Sciurini
Encyclopedia
Sciurini is a tribe that includes about forty species of squirrel
s, 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
, which includes some of the best known squirrel species; the Central American Syntheosciurus; and the American red squirrels, Tamiasciurus. Like other arboreal squirrels, they are sometimes referred to as tree squirrel
s.
in 1854, who used it for the entire squirrel family. In his influential 1945 classification of mammals, George Gaylord Simpson
included four genera
of squirrels in Sciurini, which he recognized as one of eight tribes within the subfamily Sciurinae (including all squirrels except the flying squirrel
s): Sciurus
, Syntheosciurus, Microsciurus
, and Sciurillus. He also classified Rheithrosciurus as "?Sciurini incertae sedis
" (of uncertain placement). This grouping derives from Reginald Innes Pocock
, who united these squirrels in 1923 as the subfamily Sciurinae.
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 subtribes, producing the following classification:
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:
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 flying squirrel
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. 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
; 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 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. In a 2008 monograph on Brazilian rodents, Bonvicino and others considered Guerlinguetus and Urosciurus, conventionally placed in Sciurus, as separate genera.
(about 36 million years ago) of Wyoming, Montana, and Saskatchewan, is so similar to living Sciurus that the latter has been considered a living fossil
. 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 Sciurini and speculated that other squirrels may have evolved from animals similar to Sciurini squirrels. The Oligocene
to early Miocene
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. In Europe, Sciurus first appears early in the Pliocene
. The 2005 discovery of S. olsoni provided evidence that the origin of the Sciurini lies in North America.
A Miocene squirrel from France and Spain, Freudenthalia, has been tentatively placed in Sciurini. Plesiosciurus from the Miocene of China has been interpreted as a member of Sciurini, but is unlikely to belong to the tribe.
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s, mostly from the Americas. It includes five living genera—the American dwarf squirrels, Microsciurus
Microsciurus
Microsciurus or dwarf squirrels is a genus of squirrels from the tropical regions of Central and South America.There are four recognized species, however, recent DNA analysis has shown that there is some confusion regarding the traditional classification of the Microsciurus species:Genus...
; the Bornean Rheithrosciurus; the widespread American and Eurasian tree squirrels of the genus Sciurus
Sciurus
The genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.-Species:There are 30 species.Genus Sciurus - Tree squirrels*Subgenus Sciurus...
, which includes some of the best known squirrel species; the Central American Syntheosciurus; and the American red squirrels, Tamiasciurus. Like other arboreal squirrels, they are sometimes referred to as tree squirrel
Tree squirrel
Tree squirrels include over a hundred species that are found on all continents except Antarctica, and are the members of the squirrel family most commonly referred to as "squirrels"...
s.
Taxonomy
The name "Sciurini" was first employed by Hermann BurmeisterHermann Burmeister
Karl Hermann Konrad Burmeister was a German zoologist, entomologist, and herpetologist.Burmeister was born in Stralsund and became a professor of Zoology at the Martin Luther University of Halle-Wittenberg from 1837 to 1861...
in 1854, who used it for the entire squirrel family. In his influential 1945 classification of mammals, George Gaylord Simpson
George Gaylord Simpson
George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...
included four genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of squirrels in Sciurini, which he recognized as one of eight tribes within the subfamily Sciurinae (including all squirrels except the flying squirrel
Flying squirrel
Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
s): Sciurus
Sciurus
The genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.-Species:There are 30 species.Genus Sciurus - Tree squirrels*Subgenus Sciurus...
, Syntheosciurus, Microsciurus
Microsciurus
Microsciurus or dwarf squirrels is a genus of squirrels from the tropical regions of Central and South America.There are four recognized species, however, recent DNA analysis has shown that there is some confusion regarding the traditional classification of the Microsciurus species:Genus...
, and Sciurillus. He also classified Rheithrosciurus as "?Sciurini incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
" (of uncertain placement). This grouping derives from Reginald Innes Pocock
Reginald Innes Pocock
Reginald Innes Pocock F.R.S. 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 School, Oxford. He received tutoring in zoology from Sir Edward Poulton, and was allowed...
, who united these squirrels in 1923 as the subfamily Sciurinae.
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
Baculum
The baculum is a bone found in the penis of most mammals. It is absent in humans, but present in other primates, such as the gorilla and chimpanzee.The bone aids in sexual intercourse.-Purpose:...
(penis bone). He also divided the tribe into subtribes, producing the following classification:
- Tribe Sciurini
- Subtribe Sciurina
- Genus SciurusSciurusThe genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.-Species:There are 30 species.Genus Sciurus - Tree squirrels*Subgenus Sciurus...
- Genus Guerlinguetus (currently included in Sciurus)
- Genus Rheithrosciurus
- Genus Sciurus
- Subtribe Microsciurina
- Genus MicrosciurusMicrosciurusMicrosciurus or dwarf squirrels is a genus of squirrels from the tropical regions of Central and South America.There are four recognized species, however, recent DNA analysis has shown that there is some confusion regarding the traditional classification of the Microsciurus species:Genus...
- Genus Syntheosciurus (including two species currently placed in Sciurus, S. granatensis and S. pyrrhinus)
- Genus Microsciurus
- Subtribe Sciurillina
- Genus Sciurillus
- Subtribe Sciurina
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:
- Tribe Sciurini
- Freudenthalia (fossil, early MioceneMioceneThe Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
of Europe; assignment to Sciurini "uncertain") - Rheithrosciurus
- Plesiosciurus (fossil, middle Miocene of Asia)
- Subtribe Sciurina
- Douglassciurus (fossil, late EoceneEoceneThe Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
of North America; McKenna and Bell used DouglassiaDouglassiaDouglassia is a genus of sea snails, marine gastropod mollusks in the family Drilliidae.-Species:Species within the genus Douglassia include:...
, a preoccupied name replaced by Douglassciurus) - Protosciurus (fossil, early OligoceneOligoceneThe Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
to early Miocene of North America) - Miosciurus (fossil, early Miocene of North America)
- SciurusSciurusThe genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.-Species:There are 30 species.Genus Sciurus - Tree squirrels*Subgenus Sciurus...
(including Syntheosciurus) - MicrosciurusMicrosciurusMicrosciurus or dwarf squirrels is a genus of squirrels from the tropical regions of Central and South America.There are four recognized species, however, recent DNA analysis has shown that there is some confusion regarding the traditional classification of the Microsciurus species:Genus...
- Douglassciurus (fossil, late Eocene
- Subtribe Sciurillina
- Sciurillus
- Freudenthalia (fossil, early Miocene
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 flying squirrel
Flying squirrel
Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
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. Their classification was adopted in the 2005 third edition of Mammal Species of the World
Mammal Species of the World
Mammal Species of the World, now in its 3rd edition, is a standard reference work in zoology giving descriptions and bibliographic data for the known species of mammals.An updated Third Edition of Mammal Species of the World was published late in 2005:...
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
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
; additionally, the two species of Microsciurus included in Mercer and Roth's 2003 study did not cluster with each other. A morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
study of Central American 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. In a 2008 monograph on Brazilian rodents, Bonvicino and others considered Guerlinguetus and Urosciurus, conventionally placed in Sciurus, as separate genera.
Fossil history
Douglassciurus, a fossil from the late EoceneEocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(about 36 million years ago) of Wyoming, Montana, and Saskatchewan, is so similar to living Sciurus that the latter has been considered a living fossil
Living fossil
Living fossil is an informal term for any living species which appears similar to a species otherwise only known from fossils and which has no close living relatives, or a group of organisms which have long fossil records...
. 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 Sciurini and speculated that other squirrels may have evolved from animals similar to Sciurini squirrels. The Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
to early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
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. In Europe, Sciurus first appears early in the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. The 2005 discovery of S. olsoni provided evidence that the origin of the Sciurini lies in North America.
A Miocene squirrel from France and Spain, Freudenthalia, has been tentatively placed in Sciurini. Plesiosciurus from the Miocene of China has been interpreted as a member of Sciurini, but is unlikely to belong to the tribe.
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. ISBN 978-0-231-11013-6
- 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. ISBN 978-0-8018-8221-0
- Thorington, R.W. and Ferrell, K. 2006. Squirrels: the animal answer guide. Johns Hopkins University Press, 183 pp. ISBN 978-0-8018-8402-3
- Villalobos, F. and Cervantes-Reza, F. 2007. Phylogenetic relationships of Mesoamerican species of the genus Sciurus (Rodentia: Sciuridae). Zootaxa 1525:31–40.