
analysis of Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
("rice rats"), the tribe to which O. polius belongs. He used both morphological data and molecular characters from the 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. In all of his analyses, O. polius was found to be part of clade D, one of four large groups within Oryzomyini, as the sister group to a clade containing all the other species of clade D. Clade D was supported by two shared derived (synapomorphic
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...
) molecular characters and by seven morphological synapomorphies—the tail has a different color above and below; the parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
extends to the side of the skull; the incisive foramina
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
(openings in the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
) extend back between the first molars; the 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 of the palate near the third molars) are complex; the sphenopalatine vacuities
Sphenopalatine vacuities
In rodents, sphenopalatine vacuities are perforations of the roof of the mesopterygoid fossa, the open space behind the palate, in between the parapterygoid fossae. They may perforate the presphenoid or basisphenoid bone...
(openings in the mesopterygoid fossa, the gap behind the end of the palate) are large; the pattern of the arterial circulation in the head is derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
; and the posteroloph (a crest at the back) is present on the third upper molar. Two other molecular synapomorphies supported the clade of all members of clade D except O. polius, coupled with three morphological traits—in these species, but not in O. polius, the first upper molar has an additional small root at the outer (labial) side; the first lower molar has additional small roots; and the second upper molar has the mesoflexus (one of the valleys between the cusps and crests) divided in two.
In Weksler's analysis, species placed in Oryzomys did not form a coherent (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, but instead were found at various positions across the oryzomyine tree, and he suggested that most of these species, including O. polius, should be placed in new genera. Later in 2006, Weksler and others described ten new genera for species formerly placed in Oryzomys, including Eremoryzomys for polius; thus, the species is now known as Eremoryzomys polius. In reference to its "isolated distribution", they incorporated the Greek word eremia "lonely place" into the generic name. The 2008 IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
, citing Pacheco, commented that Eremoryzomys may in fact include more than one species. In 2011, a new oryzomyine, Drymoreomys albimaculatus, was described from southeastern Brazil, and phylogenetic analysis of morphological and molecular data suggested that this animal is the closest known relative of Eremoryzomys.
Eremoryzomys is now one of about 28 genera in the tribe Oryzomyini, which includes well over a hundred species distributed mainly in South America, including nearby islands such as 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...
and some of the Antilles
Antilles
The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...
. Oryzomyini is one of several tribes recognized within 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 encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
, other members of which include 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, lemming
Lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...
s, hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s, and deermice
Peromyscus
The genus Peromyscus contains the animal species commonly referred to as deer mice. This is a genus of New World mouse only distantly related to the common house mouse and laboratory mouse, Mus musculus...
, all mainly from Eurasia and North America.
Description
Eremoryzomys polius is a large, long-tailed rice rat that in color resembles some North American woodrats (Neotoma). The fur is grayish above and lighter below, where the hairs are gray at the bases but white at the tips. The external ears (pinnae) are short and the tail is dark above and light below. The hindfeet have well-developed ungual tuftUngual tuft
In mammals, ungual tufts are tufts of hairs at the base of claws of the fore- and hindfeet. Their presence has been used as a character in cladistic studies of Cricetidae....
s (patches of hair) along the plantar margins and between all of the digits, a character shared only with Sooretamys angouya among oryzomyines. The squamae
Squamae
In some rodents, squamae are small tubercles resembling scales on the sole of the hindfeet. Among oryzomyine rodents, their development is variable; most have well-developed squamae, but in others they are indistinct or entirely absent. Delomys sublineatus and Peromyscus maniculatus also have...
, small structures resembling scales that cover the soles of the hindfeet in many oryzomyines, are well developed. The claw of the first digit extends nearly to the end of the first phalanx of the second toe and the claw of the fifth toe extends slightly beyond the first phalanx of the fourth toe. As in most oryzomyines, the female has eight mammae. Head and body length is 138 to 164 mm (5.4 to 6.5 in). In Osgood's original two specimens, an old female and an adult female, tail length is 188 and 180 mm (7.4 and 7.1 in), respectively; hindfoot length is 30 and 30 mm (1.2 and 1.2 in); and greatest skull length is 37 and 34.7 mm (1.5 and 1.37 in). Eremoryzomys polius has 12 thoracic, 7 or 8 lumbar, and 35 or 36 caudal vertebrae; the presence of 12 thoracic vertebrae is a putative synapomorphy of Oryzomyini.
Skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
, the rostrum (front part) is long and robust. The nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s are short, not extending further back than the lacrimals
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
, and the premaxillaries extend about as far back as the nasals. The zygomatic notch, an extension at the front of the zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
, is present. The plate's back margin is level with the front of the first upper molar. A strong jugal bone is present in the zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
(cheekbone), so that the maxillary and squamosal bones, which form the front and back parts of the arch, respectively, do not overlap when seen from the side.Weksler et al., 2006, p. 10; Percequillo et al., 2011, p. 388. Weksler, 2006, table 5, scores Eremoryzomys (as Oryzomys polius) as having overlapping squamosals and maxillaries (see character state definitions for character 30, p. 32). The narrowest part of the interorbital region
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....
(located between the eyes) is to the front and the region's margins exhibit strong beading. Various crests develop on the rounded braincase, especially in old animals. The parietal bones form part of the roof of the braincase and, unlike in some other rice rats, also extend to the sides of the braincase. The interparietal bone at the back of the braincase is narrow and wedge-shaped, so that the parietal and occipital
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
bones meet extensively.
The incisive foramina are very long, extending well between the molars. The posterolateral palatal pits are well-developed and recessed into a fossa (depression). The bony palate is relatively short, with the mesopterygoid fossa extending forward to the end of the molar row or even between the third molars. The roof of the fossa is perforated by large sphenopalatine vacuities
Sphenopalatine vacuities
In rodents, sphenopalatine vacuities are perforations of the roof of the mesopterygoid fossa, the open space behind the palate, in between the parapterygoid fossae. They may perforate the presphenoid or basisphenoid bone...
. Usually, 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...
is present; this extension of the alisphenoid bone separates two foramina
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
(openings) in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. The condition of various grooves and foramina of the skull indicates that the pattern of the arterial circulation of the head is derived. The subsquamosal fenestra
Subsquamosal fenestra
In some rodents, the subsquamosal fenestra is an opening between two parts of the squamosal bone, at the back of the skull. It can be seen in lateral view. Most Oryzomyini have the fenestra, but some species, including those in the genera Nectomys, Sigmodontomys, and Melanomys among others, lack...
, an opening at the back of the skull determined by the shape of the squamosal bone, is large and the mastoid bone is perforated by a fenestra (opening). The squamosal lacks a suspensory process that contacts the tegmen tympani, 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....
, a defining character of oryzomyines.
In the mandible, the mental foramen
Mental foramen
The mental foramen is one of two holes located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals.- Variations :...
, an opening in the mandible just before the first molar, opens to the outside, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, usually join into a single crest at a point below the first molar and do not extend forward beyond the molar. There is no distinct capsular process
Capsular process
In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial side of the mandible as a raising in the bone...
of the lower incisor, a trait Eremoryzomys shares with only a few other oryzomyines.
Molars
The molarsMolar (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"....
are bunodont (with the cusps higher than the connecting crests) and brachydont
Brachydont
Brachydont is a type of dentition characterized by low-crowned teeth, as opposed to high-crowned, hypsodont teeth. Human teeth are brachydont.-External links:*http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/tooth_diversity.html...
(low-crowned). On the upper first and second molar, the outer and inner valleys between the cusps and crests do not interpenetrate. Many accessory crests are present, including the mesolophs and mesolophids. The anterocone and anteroconid, the front cusps on the upper and lower first molar, are not divided into smaller outer and inner cusps. Small accessory roots are absent from the molars, so that each of the three upper molars has two roots on the outer side and one on the inner side and each of the lower molars has one root at the front and one at the back.
Distribution and status
As far as now known, Eremoryzomys polius is confined to a small area in central Peru, at an altitude of 760 to 2100 m (2490 to 6890 ft), but the species may range more widely. It occurs in forest in the dry lowlands of the upper parts of the basin of the Marañón RiverMarañón River
The Marañón River rises about 160 km to the northeast of Lima, Peru, flows through a deeply-eroded Andean valley in a northwesterly direction, along the eastern base of the Cordillera of the Andes, as far as 5 degrees 36' southern latitude; then it makes a great bend to the northeast, and...
, east of the main mountain range of the Andes. The biogeographical
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
pattern indicated by the relationship between Eremoryzomys and the Brazilian Drymoreomys is unusual. While there are some similar cases of relationships between Andean and Atlantic Forest animals, these involve inhabitants of humid forests in the Andes; Eremoryzomys, in contrast, lives in an arid area. Because E. polius is so poorly known, the 2008 IUCN Red List assesses it as "Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
". It is threatened by habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
for cattle pasture and is not known from any protected area
Protected area
Protected areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the enabling laws of each country or the regulations of the international...
s.
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
- Osgood, W.H. 1913. New Peruvian mammals. Field Museum of Natural History, Zoölogical Series 10:93–100.
- Pacheco, V., Zeballos, H., Vivar, E. and Weksler, M. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on April 9, 2010.
- 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.
- 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.