2 Taxonomic Introductionring in the Eocene and identifi ed as “fl ying” squirrels are as
old as any fossils identifi ed as tree squirrels.
How to subdivide the family Sciuridae into subfamilies
was not at all clear until the 1920s, when Reginald Pocock,
of the London Zoo, conducted a study of the bacula (the
penis bones) of squirrels, which are quite diff erent among
the various subfamilies. Based on this work, he recognized
six subfamilies, in addition to the fl ying squirrels, thus dem-
onstrating signifi cant diff erences among the tree squirrels
of Southeast Asia, those of the Americas and northern Eur-
asia, and those of Africa. However, it was unclear how these
subfamilies were related to one another.
Pocock’s conclusions served as the basis of squirrel clas-
sifi cations until 2003, when molecular studies based on the
DNA of several genes supported a classifi cation of fi ve sub-
families, modifying the Pocock arrangement in some inter-
esting ways. Our classifi cation in this book is based on the
DNA evidence. Two of the subfamilies appear to be the most
ancient lineages within the Sciuridae: the Ratufi nae, which
includes the giant tree squirrels of southern Asia (four spe-Table 1.
Classifi cation of the Sciuridae (58 genera, 285 species), based on Thorington and Hoff mann (2005), Helgen et al. (2009)
family Sciuridae Fischer de Waldheim, 1817subfamily Ratufi nae Moore, 1959 (1 genus, 4 species)
Ratufa Gray, 1867 (4)
subfamily Sciurillinae Moore, 1959 (1 genus, 1 species)
Sciurillus Thomas, 1914 (1)
subfamily Sciurinae Fischer de Waldheim, 1817 (20 genera, 81 species)
tribe Sciurini Fischer de Waldheim, 1817 (5 genera, 37 species)
Microsciurus J. A. Allen, 1895 (4)
Rheithrosciurus Gray, 1867 (1)
Sciurus Linnaeus, 1758 (28)
Syntheosciurus Bangs, 1902 (1)
Tamiasciurus Trouessart, 1880 (3)
tribe Pteromyini Brandt, 1855 (15 genera, 44 species)
Aeretes G. M. Allen, 1940 (1)
Aeromys Robinson and Kloss, 1915 (2)
Belomys Thomas, 1908 (1)
Biswamoyopterus Saha, 1981 (1)
Eoglaucomys A. H. Howell, 1915 (1)
Eupetaurus Thomas, 1888 (1)
Glaucomys Thomas, 1908 (2)
Hylopetes Thomas, 1908 (9)
Iomys Thomas, 1908 (2)
Petaurillus Thomas, 1908 (3)
Petaurista Link, 1795 (9)
Petinomys Thomas, 1908 (8)
Pteromys G. Cuvier, 1800 (2)
Pteromyscus Thomas, 1908 (1)
Trogopterus Heude, 1898 (1)
subfamily Callosciurinae Pocock, 1923 (14 genera, 67 species)
Callosciurus Gray, 1867 (14)
Dremomys Heude, 1898 (6)
Exilisciurus Moore, 1958 (3)
Funambulus Lesson, 1835 (5)
Glyphotes Thomas, 1898 (1)
Hyosciurus Archbold and Tate, 1935 (2)Lariscus Thomas and Wroughton, 1909 (4)
Menetes Thomas, 1908 (1)
Nannosciurus Trouessart, 1880 (1)
Prosciurillus Ellerman, 1947 (7)
Rhinosciurus Blyth, 1856 (1)
Rubrisciurus Ellerman, 1954 (1)
Sundasciurus Moore, 1958 (17)
Tamiops J. A. Allen, 1906 (4)
subfamily Xerinae Osborn, 1910 (22 genera, 132 species)
tribe Xerini Osborn, 1910 (3 genera, 6 species)
Atlantoxerus Forsyth Major, 1893 (1)
Spermophilopsis Blasius, 1884 (1)
Xerus Hemprich and Ehrenberg, 1833 (4)
tribe Protoxerini Moore, 1959 (6 genera, 31 species)
Epixerus Thomas, 1909 (1)
Funisciurus Trouessart, 1880 (10)
Heliosciurus Trouessart, 1880 (6)
Myosciurus Thomas, 1909 (1)
Paraxerus Forsyth Major, 1893 (11)
Protoxerus Forsyth Major, 1893 (2)
tribe Marmotini Pocock, 1923 (13 genera, 95 species)
Ammospermophilus Merriam, 1892 (5)
Callospermophilus Merriam, 1897 (3)
Cynomys Rafi nesque, 1817 (5)
Ictidomys J. A. Allen, 1877 (3)
Marmota Blumenbach, 1779 (15)
Notocitellus A. H. Howell, 1938 (2)
Otospermophilus Brandt, 1844 (3)
Poliocitellus A. H. Howell, 1938 (1)
Sciurotamias Miller, 1901 (2)
Spermophilus F. Cuvier, 1825 (15)
Tamias Illiger, 1811 (25)
Urocitellus Obolenskij, 1927 (12)
Xerospermophilus Merriam, 1892 (4)