Lundomys Temporal range: Late Pleistocene to Recent (Lujanian) | |
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Lectotype partial cranium of L. molitor. The illustrated mandible represents a different species. | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Rodentia |
Family: | Cricetidae |
Subfamily: | Sigmodontinae |
Genus: | Lundomys Voss & Carleton, 1993 |
Species: | L. molitor |
Binomial name | |
Lundomys molitor (Winge, 1887) | |
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Distribution of Lundomys molitor in South America. The current distribution is in red, and fossil records outside the current range are in blue. | |
Synonyms [2] | |
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Lundomys molitor, also known as Lund's amphibious rat [3] or the greater marsh rat, [4] 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 northward into Minas Gerais, Brazil, and southward into eastern Argentina. The Argentine 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 (7.6 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 .
Lundomys molitor was first described in 1888 by Danish zoologist Herluf Winge, 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, [5] probably Gyldenstolpia fronto . [6] 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. [7]
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). [7] In 1981, H. magnus was also recognized in the Late Pleistocene of Buenos Aires Province, Argentina, [8] and in 1982 it was recorded from Rio Grande do Sul in southern Brazil. [9]
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. [10] 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. [11] 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. [2] Since then, the species has been known as Lundomys molitor. [3]
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. [12] 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. [13] Voss and Carleton recognized five synapomorphies for the group, all of which are shared by Lundomys; [12] 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. [14]
Voss and Carleton had found some support for a close relationship between Holochilus, Lundomys, and Pseudoryzomys within Oryzomyini. [15] In subsequent years, the related species Holochilus primigenus and Noronhomys vespuccii were discovered, providing additional evidence for this grouping. [16] 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. [17] 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. [18] Subsequently, Carletonomys cailoi was described as an additional relative of Holochilus and Lundomys. [19]
Lundomys molitor is among the largest living oryzomyines, rivaled only by some large forms of Holochilus and Nectomys , but it is substantially smaller than some of the recently extinct Antillean species, such as " Ekbletomys hypenemus " and Megalomys desmarestii . [20] Unlike in Holochilus brasiliensis , which occurs in the same area, the tail is longer than the head and body. [21] 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. [22] 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. [23] As in some other semiaquatic oryzomyines, fringes of hair are present along the plantar margins and between some of the digits. [24] The forefeet also lack tufts on the digits and show very long claws, a character unique among oryzomyines. [25] The female has four pairs of teats, and the gall bladder is absent, both important characters of oryzomyines. [26] The head and body length is 160 to 230 mm (6.3 to 9.1 in), averaging 193 mm (7.6 in), the tail length is 195 to 255 mm (7.68 to 10.04 mm), averaging 235 mm (9.3 in), and the length of the hindfoot is 58 to 68 mm (2.3 to 2.7 in), averaging 62 mm (2.4 in). [fn 1] [27]
The front part of the skull is notably broad. [22] 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. [28] The interorbital region of the skull is narrow and flanked by high beads. [22] The incisive foramina, which perforate the palate between the incisors and the upper molars, are long, extending between the molars. [28] The palate itself is also long, extending beyond the posterior margin of the maxillary bones, [29] and it is perforated near the third molars by conspicuous posterolateral palatal pits. [30] 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. [31] In the mandible, the angular and coronoid processes are less well-developed than in Holochilus. [32] 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. [33]
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. [34] The main cusps are located opposite each other and have rounded edges. The enamel folds do not extend past the midlines of the molars. [34] 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. [35] 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. [36] Another accessory crest, the anteroloph, is present, though small, on the first upper molar in Lundomys, but entirely absent in both other genera. [37] As in Holochilus and Pseudoryzomys, the anterior cusp on the first lower molar, the anteroconid, contains a deep pit. [38] Each of the three upper molars has three roots; unlike in both Holochilus and Pseudoryzomys, the first upper molar lacks an accessory fourth root. [39] 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. [40]
The karyotype contains 52 chromosomes 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. [41]
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, have not been confirmed. [8] 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. [42] 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. [43]
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 . [44] 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, in addition to 16 species of cricetid rodents, but it is not certain that all remains from this cave are from the same age. [45]
Remains of Lundomys have been found at six Pleistocene localities in Buenos Aires Province, Argentina, which suggests a warm and humid paleoclimate there. [46] The oldest deposits, at Bajo San José, date to Marine Isotopic Stage 11, about 420,000 to 360,000 years ago, while younger specimens from other localities are as little as 30,000 years old. [47] 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. [48] 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. [49] The length of the upper toothrow of one specimen from this locality is 8.50 mm (0.335 in) and the length of the upper first molar is 3.48 mm (0.137 in), [50] slightly smaller than in living Lundomys, which ranges from 3.56 to 3.64 mm (0.140 to 0.143 in) in four specimens [51]
Lundomys molitor is semiaquatic in habits, spending much of its time in the water, and is active during the night. [52] An excellent swimmer, [53] it is even more specialized for swimming than is Holochilus. [54] It builds a spherical nest among reeds in up to 1.5 m (4.9 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. [55] Nests built by members of the related genus Holochilus are similar in many details. [52] Several dissected stomachs contained green plant material, suggesting that it is herbivorous, like Holochilus. [56] A female caught in April was pregnant with three embryos, which were about 12 mm (0.47 in) long. [57] The mites Gigantolaelaps wolffsohni and Amblyomma dubitatum have been found on specimens of L. molitor in Uruguay. [58] Other rodents found in association with it include Scapteromys tumidus , Oligoryzomys nigripes , Reithrodon auritus , Akodon azarae , Oxymycterus nasutus , and Holochilus brasiliensis. [59]
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. [1]
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 O. couesi of Mexico and Central America—are widespread; the six others have more restricted distributions. The species have had eventful taxonomic histories, and most species were at one time included in the marsh rice rat; additional species may be recognized in the future. The name Oryzomys was established in 1857 by Spencer Fullerton Baird for the marsh rice rat and was soon applied to over a hundred species of American rodents. Subsequently, the genus gradually became more narrowly defined until its current contents were established in 2006, when ten new genera were established for species previously placed in Oryzomys.
Oligoryzomys flavescens, also known as the flavescent colilargo or yellow pygmy rice rat is a species of rodent in the genus Oligoryzomys of family Cricetidae. It is found in southern South America, occurring in southern Brazil, Paraguay, Uruguay, and northeastern Argentina. Its karyotype has 2n = 64-66 and FNa = 66–70.
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 medium-sized species, weighing about 50 grams (1.8 oz), with gray–brown fur, long and narrow hindfeet, and a tail that is about as long as the head and body. The IUCN has assessed its conservation status as being of least concern, although almost nothing is known about its diet or reproduction.
Oryzomys dimidiatus, also known as the Nicaraguan oryzomys, Thomas's rice rat, or the Nicaraguan rice rat, is a rodent in the family Cricetidae. It is known from only three specimens, all collected in southeastern Nicaragua since 1904. Placed in Nectomys upon its discovery, it was later classified in its own subgenus of Oryzomys and finally recognized as closely related to other species now placed in Oryzomys, including the marsh rice rat and Coues' rice rat, which occurs in the same region.
Oryzomys gorgasi, also known as Gorgas's oryzomys or Gorgas's rice rat, is a rodent in the genus Oryzomys of family Cricetidae. First recorded in 1967, it is known from only a few localities, including a freshwater swamp in the lowlands of northwestern Colombia and a mangrove islet in northwestern Venezuela. It reportedly formerly occurred on the island of Curaçao off northwestern Venezuela; this extinct population has been described as a separate species, Oryzomys curasoae, but does not differ morphologically from mainland populations.
Mindomys hammondi, also known as Hammond's rice rat or Hammond's oryzomys, is an endangered species of rodent in the tribe Oryzomyini of family Cricetidae. Formerly considered to be related with Nectomys, Sigmodontomys, Megalomys, or Oryzomys, it is now placed in then genus Mindomys, but its relationships remain obscure; some evidence supports a placement near Oecomys or as a basal member of Oryzomyini.
Eremoryzomys polius, also known as the gray rice rat or the Marañon oryzomys, is a rodent species in the tribe Oryzomyini of the family Cricetidae. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in Oryzomys and named Oryzomys polius. In 2006, a cladistic analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus, Eremoryzomys. The Brazilian genus Drymoreomys, named in 2011, is probably the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River in central Peru, but may yet contain more than one species.
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the 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. It is part of the clade Oryzomyalia, which includes most of the South American Sigmodontinae.
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, but it subsequently became extinct, perhaps because of the exotic rats and mice introduced by the first explorers of the island. Numerous but fragmentary fossil remains of the animal, of uncertain but probably Holocene age, were discovered in 1973 and described in 1999.
Carletonomys cailoi is an extinct rodent from the Pleistocene (Ensenadan) 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. Discovered in 1998 and formally described in 2008, it is part of a well-defined group of oryzomyine rodents that also includes Holochilus, Noronhomys, Lundomys, and Pseudoryzomys. This group is characterized by progressive semiaquatic specializations and a reduction in the complexity of molar morphology.
Reigomys 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. On the other hand, the animal possesses a number of derived traits of the palate which document a closer relationship to living Holochilus, the genus of South American marsh rats, and for this reason it was placed in the genus Holochilus when it was first described in 1996. The subsequent discoveries of Noronhomys and Carletonomys, which may be more closely related to extant Holochilus than H. primigenus is, have cast its placement in Holochilus into doubt, and it was ultimately made the type species of a separate genus, Reigomys.
Juliomys anoblepas is a rodent in the genus Juliomys of the subfamily Sigmodontinae known from a single broken skull. The specimen was collected by Peter Wilhelm Lund in the caves of Lagoa Santa, Minas Gerais, Brazil, in the first half of the 19th century and described by Herluf Winge in 1888 as Calomys anoblepas. The species remained unstudied and its affinities unclear until 2011, when it was recognized as a member of the genus Juliomys, which includes three other species from southern Brazil and nearby Argentina and Paraguay. J. anoblepas is probably a separate extinct species of the genus, which is no longer found at Lagoa Santa.
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. Many members of the family lack them or have only simple pits, but Arvicolinae and Oryzomyini have more highly developed posterolateral palatal pits. Posterolateral palatal pits are also present in some other rodents, including Glis, Jaculus, Hystrix, Abrocoma, Ctenomys, Chinchilla, and Lagidium.
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 rest of the skull via the antorbital bridge. It is part of the maxillary bone, or upper jaw, which also contains the upper cheekteeth. Primitively, rodents have a nearly horizontal zygomatic plate. In association with specializations in zygomasseteric system, several distinct morphologies have developed across the order.
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. Their development and form are variable between and within species, and features of the sphenopalatine vacuities have been used as characters in cladistic analyses.
In mammals, ungual tufts are tufts of hairs at the base of claws of the forefeet and hindfeet. Their presence has been used as a character in cladistic studies of the Cricetidae, a large family of rodents.
Natatory fringes are rows of stiff hairs that occur along the margins of the hindfeet in some rodents. They occur along the plantar margins and in some cases also between the toes. Among sigmodontines, a mostly South American groups, natatory fringes are present in Ichthyomyini and some Oryzomyini. Among ichthyomyines, the fringes are poorly developed in Neusticomys but well-developed in other genera, and in Rheomys mexicanus the hairs of the fringes may exceed 3 millimetres (0.12 in) in length. Amphinectomys, Holochilus, Lundomys, and Nectomys are the only oryzomyines with natatory fringes, but have them only weakly developed; one study also records them in Oryzomys. In oryzomyines, the fringes are an adaptation for a semiaquatic lifestyle that appeared convergently in the Holochilus-Lundomys and Nectomys-Amphinectomys lineages. The term was introduced in 1993 by Voss and Carleton in describing Lundomys.
?Oryzomys pliocaenicus is a fossil rodent from the Hemphillian of Kansas, central United States. It is known from a single mandible with the back part missing. All three molars are present, but very worn. Together, the molars are 3.6 mm long. The fossil was discovered in 1935 and described in 1939 as a possible species of Oryzomys. Later authors doubted this allocation and suggested that it may instead belong in Bensonomys or Jacobsomys, but the material may not allow a definite identification.
Agathaeromys is an extinct genus of oryzomyine rodents from the Pleistocene of Bonaire, Netherlands Antilles. Two species are known, which differ in size and some details of tooth morphology. The larger A. donovani, the type species, is known from hundreds of teeth that are probably 900,000 to 540,000 years old, found in four localities. A. praeuniversitatis, the smaller species, is known from 35 teeth found in a single fossil site, which is probably 540,000 to 230,000 years old.
Drymoreomys is a rodent genus in the tribe Oryzomyini that lives in the Atlantic Forest of Brazil. The single species, D. albimaculatus, is known only from the states of São Paulo and Santa Catarina and was not named until 2011. It lives in the humid forest on the eastern slopes of the Serra do Mar and perhaps reproduces year-round. Although its range is relatively large and includes some protected areas, it is patchy and threatened, and the discoverers recommend that the animal be considered "Near Threatened" on the IUCN Red List. Within Oryzomyini, Drymoreomys appears to be most closely related to Eremoryzomys from the Andes of Peru, a biogeographically unusual relationship, in that the two populations are widely separated and each is adapted to an arid or a moist environment.