''Lundomys molitor'', also known as Lund's amphibious rat
[Musser and Carleton, 2005, p. 1124] or the greater marsh rat, is a
semiaquatic
In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below.
Semiaquatic animals
Semi aquatic animals include:
* Ve ...
rat
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
from southeastern
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
.
Its distribution is now restricted to
Uruguay
Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
and nearby
Rio Grande do Sul,
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, but it previously ranged northward into
Minas Gerais
Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...
, Brazil, and southward into eastern
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. The Argentine form may have been distinct from the living form from Brazil and Uruguay. ''L. molitor'' is a large
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
, with the head and body length averaging , 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, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
is similar to that of ''
Holochilus brasiliensis
''Holochilus brasiliensis'', also known as the Brazilian marsh ratMusser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)Mammal Species of the World: a taxonomic and geographic refer ...
'', 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
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
, ''Lundomys''. Within the family
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and h ...
and subfamily
Sigmodontinae
The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
, it is a member of a group of specialized
oryzomyine rodents that also includes ''
Holochilus
''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus' ...
'', ''
Noronhomys
''Noronhomys vespuccii'', also known as Vespucci's rodent, is an extinct rat species from the islands of Fernando de Noronha off northeastern Brazil. Italian explorer Amerigo Vespucci may have seen it on a visit to Fernando de Noronha in 1503, ...
'', ''
Carletonomys
''Carletonomys cailoi'' is an extinction, extinct rodent from the Pleistocene (Ensenadan) of Buenos Aires Province, Argentina. Although known only from a single maxilla (upper jaw) with the first molar (tooth), molar, its features are so distinct ...
'', and ''
Pseudoryzomys
''Pseudoryzomys simplex'', also known as the Brazilian false rice rat or false oryzomys, is a species of rodent in the family Cricetidae from south-central South America. It is found in lowland palm savanna and thorn scrub habitats. It is a me ...
''.
Taxonomy
''Lundomys molitor'' was first described in 1888 by Danish zoologist
Herluf Winge
Adolf Herluf Winge (19 March 1857 – 10 November 1923) was a Danish zoologist.
Biography
As a young student, along with his brother Oluf, Winge was interested in small mammals, particularly moles, shrews and insectivora. He studied mammalian ...
, who reviewed the materials
Peter Wilhelm Lund
Peter Wilhelm Lund (14 June 1801 – 25 May 1880) was a Danish paleontologist, zoologist, and archeologist. He spent most of his life working and living in Brazil. He is considered the father of Brazilian paleontology as well as archaeology.
He ...
had collected in the caves of
Lagoa Santa, Minas Gerais
Lagoa Santa (''Holy Lagoon'') is a municipality and region in the state of Minas Gerais, Brazil. It is located 37 km north-northeast from Belo Horizonte and belongs to the mesoregion Metropolitana de Belo Horizonte and to the microregion o ...
, Brazil. Winge used four specimens for his description, including two skull fragments and an isolated
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
(upper jaw) from the cave chamber Lapa da Escrivania Nr. 5 and a
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
(lower jaw) 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
''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 (''O. palustris'') of the United States and ...
'' or ''Calomys''.
[Voss and Carleton, 1993, p. 3]
In 1926, American zoologist
Colin Campbell Sanborn Colin Campbell Sanborn (1897–1962) was a US ecologist and biologist, employed as curator of birds and mammals at the Field Museum of Natural History in Chicago. His works include taxonomic revisions of the Chiroptera bat families, and he was reco ...
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
''Reithrodon'' is a genus of rodent in the family Cricetidae.
It contains the following living species:
* Bunny rat (''Reithrodon auritus'')
* Naked-soled conyrat (''Reithrodon typicus'')
The scientific name translates as "channel tooth" and r ...
'', and ''
Neotomys'', on the basis of its flat-crowned
molars
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
, which are
lophodont
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
(the crown consists of transverse ridges).
In 1981, ''H. magnus'' was also recognized in the
Late Pleistocene of
Buenos Aires Province, Argentina,
[Voss and Carleton, 1993, p. 10] and in 1982 it was recorded from Rio Grande do Sul in southern Brazil.
In a 1980 article, Argentine 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 is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of ...
in a
phylogenetically valid way.
[Voss and Carleton, 1993, p. 31] Previously, Oryzomyini had been a somewhat loosely defined group defined among others by a long
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...
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
''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
Central America ( es, América Central or ) is a subregion of the Americas ...
''—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''.
Description
''Lundomys molitor'' is among the largest living oryzomyines, rivaled only by some large forms of ''
Holochilus
''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus' ...
'' and ''
Nectomys
''Nectomys'' is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Musser and Carleton, 2005. It is closely related to '' Amphinectomys'' and was formerly considered congeneric with ''Sigmodontomys''. It consists of five species, whic ...
'', but it is substantially smaller than some of the recently extinct
Antillean species, such as "''
Ekbletomys hypenemus
"''Ekbletomys hypenemus''" is an extinct oryzomyine rodent from the islands of Antigua and Barbuda, Lesser Antilles. It was described as the only species of the subgenus "''Ekbletomys''" of genus ''Oryzomys'' in a 1962 Ph.D. thesis, but that nam ...
''" and ''
Megalomys desmarestii
''Megalomys desmarestii'', also known as the Martinique muskrat,Watts, 1990, p. 528 Desmarest's pilorie,Musser and Carleton, 2005 or the Martinique giant rice rat, is an extinct rice rat from Martinique in the Caribbean.
Description
It was amon ...
''. Unlike in ''
Holochilus brasiliensis
''Holochilus brasiliensis'', also known as the Brazilian marsh ratMusser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)Mammal Species of the World: a taxonomic and geographic refer ...
'', 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.
[Voss and Carleton, 1993, p. 7] The large hindfeet are characterized by conspicuous
interdigital webbing, but they lack
tufts of hair on the digits and several of the
pads
Pads (also called leg guards) are a type of protective equipment used in a number of sports and serve to protect the legs from the impact of a hard ball, puck, or other object of play travelling at high speed which could otherwise cause injuries t ...
are reduced. As in some other semiaquatic oryzomyines,
fringes of hair are present along the
plantar
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
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
In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...
is absent, both important characters of oryzomyines. The head and body length is , averaging , the tail length is 195 to 255 mm (7.68 to 10.04 mm), averaging , and the length of the hindfoot is , averaging .
[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
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the ...
, the flattened front portion of the
cheek bone
In the human skull, the zygomatic bone (from grc, ζῠγόν, zugón, yoke), also called cheekbone or malar bone, is a paired irregular bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. It is si ...
, is expansive and produced into a spinous process at the anterior margin. The
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.
Anatomy ...
bone is small, but less reduced than in ''Holochilus''.
[Voss and Carleton, 1993, p. 15] The
interorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups.
In oryzomyine rodents, for example, the width, form, an ...
of the skull is narrow and flanked by high beads.
The
incisive foramina
In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...
, which perforate the palate between the
incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s and the 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 The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone.
In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...
bone lacks a suspensory process that contacts the
tegmen tympani
The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound.
Structure
On its lateral surface, it abuts the external auditor ...
, the roof of the
tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound.
Structure
On its lateral surface, it abuts the external auditory ...
, 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
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 (outer) side of the mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest ...
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
Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...
) than in most oryzomyines, and many of the accessory crests are reduced, but they are sharply distinct from the highly
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
, hypsodont molars of ''Holochilus''.
[Voss and Carleton, 1993, p. 19] 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
roots
A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients.
Root or roots may also refer to:
Art, entertainment, and media
* ''The Root'' (magazine), an online magazine focusing ...
; 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
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s with a total of 58 major arms (2n = 52,
FN = 58). The non-sex chromosomes (autosomes) are mostly
acrocentric
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
, having a long and a short arm, or
telocentric
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
, having only one arm, but there are also three large
metacentric
Metacentric may refer to:
* Metacentric height
The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger ...
pairs, which have two major arms, and a small metacentric pair. The
Y chromosome
The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...
is metacentric and the
X chromosome
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex ...
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 Sul; records of live specimens from eastern Argentina and Lagoa Santa,
Minas Gerais
Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...
, have not been confirmed.
It is rarely encountered, and 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 , mean annual temperatures over , annual rainfall over , and a long rainy season averaging over 200 days. It is usually found in swamps or near streams.
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
fossils have been found throughout its current range and beyond it. In Uruguay and Rio Grande do Sul, the
Lujanian
The Lujanian age is a South American land mammal age within the Pleistocene and Holocene epochs of the Neogene, from 0.8–0.011 Ma or 800–11 tya. It follows the Ensenadan.
The age is usually divided into the middle Pleistocene Bonaerian stag ...
(Late Pleistocene to Early Holocene)
Sopas Formation
''Sopas'' is a Filipino macaroni soup made with elbow macaroni, various vegetables, and meat (usually chicken), in a creamy broth with evaporated milk. It is regarded as a comfort food in the Philippines and is typically eaten during breakfast ...
has yielded remains of ''L. molitor'', in addition to such other mammals as the extinct saber-toothed cat ''
Smilodon populator
''Smilodon'' is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related ...
'' and species of ''
Glyptodon
''Glyptodon'' (from Greek for 'grooved or carved tooth': γλυπτός 'sculptured' and ὀδοντ-, ὀδούς 'tooth') is a genus of glyptodont (an extinct group of large, herbivorous armadillos) that lived from the Pleistocene, around 2.5 m ...
'', ''
Macrauchenia
''Macrauchenia'' ("long llama", based on the now-invalid llama genus, ''Auchenia'', from Greek "big neck") was a large, long-necked and long-limbed, three-toed native South American mammal in the order Litopterna. The genus gives its name to its ...
'', and ''
Toxodon
''Toxodon'' (meaning "bow tooth" in reference to the curvature of the teeth) is an extinct genus of South American mammals from the Late Miocene to early Holocene epochs (Mayoan to Lujanian in the SALMA classification) (about 11.6 million to 1 ...
''. 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 sloths,
litopternans,
gomphotheres, and
glyptodonts
Glyptodonts are an extinct subfamily of large, heavily armoured armadillos. They arose in South America around 48 million years ago and spread to southern North America after the continents became connected several million years ago. The best-k ...
, 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
Marine Isotope Stage 11 or MIS 11 is a Marine Isotope Stage in the geologic temperature record, covering the interglacial period between 424,000 and 374,000 years ago. It corresponds to the Hoxnian Stage in Britain.
Interglacial periods which oc ...
, about 420,000 to 360,000 years ago, while younger specimens from other localities are as little as 30,000 years old. The younger Argentine ''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 Argentine ''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 and the length of the upper first molar is , slightly smaller than in living ''Lundomys'', which ranges from 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.
[Voss and Carleton, 1993, p. 34] An excellent swimmer, it is even more specialized for swimming than is ''Holochilus''. It builds a spherical
nest
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...
among reeds in up to deep water, usually about above the water. The material for the nest, which is 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
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
s contained green plant material, suggesting that it is
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
, like ''Holochilus''. A female caught in April was pregnant with three embryos, which were about long. The
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...
s ''
Gigantolaelaps wolffsohni'' and ''
Amblyomma dubitatum
''Amblyomma'' is a genus of hard ticks. Some are disease vectors, for example the Rocky Mountain spotted fever in Brazil or ehrlichiosis in the United States.
This genus is the third largest in the family Ixodidae, with its species primarily o ...
'' have been found on specimens of ''L. molitor'' in Uruguay. Other rodents found in association with it include ''
Scapteromys tumidus'', ''
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. Oligoryzomys nigripes is a species that has been further divided into differen ...
'', ''
Reithrodon auritus'', ''
Akodon azarae
''Akodon azarae'', also known as Azara's akodontMusser and Carleton, 2005, p. 1093 or Azara's grass mouse, is a rodent species from South America. It is found from southernmost Brazil through Paraguay and Uruguay into eastern Argentina. It is ...
'', ''
Oxymycterus nasutus'', and ''Holochilus brasiliensis''.
[Voss and Carleton, 1993, pp. 32–34]
Conservation status
The species' conservation status is currently assessed as "least concern" by the
International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
, 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.
Footnotes
References
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. .
* 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.
*
* 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).
*
* 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 Geológicos'' 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.
{{Featured article
Extant Pleistocene first appearances
Mammals of Brazil
Mammals of Uruguay
Monotypic rodent genera
Oryzomyini
Mammals described in 1888
Taxa named by Michael D. Carleton