Transandinomys
Encyclopedia
Transandinomys is a genus
of rodent
s 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. Until 2006, its members were included in the genus Oryzomys
, but phylogenetic analysis showed that they are not closely related to the type species
of that genus, and they have therefore been placed in a new genus. They may be most closely related to genera like Hylaeamys
and Euryoryzomys
, which contain very similar species. Both species of Transandinomys have had eventful taxonomic
histories.
Transandinomys bolivaris and T. talamancae are medium-sized, soft-furred rice rats. The upperparts—brownish in T. bolivaris and reddish in T. talamancae—are much darker than the whitish underparts. Both species are characterized by very long vibrissae
(whiskers), but those of T. bolivaris are particularly long. In addition to whisker length and fur color, several other morphological differences distinguish the two, including the wider first upper molar
in T. bolivaris. Species of Hylaeamys and Euryoryzomys also differ from Transandinomys in some details of the skull and teeth and have shorter whiskers. Species of Transandinomys live on the ground, are active during the night, eat both plant and animal matter, and construct nests of vegetation. Both are hosts
to various external parasites
. They are in no apparent danger of extinction and have been assessed as "Least Concern
" in the IUCN Red List
.
in 1891. Several other species were soon added to the genus Oryzomys
, then more broadly defined than currently, that are now classified in Transandinomys, including Oryzomys bolivaris (now Transandinomys bolivaris) by Allen in 1901. In his 1918 review of North American Oryzomys, Edward Alphonso Goldman
placed Oryzomys talamancae and Oryzomys bombycinus (=T. bolivaris) each in their own group, but thought them closely related. In 1960, O. talamancae was synonymized
with "Oryzomys capito" (=Hylaeamys megacephalus), but it has again been recognized as a separate species since 1983. The species was reviewed by Guy Musser
and Marina Williams in 1985 and again by Musser and colleagues in 1998, who documented the diagnostic characters of the species, its synonyms, and its distribution. The 1998 study by Musser and colleagues also documented Oryzomys bolivaris as the correct name for the species previously known as Oryzomys bombycinus and reviewed that species.
In 2006, Marcelo Weksler published a broad phylogenetic
analysis of Oryzomyini
, the tribe to which Oryzomys and related genera belong, using morphological data and DNA sequence
s from the IRBP
gene. O. talamancae appeared within "clade B", together with other species formerly associated with Oryzomys capito. Some analyses placed it closest to species now placed in Euryoryzomys
or Nephelomys
, but with low support. O. bolivaris was not included. Species of Oryzomys included in Weksler's study did not cluster together in his results, but instead appeared dispersed across Oryzomyini, indicating that the genus was polyphyletic and should be split up. Later in the same year, Weksler, Alexandre Percequillo, and Robert Voss introduced ten new genera of Oryzomyini formerly placed in Oryzomys, including Transandinomys for Oryzomys talamancae and O. bolivaris, with the former as the type species
. Transandinomys is now one of about thirty genera within Oryzomyini, a diverse group of well over a hundred species. Oryzomyini is one of several tribes within the subfamily Sigmodontinae
of the family Cricetidae
, which includes hundreds of other species of mainly small rodents, distributed chiefly in Eurasia and the Americas.
and Euryoryzomys
from Amazonia and surrounding areas and Handleyomys alfaroi from Central America and northwestern South America. In general, Transandinomys are distinguished from those animals by their very long superciliary vibrissae (whiskers above the eyes). Euryoryzomys species are in general slightly larger and Hylaeamys are about as large as Transandinomys, so that the only feature of external morphology that distinguishes the two genera is the length of the vibrissae. Handleyomys alfaroi is smaller than both species of Transandinomys, but juvenile Transandinomys may be confused with similarly colored adult H. alfaroi.
The fur is brownish (T. bolivaris) or reddish (T. talamancae) above and lighter below, appearing whitish, but the hairs on the underparts have gray bases. The snout
is large. The mystacial (above the mouth) and superciliary vibrissae both extend to at least the back margin of the ears when laid back against the head, but are much longer in T. bolivaris. The pinna (external ear) is large. On the hindfeet, which are long and narrow, ungual tuft
s of hairs surround the bases of the toes. In T. bolivaris, the sole usually entirely lacks squamae
(small, scale-like structures), but T. talamancae does have squamae on part of its sole. The claw of the first toe extends about to the middle of the first phalange of the second and that of the fifth toe extends nearly to the base of the second phalange of the fourth. The tail is at least about as long as the head and body, sometimes slightly longer. The tail is darker above than below in T. talamancae, but there may not be a difference in color in T. bolivaris. The tail appears naked, but is covered with fine hairs.
Females have four pairs of mammae, as usual in oryzomyines. Like most rice rats, Transandinomys species have twelve thoracic (chest) and seven lumbar vertebrae. According to a study in Costa Rica, T. bolivaris has 58 chromosome
s and the number of chromosomal arms (fundamental number) is 80 (2n = 58, FN = 80). Studies in Ecuador and Venezuela have recorded several different karyotype
s in T. talamancae, with the number of chromosomes ranging from 34 to 54 and the fundamental number from 60 to 67.
In the skull, the rostrum (front part) is long. The nasal bone
s are short, with their back margin not extending beyond the lacrimal bone
s, which are in contact with both the maxilla
ry and frontal bone
s. The zygomatic notch is moderately developed and the jugal bone is small, so that when seen from the side the maxillary and squamosal parts of the zygomatic arch
(cheekbone) overlap. Usually, the suture (line of fusion) between the frontal and the squamosal is continuous with that between the frontal and the parietal bone
. In T. talamancae, the parietals usually extend from the roof of the braincase broadly on to the sides, but in T. bolivaris they are more commonly restricted to the roof.
The incisive foramina
(openings in the front part of the palate
) are short, not extending between the first molars
. The posterolateral palatal pits
(small openings at the back of the palate, near the third molars) are poorly developed. The mesopterygoid fossa, the gap behind the back margin of the palate, does not usually reach forward between the maxillaries. Its roof either is wholly ossified or contains small sphenopalatine vacuities
. Unlike in some other oryzomyines, the buccinator-masticatory foramen and the foramen ovale accessorius, two foramina
(openings) in the skull, are not separated by an alisphenoid strut
. The pattern of grooves and foramina in the skull indicates that the circulation of the arteries of the head follows the primitive pattern, as in most similar species but unlike in Hylaeamys
. Usually, the mastoid bone contains small openings (fenestrations) in T. talamancae, but not in T. bolivaris. In the mandible
(lower jaw), the capsular process
(a process
at the root of the incisor
) is weak to absent and the upper and lower masseteric ridges, which anchor some of the chewing muscles, do not join into a single crest and reach their front margin below the first molar.
The upper incisor is opisthodont, with the cutting edge oriented backward. As usual in oryzomyines, the molars are brachydont
(low-crowned). The first upper molar is narrower in T. talamancae than in T. bolivaris. Unlike in many other rice rats, including Handleyomys alfaroi and Euryoryzomys
species, the mesoflexus on the second upper molar, which separates the paracone
(one of the main cusps) from the mesoloph (an accessory crest), is not divided in two by an enamel bridge. On the upper third molar, the hypoflexus (which in oryzomyines ranges from a slight indentation on the lingual, or inner, side of the tooth to a conspicuous valley between the main cusps) is more developed in Euryoryzomys than in Transandinomys. The hypoflexid on the second lower molar, the main valley between the cusps, extends more than halfway across the crown; it is much shorter in H. alfaroi, Euryoryzomys, and Hylaeamys yunganus. Each of the upper molars has three roots (two at the labial, or outer, side and one at the lingual, or inner, side) and each of the lowers has two (one at the front and one at the back); both species of Transandinomys lack the additional small roots that are present in various other oryzomyines, including species of Euryoryzomys, Nephelomys, and Handleyomys.
and the mountains. Both species are forest rats, but whereas T. bolivaris is restricted to humid forest formations, T. talamancae apparently is more tolerant of drier forest, which explains its wider South American distribution.
Both species live on the ground, are active during the night, are solitary, and feed mainly on fruits and seeds, but may also eat herbs and insects. They build nests of leaves and branches among vegetation, for example in a tree hollow, or under rocks. In Panama, T. talamancae breeds throughout the year and the average litter size is about six. Various species of mites, chigger
s, fleas, and sucking lice have been recorded as parasites on both species.
s, they are assessed as "Least Concern
" by the IUCN Red List
; deforestation
is noted as a possible threat to T. bolivaris, but T. talamancae is said to lack major threats.
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...
of rodent
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 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 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 two species—T. bolivaris and T. talamancae—found in forests from Honduras
Honduras
Honduras is a republic in Central America. It was previously known as Spanish Honduras to differentiate it from British Honduras, which became the modern-day state of Belize...
in Central America south and east to southwestern Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
and northwestern Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
in northern South America. Until 2006, its members were included in the genus 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...
, but phylogenetic analysis showed that they are not closely related to the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of that genus, and they have therefore been placed in a new genus. They may be most closely related to genera like Hylaeamys
Hylaeamys
Hylaeamys 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 Euryoryzomys
Euryoryzomys
Euryoryzomys 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...
, which contain very similar species. Both species of Transandinomys have had eventful taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
histories.
Transandinomys bolivaris and T. talamancae are medium-sized, soft-furred rice rats. The upperparts—brownish in T. bolivaris and reddish in T. talamancae—are much darker than the whitish underparts. Both species are characterized by very long vibrissae
Vibrissae
Vibrissae , or whiskers, are specialized hairs usually employed for tactile sensation. The term may also refer to the thick hairs found inside human nostrils, but these have no sensorial function and only operate as an airborne particulate barrier...
(whiskers), but those of T. bolivaris are particularly long. In addition to whisker length and fur color, several other morphological differences distinguish the two, including the wider first upper molar
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"....
in T. bolivaris. Species of Hylaeamys and Euryoryzomys also differ from Transandinomys in some details of the skull and teeth and have shorter whiskers. Species of Transandinomys live on the ground, are active during the night, eat both plant and animal matter, and construct nests of vegetation. Both are hosts
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
to various external parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
. They are in no apparent danger of extinction and have been assessed as "Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" in the 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...
.
Taxonomy
The first species of Transandinomys to be scientifically described was T. talamancae, named as Oryzomys talamancae by Joel Asaph AllenJoel Asaph Allen
Joel Asaph Allen was an American zoologist and ornithologist, born in Springfield, Massachusetts.He studied at Harvard University under Louis Agassiz...
in 1891. Several other species were soon added to the genus 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...
, then more broadly defined than currently, that are now classified in Transandinomys, including Oryzomys bolivaris (now Transandinomys bolivaris) by Allen in 1901. In his 1918 review of North American Oryzomys, Edward Alphonso Goldman
Edward Alphonso Goldman
Edward Alphonso Goldman was an American zoologist. He worked extensively in Mexico with Edward William Nelson and described and revised many groups of mammals....
placed Oryzomys talamancae and Oryzomys bombycinus (=T. bolivaris) each in their own group, but thought them closely related. In 1960, O. talamancae was synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with "Oryzomys capito" (=Hylaeamys megacephalus), but it has again been recognized as a separate species since 1983. The species was reviewed by Guy Musser
Guy Musser
Guy Graham Musser is an American zoologist. His main research field is the subfamily Murinae, in which he has described many new species.Musser was born in Salt Lake City, Utah...
and Marina Williams in 1985 and again by Musser and colleagues in 1998, who documented the diagnostic characters of the species, its synonyms, and its distribution. The 1998 study by Musser and colleagues also documented Oryzomys bolivaris as the correct name for the species previously known as Oryzomys bombycinus and reviewed that species.
In 2006, Marcelo Weksler published a broad phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
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...
, the tribe to which Oryzomys and related genera belong, using morphological data and DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
s 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. O. talamancae appeared within "clade B", together with other species formerly associated with Oryzomys capito. Some analyses placed it closest to species now placed in Euryoryzomys
Euryoryzomys
Euryoryzomys 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...
or Nephelomys
Nephelomys
Nephelomys 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...
, but with low support. O. bolivaris was not included. Species of Oryzomys included in Weksler's study did not cluster together in his results, but instead appeared dispersed across Oryzomyini, indicating that the genus was polyphyletic and should be split up. Later in the same year, Weksler, Alexandre Percequillo, and Robert Voss introduced ten new genera of Oryzomyini formerly placed in Oryzomys, including Transandinomys for Oryzomys talamancae and O. bolivaris, with the former as the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
. Transandinomys is now one of about thirty genera within Oryzomyini, a diverse group of well over a hundred species. Oryzomyini is one of several tribes 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...
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...
, which includes hundreds of other species of mainly small rodents, distributed chiefly in Eurasia and the Americas.
Description
Transandinomys species are medium-sized, soft-furred rice rats. They closely resemble other medium-sized lowland forest rice rats, such as HylaeamysHylaeamys
Hylaeamys 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 Euryoryzomys
Euryoryzomys
Euryoryzomys 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...
from Amazonia and surrounding areas and Handleyomys alfaroi from Central America and northwestern South America. In general, Transandinomys are distinguished from those animals by their very long superciliary vibrissae (whiskers above the eyes). Euryoryzomys species are in general slightly larger and Hylaeamys are about as large as Transandinomys, so that the only feature of external morphology that distinguishes the two genera is the length of the vibrissae. Handleyomys alfaroi is smaller than both species of Transandinomys, but juvenile Transandinomys may be confused with similarly colored adult H. alfaroi.
The fur is brownish (T. bolivaris) or reddish (T. talamancae) above and lighter below, appearing whitish, but the hairs on the underparts have gray bases. The snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
is large. The mystacial (above the mouth) and superciliary vibrissae both extend to at least the back margin of the ears when laid back against the head, but are much longer in T. bolivaris. The pinna (external ear) is large. On the hindfeet, which are long and narrow, ungual tuft
Ungual 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 of hairs surround the bases of the toes. In T. bolivaris, the sole usually entirely lacks 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, scale-like structures), but T. talamancae does have squamae on part of its sole. The claw of the first toe extends about to the middle of the first phalange of the second and that of the fifth toe extends nearly to the base of the second phalange of the fourth. The tail is at least about as long as the head and body, sometimes slightly longer. The tail is darker above than below in T. talamancae, but there may not be a difference in color in T. bolivaris. The tail appears naked, but is covered with fine hairs.
Females have four pairs of mammae, as usual in oryzomyines. Like most rice rats, Transandinomys species have twelve thoracic (chest) and seven lumbar vertebrae. According to a study in Costa Rica, T. bolivaris has 58 chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s and the number of chromosomal arms (fundamental number) is 80 (2n = 58, FN = 80). Studies in Ecuador and Venezuela have recorded several different karyotype
Karyotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
s in T. talamancae, with the number of chromosomes ranging from 34 to 54 and the fundamental number from 60 to 67.
Skull and teeth
| Species | Head and body | Tail | Hindfoot | Ear | Mass |
|---|---|---|---|---|---|
| T. bolivaris | 100–140 | 99–130 | 27–33 | 16–21 | 39–75 |
| T. talamancae | 105–146 | 105–152 | 28–32 | 17–24 | 47–74 |
| Measurements are in millimeters, except mass in grams. | |||||
In the skull, the rostrum (front part) is long. 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, with their back margin not extending beyond the lacrimal bone
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:...
s, which are in contact with both the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry and frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s. The zygomatic notch is moderately developed and the jugal bone is small, so that when seen from the side the maxillary and squamosal parts of 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) overlap. Usually, the suture (line of fusion) between the frontal and the squamosal is continuous with that between the frontal and 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....
. In T. talamancae, the parietals usually extend from the roof of the braincase broadly on to the sides, but in T. bolivaris they are more commonly restricted to the roof.
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 front part of 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...
) are short, not extending between the first 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"....
. 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...
(small openings at the back of the palate, near the third molars) are poorly developed. The mesopterygoid fossa, the gap behind the back margin of the palate, does not usually reach forward between the maxillaries. Its roof either is wholly ossified or contains small 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...
. Unlike in some other oryzomyines, the buccinator-masticatory foramen and the foramen ovale accessorius, 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, are not separated by 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...
. The pattern of grooves and foramina in the skull indicates that the circulation of the arteries of the head follows the primitive pattern, as in most similar species but unlike in Hylaeamys
Hylaeamys
Hylaeamys 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...
. Usually, the mastoid bone contains small openings (fenestrations) in T. talamancae, but not in T. bolivaris. In the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(lower jaw), the 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...
(a process
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
at the root of the incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
) is weak to absent and the upper and lower masseteric ridges, which anchor some of the chewing muscles, do not join into a single crest and reach their front margin below the first molar.
The upper incisor is opisthodont, with the cutting edge oriented backward. As usual in oryzomyines, the molars are 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). The first upper molar is narrower in T. talamancae than in T. bolivaris. Unlike in many other rice rats, including Handleyomys alfaroi and Euryoryzomys
Euryoryzomys
Euryoryzomys 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...
species, the mesoflexus on the second upper molar, which separates the paracone
Paracone
An atmospheric reentry or spaceflight mission abort concept using an inflatable cone.A notable feature of the paracone concept is that it facilitates an abort throughout the entire flight profile....
(one of the main cusps) from the mesoloph (an accessory crest), is not divided in two by an enamel bridge. On the upper third molar, the hypoflexus (which in oryzomyines ranges from a slight indentation on the lingual, or inner, side of the tooth to a conspicuous valley between the main cusps) is more developed in Euryoryzomys than in Transandinomys. The hypoflexid on the second lower molar, the main valley between the cusps, extends more than halfway across the crown; it is much shorter in H. alfaroi, Euryoryzomys, and Hylaeamys yunganus. Each of the upper molars has three roots (two at the labial, or outer, side and one at the lingual, or inner, side) and each of the lowers has two (one at the front and one at the back); both species of Transandinomys lack the additional small roots that are present in various other oryzomyines, including species of Euryoryzomys, Nephelomys, and Handleyomys.
Distribution, ecology, and behavior
The distribution of Transandinomys extends from eastern Honduras through Nicaragua, Costa Rica, Panama, and Colombia south and east to southwestern Ecuador and northern Venezuela, generally west and north of the Andes. The ranges of the two species overlap, but are distinct. T. bolivaris occurs from Honduras mainly on the Caribbean side of Central America south to western Colombia and northwestern Ecuador, up to 1800 m (5900 ft) above sea level. T. talamancae, which is found up to 1525 m (5000 ft) above sea level, is less widely distributed in Central America, as it is not known further north than northwestern Costa Rica, but is more widely distributed in South America, occurring into far southwestern Ecuador and northern Venezuela. It has also been recorded south of the Venezuelan Andes, in the narrow strip of forest between the LlanosLlanos
The Llanos is a vast tropical grassland plain situated to the east of the Andes in Colombia and Venezuela, in northwestern South America. It is an ecoregion of the Flooded grasslands and savannas Biome....
and the mountains. Both species are forest rats, but whereas T. bolivaris is restricted to humid forest formations, T. talamancae apparently is more tolerant of drier forest, which explains its wider South American distribution.
Both species live on the ground, are active during the night, are solitary, and feed mainly on fruits and seeds, but may also eat herbs and insects. They build nests of leaves and branches among vegetation, for example in a tree hollow, or under rocks. In Panama, T. talamancae breeds throughout the year and the average litter size is about six. Various species of mites, chigger
Chigger
A chigger or harvest mite is a mite in the family Trombiculidae that lives in North American forests and grasslands.Chigger may also refer to:...
s, fleas, and sucking lice have been recorded as parasites on both species.
Conservation status
Transandinomys talamancae is common or even abundant, but T. bolivaris generally occurs less frequently. Because both species are widespread, presumably have large populations, and occur in numerous protected areaProtected 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, they are assessed as "Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" by the 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...
; deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
is noted as a possible threat to T. bolivaris, but T. talamancae is said to lack major threats.
Literature cited
- Allen, J.A. 1891. Descriptions of two supposed new species of mice from Costa Rica and Mexico, with remarks on Hesperomys melanophrys of Coues. Proceedings of the United States National Museum 14(850):193–196.
- Allen, J.A. 1901. New South American Muridae and a new Metachirus. Bulletin of the American Museum of Natural History 14:405–412.
- Anderson, R.P., Aguilera, M., Gómez-Laverde, M., Samudio, R. and Pino, J. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on June 26, 2010.
- Brennan, J.M. and Yunker, C.E. 1966. The chiggers of Panama (Acarina: Trombiculidae). Pp. 221–266 in Wenzel, R.L. and Tipton, V.J. (eds.). Ectoparasites of Panama. Chicago: Field Museum of Natural History.
- Fleming, T.H. 1971. Population ecology of three species of Neotropical rodents. Miscellaneous Publications of the Museum of Zoology, University of Michigan 143:1–77.
- Goldman, E.A. 1918. The rice rats of North America. North American Fauna 43:1–100.
- Gómez-Laverde, M., Rivas, B., Timm, R. and Pino, J. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on June 26, 2010.
- 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
- Musser, G.G., Carleton, M.D., Brothers, E.M. and Gardner, A.L. 1998. Systematic studies of oryzomyine rodents (Muridae: Sigmodontinae): diagnoses and distributions of species formerly assigned to Oryzomys "capito". Bulletin of the American Museum of Natural History 236:1–376.
- Reid, F. 2009. A Field Guide to the Mammals of Central America and Southeast Mexico. 2nd edition. Oxford University Press US, 346 pp. ISBN 978-0-19-534322-9
- Steppan, S.J. 1995. Revision of the tribe Phyllotini (Rodentia: Sigmodontinae), with a phylogenetic hypothesis for the Sigmodontinae. Fieldiana Zoology 80:1–112.
- Tipton, V.J. and Méndez, E. 1966. The fleas (Siphonaptera) of Panama. Pp. 289–385 in Wenzel, R.L. and Tipton, V.J. (eds.). Ectoparasites of Panama. Chicago: Field Museum of Natural History.
- Tipton, V.J., Altman, R.M. and Keenan, C.M. 1966. Mites of the subfamily Laelaptinae in Panama (Acarina: Laelaptidae). Pp. 23–82 in Wenzel, R.L. and Tipton, V.J. (eds.). Ectoparasites of Panama. Chicago: Field Museum of Natural History.
- Tirira, D. 2007. Guia de campo de los mamíferos del Ecuador. Quito: Ediciones Murciélago Blanco, publicación especial sobre los mamíferos del Ecuador 6, 576 pp. (in Spanish). ISBN 9978-44-651-6
- 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.