Transandinomys

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Transandinomys
Skull of 'Transandinomys bolivaris from Cerro Azul, Panama, as seen from above
Skull of Transandinomys bolivaris from Cerro Azul, Panama, seen from above[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Tribe: Oryzomyini
Genus: Transandinomys
Weksler, Percequillo, & Voss, 2006
Type species
Oryzomys talamancae
Species
Map of Transandinomys bolivaris distribution
Map of Transandinomys talamancae distribution
Distribution of Transandinomys bolivaris (top) and T. talamancae (bottom) in Central America and northwestern South America.

Transandinomys is a

phylogenetic analysis showed that they are not closely related to the type species of that genus, and they have therefore been placed in a new genus. They may be most closely related to genera like Hylaeamys and Euryoryzomys, which contain very similar species. Both species of Transandinomys have had eventful taxonomic
histories.

Transandinomys bolivaris and T. talamancae are medium-sized, soft-furred rice rats. The upperparts—brownish in T. bolivaris and reddish in T. talamancae—are much darker than the whitish underparts. Both species are characterized by very long

Least Concern" in the IUCN Red List
.

Taxonomy

The first species of Transandinomys (from Neo-Latin transandinus: "transandean", i.e., "crossing or beyond the

adj.) and Greek mys: "mouse, rat")[2] to be scientifically described was T. talamancae, named as Oryzomys talamancae by Joel A Allen in 1891.[3] Several other species were soon added to the genus Oryzomys, then more broadly defined than currently, that are now classified in Transandinomys,[4] including Oryzomys bolivaris (now Transandinomys bolivaris) by Allen in 1901.[5] In his 1918 review of North American Oryzomys, Edward Alphonso Goldman placed Oryzomys talamancae and Oryzomys bombycinus (=T. bolivaris) each in their own group, but thought them closely related.[6] In 1960, O. talamancae was synonymized with "Oryzomys capito" (=Hylaeamys megacephalus), but it has again been recognized as a separate species since 1983. The species was reviewed by Guy Musser and Marina Williams in 1985 and again by Musser and colleagues in 1998, who documented the diagnostic characters of the species, its synonyms, and its distribution.[7] The 1998 study by Musser and colleagues also documented Oryzomys bolivaris as the correct name for the species previously known as Oryzomys bombycinus and reviewed that species.[8]

In 2006, Marcelo Weksler published a broad

polyphyletic and should be split up.[10] Later in the same year, Weksler, Alexandre Percequillo, and Robert Voss introduced ten new genera of Oryzomyini formerly placed in Oryzomys, including Transandinomys for Oryzomys talamancae and O. bolivaris, with the former as the type species.[4] Transandinomys is now one of about thirty genera within Oryzomyini, a diverse group of well over a hundred species.[11] Oryzomyini is one of several tribes within the subfamily Sigmodontinae of the family Cricetidae, which includes hundreds of other species of mainly small rodents, distributed chiefly in Eurasia and the Americas.[12]

Description

Transandinomys species are medium-sized, soft-furred rice rats.

morphology that distinguishes the two genera is the length of the vibrissae.[17] Handleyomys alfaroi is smaller than both species of Transandinomys, but juvenile Transandinomys may be confused with similarly colored adult H. alfaroi.[18]

The fur is brownish (T. bolivaris) or reddish (T. talamancae) above and lighter below, appearing whitish, but the hairs on the underparts have gray bases.

pinna (external ear) is large.[4] On the hindfeet, which are long and narrow,[13] ungual tufts of hairs surround the bases of the toes. In T. bolivaris, the sole usually entirely lacks squamae (small, scale-like structures), but T. talamancae does have squamae on part of its sole. The claw of the first toe extends about to the middle of the first phalange of the second and that of the fifth toe extends nearly to the base of the second phalange of the fourth. The tail is at least about as long as the head and body, sometimes slightly longer. The tail is darker above than below in T. talamancae,[4] but there may not be a difference in color in T. bolivaris.[Note 1] The tail appears naked, but is covered with fine hairs.[13]

Females have four pairs of

lumbar vertebrae.[21] According to a study in Costa Rica, T. bolivaris has 58 chromosomes and the number of chromosomal arms (fundamental number) is 80 (2n = 58, FN = 80).[22] Studies in Ecuador and Venezuela have recorded several different karyotypes in T. talamancae, with the number of chromosomes ranging from 34 to 54 and the fundamental number from 60 to 67.[23]

Skull and teeth

Measurements[24]
Species Head and body Tail Hindfoot Ear Mass
T. bolivaris 100–140 99–130 27–33 16–21 39–75
T. talamancae 105–146 105–152 28–32 17–24 47–74
Measurements are in millimeters, except mass in grams.

In the skull, the rostrum (front part) is long. The

zygomatic notch is moderately developed and the jugal bone is small, so that when seen from the side the maxillary and squamosal parts of the zygomatic arch (cheekbone) overlap. Usually, the suture (line of fusion) between the frontal and the squamosal is continuous with that between the frontal and the parietal bone. In T. talamancae, the parietals usually extend from the roof of the braincase broadly on to the sides, but in T. bolivaris they are more commonly restricted to the roof.[4]

The

mastoid bone contains small openings (fenestrations) in T. talamancae, but not in T. bolivaris. In the mandible (lower jaw), the capsular process (a process at the root of the incisor) is weak to absent and the upper and lower masseteric ridges, which anchor some of the chewing muscles, do not join into a single crest and reach their front margin below the first molar.[4]

The upper incisor is

hypoflexid on the second lower molar, the main valley between the cusps, extends more than halfway across the crown; it is much shorter in H. alfaroi, Euryoryzomys, and Hylaeamys yunganus.[29] Each of the upper molars has three roots (two at the labial, or outer, side and one at the lingual, or inner, side) and each of the lowers has two (one at the front and one at the back); both species of Transandinomys lack the additional small roots that are present in various other oryzomyines, including species of Euryoryzomys, Nephelomys, and Handleyomys.[30]

Distribution, ecology, and behavior

Three teeth both at the left and right, decreasing in size from top to bottom.
Three teeth both at the left and right, decreasing in size from top to bottom.
Molars of Transandinomys talamancae (left; subadult) and T. bolivaris (right; adult), both with the upper molars on the left and the lower molars on the right, and with the first molars at the top.[31]

The distribution of Transandinomys extends from eastern Honduras through Nicaragua, Costa Rica, Panama, and Colombia south and east to southwestern Ecuador and northern Venezuela, generally west and north of the Andes.[32] The ranges of the two species overlap but are distinct. T. bolivaris occurs from Honduras mainly on the Caribbean side of Central America south to western Colombia and northwestern Ecuador, up to 1800 m (5900 ft) above sea level.[33] T. talamancae, which is found up to 1525 m (5000 ft) above sea level, is less widely distributed in Central America, as it is not known further north than northwestern Costa Rica, but is more widely distributed in South America, occurring into far southwestern Ecuador and northern Venezuela. It has also been recorded south of the Venezuelan Andes, in the narrow strip of forest between the Llanos and the mountains.[34] Both species are forest rats, but whereas T. bolivaris is restricted to humid forest formations, T. talamancae apparently is more tolerant of drier forest, which explains its wider South American distribution.[35]

Both species live on the ground, are active during the night, are solitary, and feed mainly on fruits and seeds, but may also eat herbs and insects. They build nests of leaves and branches among vegetation, for example in a tree hollow, or under rocks.

sucking lice have been recorded as parasites on both species.[39]

Conservation status

Transandinomys talamancae is common or even abundant, but T. bolivaris generally occurs less frequently.

Least Concern" by the IUCN Red List; deforestation is noted as a possible threat to T. bolivaris, but T. talamancae is said to lack major threats.[41]

Notes

  1. ^ Descriptions of tail coloration in the latter species vary;[19] see Transandinomys bolivaris: Description.

References

  1. ^ Goldman, 1918, plate II
  2. Perseus Project
    .
  3. ^ Allen, 1890, p. 193
  4. ^ a b c d e f g Weksler et al., 2006, p. 25
  5. ^ Allen, 1901, p. 405
  6. ^ Goldman, 1918, p. 73
  7. ^ Musser and Carleton, 2005, p. 1155
  8. ^ Musser and Carleton, 2005, p. 1146
  9. ^ Weksler, 2006, figs. 34–39
  10. ^ Weksler, 2006, pp. 75–77
  11. ^ Weksler, 2006, pp. 1, 10; Weksler et al., 2006, p. 1, table 1
  12. ^ Musser and Carleton, 2005
  13. ^ a b c d Tirira, 2007, p. 198
  14. ^ Musser et al., 1998, pp. 125, 167, 169; Weksler et al., 2006, p. 13
  15. ^ Weksler et al., 2006, pp. 13, 15, 25–26
  16. ^ Musser et al., 1998, p. 13
  17. ^ Weksler et al., 2006, p. 15
  18. ^ Musser et al., 1998, pp. 125, 143, 167, 169
  19. ^ Musser et al., 1998, p. 123; Weksler et al., 2006, p. 25; Tirira, 2007, p. 199; Reid, 2009, p. 208
  20. ^ Musser et al., 1998, p. 124; Weksler, 2006, pp. 17, 19
  21. ^ Steppan, 1995, table 5
  22. ^ Musser et al., 1998, p. 125
  23. ^ Musser et al., 1998, table 13
  24. ^ Reid, 2009, p. 208
  25. ^ Musser et al., 1998, p. 125; Weksler, 2006, pp. 43–44
  26. ^ Musser et al., 1998, pp. 140, 143; Weksler et al., 2006, p. 14
  27. ^ Weksler, 2006, pp. 48–49
  28. ^ Weksler et al., 2006, p. 14
  29. ^ Musser et al., 1998, pp. 140–141; Weksler et al., 2006, p. 14
  30. ^ Musser et al., 1998, p. 142; Weksler, 2006, pp. 42–43; Weksler et al., 2006, p. 26
  31. ^ Goldman, 1918, plate VI
  32. ^ Weksler et al., 2006, p. 24; Musser et al., 1998, p. 113
  33. ^ Musser et al., 1998, p. 113
  34. ^ Musser et al., 1998, p. 157; Musser and Carleton, 2005, p. 1255
  35. ^ Musser et al., 1998, p. 157; Weksler et al., 2006, p. 24
  36. ^ Tirira, 2007, p. 199
  37. ^ Fleming, 1971, p. 40
  38. ^ Fleming, 1971, table 11
  39. ^ Brennan and Yunker, 1966, pp. 262, 266; Tipton and Méndez, 1966, pp. 323, 330; Tipton et al., 1966, p. 42; Durden and Musser, 1994, p. 30
  40. ^ Tirira, 2007, p. 200; Reid, 2009, p. 208
  41. ^ Anderson et al., 2008; Gómez-Laverde et al., 2008

Literature cited

External links

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