Sciurini 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 is in the discipline of anthropology. This definition is contested, in part due to confl ...

that includes about forty species of squirrels,Thorington and Hoffmann, 2005, p. 754 mostly from the Americas. It includes five living genera—the American dwarf squirrels, '' Microsciurus''; the Bornean ''

Rheithrosciurus The tufted ground squirrel or groove-toothed squirrel (''Rheithrosciurus macrotis'') is a species of rodent in the family Sciuridae. It is the sole species in the genus ''Rheithrosciurus''. It is found only on the island of Borneo. Confirmed elem ...

''; the widespread American and Eurasian tree squirrels of the genus '' Sciurus'', which includes some of the best known squirrel species; the Central American '' Syntheosciurus''; and the American pine squirrels, ''

Tamiasciurus Pine squirrels are squirrels of the genus ''Tamiasciurus'', in the Sciurini tribe, of the large family Sciuridae. Species This genus includes three species: *''Tamiasciurus hudsonicus'' — American red squirrel *''Tamiasciurus douglasi ...

''. Like other

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose num ...

squirrels, they are sometimes referred to as

tree squirrel Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels." They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, o ...

Taxonomy

The name "Sciurini" was first employed by

Hermann Burmeister Karl Hermann Konrad Burmeister (also known as Carlos Germán Conrado Burmeister) (15 January 1807 – 2 May 1892) was a German Argentine zoologist, entomologist, herpetologist, botanist, and coleopterologist. He served as a professor at the Univ ...

in 1854, who used it for the entire squirrel family. In his influential 1945 classification of mammals,

George Gaylord Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...

included 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 ...

of squirrels in Sciurini, which he recognized as one of eight

tribes 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 is in the discipline of anthropology. This definition is contested, in part due to confl ...

within the subfamily Sciurinae (including all squirrels except the flying squirrels): '' Sciurus'', '' Syntheosciurus'', '' Microsciurus'', and '' Sciurillus''. He also classified ''

'' as "?Sciurini ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

''" (of uncertain placement).Simpson, 1945, p. 78 This grouping derives from

Reginald Innes Pocock Reginald Innes Pocock F.R.S. (4 March 1863 – 9 August 1947) was a British zoologist. Pocock was born in Clifton, Bristol, the fourth son of Rev. Nicholas Pocock and Edith Prichard. He began showing interest in natural history at St. Edwar ...

, who united these squirrels in 1923 as the subfamily Sciurinae.Moore, 1959, p. 177 In 1959, Joseph Curtis Moore published a review of the interrelationships of the squirrels. His definition of Sciurini was similar to Simpson's, but he no longer considered ''Rheithrosciurus'' to be ''incertae sedis''. He noted that the members of Sciurini were united only by the possession of a special type of baculum (penis bone). He also divided the tribe into

subtribe Subtribe is a taxonomic category ranking which is below the rank of tribe and above genus. The standard suffix for a subtribe is -ina (in animals) or -inae (in plants). The early use of this word is from 19th century. An example of subtribe i ...

s, producing the following classification: *Tribe Sciurini **Subtribe Sciurina ***Genus '' Sciurus'' ***Genus ''

Guerlinguetus The genus ''Sciurus'' contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America. Species The number of species in the genus is subject to change. In 2005, Thorington & Hoffma ...

'' (currently included in ''Sciurus'')Thorington and Hoffmann, 2005, p. 758 ***Genus ''

'' **Subtribe Microsciurina ***Genus '' Microsciurus'' ***Genus '' Syntheosciurus'' **Subtribe Sciurillina ***Genus '' Sciurillus'' In their 1997 update to Simpson's classification, McKenna and Bell retained a similar definition for Sciurini, but also included several extinct genera, as follows:McKenna and Bell, 1997, p. 122 *Tribe Sciurini **'' Freudenthalia'' (fossil, early

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

of Europe; assignment to Sciurini "uncertain") **''

'' **'' Plesiosciurus'' (fossil, middle Miocene of Asia) **Subtribe Sciurina ***'' Douglassciurus'' (fossil, late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

of North America; McKenna and Bell used '' Douglassia'', a

preoccupied name In biology, a homonym is a name for a taxon that is identical in spelling to another such name, that belongs to a different taxon. The rule in the International Code of Zoological Nomenclature is that the first such name to be published is the se ...

replaced by ''Douglassciurus'')Emry and Korth, 2001 ***'' Protosciurus'' (fossil, early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but ...

to early Miocene of North America) ***'' Miosciurus'' (fossil, early Miocene of North America) ***'' Sciurus'' (including ''Syntheosciurus'') ***'' Microsciurus'' **Subtribe Sciurillina ***'' Sciurillus'' In the early 2000s, several studies were published using DNA sequences to study the interrelationships of squirrels. Two, published in 2003 and 2004 and both based on several different genes, produced largely concordant results, concluding that ''Sciurillus'' is not related to other Sciurini, but rather forms one of the most distinctive lineages of all squirrels; that ''

'' is the closest relative to the other Sciurini; and that the group of ''Tamiasciurus'' and the other Sciurini is most closely related to the flying squirrels. The authors of the 2004 study formalized these results into a revised classification of squirrels. They removed ''Sciurillus'' from Sciurini, placed ''Tamiasciurus'' in it, and classified Sciurini with the flying squirrels (tribe Pteromyini) in a subfamily Sciurinae.Steppan et al., 2004, p. 715 Their classification was adopted in the 2005 third edition of '' Mammal Species of the World'' and remains current. The same studies also provided insights into the interrelationships of genera within Sciurini. ''Microsciurus'', ''Syntheosciurus'', and ''Rheithrosciurus'' all appear among the various species of ''Sciurus'' included, making the latter genus

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

; additionally, the two species of ''Microsciurus'' included in Mercer and Roth's 2003 study did not cluster with each other. A morphological study of

Central American Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. C ...

Sciurini also found that ''Microsciurus'' and ''Syntheosciurus'' are part of the ''Sciurus'' radiation, and suggested that ''Syntheosciurus'' be lumped into ''Sciurus'' while further work is needed on ''Microsciurus''.Villalobos and Cervantes-Reza, 2007 In a 2008 monograph on Brazilian rodents, Bonvicino and others considered ''

'' and '' Urosciurus'', conventionally placed in ''Sciurus'', as separate genera.

Fossil history

'' Douglassciurus'', a fossil from the late

(about 36 million years ago) of

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the sou ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

, and

Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North ...

, is so similar to living ''Sciurus'' that the latter has been considered a

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...

. but some exclude this animal from the squirrel family because of several primitive characters. Emry and Korth, who re-described the animal in 1996, classified it within SciuriniEmry and Korth, 1996, p. 775 and speculated that other squirrels may have evolved from animals similar to Sciurini squirrels.Emry and Korth, 1996, p. 778 The

to early

North American genera '' Protosciurus'' and '' Miosciurus'' are classified in Sciurini and may have given rise to the earliest known member of ''Sciurus'', '' S. olsoni'' from the early late Miocene (about 10 million years ago) of

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

. In

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

, ''Sciurus'' first appears early in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...

and

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

, '' Freudenthalia'', has been tentatively placed in Sciurini.Cuenca Bescós, 1988, p. 92; Aguilar, 2002, p. 388 '' Plesiosciurus'' from the Miocene of China has been interpreted as a member of Sciurini, but is unlikely to belong to the tribe.Emry et al., 2005, p. 228

Footnotes

References

Literature cited

*Aguilar, J.-P. 2002
Les sciuridés des gisements karstiques du Miocène inférieur à moyen du sud de la France : nouvelles espèces, phylogénie, paléoenvironnement
(subscription required). Geobios 35:375–394 (in French). *Bonvicino, C.R., Oliveira, J.A. and D'Andrea, P.S. 2008
Guia dos Roedores do Brasil, com chaves para gêneros baseadas em characteres externos
Série de Manuais Técnicos 11:1–120. Rio de Janeiro: Centro Pan-Americano de Febre Aftosa – OPAS/OMS (in Portuguese). *Burmeister, H. 1854
Systematische Uebersicht der Thiere Brasiliens, welche während einer Reise durch die Provinzen von Rio de Janeiro und Minas geraës gesammelt oder beobachtet wurden. Erster Theil. Säugethiere (Mammalia)
Berlin: G. Reimer (in German). *Cuenca Bescós, G. 1988
Revisión de los Sciuridae del Aragoniense y del Rambliense en la fosa de Calatayud-Montalbán
Scripta Geologica 87:1–116 (in Spanish). *Emry, R.J. and Korth, W.W. 1996
The Chadronian ''"Sciurus" jeffersoni'' Douglass, 1901: a new generic name, new material, and its bearing on the early evolution of Sciuridae (Rodentia)
Journal of Vertebrate Paleontology 16:775–780. *Emry, R.J. and Korth, W.V. 2001
''Douglassciurus'', new name for ''Douglassia'' Emry and Korth, 1996, not ''Douglassia'' Bartsch, 1934
(subscription required). Journal of Vertebrate Paleontology 21(5):400. *Emry, R.J., Korth, W.W. and Bell, M.A. 2005
A tree squirrel (Rodentia, Sciuridae, Sciurini) from the Late Miocene (Clarendonian) of Nevada
(subscription required). Journal of Vertebrate Paleontology 25(1):228–235. *McKenna, M.C. and Bell, S.K. 1997. Classification of Mammals: Above the species level. New York: Columbia University Press, 631 pp. *Mercer, J.M. and Roth, V.L. 2003
The effects of Cenozoic global change on squirrel phylogeny
(subscription required). Science 299:1568–1572. *Moore, J.C. 1959
Relationships among the living squirrels of the Sciurinae
Bulletin of the American Museum of Natural History 118:157–206. *Simpson, G.G. 1945
The principles of classification and a classification of mammals
Bulletin of the American Museum Natural History 85:1–350. *Steppan, S.J., Storz, B.L. and Hoffmann, R.S. 2004
Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1
Molecular Phylogenetics and Evolution 30:703–719. *Thorington, R.W., Jr. and Hoffmann, R.S. 2005. Family Sciuridae. Pp. 754–818 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. *Thorington, R.W. and Ferrell, K. 2006
Squirrels: the animal answer guide
Johns Hopkins University Press, 183 pp. *Villalobos, F. and Cervantes-Reza, F. 2007
Phylogenetic relationships of Mesoamerican species of the genus ''Sciurus'' (Rodentia: Sciuridae)
Zootaxa 1525:31–40. {{Taxonbar, from=Q2294121 * Mammal tribes Extant Eocene first appearances Taxa named by Gotthelf Fischer von Waldheim

Taxonomy

Fossil history

See also

Footnotes

References

Literature cited