| Sciurini | |
|---|---|
 | |
| Eastern gray squirrel (Sciurus carolinensis) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Sciuridae |
| Subfamily: | Sciurinae |
| Tribe: | Sciurini G. Fischer, 1817 |
| Type genus | |
| Sciurus | |
| Genera | |
| |
| Diversity[2] | |
| Five living genera and about forty species. | |
Sciurini (/sɪˈjuːrɪniː/) is atribe that includes about forty species ofsquirrels,[2] mostly from the Americas. It includes five living genera—the American dwarf squirrels,Microsciurus; the BorneanRheithrosciurus; the widespread American and Eurasian tree squirrels of the genusSciurus, which includes some of the best known squirrel species; the Central AmericanSyntheosciurus; and the American pine squirrels,Tamiasciurus. Like otherarboreal squirrels, they are sometimes referred to astree squirrels.[3]
The name "Sciurini" was first employed byHermann Burmeister in 1854, who used it for the entire squirrel family.[4] In his influential 1945 classification of mammals,George Gaylord Simpson included fourgenera of squirrels in Sciurini, which he recognized as one of eighttribes within the subfamily Sciurinae (including all squirrels except theflying squirrels):Sciurus,Syntheosciurus,Microsciurus, andSciurillus. He also classifiedRheithrosciurus as "?Sciuriniincertae sedis" (of uncertain placement).[5] This grouping derives fromReginald Innes Pocock, who united these squirrels in 1923 as the subfamily Sciurinae.[6]
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 consideredRheithrosciurus to beincertae sedis. He noted that the members of Sciurini were united only by the possession of a special type ofbaculum (penis bone).[7] He also divided the tribe intosubtribes, producing the following classification:[8]
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:[10]
| Phylogeny of the squirrels.[12] |
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 thatSciurillus is not related to other Sciurini, but rather forms one of the most distinctive lineages of all squirrels; thatTamiasciurus is the closest relative to the other Sciurini; and that the group ofTamiasciurus and the other Sciurini is most closely related to theflying squirrels.[12] The authors of the 2004 study formalized these results into a revised classification of squirrels. They removedSciurillus from Sciurini, placedTamiasciurus in it, and classified Sciurini with the flying squirrels (tribe Pteromyini) in a subfamily Sciurinae.[13] Their classification was adopted in the 2005 third edition ofMammal Species of the World[2] and remains current.
The same studies also provided insights into the interrelationships of genera within Sciurini.Microsciurus,Syntheosciurus, andRheithrosciurus all appear among the various species ofSciurus included, making the latter genusparaphyletic; additionally, the two species ofMicrosciurus included in Mercer and Roth's 2003 study did not cluster with each other.[12] Amorphological study ofCentral American Sciurini also found thatMicrosciurus andSyntheosciurus are part of theSciurus radiation, and suggested thatSyntheosciurus be lumped intoSciurus while further work is needed onMicrosciurus.[14] In a 2008 monograph onBrazilian rodents, Bonvicino and others consideredGuerlinguetus andUrosciurus, conventionally placed inSciurus, as separate genera.[15]
Douglassciurus, a fossil from the lateEocene (about 36 million years ago) ofWyoming,Montana, andSaskatchewan, is so similar to livingSciurus that the latter has been considered aliving fossil.[16] but some exclude this animal from the squirrel family because of several primitive characters.[17] Emry and Korth, who re-described the animal in 1996, classified it within Sciurini[1] and speculated that other squirrels may have evolved from animals similar to Sciurini squirrels.[18] TheOligocene to earlyMiocene North American generaProtosciurus andMiosciurus are classified in Sciurini and may have given rise to the earliest known member ofSciurus,S. olsoni from the early late Miocene (about 10 million years ago) ofNevada. InEurope,Sciurus first appears early in thePliocene. The 2005 discovery ofS. olsoni provided evidence that the origin of the Sciurini lies in North America.[19]
A Miocene squirrel fromFrance andSpain,Freudenthalia, has been tentatively placed in Sciurini.[20]Plesiosciurus from the Miocene ofChina has been interpreted as a member of Sciurini, but is unlikely to belong to the tribe.[21]
