Thomasomys ucucha

Last updated

Thomasomys ucucha
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Genus: Thomasomys
T. ucucha
Binomial name
Thomasomys ucucha
Voss, 2003
Thomasomys ucucha distribution.png

Thomasomys ucucha, also known as the ucucha thomasomys, [2] is a rodent in the genus Thomasomys of the family Cricetidae. It is known only from high altitude forest and grassland habitats in the Cordillera Oriental of Ecuador. Seven other species of Thomasomys live in the same areas. First collected in 1903, T. ucucha was formally described as a new species in 2003 and most closely resembles T. hylophilus , which occurs further to the north. The species is listed as "vulnerable" in the IUCN Red List as a result of habitat destruction.


Medium-sized, dark-furred, and long-tailed, T. ucucha can be distinguished from all other species of Thomasomys by its large, broad, procumbent upper incisors. Head and body length is 94 to 119 mm (3.7 to 4.7 in) and body mass is 24 to 46 g (0.85 to 1.62 oz). The tail is scarcely furred. The front part of the skull is flat, short, and broad. The incisive foramina, openings at the front of the palate, are short, and the palate itself is broad and smooth. The root of the lower incisor is contained in a prominent capsular process.


The first three specimens of Thomasomys ucucha were collected in 1903 at Tablón in Pichincha Province, Ecuador, by L. Söderström. It was not found again until Robert S. Voss of the American Museum of Natural History collected a total of forty-three specimens at nearby Papallacta, Napo Province, in 1978 and 1980 (the type locality is described as the valley of the Rio Papallacta). [3] Papallacta is in a remote area that is difficult to access, and the mammal fauna of the region remains poorly known. [4] In 2003, he formally described the animal as a new species, Thomasomys ucucha, [3] in a publication in American Museum Novitates in which he also reviewed the mammal fauna of Papallacta. [4] The generic name, Thomasomys , honors English zoologist Oldfield Thomas, who named about 2,900 taxa of mammals, [5] and the specific name, ucucha, is the local Quechua word for "mouse". [3] T. ucucha most closely resembles T. hylophilus , which is found further north in Colombia and Venezuela. [6] A comparison of mitochondrial DNA found that T. ucucha was closest to specimens identified as T. caudivarius and T. silvestris , but T. hylophilus was not included in this study. [7] All are members of Thomasomys, a diverse genus that occurs in the northern Andes, from Bolivia to Venezuela. [8] Together with Rhipidomys and a few other, smaller genera, Thomasomys forms the tribe Thomasomyini, which includes over fifty species found in South America and Panama. Thomasomyini in turn is part of the subfamily Sigmodontinae of the family Cricetidae, along with hundreds of other species of mainly small rodents. [9]


Thomasomys ucucha is a medium-sized Thomasomys with a relatively long tail. The dense, fine, and soft fur is dark brown on the upperparts, changing gradually into the grey underparts. The mystacial vibrissae (whiskers above the mouth) are long and extend beyond the ears when laid back against the head. Sparse short, dark hairs are present on the ears. [3] The digits and metapodials (bones of the centers of the hand and feet) of the hands and feet are covered with dark hairs, but the ungual tufts at the bases of the claws consist of longer, gray hairs. The fifth digit of the foot is long, with the tip of its claw almost reaching the base of the claw of the fourth digit. The tail is dark and hardly furred, except for a pencil of long hairs at the end; some animals have a white tail tip. Females have six mammae. [10] In thirty-six specimens, head and body length is 94 to 119 mm (3.7 to 4.7 in), averaging 110 mm (4.3 in); tail length is 122 to 151 mm (4.8 to 5.9 in), averaging 140 mm (5.5 in); hindfoot length is 26 to 30 mm (1.0 to 1.2 in), averaging 28 mm (1.1 in); ear length is 17 to 20 mm (0.67 to 0.79 in), averaging 18 mm (0.71 in); and weight is 24 to 46 g (0.85 to 1.62 oz), averaging 36 g (1.3 oz). [11]

The front (rostral) part of the skull is shortshorter and broader than in T. hylophilus [12] and flat and the notches in the zygomatic plates at the sides are poorly developed. [10] The plates themselves are broad. [13] The zygomatic arches (cheekbones) spread broadly and are rounded in shape. [12] The narrow interorbital region (between the eyes) is hourglass-shaped. The braincase is robust. [10]

The incisive foramina, which perforate the palate between the incisors and the molars, are short and do not reach near the first molars; [10] they are longer in T. hylophilus. [12] They are widest where the premaxillary and maxillary bones meet. The palate itself is also short, not extending beyond the third molars, and is broad and lacks ridges or grooves. There are simple posterolateral palatal pits at the back of the palate, near the third molars. The mesopterygoid fossa, an opening located behind the end of the palate, is broad and its roof is either fully ossified or perforated by small sphenopalatine vacuities where the presphenoid and basisphenoid bones meet. An alisphenoid strut separates two foramina (openings) at the base of the skull, the buccinator-masticatory foramen and the foramen ovale accessorium. The pattern of grooves and foramina on the head indicates that the circulation of the arteries in the head of T. ucucha follows the primitive pattern. The tegmen tympani, the roof of the tympanic cavity, overlaps the suspensory process of the squamosal bone. At the back of the mandible (lower jaw), there is a capsular process to receive the root of the lower incisor, [10] which is absent in T. hylophilus. [12]

The large upper incisors are orthodont, with their cutting edge at about a right angle to the upper molars, and heavily pigmented with orange. Those of T. hylophilus are narrower, less procumbent, and less pigmented. [12] The orthodont upper incisors suffice to distinguish T. ucucha from all other members of the genus but T. australis and T. daphne , which have much shorter and narrower incisors. [14] The left and right molar rows are parallel. The molars are more hypsodont (high-crowned) than in other Thomasomys. The anterocone, the cusp at the front of the first upper molar, is divided into distinct cuspules at the lingual (inner) and labial (outer) sides by an anteromedian flexus. [10] The accessory ridges on the upper molars, the anterolophs and mesolophs, are less well-developed than in T. hylophilus. The third upper molar is reduced relative to the second, much more so than in T. hylophilus. [12] The lower molars are generally similar to the uppers, but the anteroconid (the equivalent of the anterocone on the first lower molar) is often undivided and the third molar is unreduced. [10]

The glans penis is rounded, short, and small and is superficially divided into left and right halves by a trough at the top and a ridge at the bottom. Most of the glans is covered with penile spines, except for an area near the tip. [10]

Distribution and ecology

Thomasomys ucucha occurs only in the Cordillera Oriental of Ecuador in the provinces of Pichincha, Napo, and Carchi. [3] [15] At Papallacta, Thomasomys ucucha was collected in a variety of habitats at 3,380 to 3,720 m (11,090 to 12,200 ft) altitude, including páramo (high-mountain grassland with shrubs and forest patches) and subalpine rainforest. [14] Most were taken in runways (paths through vegetation made by animals) and a few alongside small streams or on a low tree. [16] At Guandera Biological Reserve in Carchi, the species has been found at a slightly lower elevation, 3,340 m (10,960 ft). [15] Other muroid rodents found at the same places as T. ucucha include two akodontines (grass mice), Akodon latebricola and Akodon mollis ; two ichthyomyines (water rats), Anotomys leander and Neusticomys monticolus ; two oryzomyines (rice rats), Microryzomys altissimus and M. minutus ; the thomasomyine Chilomys instans ; and five other species of Thomasomys, T. aureus , T. baeops , T. cinnameus , T. erro , and T. paramorum . [17] Other species have been recorded nearby, and Voss wrote that T. ucucha may occur sympatrically with seven other species of Thomasomys. [8] With Akodon latebricola and Thomasomys erro, T. ucucha is one of three species that are known only from the northeastern Andes of Ecuador. [18]

Conservation status

Thomasomys ucucha is locally common, but has a very limited known distribution. [19] Its conservation status has been assessed as "vulnerable" by the IUCN because of its highly localized distribution; it may be threatened by the destruction of its habitat for agricultural purposes, [1] but occurs near or in several protected areas. [19] [15]

Related Research Articles

<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>Lundomys</i> A semiaquatic rat species from southeastern South America.

Lundomys molitor, also known as Lund's amphibious rat or the greater marsh rat, is a semiaquatic rat species from southeastern South America.

<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>Akodon spegazzinii</i> Rodent in the family Cricetidae found in northwestern Argentina

Akodon spegazzinii, also known as Spegazzini's akodont or Spegazzini's grass mouse, is a rodent in the genus Akodon found in northwestern Argentina. It occurs in grassland and forest at 400 to 3,500 m above sea level. After the species was first named in 1897, several other names were given to various populations now included in A. spegazzinii. They are now all recognized as part of a single, widespread and variable species. Akodon spegazzinii is related to Akodon boliviensis and other members of the A. boliviensis species group. It reproduces year-round. Because it is widely distributed and common, Akodon spegazzinii is listed as "least concern" on the IUCN Red List.

<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>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 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.

<i>Eremoryzomys</i> Rodent species in the family Cricetidae from central Peru

Eremoryzomys polius, also known as the gray rice rat or the Marañon oryzomys, is a rodent species in the tribe Oryzomyini of the family Cricetidae. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in Oryzomys and named Oryzomys polius. In 2006, a cladistic analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus, Eremoryzomys. The Brazilian genus Drymoreomys, named in 2011, is probably the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River in central Peru, but may yet contain more than one species.

<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.

<i>Akodon caenosus</i> Species of rodent

Akodon caenosus is a rodent in the genus Akodon found in northwestern Argentina and south-central Bolivia. Since its description in 1918, it has been alternatively classified as a separate species or a subspecies of Akodon lutescens. The species Akodon aliquantulus, described from some very small Argentine specimens in 1999, is now recognized as a synonym of A. caenosus.

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>Carletonomys</i> Extinct genus of rodents

Carletonomys cailoi is an extinct rodent from the Pleistocene (Ensenadan) of Buenos Aires Province, Argentina. Although known only from a single maxilla with the first molar, its features are so distinctive that it is placed in its own genus, Carletonomys. Discovered in 1998 and formally described in 2008, it is part of a well-defined group of oryzomyine rodents that also includes Holochilus, Noronhomys, Lundomys, and Pseudoryzomys. This group is characterized by progressive semiaquatic specializations and a reduction in the complexity of molar morphology.

<i>Juliomys anoblepas</i> Species of rodent

Juliomys anoblepas is a rodent in the genus Juliomys of the subfamily Sigmodontinae known from a single broken skull. The specimen was collected by Peter Wilhelm Lund in the caves of Lagoa Santa, Minas Gerais, Brazil, in the first half of the 19th century and described by Herluf Winge in 1888 as Calomys anoblepas. The species remained unstudied and its affinities unclear until 2011, when it was recognized as a member of the genus Juliomys, which includes three other species from southern Brazil and nearby Argentina and Paraguay. J. anoblepas is probably a separate extinct species of the genus, which is no longer found at Lagoa Santa.

<i>Transandinomys</i> Genus of small rodents from Central and South America

Transandinomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—T. bolivaris and T. talamancae—found in forests from Honduras in Central America south and east to southwestern Ecuador and northwestern Venezuela in northern South America. Until 2006, its members were included in the genus Oryzomys, but 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.

<i>Oecomys sydandersoni</i> Species of rodent

Oecomys sydandersoni is an arboreal species of rodent in the genus Oecomys. It lives in forest patches in a small area in eastern Bolivia. It is a medium-sized species, weighing about 45 g (1.6 oz), with mostly grayish and brownish fur and short and broad hindfeet with well-developed pads.

<span class="mw-page-title-main">Northern voalavo</span> Rodent in the family Nesomyidae

The northern voalavo, also known as the naked-tailed voalavo or simply the voalavo, is a rodent in the family Nesomyidae found in the Northern Highlands of Madagascar. Discovered in 1994 and formally described in 1998, it is the type species of the genus Voalavo; its closest relative is the eastern voalavo of the Central Highlands. DNA sequencing suggests that it may be more closely related to Grandidier's tufted-tailed rat than to other species of the closely related genus Eliurus. The northern voalavo is found at 1,250 to 1,950 m above sea level in montane wet and dry forests in the Marojejy and Anjanaharibe-Sud massifs. Nocturnal and solitary, it lives mainly on the ground, but it can climb and probably eats plant matter. Despite having a small range, the species is classified as being of least concern because it lacks obvious threats and much of its range is within protected areas.

<i>Lagidium ahuacaense</i> Species of rodent

Lagidium ahuacaense is a rodent in the mountain viscacha genus (Lagidium) that occurs in southern Ecuador. First observed in 2005 and formally described in 2009, it occurs more than 500 km (310 mi) north of the nearest previously known population of mountain viscachas in central Peru. Only a single population is known, found on rocky habitats on Cerro El Ahuaca, an isolated granite mountain in southern Ecuador, and as few as several dozen individuals remain. The species is threatened by fires and grazing cattle, and the discoverers recommended its conservation status be assessed as critically endangered.

Petter's tufted-tailed rat is a rodent in the genus Eliurus found in lowland eastern Madagascar. First described in 1994, it is most closely related to the smaller Eliurus grandidieri. Virtually nothing is known of its natural history, except that it occurs in rainforest and is nocturnal and solitary. It is threatened by destruction and fragmentation of its habitat and is listed as "Vulnerable" on the IUCN Red List.

<i>Drymoreomys</i> A rodent genus with one species in the family Cricetidae from the Atlantic Forest of Brazil.

Drymoreomys is a rodent genus in the tribe Oryzomyini that lives in the Atlantic Forest of Brazil. The single species, D. albimaculatus, is known only from the states of São Paulo and Santa Catarina and was not named until 2011. It lives in the humid forest on the eastern slopes of the Serra do Mar and perhaps reproduces year-round. Although its range is relatively large and includes some protected areas, it is patchy and threatened, and the discoverers recommend that the animal be considered "Near Threatened" on the IUCN Red List. Within Oryzomyini, Drymoreomys appears to be most closely related to Eremoryzomys from the Andes of Peru, a biogeographically unusual relationship, in that the two populations are widely separated and each is adapted to an arid or a moist environment.


  1. 1 2 Barriga, C.; Pacheco, V. (2018). "Thomasomys ucucha". IUCN Red List of Threatened Species . 2018: e.T136487A22366894. doi: 10.2305/IUCN.UK.2018-1.RLTS.T136487A22366894.en . Retrieved 19 November 2021.
  2. Musser and Carleton, 2005, p. 1184
  3. 1 2 3 4 5 Voss, 2003, p. 10
  4. 1 2 Voss, 2003, p. 2
  5. Beolens et al., 2009, pp. 410–411
  6. Voss, 2003, p. 12
  7. Lee et al., 2015, fig. 2
  8. 1 2 Voss, 2003, p. 8
  9. Musser and Carleton, 2005
  10. 1 2 3 4 5 6 7 8 Voss, 2003, p. 11
  11. Voss, 2003, table 1
  12. 1 2 3 4 5 6 Voss, 2003, p. 13
  13. Voss, 2003, table 2
  14. 1 2 Voss, 2003, p. 14
  15. 1 2 3 Lee et al., 2015, p. 7
  16. Voss, 2003, pp. 1415
  17. Voss, 2003, p. 15
  18. Voss, 2003, p. 37
  19. 1 2 Tirira, 2007, p. 198

Literature cited

External sources