Reigomys

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Reigomys
Temporal range:
Ma
↓
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Tribe: Oryzomyini
Genus: †Reigomys
Machado et al., 2014
Species:
†R. primigenus
Binomial name
†Reigomys primigenus
(Steppan 1996)

Reigomys primigenus is an

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.

Taxonomy

Material of Reigomys primigenus was collected in 1924 and 1927 by Elmer Riggs of the

Sigmodon.[3] His results supported a close relation between R. primigenus and extant Holochilus, with Lundomys and Pseudoryzomys more distantly related.[4]

In 1999, another rodent from the same group was described:

Storrs Olson, who described the animal, argued that Holochilus primigenus was probably outside the clade of Noronhomys and extant Holochilus and that H. primigenus should probably be excluded from the genus.[5] When Ulyses Pardiñas described another extinct rodent from this group, Carletonomys from the Pleistocene of Argentina, he suggested that H. primigenus should be placed in its own genus because of its mosaic of Holochilus- and Lundomys-like features.[6]

The phylogenetic analysis conducted by Machado et al. (2014) confirmed that living members of the genus Holochilus are more closely related to Noronhomys and Carletonomys than to H. primigenus. The authors moved H. primigenus to its own genus, which they named Reigomys.[7]

Description

Reigomys primigenus was a large rat, though smaller than both Lundomys and living Holochilus, characterized by an S-shaped ("sigmodont") crown on the third lower molar. Features of the molars are nearly indistinguishable from those of Lundomys and include cusps located opposite each other, enamel valleys that barely reach the midline of the molars, and short

mesolophids (accessory crests). Other notable features include a robust mandible (lower jaw) with a steeply rising coronoid process, short incisive foramina (perforations of the front part of the palate) that barely extend between the first molars, and a short bony palate that hardly extends beyonds the third molars, all of which are shared with extant species of Holochilus to the exclusion of Lundomys. Also unlike in Lundomys, there is an additional small root present at the labial (outer) side of the first upper molar.[2] In eight specimens that could be measured, the length of the lower toothrow is 6.79 to 7.58 mm, averaging 7.28 mm; the first lower molar is 2.62 to 3.08 mm long, averaging 2.89 mm, and 1.75 to 1.93 mm broad, averaging 1.85 mm in seven measured teeth; the only preserved complete upper toothrow is 6.64 mm long; and the first upper molar is 2.63 to 2.70 mm long and 2.03 mm broad in two specimens.[8]

Distribution and ecology

Remains of Reigomys primigenus come from several localities in river sediments of the

Kunsia, Nectomys, Oxymycterus, Phyllotis, and another akodontine, probably Akodon, Necromys, or a related genus. The deposits were deposited by a river and the paleoenvironment was probably a floodplain or channel.[1] Reigomys primigenus is not known from any other localities and is considered to be extinct.[9]

References

  1. ^ a b Steppan, 1996, p. 523
  2. ^ a b Steppan, 1996, p. 524
  3. ^ Steppan, 1996, table 2; Weksler et al., 2006, for nomenclature
  4. ^ Steppan, 1996, fig. 4A
  5. ^ Carleton and Olson, 1999, p. 50
  6. ^ Pardiñas, 2008, p. 1275
  7. S2CID 84742911
    .
  8. ^ Steppan, 1996, table 1
  9. ^ Steppan, 1996, p. 527

Bibliography

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