Sciurini - Taxonomy

Taxonomy

The name "Sciurini" was first employed by Hermann Burmeister 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 squirrels): 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:

• Tribe Sciurini
  • Subtribe Sciurina
    • Genus Sciurus
    • Genus Guerlinguetus (currently included in Sciurus)
    • Genus Rheithrosciurus
  • Subtribe Microsciurina
    • Genus Microsciurus
    • Genus Syntheosciurus (including two species currently placed in Sciurus, S. granatensis and S. pyrrhinus)
  • 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:

• Tribe Sciurini
  • Freudenthalia (fossil, early Miocene of Europe; assignment to Sciurini "uncertain")
  • Rheithrosciurus
  • Plesiosciurus (fossil, middle Miocene of Asia)
  • Subtribe Sciurina
    • Douglassciurus (fossil, late Eocene of North America; McKenna and Bell used Douglassia, a preoccupied name replaced by Douglassciurus)
    • Protosciurus (fossil, early Oligocene 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 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 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. 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.