Cane Mouse
Encyclopedia
Lundomys molitor, also known as Lund's Amphibious Rat or the Greater Marsh Rat, is a semiaquatic rat species
from southeastern South America. Its distribution is now restricted to Uruguay and nearby Rio Grande do Sul
, Brazil, but it previously ranged east into Minas Gerais
, Brazil, and west into eastern Argentina. The Argentinean form may have been distinct from the living form from Brazil and Uruguay. L. molitor is a large rodent
, with the head and body length averaging 193 mm (7.60 in), characterized by a long tail, large hindfeet, and long and dense fur. It builds nests above the water, supported by reeds, and it is not currently threatened.
Its external morphology
is similar to that of Holochilus brasiliensis and over the course of its complex taxonomic
history, it has been confused with that species, but other features support its placement in a distinct genus
, Lundomys. Within the family Cricetidae
and subfamily Sigmodontinae
, it is a member of a group of specialized oryzomyine
rodents that also includes Holochilus
, Noronhomys, Carletonomys
, and Pseudoryzomys.
, who reviewed the materials Peter Wilhelm Lund
had collected in the caves of Lagoa Santa
, Minas Gerais
, Brazil. Winge used four specimens for his description, including two skull fragments and an isolated maxilla
(upper jaw) from the cave chamber Lapa da Escrivania Nr. 5 and a mandible
(lower jaw) from Lapa da Serra das Abelhas, but the latter later turned out to be from a different species, probably Gyldenstolpia fronto. Lund named the animal Hesperomys molitor and placed it in the same genus (Hesperomys
) as what is now Pseudoryzomys simplex and two species of Calomys. Subsequently, it was rarely mentioned in the literature on South American rodents; those authors who did mention it placed it in either Oryzomys
or Calomys.
In 1926, American zoologist Colin Campbell Sanborn collected some rodents in Uruguay, which he identified as Holochilus vulpinus (currently Holochilus brasiliensis) in his 1929 report on the collection. When his successor at the Field Museum of Natural History
, Philip Hershkovitz
, reviewed Holochilus in 1955, he recognized that the series from Uruguay contained two species, one close to the forms of Holochilus found across much of South America, and another unique to Uruguay and southern Brazil; he named the latter as a new species, Holochilus magnus. Hershkovitz identified Holochilus as one of the members of a "sigmodont" group of American rodents, also including Sigmodon
, Reithrodon
, and Neotomys, on the basis of its flat-crowned molars, which are lophodont (the crown consists of transverse ridges). In 1981, H. magnus was also recognized in the Late Pleistocene
of Buenos Aires Province
, Argentina, and in 1982 it was recorded from Rio Grande do Sul in southern Brazil.
In a 1980 article, Argentinean zoologist Elio Massoia recognized the resemblance between Winge's Hesperomys molitor and Hershkovitz's Holochilus magnus, and recommended that the former be reclassified as a species of Holochilus, Holochilus molitor. When American zoologists Voss and Carleton restudied Winge's material in a 1993 paper, they were unable to find any consistent differences between the two and accordingly considered them to pertain to the same species. In addition, they reviewed the differences between this species and other Holochilus and concluded that these were significant enough to place the former in a distinct genus, which they named Lundomys after Lund, who had collected the original material. Since then, the species has been known as Lundomys molitor.
In the same paper in which they described Lundomys, Voss and Carleton also, for the first time, diagnosed the tribe Oryzomyini
in a phylogenetically
valid way. Previously, Oryzomyini had been a somewhat loosely defined group defined among others by a long palate
and the presence of a crest known as the mesoloph on the upper molars and mesolophid on the lower molars; this crest is absent or reduced in Holochilus and Lundomys. Voss and Carleton recognized five synapomorphies
for the group, all of which are shared by Lundomys; the placement in Oryzomyini of Lundomys and of three other genera—Holochilus, Pseudoryzomys, and Zygodontomys
—which also lack complete mesoloph(id)s has been universally supported since.
Voss and Carleton had found some support for a close relationship between Holochilus, Lundomys, and Pseudoryzomys within Oryzomyini. In subsequent years, the related species Holochilus primigenus
and Noronhomys vespuccii were discovered, providing additional evidence for this grouping. The allocation of the former, which is similar to Lundomys in features of the dentition, to Holochilus is controversial and placement as a second species of Lundomys has been suggested as an alternative. A comprehensive phylogenetic analysis of oryzomyines by Marcelo Weksler, published in 2006, supported a close relationship among Lundomys, Holochilus, and Pseudoryzomys; the other species of the group were not included. Data from the sequence of the IRBP
gene supported a closer relationship between Holochilus and Pseudoryzomys, with Lundomys more distantly related, but morphological
data placed Holochilus and Lundomys closer together, as did the combined analysis of both morphological and IRPB data. Subsequently, Carletonomys cailoi
was described as an additional relative of Holochilus and Lundomys.
and Nectomys
, but it is substantially smaller than some of the recently extinct Antillean species, such as "Ekbletomys hypenemus" and Megalomys desmarestii. Unlike in Holochilus brasiliensis, which occurs in the same area, the tail is longer than the head and body. It is sparsely haired and dark, and there is no difference in color between the upper and lower side. The coat, which is long, dense, and soft, is yellow–brown at the sides, but becomes darker on the upperparts and lighter on the underparts. The large hindfeet are characterized by conspicuous interdigital webbing
, but they lack tufts of hair
on the digits and several of the pads are reduced. As in some other semiaquatic oryzomyines, fringes of hair are present along the plantar margins and between some of the digits. The forefeet also lack tufts on the digits and show very long claws, a character unique among oryzomyines. The female has four pairs of teats
and the gall bladder
is absent, both important characters of oryzomyines. The head and body length is 160 to 230 mm (6.30 to 9.06 in), averaging 193 mm (7.60 in), the tail length is 195 to 255 mm (7.68 to 10.04 mm), averaging 235 mm (9.25 in), and the length of the hindfoot is 58 to 68 mm (2.28 to 2.68 in), averaging 62 mm (2.44 in).Measurements for head and body length and tail length are from 10 specimens and those for hindfoot length are from 12 specimens, all from Uruguay.
The front part of the skull is notably broad. As in Holochilus, the zygomatic plate
, the flattened front portion of the cheek bone
, is expansive and produced into a spinous process at the anterior margin. The jugal
bone is small, but less reduced than in Holochilus. The interorbital region
of the skull is narrow and flanked by high beads. The incisive foramina
, which perforate the palate between the incisor
s and the upper molars, are long, extending between the molars. The palate itself is also long, extending beyond the posterior margin of the maxillary bones, and it is perforated near the third molars by conspicuous posterolateral palatal pits. As in all oryzomyines, the squamosal
bone lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
, but Lundomys is unusual in that the squamosal and the tegmen tympani usually overlap when viewed from the side. In the mandible, the angular and coronoid processes
are less well-developed than in Holochilus. The capsular process
of the lower incisor, a slight raising of the mandibular bone at the back end of the incisor, near the coronoid process, is small. The two masseteric ridges, to which some of the chewing muscles are attached, are entirely separate, joining only at their anterior edges, which are located below the first molar.
The molars
are slightly more high-crowned (hypsodont
) than in most oryzomyines and many of the accessory crests are reduced, but they are sharply distinct from the highly derived
, hypsodont molars of Holochilus. The main cusps are located opposite each other and have rounded edges. The enamel folds do not extend past the midlines of the molars. The mesoloph, an accessory crest on the upper molars that is usually well-developed in oryzomyines, is present but short on the first and second upper molar; it is much more reduced in Holochilus and Pseudoryzomys. The corresponding structure on the lower molars, the mesolophid, is present on the first and second molars in Lundomys, but absent in both Holochilus and Pseudoryzomys. Another accessory crest, the anteroloph, is present, though small, on the first upper molar in Lundomys, but entirely absent in both other genera. As in Holochilus and Pseudoryzomys, the anterior cusp on the first lower molar, the anteroconid, contains a deep pit. Each of the three upper molars has three root
s; unlike in both Holochilus and Pseudoryzomys, the first upper molar lacks an accessory fourth root. The first lower molar has four roots, including two small accessory roots located between larger anterior and posterior roots. The second molar has either two or three roots, with the anterior root split into two smaller roots in some specimens.
The karyotype
contains 52 chromosome
s with a total of 58 major arms (2n = 52, FN = 58). The non-sex chromosomes (autosomes) are mostly acrocentric, having a long and a short arm, or telocentric, having only one arm, but there are also three large metacentric pairs, which have two major arms, and a small metacentric pair. The Y chromosome
is metacentric and the X chromosome
is variable, ranging from nearly metacentric to acrocentric in five specimens studied.
; records of live specimens from eastern Argentina and Lagoa Santa, Minas Gerais
, have not been confirmed. It is rarely encountered and it has been collected in only one location in Rio Grande do Sul, but this may be due to insufficient efforts to locate it, rather than genuine rarity. Its distribution is generally limited to areas with mean winter temperatures over 12 °C (54 °F), mean annual temperatures over 18 °C (64 °F), annual rainfall over 1,100 mm (43 in), and a long rainy season averaging over 200 days. It is usually found in swamps or near streams.
Pleistocene
fossils have been found throughout its current range and beyond it. In Uruguay and Rio Grande do Sul, the Lujanian
(Late Pleistocene to Early Holocene) Sopas Formation has yielded remains of L. molitor, in addition to such other mammals as the extinct saber-toothed cat Smilodon populator and species of Glyptodon
, Macrauchenia
, and Toxodon
. The type locality, Lagoa Santa, lies far northeast of the nearest record of live L. molitor; there, it is known only from three skull fragments from a cave known as Laga da Escrivania Nr. 5. This cave also contains numerous remains of members of the extinct South American megafauna
, such as ground sloth
s, litopterna
ns, gomphothere
s, and glyptodonts
, in addition to 16 species of cricetid
rodents, but it is not certain that all remains from this cave are from the same age.
Remains of Lundomys have been found at six Pleistocene localities in Buenos Aires Province
, Argentina, which suggests a warm and humid paleoclimate there. The oldest deposits, at Bajo San José, date to Marine Isotopic Stage 11
, about 420,000 to 360,000 years ago, younger specimens from other localities are as little as 30,000 years old. The younger Argentinean Lundomys specimens are subtly distinct from living Lundomys in some features of the first lower molar and may represent a distinct species. One lower first molar of this form has length 3.28 mm. Because the Bajo San José material does not contain lower first molars, it is impossible to determine whether this material also pertains to the later Argentinean Lundomys form. The morphology of the upper and lower jaw precludes an identification as Holochilus primigenus
, a fossil species with molar traits almost identical to those of Lundomys. The length of the upper toothrow of one specimen from this locality is 8.50 mm (0.3346 in) and the length of the upper first molar is 3.48 mm (0.1370 in), slightly smaller than in living Lundomys, which ranges from 3.56 to 3.64 mm (0.1402 to 0.1433 in) in four specimens
s contained green plant material, suggesting that it is herbivorous
, like Holochilus. A female caught in April was pregnant with three embryos, which were about 12 mm (0.47 in) long. The mite
s Gigantolaelaps wolffsohni and Amblyomma dubitatum have been found on specimens of L. molitor in Uruguay. Other rodents found in association with it include Scapteromys tumidus, Oligoryzomys nigripes
, Reithrodon auritus, Akodon azarae, Oxymycterus nasutus, and Holochilus brasiliensis.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
from southeastern South America. Its distribution is now restricted to Uruguay and nearby Rio Grande do Sul
Rio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
, Brazil, but it previously ranged east into Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...
, Brazil, and west into eastern Argentina. The Argentinean form may have been distinct from the living form from Brazil and Uruguay. L. molitor is a large 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....
, with the head and body length averaging 193 mm (7.60 in), characterized by a long tail, large hindfeet, and long and dense fur. It builds nests above the water, supported by reeds, and it is not currently threatened.
Its external morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
is similar to that of Holochilus brasiliensis and over the course of its complex 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...
history, it has been confused with that species, but other features support its placement in a distinct 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...
, Lundomys. Within 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...
and 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...
, it is a member of a group of specialized oryzomyine
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...
rodents that also includes Holochilus
Holochilus
Holochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
, Noronhomys, Carletonomys
Carletonomys
Carletonomys cailoi is an extinct rodent from the Pleistocene of Buenos Aires Province, Argentina. Although known only from a single maxilla with the first molar, its features are so distinctive that it is placed in its own genus, Carletonomys...
, and Pseudoryzomys.
Taxonomy
Lundomys molitor was first described in 1887 by Danish zoologist Herluf WingeHerluf Winge
Adolf Herluf Winge was a Danish zoologist.-Biography:As a young student, Winge was interested in small mammals, particularly moles, shrews and insectivora. He studied mammalian dentition and produced a comparison of cusp similarities...
, who reviewed the materials Peter Wilhelm Lund
Peter Wilhelm Lund
Peter Wilhelm Lund was a Danish paleontologist, zoologist, archeologist and who spent most of his life working and living in Brazil...
had collected in the caves of Lagoa Santa
Lagoa Santa
For Lagoa Santa, a municipality in Goiás see Lagoa Santa, GoiásLagoa Santa is a municipality and region in the state of Minas Gerais, Brazil...
, Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...
, Brazil. Winge used four specimens for his description, including two skull fragments and an isolated 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...
(upper jaw) from the cave chamber Lapa da Escrivania Nr. 5 and a mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(lower jaw) from Lapa da Serra das Abelhas, but the latter later turned out to be from a different species, probably Gyldenstolpia fronto. Lund named the animal Hesperomys molitor and placed it in the same genus (Hesperomys
Hesperomys
Hesperomys is an obsolete genus of American rodents. It was initially broadly defined to include most of the cricetid rodents of the Americas, except the Arvicolinae, but later became restricted to the members of the modern genus Calomys; the latter name has been in use for this genus instead of...
) as what is now Pseudoryzomys simplex and two species of Calomys. Subsequently, it was rarely mentioned in the literature on South American rodents; those authors who did mention it placed it in either 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...
or Calomys.
In 1926, American zoologist Colin Campbell Sanborn collected some rodents in Uruguay, which he identified as Holochilus vulpinus (currently Holochilus brasiliensis) in his 1929 report on the collection. When his successor at the Field Museum of Natural History
Field Museum of Natural History
The Field Museum of Natural History is located in Chicago, Illinois, USA. It sits on Lake Shore Drive next to Lake Michigan, part of a scenic complex known as the Museum Campus Chicago...
, Philip Hershkovitz
Philip Hershkovitz
Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...
, reviewed Holochilus in 1955, he recognized that the series from Uruguay contained two species, one close to the forms of Holochilus found across much of South America, and another unique to Uruguay and southern Brazil; he named the latter as a new species, Holochilus magnus. Hershkovitz identified Holochilus as one of the members of a "sigmodont" group of American rodents, also including Sigmodon
Cotton rat
A cotton rat is any member of the rodent genus Sigmodon. They are called cotton rats because they build their nests out of cotton, and can damage cotton crops. Cotton rats have small ears and dark coats, and are found in North and South America....
, Reithrodon
Reithrodon
Reithrodon is a genus of rodent in the family Cricetidae.It contains the following species:* Bunny Rat * Naked-soled Conyrat...
, and Neotomys, on the basis of its flat-crowned molars, which are lophodont (the crown consists of transverse ridges). In 1981, H. magnus was also recognized in the Late Pleistocene
Late Pleistocene
The Late Pleistocene is a stage of the Pleistocene Epoch. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. The end of the stage is defined exactly at 10,000 Carbon-14 years BP...
of Buenos Aires Province
Buenos Aires Province
The Province of Buenos Aires is the largest and most populous province of Argentina. It takes the name from the city of Buenos Aires, which used to be the provincial capital until it was federalized in 1880...
, Argentina, and in 1982 it was recorded from Rio Grande do Sul in southern Brazil.
In a 1980 article, Argentinean zoologist Elio Massoia recognized the resemblance between Winge's Hesperomys molitor and Hershkovitz's Holochilus magnus, and recommended that the former be reclassified as a species of Holochilus, Holochilus molitor. When American zoologists Voss and Carleton restudied Winge's material in a 1993 paper, they were unable to find any consistent differences between the two and accordingly considered them to pertain to the same species. In addition, they reviewed the differences between this species and other Holochilus and concluded that these were significant enough to place the former in a distinct genus, which they named Lundomys after Lund, who had collected the original material. Since then, the species has been known as Lundomys molitor.
In the same paper in which they described Lundomys, Voss and Carleton also, for the first time, diagnosed 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...
in a phylogenetically
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...
valid way. Previously, Oryzomyini had been a somewhat loosely defined group defined among others by a long palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
and the presence of a crest known as the mesoloph on the upper molars and mesolophid on the lower molars; this crest is absent or reduced in Holochilus and Lundomys. Voss and Carleton recognized five synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
for the group, all of which are shared by Lundomys; the placement in Oryzomyini of Lundomys and of three other genera—Holochilus, Pseudoryzomys, and Zygodontomys
Zygodontomys
Zygodontomys is a genus of rodent in the tribe Oryzomyini of the family Cricetidae. Its closest relative may be Scolomys. It ranges from Central America east to the Guianas. It contains two species: Zygodontomys brunneus and Zygodontomys brevicauda....
—which also lack complete mesoloph(id)s has been universally supported since.
Voss and Carleton had found some support for a close relationship between Holochilus, Lundomys, and Pseudoryzomys within Oryzomyini. In subsequent years, the related species Holochilus primigenus
Holochilus primigenus
Holochilus primigenus is an extinct oryzomyine rodent known from Pleistocene deposits in Tarija Department, southeastern Bolivia. It is known from a number of isolated jaws and molars, which show that its molars were almost identical to those of the living Lundomys...
and Noronhomys vespuccii were discovered, providing additional evidence for this grouping. The allocation of the former, which is similar to Lundomys in features of the dentition, to Holochilus is controversial and placement as a second species of Lundomys has been suggested as an alternative. A comprehensive phylogenetic analysis of oryzomyines by Marcelo Weksler, published in 2006, supported a close relationship among Lundomys, Holochilus, and Pseudoryzomys; the other species of the group were not included. Data from the sequence of 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 supported a closer relationship between Holochilus and Pseudoryzomys, with Lundomys more distantly related, but morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
data placed Holochilus and Lundomys closer together, as did the combined analysis of both morphological and IRPB data. Subsequently, Carletonomys cailoi
Carletonomys
Carletonomys cailoi is an extinct rodent from the Pleistocene of Buenos Aires Province, Argentina. Although known only from a single maxilla with the first molar, its features are so distinctive that it is placed in its own genus, Carletonomys...
was described as an additional relative of Holochilus and Lundomys.
Description
Lundomys molitor is among the largest living oryzomyines, rivaled only by some large forms of HolochilusHolochilus
Holochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
and Nectomys
Nectomys
Nectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...
, but it is substantially smaller than some of the recently extinct Antillean species, such as "Ekbletomys hypenemus" and Megalomys desmarestii. Unlike in Holochilus brasiliensis, which occurs in the same area, the tail is longer than the head and body. It is sparsely haired and dark, and there is no difference in color between the upper and lower side. The coat, which is long, dense, and soft, is yellow–brown at the sides, but becomes darker on the upperparts and lighter on the underparts. The large hindfeet are characterized by conspicuous interdigital webbing
Interdigital webbing
Interdigital webbing is the presence of membranes of skin between the digits. Normally in mammals, webbing is present in the embryo but resorbed later in development, but in various mammal species it occasionally persists in adulthood...
, but they lack tufts of hair
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....
on the digits and several of the pads are reduced. As in some other semiaquatic oryzomyines, fringes of hair are present along the plantar margins and between some of the digits. The forefeet also lack tufts on the digits and show very long claws, a character unique among oryzomyines. The female has four pairs of teats
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
and the gall bladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
is absent, both important characters of oryzomyines. The head and body length is 160 to 230 mm (6.30 to 9.06 in), averaging 193 mm (7.60 in), the tail length is 195 to 255 mm (7.68 to 10.04 mm), averaging 235 mm (9.25 in), and the length of the hindfoot is 58 to 68 mm (2.28 to 2.68 in), averaging 62 mm (2.44 in).Measurements for head and body length and tail length are from 10 specimens and those for hindfoot length are from 12 specimens, all from Uruguay.
The front part of the skull is notably broad. As in Holochilus, 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...
, the flattened front portion of the cheek bone
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...
, is expansive and produced into a spinous process at the anterior margin. The jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
bone is small, but less reduced than in Holochilus. 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....
of the skull is narrow and flanked by high beads. 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:...
, which perforate the palate between the incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s and the upper molars, are long, extending between the molars. The palate itself is also long, extending beyond the posterior margin of the maxillary bones, and it is perforated near the third molars by conspicuous posterolateral palatal pits. As in all oryzomyines, the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
bone 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....
, but Lundomys is unusual in that the squamosal and the tegmen tympani usually overlap when viewed from the side. In the mandible, the angular and coronoid processes
Coronoid process of the mandible
The mandible's coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size....
are less well-developed than in Holochilus. 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...
of the lower incisor, a slight raising of the mandibular bone at the back end of the incisor, near the coronoid process, is small. The two masseteric ridges, to which some of the chewing muscles are attached, are entirely separate, joining only at their anterior edges, which are located below the first molar.
The 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"....
are slightly more high-crowned (hypsodont
Hypsodont
Hypsodont dentition is characterized by high-crowned teeth and enamel which extends past the gum line. This provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cows, horses and deer; all animals that feed on gritty, fibrous material. The opposite...
) than in most oryzomyines and many of the accessory crests are reduced, but they are sharply distinct from the highly 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...
, hypsodont molars of Holochilus. The main cusps are located opposite each other and have rounded edges. The enamel folds do not extend past the midlines of the molars. The mesoloph, an accessory crest on the upper molars that is usually well-developed in oryzomyines, is present but short on the first and second upper molar; it is much more reduced in Holochilus and Pseudoryzomys. The corresponding structure on the lower molars, the mesolophid, is present on the first and second molars in Lundomys, but absent in both Holochilus and Pseudoryzomys. Another accessory crest, the anteroloph, is present, though small, on the first upper molar in Lundomys, but entirely absent in both other genera. As in Holochilus and Pseudoryzomys, the anterior cusp on the first lower molar, the anteroconid, contains a deep pit. Each of the three upper molars has three root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s; unlike in both Holochilus and Pseudoryzomys, the first upper molar lacks an accessory fourth root. The first lower molar has four roots, including two small accessory roots located between larger anterior and posterior roots. The second molar has either two or three roots, with the anterior root split into two smaller roots in some specimens.
The 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...
contains 52 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 with a total of 58 major arms (2n = 52, FN = 58). The non-sex chromosomes (autosomes) are mostly acrocentric, having a long and a short arm, or telocentric, having only one arm, but there are also three large metacentric pairs, which have two major arms, and a small metacentric pair. The Y chromosome
Y chromosome
The Y chromosome is one of the two sex-determining chromosomes in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development if present. The human Y chromosome is composed of about 60 million base pairs...
is metacentric and the X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
is variable, ranging from nearly metacentric to acrocentric in five specimens studied.
Distribution and ecology
Lundomys molitor has been found as a living animal only in Uruguay and nearby Rio Grande do SulRio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
; records of live specimens from eastern Argentina and Lagoa Santa, Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...
, have not been confirmed. It is rarely encountered and it has been collected in only one location in Rio Grande do Sul, but this may be due to insufficient efforts to locate it, rather than genuine rarity. Its distribution is generally limited to areas with mean winter temperatures over 12 °C (54 °F), mean annual temperatures over 18 °C (64 °F), annual rainfall over 1,100 mm (43 in), and a long rainy season averaging over 200 days. It is usually found in swamps or near streams.
Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
fossils have been found throughout its current range and beyond it. In Uruguay and Rio Grande do Sul, the Lujanian
Lujanian
The Lujanian age is a period of geologic time within the Pleistocene and Holocene epochs of the Neogene used more specifically with South American Land Mammal Ages...
(Late Pleistocene to Early Holocene) Sopas Formation has yielded remains of L. molitor, in addition to such other mammals as the extinct saber-toothed cat Smilodon populator and species of Glyptodon
Glyptodon
Glyptodon was a large, armored mammal of the family Glyptodontidae, a relative of armadillos that lived during the Pleistocene Epoch. It was roughly the same size and weight as a Volkswagen Beetle, though flatter in shape...
, Macrauchenia
Macrauchenia
Macrauchenia was a long-necked and long-limbed, three-toed South American ungulate mammal, typifying the order Litopterna. The oldest fossils date back to around 7 million years ago, and M...
, and Toxodon
Toxodon
Toxodon is an extinct mammal of the late Pliocene and Pleistocene epochs about 2.6 million to 16,500 years ago. It was indigenous to South America, and was probably the most common large-hoofed mammal in South America at the time of its existence....
. The type locality, Lagoa Santa, lies far northeast of the nearest record of live L. molitor; there, it is known only from three skull fragments from a cave known as Laga da Escrivania Nr. 5. This cave also contains numerous remains of members of the extinct South American megafauna
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...
, such as ground sloth
Ground sloth
Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may have survived until 1550 CE; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP...
s, litopterna
Litopterna
Litopterna is an extinct order of fossil hoofed mammals from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed....
ns, gomphothere
Gomphothere
Gomphotheriidae is a diverse taxonomic family of extinct elephant-like animals , called gomphotheres. They were widespread in North America during the Miocene and Pliocene epochs, 12-1.6 million years ago. Some lived in parts of Eurasia, Beringia and, following the Great American Interchange,...
s, and glyptodonts
Glyptodontidae
Glyptodonts were large, more heavily armored relatives of extinct pampatheres and modern armadillos.They first evolved during the Miocene in South America, which remained their center of species diversity...
, in addition to 16 species of cricetid
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...
rodents, but it is not certain that all remains from this cave are from the same age.
Remains of Lundomys have been found at six Pleistocene localities in Buenos Aires Province
Buenos Aires Province
The Province of Buenos Aires is the largest and most populous province of Argentina. It takes the name from the city of Buenos Aires, which used to be the provincial capital until it was federalized in 1880...
, Argentina, which suggests a warm and humid paleoclimate there. The oldest deposits, at Bajo San José, date to Marine Isotopic Stage 11
Marine Isotopic Stage 11
Interglacial periods that occurred during Pleistocene times have been recently put under investigation, in order to better understand our present and future climates. In fact, paleoclimatic interpretations often depends on observations drawn from the study of modern/historical processes...
, about 420,000 to 360,000 years ago, younger specimens from other localities are as little as 30,000 years old. The younger Argentinean Lundomys specimens are subtly distinct from living Lundomys in some features of the first lower molar and may represent a distinct species. One lower first molar of this form has length 3.28 mm. Because the Bajo San José material does not contain lower first molars, it is impossible to determine whether this material also pertains to the later Argentinean Lundomys form. The morphology of the upper and lower jaw precludes an identification as Holochilus primigenus
Holochilus primigenus
Holochilus primigenus is an extinct oryzomyine rodent known from Pleistocene deposits in Tarija Department, southeastern Bolivia. It is known from a number of isolated jaws and molars, which show that its molars were almost identical to those of the living Lundomys...
, a fossil species with molar traits almost identical to those of Lundomys. The length of the upper toothrow of one specimen from this locality is 8.50 mm (0.3346 in) and the length of the upper first molar is 3.48 mm (0.1370 in), slightly smaller than in living Lundomys, which ranges from 3.56 to 3.64 mm (0.1402 to 0.1433 in) in four specimens
Natural history
Lundomys molitor is semiaquatic in habits, spending much of its time in the water, and is active during the night. An excellent swimmer, it is even more specialized for swimming than is Holochilus. It builds a spherical nest among reeds in up to 1.5 m (5 ft) deep water, usually about 20 cm (8 in) above the water. The material for the nest, which is 25 to 30 cm (10 to 12 in) in diameter and 9 to 11 cm (about 4 in) in height, comes from the surrounding reeds. Its wall consists of three layers, surrounding a central chamber, which is connected to the water by a ramp, also composed of reeds. Nests built by members of the related genus Holochilus are similar in many details. Several dissected stomachStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
s contained green plant material, suggesting that it is herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, like Holochilus. A female caught in April was pregnant with three embryos, which were about 12 mm (0.47 in) long. The mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s Gigantolaelaps wolffsohni and Amblyomma dubitatum have been found on specimens of L. molitor in Uruguay. Other rodents found in association with it include Scapteromys tumidus, Oligoryzomys nigripes
Oligoryzomys nigripes
Oligoryzomys nigripes, also known as the Black-footed Colilargo or the Black-footed Pygmy Rice Rat, is a rodent in the genus Oligoryzomys of family Cricetidae. It is found from Pernambuco in northeastern Brazil through the Atlantic Forest and Cerrado into Paraguay, Uruguay, and Argentina, where it...
, Reithrodon auritus, Akodon azarae, Oxymycterus nasutus, and Holochilus brasiliensis.
Conservation status
The species' conservation status is currently assessed as "least concern" by the International Union for Conservation of Nature, reflecting a relatively wide distribution and the absence of evidence for a decline in populations. Several of the areas where it occurs are protected, but the destruction of its habitat may pose a threat to its continued existence.Literature cited
- Bonvicino, C.R., Oliveira, J.A. and D'Andrea, P.S. 2008. Guia dos Roedores do Brasil, com chaves para gêneros baseadas em characteres externos. Série de Manuais Técnicos 11:1–120. Rio de Janeiro: Centro Pan-Americano de Febre Aftosa – OPAS/OMS (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.
- Duff, A. and Lawson, A. 2004. Mammals of the World: A checklist. New Haven: A & C Black, 312 pp. ISBN 0-7136-6021-X.
- Freitas, T.R.O., Mattevi, M.S., Oliveira, L.F.B., Souza, M.J., Yonenaga-Yassuda, Y. and Salzano, F.M. 1983. Chromosome relationships in three representatives of the genus Holochilus (Rodentia, Cricetidae) from Brazil (subscription required). Genetica 61:13–20.
- Gonzalez, E., D'Elia, G. and Pardinas, U. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on February 1, 2010.
- González, E., D'Elía, G. and Pardiñas, U. 2008. Lundomys molitor. In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on November 3, 2009.
- Hershkovitz, P.M. 1955. South American marsh rats, genus Holochilus, with a summary of sigmodont rodents. Fieldiana Zoology 37:619–673.
- Lareschi, M., Gettinger, D., Venzal, J.M., Arzua, M., Nieri-Bastos, F.A., Barros-Battesti, D.M. and Gonzalez, E.M. 2006. Primer registro de ácaros (Gamasida: Laelapidae) parásitos de roedores silvestres en Uruguay, con nuevos registros de hospedadores. Neotropical Entomology 35(5):596–601 (in Spanish).
- 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
- Nava, S., Venzal, J.M., Labruna, M.B., Mastropaolo, M., González, E.M., Mangold, A.J. and Guglielmone, A.A. 2010. Hosts, distribution and genetic divergence (16S rDNA) of Amblyomma dubitatum (Acari: Ixodidae) (subscription required). Experimental and Applied Acarology 51(4):335–351.
- Oliveira, É.V. and Kerber, L. 2009. Paleontologia e aspectos geológicos das sucessões do final do Neógeno no sudoeste do Rio Grande do Sul, Brasil. Gaea 5(1):21–34 (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. and Deschamps, C. 1996. Sigmodontinos (Mammalia, Rodentia) Pleistocenicos del sudoeste de la provincia de Buenos Aires (Argentina): Aspectos sistematicos, paleozoogeograficos y paleoambientales. Estudios Geologicos 52:367–379 (in Spanish).
- Pardiñas, U.F.J. and Lezcano, M.J. 1995. Cricetidos (Mammalia: Rodentia) del Pleistoceno tardio del nordeste de la provincia de Buenos Aires (Argentina). Aspectos sistematicos y paleoambientales. Ameghiniana 32(3):249–265 (in Spanish).
- Pardiñas, U.F.J., D'Elía, G. and Teta, P. 2008. Una introducción a los mayores sigmodontinos vivientes: Revisión de Kunsia Hershkovitz, 1966 y descripción de un nuevo género (Rodentia: Cricetidae). Arquivos do Museu Nacional 66(3–4):509–594.
- Ray, C.E. 1962. The Oryzomyine Rodents of the Antillean Subregion. Doctor of Philosophy thesis, Harvard University, 211 pp.
- Steppan, S.J. 1996. A new species of Holochilus (Rodentia: Sigmodontinae) from the Middle Pleistocene of Bolivia and its phylogenetic significance (subscription required). Journal of Vertebrate Paleontology 16(3):522–530.
- Teta, P. and Pardiñas, U.F.J. 2006. Pleistocene record of marsh rats of the genus Lundomys in southern South America: Paleoclimatic significance. Current Research in the Pleistocene 23:179–181.
- Ubilla, M., Perea, D., Aguilar, C.G. and Lorenzo, N. 2004. Late Pleistocene vertebrates from northern Uruguay: tools for biostratigraphic, climatic and environmental reconstruction (subscription required). Quaternary International 114:129–142.
- 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.