Lundomys

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Lundomys
Temporal range: Late Pleistocene to Recent (Lujanian)
From top to bottom: side view of skull with mandible, missing the upper incisor and much of the posterior part; text "2. Hesperomys molitor"; and views of the same skull from above and below
cranium of L. molitor. The illustrated mandible
represents a different species.

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this 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)
Map of South America marked by red and blue colors, with the red color extending over Uruguay and into Rio Grande do Sul, southern Brazil, and the blue color in southeastern Minas Gerais, eastern Brazil, and in two different areas in northern and southern Buenos Aires Province, eastern Argentina
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]
  • Hesperomys molitor Winge, 1888
  • Oryzomys molitor: Trouessart, 1898
  • Holochilus magnus Hershkovitz, 1955
  • Calomys molitor: Hershkovitz, 1962
  • Holochilus molitor: Massoia, 1980
  • Lundomys molitor: Voss and Carleton, 1993

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.

Taxonomy

Lundomys molitor was first described in 1888 by Danish zoologist

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

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

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.

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]

Description

Lundomys molitor is among the largest living oryzomyines, rivaled only by some large forms of

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.

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 (

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

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]

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, 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]

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

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]

Natural history

Lundomys molitor is semiaquatic in habits, spending much of its time in the water, and is active during the night.

Oxymycterus nasutus, and Holochilus brasiliensis.[59]

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.[1]

Footnotes

  1. ^ 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.

References

  1. ^ a b González et al., 2016
  2. ^ a b Voss and Carleton, 1993, p. 5
  3. ^ a b Musser and Carleton, 2005, p. 1124
  4. ^ González et al., 2016; Duff and Lawson, 2004, p. 56
  5. ^ Voss and Carleton, 1993, p. 6
  6. ^ Pardiñas et al., 2008, pp. 556–557
  7. ^ a b Voss and Carleton, 1993, p. 3
  8. ^ a b Voss and Carleton, 1993, p. 10
  9. ^ Oliveira et al. in Freitas et al., 1983
  10. ^ Voss and Carleton, 1993, pp. 3, 6
  11. ^ Voss and Carleton, 1993, p. 4
  12. ^ a b Voss and Carleton, 1993, p. 31
  13. ^ Voss and Carleton, 1993
  14. ^ Musser and Carleton, 2005; Weksler, 2006
  15. ^ Voss and Carleton, 1993, p. 1
  16. ^ Steppan, 1996; Carleton and Olson, 1999
  17. ^ Pardiñas, 2008, p. 1275
  18. ^ Weksler, 2006
  19. ^ Pardiñas, 2008
  20. ^ Weksler, 2006, table 8; Voss and Myers, 1991, table 1; Ray, 1962, tables 7, 11
  21. ^ Voss and Carleton, 1993, p. 13
  22. ^ a b c Voss and Carleton, 1993, p. 7
  23. ^ Voss and Carleton, 1993, p. 6; Weksler, 2006, p. 23
  24. ^ Voss and Carleton, 1993, p. 7; Weksler, 2006, pp. 24–25
  25. ^ Weksler, 2006, pp. 19, 23
  26. ^ Voss and Carleton, 1993; Weksler, 2006, table 5
  27. ^ Voss and Carleton, 1993, table 2.
  28. ^ a b Voss and Carleton, 1993, p. 15
  29. ^ Voss and Carleton, 1993, p. 16; Weksler, 2006, pp. 34–35
  30. ^ Voss and Carleton, 1993, p. 16
  31. ^ Weksler, 2006, p. 40; Voss and Carleton, 1993, p. 17
  32. ^ Voss and Carleton, 1993, p. 17
  33. ^ Weksler, 2006, p. 47
  34. ^ a b Voss and Carleton, 1993, p. 19
  35. ^ Voss and Carleton, 1993, p. 20; Weksler, 2006, fig. 25
  36. ^ Voss and Carleton, 1993, p. 20; Weksler, 2006, p. 49
  37. ^ Weksler, 2006, p. 45
  38. ^ Voss and Carleton, 1993, p. 20
  39. ^ Weksler, 2006, pp. 42–43
  40. ^ Weksler, 2006, p. 43
  41. ^ Freitas et al., 1983; Voss and Carleton, 1993, p. 10
  42. ^ González et al., 2016; Bonvicino et al., 2008
  43. ^ Teta and Pardiñas, 2006, p. 179
  44. ^ Oliveira and Kerber, 2009; Ubilla et al., 2004
  45. ^ Voss and Myers, 1991, table 5, p. 429
  46. ^ Teta and Pardiñas, 2006
  47. ^ Teta and Pardiñas, 2006, p. 180
  48. ^ Pardiñas and Lezcano, 1995, pp. 258–259
  49. ^ Pardiñas and Deschamps, 1995, p. 850
  50. ^ Pardiñas and Deschamps, 1995, table 2
  51. ^ Pardiñas, 2008, table 1
  52. ^ a b Voss and Carleton, 1993, p. 34
  53. ^ Carleton and Olson, 1999, p. 52
  54. ^ Hershkovitz, 1955, p. 658
  55. ^ Sierra de Soriano in Voss and Carleton, 1993, p. 34
  56. ^ Barley in Voss and Carleton, 1993, p. 34
  57. ^ Tuttle in Voss and Carleton, 1993, p. 32
  58. ^ Lareschi et al., 2006; Nava et al., 2010, table 1
  59. ^ Voss and Carleton, 1993, pp. 32–34

Literature cited

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