Oryzomys dimidiatus: Difference between revisions
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|genus=''[[Oryzomys]]'' |
|genus=''[[Oryzomys]]'' |
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|species='''''O. dimidiatus''''' |
|species='''''O. dimidiatus''''' |
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|binomial=''Oryzomys |
|binomial=''Oryzomys dimidiatus'' |
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dimidiatus'' |
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1905) |
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|synonyms= |
|synonyms= |
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*''Nectomys dimidiatus'' <small>Thomas, |
*''Nectomys dimidiatus'' <small>Thomas, 1905</small><ref name=T586>Thomas, 1905, p. 586</ref> |
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*''[Oryzomys] dimidiatus'': <small>Hershkovitz, 1948</small><ref name=H55>Hershkovitz, 1948, p. 55</ref> |
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p. 586</ref> |
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*''[Oryzomys] dimidiatus'': |
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|range_map_caption=Range of ''Oryzomys dimidiatus'' (yellow) and the related ''[[Oryzomys couesi|O. couesi]]'' (red and yellow) in Central America.}} |
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<small>Hershkovitz, 1948</small><ref name=H55>Hershkovitz, 1948, |
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'''''Oryzomys dimidiatus''''', also known as the '''Nicaraguan Oryzomys''',<ref>Musser and Carleton, 2005, p. 1148</ref> '''Thomas's Rice Rat''',<ref name=iucn/> or '''Nicaraguan Rice Rat''',<ref>Duff and Lawson, 2004, p. 54; Jones and Engstrom, 1986, p. 12</ref> is a [[rodent]] in the genus ''[[Oryzomys]]'' of 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 ''[[Oryzomys couesi]]'', which occurs in the same region. |
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p. 55</ref> |
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|range_map_alt=Map of Central America, |
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|range_map_caption=Range |
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of ''Oryzomys |
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dimidiatus'' (yellow) and the |
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related ''[[Oryzomys couesi|O. couesi]]'' |
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(red and yellow) in Central America. |
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|}} |
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'''''Oryzomys dimidiatus''''', |
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also known as the '''Nicaraguan |
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Oryzomys''',<ref>Musser and Carleton, 2005, |
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p. 1148</ref> '''Thomas's Rice Rat''',<ref name=iucn/> or '''Nicaraguan Rice Rat''',<ref>Duff |
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and Lawson, 2004, p. 54; Jones and Engstrom, 1986, |
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p. 12</ref> is a [[rodent]] in the genus ''[[Oryzomys]]'' |
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of family [[Cricetidae]]. |
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It is known from only three specimens, all collected in southeastern |
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Nicaragua since 1904. Placed in ''[[Nectomys]]'' |
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upon its discovery, it was later classified in its own [[subgenus]] of ''[[Oryzomys]]'' |
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and finally recognized as closely related to other species now placed |
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in ''Oryzomys'', including the [[marsh rice rat]] |
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and ''[[Oryzomys couesi]]'', which occurs in the same region. |
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With a head and body length of 110 to 128 mm (4.3 to 5.0 in), ''Oryzomys dimidiatus'' is a medium-sized species. The upperparts are gray-brown and the underparts are grayish, not buffy as in ''O. couesi''. The tail is only slightly darker above than below. All three specimens were caught near water and the species may be [[semiaquatic]], spending some time in the water. Its [[conservation status]] is currently assessed as "least concern". |
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With |
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a head and body length of 110 to 128 mm (4.3 to |
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5.0 in), ''Oryzomys |
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dimidiatus'' is a medium-sized species. |
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The upperparts are gray-brown and the underparts are grayish, not buffy as in ''O. couesi''. The tail is only slightly darker |
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above than below. All three specimens were caught near water and the |
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species may be [[semiaquatic]], |
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spending some time in the water. Its [[conservation |
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status]] is currently |
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assessed as "least concern". |
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==Taxonomy== |
==Taxonomy== |
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The first known specimen was obtained by W.G. Palmer in 1904<ref name=T587>Thomas, 1905, p. 587</ref> and the next year, [[Oldfield Thomas]] of the [[British Museum of Natural History]] used this animal to describe a new [[species]] under the name ''Nectomys dimidiatus''.<ref name=T586/> He placed it in the genus ''[[Nectomys]]'', commenting that it was much smaller than but otherwise similar to previously known members of that genus.<ref name=T586/> The species was listed as a ''Nectomys'' in [[taxonomy|taxonomic]] overviews in the next decades, including in a 1944 review of ''Nectomys'' by Philip Hershkovitz.<ref name=H80>Hershkovitz, 1944, p. 80</ref> |
The first known specimen was obtained by W.G. Palmer in 1904<ref name=T587>Thomas, 1905, p. 587</ref> and the next year, [[Oldfield Thomas]] of the [[British Museum of Natural History]] used this animal to describe a new [[species]] under the name ''Nectomys dimidiatus''.<ref name=T586/> He placed it in the genus ''[[Nectomys]]'', commenting that it was much smaller than but otherwise similar to previously known members of that genus.<ref name=T586/> The species was listed as a ''Nectomys'' in [[taxonomy|taxonomic]] overviews in the next decades, including in a 1944 review of ''Nectomys'' by Philip Hershkovitz.<ref name=H80>Hershkovitz, 1944, p. 80</ref> |
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Revision as of 02:09, 21 March 2010
| Oryzomys dimidiatus | |
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| Scientific classification | |
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| Species: | O. dimidiatus
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| Binomial name | |
| Oryzomys dimidiatus (Thomas, 1905)
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| Range of Oryzomys dimidiatus (yellow) and the related O. couesi (red and yellow) in Central America. | |
| Synonyms | |
Oryzomys dimidiatus, also known as the Nicaraguan Oryzomys,[4] Thomas's Rice Rat,[1] or Nicaraguan Rice Rat,[5] is a rodent in the genus Oryzomys of 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 Oryzomys couesi, which occurs in the same region.
With a head and body length of 110 to 128 mm (4.3 to 5.0 in), Oryzomys dimidiatus is a medium-sized species. The upperparts are gray-brown and the underparts are grayish, not buffy as in O. couesi. The tail is only slightly darker above than below. All three specimens were caught near water and the species may be semiaquatic, spending some time in the water. Its conservation status is currently assessed as "least concern".
Taxonomy
The first known specimen was obtained by W.G. Palmer in 1904[6] and the next year, Oldfield Thomas of the British Museum of Natural History used this animal to describe a new species under the name Nectomys dimidiatus.[2] He placed it in the genus Nectomys, commenting that it was much smaller than but otherwise similar to previously known members of that genus.[2] The species was listed as a Nectomys in taxonomic overviews in the next decades, including in a 1944 review of Nectomys by Philip Hershkovitz.[7]
After examining the only known specimen in London, in 1948 Hershkovitz instead placed the species in Oryzomys as the only species of the subgenus Micronectomys, remarking that it was an especially distinctive member of that genus.[8] J. Hernández-Camacho described a second species of Micronectomys, Oryzomys (Micronectomys) borreroi, from Colombia in 1957.[9] In 1970, Hershkovitz treated O. dimidiatus in another publication and noted that his name Micronectomys was a nomen nudum ("naked name") because he had not explicitly mentioned characters differentiating it from other taxa in his 1948 publication.[10] Nevertheless, he did not do anything to rectify the situation, and Micronectomys remains a nomen nudum.[11] Hershkovitz also noted that while O. dimidiatus resembles a juvenile Nectomys in external anatomy, it is otherwise similar to the marsh rice rat (Oryzomys palustris).[10]. He accepted O. borreroi as an Oryzomys, did not think it closely related to O. dimidiatus.[9] Six years later, Gardner and Patton instead suggested that O. borreroi was a Zygodontomys, and in his 1991 review of that genus Robert Voss confirmed that it is the same as Zygodontomys brunneus.[12]
In 1966, a second specimen was obtained, and the find was published in 1971 by Hugh Genoways and Knox Jones, who noted that the species is closely similar to O. palustris.[13] Later workers affirmed the relationship between O. dimidiatus, O. palustris and associated species like O. couesi.[14] Fiona Reid reported in 1997 that a third specimen had been found.[15] In 2006, Marcelo Weksler and coworkers removed most of the species formerly placed in Oryzomys from the genus, because they are not closely related to the type species O. palustris, but kept O. dimidiatus as an Oryzomys.[14]
Oryzomys dimidiatus is now recognized as one of eight species in the genus Oryzomys.[16] O. dimidiatus is further part of the O. couesi section, which is centered around the widespread Central American O. couesi and also includes six other species with more limited and peripheral distributions.[17] O. couesi occurs with O. dimidiatus in southeastern Nicaragua.[18] Many aspects of the systematics of the O. couesi section remain unclear and it is likely that the current classification underestimates the true diversity of the group.[19] Oryzomys is classified in the tribe Oryzomyini ("rice rats"), a diverse assemblage of American rodents of over a hundred species,[20] and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.[21]
Description
Oryzomys dimidiatus is a medium-sized rice rat, smaller than O. couesi, with thick, glossy fur and velvety underfur. The hairs on the back are about 6 mm in length. The upperparts are gray-brown with some dark hairs, appearing darker overall than in O. couesi; towards the sides the color becomes more yellowish. According to Thomas, a faint buff line extends from the sides to the inner sides of the hindlegs. The underparts are grayish, contrasting with the buffy underparts of O. couesi. The snout is short and the well-haired ears are partly hidden by the fur. The hands and feet are off-white or brownish above, not white as in O. couesi. The hindfeet show small interdigital webs, but they lack long tufts of hair on the digits and some of the pads are reduced or absent. Fringes of hair are present along the plantar margins and between some of the digits. The tail is about as long as the head and body and contains about 15 rings per centimeter. It is slightly darker (grayish) above than below (whitish), but the difference in color is much less pronounced than in O. couesi.[22]
Compared to that of Nectomys, the skull is lightly built and has narrow nasals and a broad, round braincase without conspicuous ridges on it. The zygomatic plate is broad. The incisive foramina (perforations of the front part of the palate) extend between the first molars and are broadest in their back halves. The broad mesopterygoid fossa, the gap behind the end of the palate, is perforated by sphenopalatine vacuities. The molar crowns are not as simplified as in Nectomys species, but the front cusps of the upper (anterocone) and lower first molar (anteroconid) are not divided in two. In addition to the main roots, the upper and lower first molars have smaller additional roots.[23]
Measurements for the first two known examples are as follows (in each case, the first measurement given is from the holotype, taken in 1904, the second, from the specimen taken in 1966): head and body length 125 and 118 mm (4.9 and 4.6 in), tail length 115 and 110 mm (4.5 and 4.3 in), hindfoot length 27 and 28 mm (1.1 and 1.1 in), ear length 13 and 15 mm (0.51 and 0.59 in), skull length 29.8 and 29.0 mm (1.17 and 1.14 in). The 1966 specimen weighed 46.0 g (1.62 oz) and had testes 11 mm (0.43 in) long; these measurements were not recorded in the 1904 specimen.[24] Reid, who mentioned the third specimen, reported a maximum head and body length of 128 mm (5.0 in), tail length of 150 mm (5.9 in), hindfoot length of 31 mm (1.2 in), and ear length of 19 mm (0.75 in).[25]
Distribution, ecology, and behavior
Oryzomys dimidiatus is known from three specimens collected in the lowlands of the Región Autónoma del Atlántico Sur, southeastern Nicaragua.[26] The first, an old male, was collected on November 5, 1904, in a banana plantation with very moist red clay on the Río Escondido near El Rama.[6] The second, a young adult male, was caught on July 26, 1966, in dense cane on the south bank of the Río Mico at El Recreo, 15 km west from the location of the first specimen, along with three other rice rats (O. couesi, Melanomys caliginosus, and Oligoryzomys fulvescens), the cotton rat Sigmodon hirsutus, and the cottontail rabbit Sylvilagus brasiliensis.[27] The third was caught at a stream near Bluefields. Reid suggested that the species is semiaquatic, spending some time in the water,[25] like other Oryzomys.[28]
Conservation status
The 2009 IUCN Red List assessed the conservation status of Oryzomys dimidiatus as "least concern", noting that its distribution may be larger than currently known. Its population is presumably large and no threats to its habitat are known.[1]
References
- ^ a b c Timm and Reid, 2008
- ^ a b c Thomas, 1905, p. 586
- ^ Hershkovitz, 1948, p. 55
- ^ Musser and Carleton, 2005, p. 1148
- ^ Duff and Lawson, 2004, p. 54; Jones and Engstrom, 1986, p. 12
- ^ a b Thomas, 1905, p. 587
- ^ Hershkovitz, 1944, p. 80
- ^ Hershkovitz, 1948, pp. 54–55
- ^ a b Hershkovitz, 1970, p. 792
- ^ a b Hershkovitz, 1970, p. 791
- ^ Musser and Carleton, 2005, p. 1144
- ^ Voss, 1991, p. 46
- ^ a b Genoways and Jones, 1971, p. 433
- ^ a b Weksler et al., 2006, table 1, footnote e
- ^ Reid, 1997, p. 204
- ^ Carleton and Arroyo-Cabrales, 2009, p. 116
- ^ Carleton and Arroyo-Cabrales, 2009, p. 117
- ^ Jones and Engstrom, 1986, p. 12
- ^ Carleton and Arroyo-Cabrales, 2009, p. 107
- ^ Weksler, 2006, p. 3
- ^ Musser and Carleton, 2005
- ^ Thomas, 1905, p. 586; Genoways and Jones, 1971, p. 833; Sánchez et al., 2001, pp. 209–210; Reid, 2009, p. 207
- ^ Hershkovitz, 1948, p. 55; Sánchez et al., 2001, pp. 209–210
- ^ Jones and Engstrom, 1986, p. 13
- ^ a b Reid, 2009, p. 207
- ^ Timm and Reid, 2008; Reid, 2009, p. 207
- ^ Genoways and Jones, 1971, p. 833; Musser and Carleton, 2005, pp. 1125, 1141, 1147, 1175
- ^ Carleton and Arroyo-Cabrales, 2009, p. 114
Literature cited
- Carleton, M.D. and Arroyo-Cabrales, J. 2009. Review of the Oryzomys couesi complex (Rodentia: Cricetidae: Sigmodontinae) in western Mexico. Bulletin of the American Museum of Natural History 331:94–127.
- Duff, A. and Lawson, A. 2004. Mammals of the World: A checklist. New Haven, Connecticut: Yale University Press, 312 pp. ISBN 071366021X
- Genoways, H.H. and Jones, J.K., Jr. 1971. Second specimen of Oryzomys dimidiatus. Journal of Mammalogy 52:833–834.
- Hershkovitz, P. 1944. A systematic review of the Neotropical water rats of the genus Nectomys (Cricetinae). Miscellaneous Publications, Museum of Zoology, University of Michigan 58:1–88.
- Hershkovitz, P. 1948. Mammals of northern Colombia. Preliminary report No. 3: Water rats (genus Nectomys), with supplemental notes on related forms. Proceedings of the United States National Museum 98:49–56.
- Hershkovitz, P. 1970. Supplementary notes on Neotropical Oryzomys dimidiatus and Oryzomys hammondi (Cricetinae) (subscription required). Journal of Mammalogy 51(4):789–794.
- Jones, J.K., Jr. and Engstrom, M.D. 1986. Synopsis of the rice rats (genus Oryzomys) of Nicaragua. Occasional Papers, The Museum, Texas Tech University 103:1–23.
- Musser, 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 reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
- Reid, F. 1997. A Field Guide to the Mammals of Central America and Southeast Mexico. 1st edition. Oxford University Press US, 334 pp. ISBN 9780195064018
- Reid, F. 2009. A Field Guide to the Mammals of Central America and Southeast Mexico. 2nd edition. Oxford University Press US, 346 pp. ISBN 9780195343229
- Sánchez H., J., Ochoa G., J. and Voss, R.S. 2001. Rediscovery of Oryzomys gorgasi (Rodentia: Muridae) with notes on taxonomy and natural history (subscription required). Mammalia 65:205–214.
- Thomas, O. 1905. New Neotropical Molossus, Conepatus, Nectomys, Proechimys, and Agouti, with a note on the genus Mesomys. Annals and Magazine of Natural History (7)15:584-591.
- Timm, R. and Reid, F. 2008. Oryzomys dimidiatus. In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on December 8, 2009.
- Voss, R.S. 1991. An introduction to the neotropical muroid rodent genus Zygodontomys. Bulletin of the American Museum of Natural History 210:1–113.
- Weksler, M., Percequillo, A.R. and Voss, R.S. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.