Thomasomys ucucha
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''Thomasomys ucucha'', also known as the ucucha thomasomys, is a
rodent Rodents (from Latin , 'to gnaw') 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 na ...
in the genus ''
Thomasomys ''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: * Anderson' ...
'' of the family
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...
. It is known only from
high altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
forest and grassland habitats in the Cordillera Oriental of
Ecuador Ecuador ( ; ; Quechua: ''Ikwayur''; Shuar: ''Ecuador'' or ''Ekuatur''), officially the Republic of Ecuador ( es, República del Ecuador, which literally translates as "Republic of the Equator"; Quechua: ''Ikwadur Ripuwlika''; Shuar: ''Eku ...
. 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 The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
as a result of
habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
. Medium-sized, dark-furred, and long-tailed, ''T. ucucha'' can be distinguished from all other species of ''Thomasomys'' by its large, broad,
procumbent This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnify ...
upper
incisor Incisors (from Latin ''incidere'', "to cut") 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 (two on each side, top and bottom). Opossums have 18, whe ...
s. Head and body length is and body mass is . The tail is scarcely furred. The front part of the skull is flat, short, and broad. The
incisive foramina In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...
, openings at the front of the
palate 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 sepa ...
, are short, and the palate itself is broad and smooth. The root of the lower incisor is contained in a prominent
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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest ...
.


Taxonomy

The first three specimens of ''Thomasomys ucucha'' were collected in 1903 at Tablón in
Pichincha Province 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 ...
, Ecuador, by L. Söderström. It was not found again until Robert S. Voss of the
American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
collected a total of forty-three specimens at nearby
Papallacta Papallacta is a small village at an altitude of in Napo Province, Ecuador. The village is located off the Eastern Cordilleras, on the road from Quito into the Amazon rainforest. It is known for its hot springs. How to reach The drive from ...
,
Napo Province Napo () is a province in Ecuador. Its capital is Tena. The province contains the Napo River. The province is low developed without much industrial presence. The thick rainforest is home to many natives that remain isolated by preference, descendan ...
, in 1978 and 1980 (the type locality is described as the valley of the Rio Papallacta). Papallacta is in a remote area that is difficult to access, and the mammal fauna of the region remains poorly known. In 2003, he formally described the animal as a new species, ''Thomasomys ucucha'',Voss, 2003, p. 10 in a publication in ''
American Museum Novitates ''American Museum Novitates'' is a peer-reviewed academic journal published by the American Museum of Natural History. It was established in 1921. According to the ''Journal Citation Reports'', the journal has a 2013 impact factor The impact f ...
'' in which he also reviewed the mammal fauna of Papallacta.Voss, 2003, p. 2 The generic name, ''
Thomasomys ''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: * Anderson' ...
'', honors English zoologist
Oldfield Thomas Michael Rogers Oldfield Thomas (21 February 1858 – 16 June 1929) was a British zoologist. Career Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and subspecies for the first time. He was appoin ...
, who named about 2,900
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
of mammals, and the specific name, ''ucucha'', is the local
Quechua Quechua may refer to: *Quechua people, several indigenous ethnic groups in South America, especially in Peru *Quechuan languages, a Native South American language family spoken primarily in the Andes, derived from a common ancestral language **So ...
word for "mouse". ''T. ucucha'' most closely resembles '' T. hylophilus'', which is found further north in Colombia and Venezuela.Voss, 2003, p. 12 A comparison of
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
found that ''T. ucucha'' was closest to specimens identified as '' T. caudivarius'' and '' T. silvestris'', but ''T. hylophilus'' was not included in this study.Lee et al., 2015, fig. 2 All are members of ''Thomasomys'', a diverse genus that occurs in the northern Andes, from Bolivia to Venezuela.Voss, 2003, p. 8 Together with ''
Rhipidomys ''Rhipidomys'' is a genus of rodents in the family Cricetidae, The following 24 species of climbing mouse species are currently recognised: * '' Rhipidomys albujai'' * Southern climbing mouse (''Rhipidomys austrinus'') * Cariri climbing mouse ( ...
'' 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 The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
of the family
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...
, along with hundreds of other species of mainly small rodents.


Description

''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 Vibrissae (; singular: vibrissa; ), more generally called Whiskers, are a type of stiff, functional hair used by mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser ...
(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. The digits and
metapodial Metapodials are long bones of the hand (metacarpals) and feet (metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. ...
s (bones of the centers of the hand and feet) of the hands and feet are covered with dark hairs, but the
ungual tufts In mammals, ungual tufts are tufts of hairs at the base of claws of the forefeet and hindfeet. Their presence has been used as a character in cladistic studies of the Cricetidae, a large family of rodents.Weksler, 2006, p. 19 Rice rats Membe ...
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 A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primat ...
.Voss, 2003, p. 11 In thirty-six specimens, head and body length is , averaging ; tail length is , averaging ; hindfoot length is , averaging ; ear length is , averaging ; and weight is , averaging . The front (rostral) part of the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
is short—shorter and broader than in ''T. hylophilus''Voss, 2003, p. 13—and flat and the notches in the
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 ...
s at the sides are poorly developed. The plates themselves are broad. The
zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygomati ...
es (cheekbones) spread broadly and are rounded in shape. The narrow
interorbital region The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups. In oryzomyine rodents, for example, the width, form, an ...
(between the eyes) is hourglass-shaped. The
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...
is robust. The
incisive foramina In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...
, which perforate the
palate 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 sepa ...
between the
incisor Incisors (from Latin ''incidere'', "to cut") 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 (two on each side, top and bottom). Opossums have 18, whe ...
s and the
molars 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 to ...
, are short and do not reach near the first molars; they are longer in ''T. hylophilus''. They are widest where the
premaxilla The premaxilla (or praemaxilla) 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. The "premaxilla" of therian mammal has b ...
ry and
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
ry 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 In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars.Weksler, 2006, p. 34 Posterolateral palatal pits are present, in various degrees of development, in several members of the roden ...
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 In some rodents, the alisphenoid strut is an extension of the alisphenoid bone that separates two foramina in the skull, the masticatory–buccinator foramen and the foramen ovale accessorium. The presence or absence of this strut is variable be ...
separates two
foramina In anatomy and osteology, a foramen (;Entry "foramen"
in
(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 tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditor ...
, the roof of the
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...
, overlaps the suspensory
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
of the
squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral c ...
. At the back of the
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
(lower jaw), there is a
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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest ...
to receive the root of the lower
incisor Incisors (from Latin ''incidere'', "to cut") 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 (two on each side, top and bottom). Opossums have 18, whe ...
, which is absent in ''T. hylophilus''. 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. 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. The left and right molar rows are parallel. The molars are more
hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...
(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. The accessory ridges on the upper molars, the anterolophs and
mesoloph Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...
s, 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''. 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. The
glans penis In male human anatomy, the glans penis, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and their primary anatomical source of sexual p ...
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 Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two o ...
, except for an area near the tip.


Distribution and ecology

''Thomasomys ucucha'' occurs only in the Cordillera Oriental of Ecuador in the provinces of Pichincha, Napo, and
Carchi Carchi () is a Provinces of Ecuador, province in Ecuador. The capital is Tulcán. The Carchi River rises on the slopes of Chiles (volcano), Chiles volcano and forms the boundary between Colombia and Ecuador near Tulcan. Rumichaca Bridge is the m ...
.Lee et al., 2015, p. 7 At Papallacta, ''Thomasomys ucucha'' was collected in a variety of habitats at altitude, including ''
páramo Páramo () can refer to a variety of alpine tundra ecosystems located in the Andes Mountain Range, South America. Some ecologists describe the páramo broadly as "all high, tropical, montane vegetation above the continuous timberline". A narrower ...
'' (high-mountain grassland with shrubs and forest patches) and subalpine rainforest.Voss, 2003, p. 14 Most were taken in runways (paths through vegetation made by animals) and a few alongside small streams or on a low tree. At Guandera Biological Reserve in Carchi, the species has been found at a slightly lower elevation, . Other
muroid The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, lemmings, gerbils, and many other relatives. Although the Muroidea originated in Eurasia, they occupy a vast variety of habitats on every continent except A ...
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 ''Microryzomys altissimus'', also known as the Páramo colilargo or highland small rice rat, is a species of rodent in the genus ''Microryzomys'' of family Cricetidae. It is found in Colombia, Ecuador, and Peru, but the Colombian segment may be a ...
'' and '' M. minutus''; the thomasomyine '' Chilomys instans''; and five other species of ''Thomasomys'', '' T. aureus'', '' T. baeops'', '' T. cinnameus'', '' T. erro'', and '' T. paramorum''.Voss, 2003, p. 15 Other species have been recorded nearby, and Voss wrote that ''T. ucucha'' may occur
sympatric In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
ally with seven other species of ''Thomasomys''. With ''Akodon latebricola'' and ''Thomasomys erro'', ''T. ucucha'' is one of three species that are known only from the northeastern Andes of Ecuador.Voss, 2003, p. 37


Conservation status

''Thomasomys ucucha'' is locally common, but has a very limited known distribution. Its conservation status has been assessed as " vulnerable" by the
IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
because of its highly localized distribution; it may be threatened by the destruction of its habitat for
agricultural Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...
purposes, but occurs near or in several
protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural, ecological or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the ena ...
s.Tirira, 2007, p. 198


References


Literature cited

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External sources


Pontificia Universidad Católica del Ecuador, Bioweb
data, maps and photographs {{Taxonbar, from=Q1766324 Mammals of Ecuador Thomasomys Mammals described in 2003 Páramo fauna