Thomasomys ucucha

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Thomasomys ucucha
Scientific classification Red Pencil Icon.png
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.

Rodent Diverse order of mammals

Rodents are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents ; they are found in vast numbers on all continents except Antarctica. They are the most diversified mammalian order and live in a variety of terrestrial habitats, including human-made environments.

<i>Thomasomys</i> genus of mammals

Thomasomys is a genus of rodent in the family Cricetidae, named after British zoologist Oldfield Thomas. Nuclear DNA sequence analysis has indicated that it is a sister taxon to Rhagomys. It contains the following species:

Cricetidae family of mammals

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has members throughout the Americas, Europe and Asia.


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.

Incisor front teeth present in most (but not all — e.g. armadillos) mammals, located in the premaxilla above and on the mandible below; humans have a total of 8 (2 on each side, top and bottom); opossums have 18

Incisors are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight. Opossums have 18, whereas armadillos have none.

Palate roof of the mouth

The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior bony hard palate and the posterior fleshy soft palate.

Capsular process

In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial (outer) side of the mandible as a raising in the bone. There is marked variation within species in the development of this 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. [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]

Pichincha Province Province in Ecuador

Pichincha is a province of Ecuador located in the northern sierra region; its capital and largest city is Quito. It is bordered by Imbabura and Esmeraldas to the north, Cotopaxi and Santo Domingo de los Tsáchilas to the south, Napo and Sucumbíos to the east, and Esmeraldas and Santo Domingo de los Tsáchilas to the west.

American Museum of Natural History natural history museum in New York City

The American Museum of Natural History, located on the Upper West Side of Manhattan, New York City, is one of the largest natural history museums in the world. Located in Theodore Roosevelt Park across the street from Central Park, the museum complex comprises 28 interconnected buildings housing 45 permanent exhibition halls, in addition to a planetarium and a library. The museum collections contain over 33 million specimens of plants, animals, fossils, minerals, rocks, meteorites, human remains, and human cultural artifacts, of which only a small fraction can be displayed at any given time, and occupies more than 2 million square feet. The museum has a full-time scientific staff of 225, sponsors over 120 special field expeditions each year, and averages about five million visits annually.

Papallacta human settlement

Papallacta is a small village in Napo Province, Ecuador located at an altitude of 3,300 m in the Andes just off the Eastern Cordilleras on the road from Quito which leads into the Amazon jungle. The scenic drive from Quito to Papallacta passes through several towns and small villages before ascending to a peak of over 4,000 m, from where mountains and glaciers are visible. Descending from the peak to Papallacta, the ecosystems transform from alpine to tropical jungle.


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]

Metapodials are long bones of the hand (metacarpals) and feet (metatarsals) which connect the digits to the lower leg bones. In humans, five are present in each hand and foot. In quadrupeds, these form the lower limb, rather than being part of the extremity, thus what looks to be the elbow of a sheep is actually the wrist.

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]

Skull bony structure that forms the skeleton of head in most vertebrates, supports the structures of the face and provides a protective cavity for the brain, composed of two parts: the cranium and the mandible

The skull is a bony structure that forms the head in vertebrates. It supports the structures of the face and provides a protective cavity for the brain. The skull is composed of two parts: the cranium and the mandible. In the human, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone. The skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans these sensory structures are part of the facial skeleton.

Zygomatic plate

In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary bone, or upper jaw, which also contains the upper cheekteeth. Primitively, rodents have a nearly horizontal zygomatic plate. In association with specializations in zygomasseteric system, several distinct morphologies have developed across the order.

Zygomatic arch cheek bone

The zygomatic arch, or cheek bone, is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone, the two being united by an oblique suture ; the tendon of the temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible. The jugal point is the point at the anterior end of the upper border of the zygomatic arch where the masseteric and maxillary edges meet at an angle. The jugal point is the anterior end of upper border of the zygomatic arch where it meets the process of the zygomatic bone.

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]

Incisive foramen

In the human mouth, the incisive foramen, also called anterior palatine foramen, or nasopalatine foramen is a funnel-shaped opening in the bone of the oral hard palate immediately behind the incisor teeth where blood vessels and nerves pass. The incisive foramen is continuous with the incisive canal, this foramen or group of foramina is located behind the central incisor teeth in the incisive fossa of the maxilla.

Molar (tooth) large tooth at the back of the mouth

The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name molar derives from Latin, molaris dens, meaning "millstone tooth", from mola, millstone and dens, tooth. Molars show a great deal of diversity in size and shape across mammal groups.


The premaxilla is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla and usually termed as the incisive bone. Other terms used for this structure include premaxillary bone or os premaxillare, and intermaxillary bone or os intermaxillare.

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]

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  1. 1 2 Barriga & Pacheco, 2018
  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