Sciurus niger, the eastern fox squirrel, is the largest tree squirrel in North America. Squirrels are interesting in that their skulls are highly conserved, having changed little since the oldest-known squirrel (Protosciurus) appeared in the late Oligocene. This can be easily seen by comparing Sciurus to Cynomys ludovicianus, the black-tailed prairie dog, Spermophilus columbianus, the Columbian ground squirrel, and S. variegatus, the rock squirrel. For this reason, one could call squirrels 'living fossils'.
To date, the lack of significant variation between squirrel species has frustrated efforts to discover their phylogenetic relationships. However, allozyme studies suggest that Sciurus is most closely related to Microsciurus, the neotropical dwarf squirrels, and together they form a clade that is the sister taxon to Tamiasciurus, the red squirrels. CT scanning offers the opportunity to easily acquire information on the internal anatomy of squirrel skulls, and to apply morphometric tools to their study. It is hoped that this will contribute to the eventual resolution of the squirrel family tree.
This specimen was collected in Wadesboro, Anson County, North Carolina, by J. D. Billingsley on December 29, 1955. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Donald Swiderski of the University of Michigan Museum of Zoology. Funding for scanning was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.
Literature
Black, C. C. 1963. A review of the North American Tertiary Sciuridae. Bulletin of the Museum of Comparative Zoology 130:109-248.
Emry, R. J., and R. W. Thorington, Jr. 1982. Descriptive and comparative osteology of the oldest fossil squirrel, Protosciurus (Rodentia: Sciuridae). Smithsonian Contributions to Paleobiology 47:1-35.
Emry, R. J., and R. W. Thorington, Jr. 1984. The tree squirrel Sciurus (Sciuridae, Rodentia) as a living fossil; pp. 23-31 in N. Eldredge and S. M. Stanley (eds.), Living Fossils. Springer-Verlag, New York.
Hafner, M. S., L. J. Barkley, and J. M. Chupasko. 1994. Evolutionary genetics of New World tree squirrels (tribe Sciurini). Journal of Mammalogy 75:102-109.
Koprowski, J. L. 1994. Sciurus niger. Mammalian Species 479:1-9.
Roth, V. L. 1996. Cranial integration in the Sciuridae. American Zoologist 36:14-23.
Links
Mammalian Species account of Sciurus niger (American Society of Mammalogists)
The brain of Sciurus carolinensis (Comparative Mammalian Brain Collections website)
Sciurus niger on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Sciurus niger on The Mammals of Texas Online Edition
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