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 use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

that includes about forty species of

squirrel Squirrels are members of the family Sciuridae (), a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrel ...

s,Thorington and Hoffmann, 2005, p. 754 mostly from the Americas. It includes five living genera—the American dwarf squirrels, '' Microsciurus''; the Bornean '' Rheithrosciurus''; the widespread American and Eurasian tree squirrels of the genus ''

Sciurus The genus ''Sciurus'' ( or ) contains most of the common, bushy-tailed squirrels in North America, Europe, Temperate zone, temperate Asia, Central America and South America. Species The number of species in the genus is subject to change. In 200 ...

'', which includes some of the best known squirrel species; the Central American '' Syntheosciurus''; and the American pine squirrels, '' Tamiasciurus''. 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 (scansorial), but others are exclusively arboreal. The hab ...

squirrels, they are sometimes referred to as

tree squirrel Tree squirrels are the members of the squirrel Family (biology), 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 ...

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, botany, botanist, and coleopterologist. He served as a professor at ...

in 1854, who used it for the entire squirrel family. In his influential 1945 classification of mammals, George Gaylord Simpson included four

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

of squirrels in Sciurini, which he recognized as one of eight tribes within the subfamily Sciurinae (including all squirrels except the

flying squirrel Flying squirrels (scientifically known as Pteromyini or Petauristini) are a tribe (biology), tribe of 50 species of squirrels in the family (biology), family Squirrel, Sciuridae. Despite their name, they are not in fact capable of full flight i ...

s): ''

'', '' Syntheosciurus'', '' Microsciurus'', and '' Sciurillus''. He also classified '' Rheithrosciurus'' as "?Sciurini ''

incertae sedis or is a term used for a taxonomy (biology), 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, uncertainty ...

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

Reginald Innes Pocock Reginald Innes Pocock, (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. Edward's ...

, 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 The baculum (: bacula), also known as the penis bone, penile bone, ''os penis'', ''os genitale'', or ''os priapi'', is a bone in the penis of many placental mammals. It is not present in humans, but is present in the penises of some primates, ...

(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 first use of this word dates back to the late 19th century. An example of ...

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

'' ***Genus '' Guerlinguetus'' (currently included in ''Sciurus'')Thorington and Hoffmann, 2005, p. 758 ***Genus '' Rheithrosciurus'' **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 epoch (geology), 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 mea ...

of Europe; assignment to Sciurini "uncertain") **'' Rheithrosciurus'' **'' Plesiosciurus'' (fossil, middle Miocene of Asia) **Subtribe Sciurina ***'' Douglassciurus'' (fossil, late

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

of North America; McKenna and Bell used '' Douglassia'', a preoccupied name replaced by ''Douglassciurus'')Emry and Korth, 2001 ***'' Protosciurus'' (fossil, early

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

to early Miocene of North America) ***'' Miosciurus'' (fossil, early Miocene of North America) ***''

'' (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 '' Tamiasciurus'' is the closest relative to the other Sciurini; and that the group of ''Tamiasciurus'' and the other Sciurini is most closely related to the

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

'' 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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

; 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 America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

n 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

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

ian rodents, Bonvicino and others considered '' Guerlinguetus'' 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 landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

, and

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

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

living fossil A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically 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 or ...

. 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 landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

. In

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, ''Sciurus'' first appears early in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

and

Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...

, '' Freudenthalia'', has been tentatively placed in Sciurini.Cuenca Bescós, 1988, p. 92; Aguilar, 2002, p. 388 '' Plesiosciurus'' from the Miocene of

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

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