Abrotrichini, also known as the Andean clade or southern Andean clade,Musser and Carleton, 2005, p. 1087 is a

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English language, English is in the discipline of anthropology. This definition is contested, in p ...

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 ...

s in 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 ...

.D'Elía et al., 2007, p. 188 It includes about fifteen

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in four

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

,Musser and Carleton, 2005 distributed in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

from southern

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

to southernmost South America, including the

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

n steppes. The earliest known

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s are from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Taxonomy

Abrotrichines were universally placed in the tribe Akodontini until the 1990s, and some were even classified within the genus ''

Akodon ''Akodon'' is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west ...

''.

Allozyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that perfo ...

studies in the early 1990s first provided evidence for their distinction from Akodontini, and in 1999 a study analyzing sequences of the mitochondrial cytochrome ''b'' gene found further evidence for the distinction between Akodontini and this group and proposed the name Abrotrichini for the latter.Smith and Patton, 1999, p. 106 The name Abrotrichini remained formally unavailable under the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...

, however, because their proposal had been conditional. Thus, the clade remained without a valid name and for this reason it was included in Akodontini in the 2005 third edition of ''

Mammal Species of the World ''Mammal Species of the World: A Taxonomic and Geographic Reference'' is a standard reference work in mammalogy giving descriptions and bibliographic data for the known species of mammals. It is now in its third edition, published in late 2005, ...

''. Other phylogenetic studies, which also incorporated

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: * Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...

genes, affirmed the distinction between Akodontini and the new group. In 2007, Guillermo D'Elía and coworkers published a full diagnosis of the tribe Abrotrichini, validating the name. Abrotrichini includes four genera—''

Abrothrix ''Abrothrix'' is a genus of rodent in the tribe Abrotrichini of family Cricetidae. It contains the following living species:Teta et al., 2017 *''Abrothrix andina'' *''Abrothrix hershkovitzi'' *''Abrothrix hirta'' *''Abrothrix illutea'' *''Abrothri ...

'', ''

Chelemys ''Chelemys'' is a genus of South American rodents in the tribe Abrotrichini of family Cricetidae. Three species—'' Chelemys delfini'', '' Chelemys macronyx'', and '' Chelemys megalonyx''—are known, all found in central and southern Chile and A ...

'', ''

Geoxus ''Geoxus'' is a genus of South American rodents in the tribe Abrotrichini of family Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and ...

'', and ''

Notiomys ''Notiomys edwardsii'', also known as Edwards's long-clawed mouse, Edward's long-clawed akodont,Musser and Carleton, 2005, p. 1136 or Milne-Edwards' long-clawed mouse, is a rodent in the tribe Abrotrichini from southern Argentina. It is the ...

''—which fall into two major subgroups, one including only ''Abrothrix'' and one including the four other genera.D'Elía et al., 2007, p. 190 ''Abrothrix'' has formerly been included in ''Akodon'' and includes about nine species, among which are the northernmost abrotrichine, ''

Abrothrix jelskii ''Abrothrix jelskii'', also known as Jelski's Altiplano mouse, Jelski's grass mouse,Duff and Lawson, 2004 or the ornate akodont,Musser and Carleton, 2005, p. 1089 is a species of rodent in the genus ''Abrothrix'' of family Cricetidae. It is ...

'' as well as far southern forms such as ''

Abrothrix lanosus ''Abrothrix lanosus'', also known as the woolly grass mouse or woolly akodont,Musser and Carleton, 2005, p. 1089 is a species of rodent in the family Cricetidae. It is found in southern Argentina and Chile. It was previously classified in th ...

''. Within the remaining group, ''Chelemys'' is sister to the remaining genera; it includes three species found in central and southern Chile and nearby Argentina. The remaining three genera, each of which includes a single species, are closely related and share

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric eviden ...

(digging) habits. ''Geoxus'' occurs in central and southern Chile and nearby Argentina, and ''Notiomys'' in southern Argentina, The tribe is part of the clade Oryzomyalia, which includes most of the subfamily

.D'Elía et al., 2006, fig. 1 Within Oryzomyalia, some studies have recovered '' Wiedomys'' as the closest relative of Abrotrichini, but the basal relationships among the components of Oryzomyalia remain elusive.D'Elía et al., 2006, p. 563 Sigmodontinae encompasses hundreds of species found throughout South America and into North America. It is one of several subfamilies recognized in 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 ...

, which includes many more species, mainly from Eurasia and North America.

Description

Abrotrichines are small to medium-sized sigmodontine rodents with long and soft, usually gray or brown fur, a short, hairy tail and large, strong feet with well-developed claws. In 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 ...

, the snout is long, the

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 ...

hourglass-shaped, and 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 ...

rounded. 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 ...

is long (extending back beyond the third molars). There are no grooves in the 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 and the molars are not

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). The molars lack many accessory features, in particularly the third upper molar. There are 13

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

(chest)

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e with associated ribs, 6

lumbar In tetrapod anatomy, lumbar is an adjective that means ''of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum.'' The lumbar region is sometimes referred to as the lower spine, or as an area of the back i ...

vertebrae, and 18 to 29 caudal (tail) vertebrae. A

karyotype A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...

of 52

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s (2n = 52), present in several species, has been suggested as a

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of the tribe,Smith and Patton, 1999, p. 105 but while this possibility is yet to be tested, ''Pearsonomys'' is now known to have 2n = 56 and some '' Abrothrix olivaceus'' have 2n = 44.

References

Literature cited

*D'Elía, G. 2003
Phylogenetics of Sigmodontinae (Rodentia, Muroidea, Cricetidae), with special reference to the akodont group, and with additional comments on historical biogeography
(subscription only). Cladistics 19:307–323. *D'Elía, G., González, E.M. and Pardiñas, U.F.J. 2003
Phylogenetic analysis of sigmodontine rodents (Muroidea), with special reference to the akodont genus ''Deltamys''
(subscription only). Mammalian Biology 68:351–364. *D'Elía, G., Luna, L., González, E.M. and Patterson, B.D. 2006
On the sigmodontine radiation (Rodentia, Cricetidae): An appraisal of the phylogenetic position of ''Rhagomys''
(subscription only). Molecular Phylogenetics and Evolution 38:558–564. *D'Elía, G., Pardiñas, U.F.J., Teta, P. and Patton, J.L. 2007
Definition and diagnosis of a new tribe of sigmodontine rodents (Cricetidae: Sigmodontinae), and a revised classification of the subfamily.
Gayana 71(2):187–194. *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. *Smith, M.F. & Patton, J.L. 1999
Phylogenetic relationships and the radiation of sigmodontine rodents in South America: evidence from cytochrome ''b''
(subscription only). Journal of Mammalian Evolution 6:89–128. {{Taxonbar, from=Q2540613 Mammal tribes