Spermophile Ground Squirrels—Spermophile Ground Squirrels // Callospermophilus lateralis—Golden-mantled Ground Squirrel // Ictidomys/Xerospermophilus)—Ictidomys or Xerospermophilus Ground Squirrel // Ictidomys tridecemlineatus—Thirteen-lined Ground Squirrel // Otospermophilus bensoni—Benson Rock Squirrel // Otospermophilus variegatus—Rock Squirrel // "Spermophilus" cochisei—Cochise Ground Squirrel // Urocitellus elegans—Wyoming Ground Squirrel // Xerospermophilus spilosoma—Spotted Ground Squirrel
Since the naming of the genus Spermophilus by Cuvier in 1825, members of the genus have been split and lumped taxonomically in various ways, with Spermophilus recognized in recent years as consisting of a number of subgenera. In a far-reaching study including both molecular and morphological data, Helgen et al. (2009) have split the genus into eight genera. The restricted genus Spermophilus is limited to Eurasia. Anticipating that this taxonomy will be widely accepted, the system is adopted here. The changes are not without problems for fossil material, however. This is especially problematic in regards to taxa formerly relegated to the subgenus Ictidomys, specifically, S. spilosoma and S. tridecemlineatus. The former species has been transferred to a different genus from the latter, but identifications to subgeneric levels generally have been on the basis of dental characters shared by both.
In our region, fossils of species formerly recognized as belonging to Spermophilus include Callospermophilus lateralis (Golden-mantled Ground Squirrel), Ictidomys tridecemlineatus (Thirteen-lined Ground Squirrel), Otospermophilus variegatus (Rock Squirrel), Xerospermophilus spilosoma (Spotted Ground Squirrel), and Urocitellus elegans (Wyoming Ground Squirrel). Ictidomys mexicanus (Mexican Ground Squirrel) currently occurs in our region but has not been recognized in our fossil record.
Synonyms. Most literature after about 1950 until the recent publication of Helgen et al. (2009) uses Spermophilus for all of the genera noted above.
Ground squirrels are widespread in both the New World and the Old. They are mostly inhabitants of grasslands or shrublands. Being active during the daylight hours places a premium on being able to spot predators in time to take cover. Activity usually is close to a burrow opening that is a haven from most predators except snakes and certain members of the weasel family (various weasels of appropriate size that are able to enter the burrow and the American Badger that is expert at digging out burrows).
Tamias (chipmunks) and Ammospermophilus (antelope squirrels) have many similarities with the ground squirrels. Dental characteristics generally will separate Tamias (see Sciuridae and Tamias accounts). To repeat from the Ammospermophilus account, the masseteric tubercle is directly below a narrowly oval infraorbital foramen, whereas in taxa formerly assigned to Spermophilus, the masseteric tubercle is medium to large and ventral to slightly lateral to an oval or subtriangular infraorbital foramen (Hall 1981). Other differences are more subtle and most identifications depend on direct comparison with modern specimens.
Literature. Hall 1981; Helgen et al. 2009.
With a number of species possible, including those with considerable overlap in size, many elements that can be identified as a ground squirrel cannot be identified to a lower taxonomic level. Most were identified originally as members of the genus Spermophilus; with the split-up of that genus into several genera, it becomes problematical as to which of the present genera are involved.
Pleistocene: Perico Creek (Morgan and Lucas 2005).
Latest Blancan: La Union (Morgan and Lucas 2003).
Irvingtonian: El Golfo (Croxen et al. 2007).
Rancholabrean:) Tramperos Creek (Morgan and Lucas 2005).
Wisconsin: CC:5:5 (Mead et al. 2003).
Mid/Late Wisconsin: Rampart Cave (Lindsay and Tessman 1974).
Late Wisconsin: Folsom Site (Morgan and Lucas 2005).
Late Wisconsin/Holocene: Conkling Cavern (Conkling 1932); Isleta Cave No. 2 (?) (UTEP).
Literature. Conkling 1932; Croxen et al. 2007; Lindsay and Tessman 1974; Mead et al. 2003; Morgan and Lucas 2003, 2005.
There is insufficient information to allow placement within one of the currently recognized North American genera.
Late Blancan: Curtis Ranch (Lindsay 1984); Prospect (Johnson et al. 1975).
Literature. Lindsay 1984; Johnson et al. 1975.
Last Update: 21 Oct 2013