Oryzomys dimidiatus

Last updated

Oryzomys dimidiatus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Genus: Oryzomys
Species:
O. dimidiatus
Binomial name
Oryzomys dimidiatus
(Thomas, 1905)
Oryzomys distribution C America.png
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 the Nicaraguan rice rat, [5] 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.

Contents

With a head and body length of 110 to 128 mm (4.3 to 5.0 in), Oryzomys dimidiatus is a medium-sized rice rat. 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 "Data Deficient".

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 described this animal as the holotype of a new species he named 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 a 1944 review of the genus by Philip Hershkovitz. [7]

After examining the holotype in London, Hershkovitz instead placed the species in the genus Oryzomys in 1948. He remarked that it was an especially distinctive member of that genus, and hence classified it in its own subgenus Micronectomys. [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 conceded 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, but did not think it closely related to O. dimidiatus. [9] Six years later, Alfred Gardner and James Patton instead suggested 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]

A second specimen was obtained in 1966 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 on 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]

Oryzomys dimidiatus or "divided in the middle rice rat" derives respectively from the Greek oryza "rice", mys "mouse, rat", [22] and the Latin dimidiatus "divided in the middle", [23] from dimidio "halve, divide in two equal parts". [24]

Description

The marsh rice rat (Oryzomys palustris) is similar to O. dimidiatus. Oryzomys palustris in vegetation.jpg
The marsh rice rat (Oryzomys palustris) is similar to O. dimidiatus.

Oryzomys dimidiatus is a medium-sized rice rat, smaller than O. couesi, with thick, lustrous 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; the color becomes more yellowish towards the sides. 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. 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. [25]

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. [26]

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. [27] 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). [28]

Distribution, ecology, and behavior

Oryzomys dimidiatus is known from three specimens collected in the lowlands of the South Caribbean Coast Autonomous Region in southeastern Nicaragua. [29] 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 (9 mi) 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 . [30] The third was caught at a stream near Bluefields. Reid suggested that the species is semiaquatic, spending some time in the water, [28] like other Oryzomys. [31]

The 2019 IUCN Red List assessed the conservation status of Oryzomys dimidiatus as "Data Deficient", noting that very little is currently known about the species. [1]

Related Research Articles

<i>Oryzomys nelsoni</i> Extinct species of rodent

Oryzomys nelsoni is an extinct rodent of María Madre Island, Nayarit, Mexico. Within the genus Oryzomys of the family Cricetidae, it may have been most closely related to the mainland species O. albiventer. Since its first description in 1898, most authors have regarded it as a distinct species, but it has also been classified as a mere subspecies of the marsh rice rat (O. palustris).

<i>Oryzomys couesi</i> Semiaquatic rodent in the family Cricetidae

Oryzomys couesi, also known as Coues's rice rat, is a semiaquatic rodent in the family Cricetidae occurring from southernmost Texas through Mexico and Central America into northwestern Colombia. It is usually found in wet habitats, such as marshes, but also lives in drier forests and shrublands. Weighing about 43 to 82 g, O. couesi is a medium-sized to large rat. The coarse fur is buff to reddish above and white to buff below. The hindfeet show some specializations for life in the water, such as reduced ungual tufts of hair around the digits. It has 56 chromosomes. There is much geographic variation in size, proportions, color, and skull features. Oryzomys couesi is active during the night and builds nests of vegetation that are suspended among reeds about 1 m (3.3 ft) above the ground. It is an excellent swimmer and dives well, but can also climb in vegetation. An omnivore, it eats both plant and animal food, including seeds and insects. It breeds throughout the year; females give birth to about four young after a pregnancy of 21 to 28 days. The species may be infected by several different parasites and by two hantaviruses.

<i>Oryzomys</i> Genus of semiaquatic rodents

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.

<i>Euryoryzomys emmonsae</i> Amazonian rodent

Euryoryzomys emmonsae, also known as Emmons' rice rat or Emmons' oryzomys, is a rodent from the Amazon rainforest of Brazil in the genus Euryoryzomys of the family Cricetidae. Initially misidentified as E. macconnelli or E. nitidus, it was formally described in 1998. A rainforest species, it may be scansorial, climbing but also spending time on the ground. It lives only in a limited area south of the Amazon River in the state of Pará, a distribution that is apparently unique among the muroid rodents of the region.

<i>Pseudoryzomys</i> Genus of rodent from South America with one species

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.

<i>Transandinomys bolivaris</i> Small rodent found from northeastern Honduras to western Ecuador

Transandinomys bolivaris, also known as the long-whiskered rice rat, is a rodent in the family Cricetidae. It is found in humid forest from northeastern Honduras to western Ecuador, up to 1,800 m (5,900 ft) above sea level. Since it was first described in 1901 from Ecuador, six scientific names have been introduced for it, but their common identity was not documented until 1998 and the species has long been known under the name Oryzomys bombycinus, described from Panama in 1912. The name Oryzomys bolivaris was used before it was moved to the new genus Transandinomys with Transandinomys talamancae in 2006.

<i>Nephelomys devius</i> Species of rodent

Nephelomys devius, also known as the Talamancan oryzomys, Boquete rice rat, Chiriqui rice rat, or montane rice rat, is a species of rodent in the genus Nephelomys of family Cricetidae. It is found in cloud forest in the highlands of Costa Rica and western Panama.

<i>Oryzomys gorgasi</i> Rodent from the family Cricetidae from northwestern Colombia and Venezuela

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.

<span class="mw-page-title-main">Hammond's rice rat</span> Species of rodent in the family Cricetidae from Ecuador

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.

Nephelomys keaysi, also known as Keays's oryzomys or Keays's rice rat, is a species of rodent in the genus Nephelomys of family Cricetidae. It is found from southeastern Peru to northern Bolivia on the eastern slope of the Andes in Yungas humid forest at altitudes of 1000 to 2600 m. Although its continued existence is not in serious danger and it is listed as "least concern", destruction of its habitat may pose a threat to some populations.

Nephelomys levipes, also known as the nimble-footed oryzomys or light-footed rice rat, is a species of rodent in the genus Nephelomys of family Cricetidae. It is found on the eastern slope of the Andes from southeastern Peru into west-central Bolivia in cloud forest at elevations from 1,800 to 3,200 metres. It occurs in the same general area as its congener N. keaysi, but at higher altitudes.

<span class="mw-page-title-main">Marsh rice rat</span> North American species of rodent

The marsh rice rat is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, from New Jersey and Kansas south to Florida and northeasternmost Tamaulipas, Mexico; its range previously extended further west and north, where it may have been a commensal in corn-cultivating communities. Weighing about 40 to 80 g, the marsh rice rat is a medium-sized rodent that resembles the common black and brown rat. The upperparts are generally gray-brown, but are reddish in many Florida populations. The feet show several specializations for life in the water. The skull is large and flattened, and is short at the front.

Handleyomys rostratus, also known as the long-nosed oryzomys, long-nosed rice rat, or rusty rice rat is a species of rodent in the genus Handleyomys of family Cricetidae. It is found in Belize, El Salvador, Guatemala, Honduras, Mexico, and Nicaragua. It is nocturnal and is found in forests at elevations above sea level to 1200 meters. The Handleyomys rostratus attains its highest level of development in south and Central America. High rates of deforestation and habitat destruction are the biggest threat to the Handleyomys rostratus.

<i>Transandinomys talamancae</i> Small rodent found from Costa Rica to northern South America

Transandinomys talamancae is a rodent in the family Cricetidae that occurs from Costa Rica to southwestern Ecuador and northern Venezuela. Its habitat consists of lowland forests up to 1,500 m (5,000 ft) above sea level. With a body mass of 38 to 74 g, it is a medium-sized rice rat. The fur is soft and is reddish to brownish on the upperparts and white to buff on the underparts. The tail is dark brown above and lighter below and the ears and feet are long. The vibrissae (whiskers) are very long. In the skull, the rostrum is long and the braincase is low. The number of chromosomes varies from 34 to 54.

<span class="mw-page-title-main">Oryzomyini</span> Tribe of rodents

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.

<i>Oryzomys antillarum</i> Extinct rodent species from Jamaica

Oryzomys antillarum, also known as the Jamaican rice rat, is an extinct rodent of Jamaica. A member of the genus Oryzomys within the family Cricetidae, it is similar to O. couesi of mainland Central America, from where it may have dispersed to its island during the last glacial period. O. antillarum is common in subfossil cave faunas and is also known from three specimens collected live in the 19th century. Some historical records of Jamaican rats may pertain to it. The species probably became extinct late in the 19th century, perhaps due to the introduction of the small Indian mongoose, competition with introduced rodents such as the brown rat, and habitat destruction.

Nephelomys meridensis, also known as the Mérida oryzomys, is a species of rodent in the genus Nephelomys of family Cricetidae. It is found in cloud forest in the Sierra Nevada de Mérida of western Venezuela at elevations from 1100 to 4000 m. It is solitary, nocturnal and terrestrial, and has a varied diet.

<i>Oryzomys peninsulae</i> Species of rodent from western Mexico

Oryzomys peninsulae, also known as the Lower California rice rat, is a species of rodent from western Mexico. Restricted to the southern tip of the Baja California peninsula, it is a member of the genus Oryzomys of family Cricetidae. Only about twenty individuals, collected around 1900, are known, and subsequent destruction of its riverine habitat may have driven the species to extinction.

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.

<i>Oryzomys albiventer</i> Species of rodent

Oryzomys albiventer is a rodent in the genus Oryzomys of family Cricetidae from interior western Mexico, in the states of Jalisco, Guanajuato, and Michoacán. First described in 1901 as a separate species, it was later lumped under O. couesi and the marsh rice rat (O. palustris) until it was reinstated as a species in 2009. It differs from neighboring Oryzomys populations in size and measurements and is a large, brightly colored species with a long tail and robust skull and molars. Its range has been much impacted by agricultural development, but isolated populations are thought to persist.

References

  1. 1 2 3 Timm, R.; Reid, F. (2019). "Oryzomys dimidiatus". IUCN Red List of Threatened Species . 2019: e.T15594A22387864. doi: 10.2305/IUCN.UK.2019-1.RLTS.T15594A22387864.en . Retrieved 15 November 2021.
  2. 1 2 3 Thomas, 1905, p. 586
  3. ↑ Hershkovitz, 1948, p. 55
  4. ↑ Musser and Carleton, 2005, p. 1148
  5. ↑ Duff and Lawson, 2004, p. 54; Jones and Engstrom, 1986, p. 12
  6. 1 2 Thomas, 1905, p. 587
  7. ↑ Hershkovitz, 1944, p. 80
  8. ↑ Hershkovitz, 1948, pp. 54–55
  9. 1 2 Hershkovitz, 1970, p. 792
  10. 1 2 Hershkovitz, 1970, p. 791
  11. ↑ Musser and Carleton, 2005, p. 1144
  12. ↑ Voss, 1991, p. 46
  13. 1 2 Genoways and Jones, 1971, p. 433
  14. 1 2 Weksler et al., 2006, table 1, footnote e
  15. ↑ Reid, 1997, p. 204
  16. ↑ Carleton and Arroyo-Cabrales, 2009, p. 116
  17. ↑ Carleton and Arroyo-Cabrales, 2009, p. 117
  18. ↑ Jones and Engstrom, 1986, p. 12
  19. ↑ Carleton and Arroyo-Cabrales, 2009, p. 107
  20. ↑ Weksler, 2006, p. 3
  21. ↑ Musser and Carleton, 2005
  22. ↑ ὄρυζα, μῦς . Liddell, Henry George ; Scott, Robert ; A Greek–English Lexicon at the Perseus Project.
  23. ↑ dimidiatus . Charlton T. Lewis. An Elementary Latin Dictionary on Perseus Project .
  24. ↑ dimidio . Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project .
  25. ↑ Thomas, 1905, p. 586; Genoways and Jones, 1971, p. 833; Sánchez et al., 2001, pp. 209–210; Reid, 2009, p. 207
  26. ↑ Hershkovitz, 1948, p. 55; Sánchez et al., 2001, pp. 209–210
  27. ↑ Jones and Engstrom, 1986, p. 13
  28. 1 2 Reid, 2009, p. 207
  29. ↑ Timm and Reid, 2008; Reid, 2009, p. 207
  30. ↑ Genoways and Jones, 1971, p. 833; Musser and Carleton, 2005, pp. 1125, 1141, 1147, 1175
  31. ↑ Carleton and Arroyo-Cabrales, 2009, p. 114

Literature cited

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.