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Ichnology of the late Pleistocene "Citellus zone" ichnofabric, the taphonomy of its ground squirrel remains and the paleoclimate during its development

Robert J Tobin, University of Nebraska - Lincoln


The "Citellus zone" is a regionally extensive ichnofabric with abundant burrows and remains of ground squirrels, gophers, prairie dogs, voles, mice and ferrets. "Citellus zone" bioturbation exists over the entire 1,700 km 2 study area in south-central Nebraska and was synchronous with mid-Wisconsinan Gilman Canyon loess deposition, because burrow abundances are constant throughout its thickness. In the lower part of the zone, decline in burrow abundance with increasing depth in the Loveland Formation suggests that it predates burrowing. Thomomys (Northern Pocket Gopher)-sized geomyid (gopher) trace fossils are less common with increasing depth, showing the transition from fodinichnia (feeding traces) to domichnia (living tunnel traces), as Spermophilus richardsonii (Richardson's Ground Squirrel)-sized spermophiline and prairie dog domichnia become more common. To determine the spatial relationship of the ground squirrel remains to the "Citellus zone" ichnofabric, sediment was screen-washed from burrow fill and adjacent matrix. Within the upper portion of the zone, most remains are in matrix. All of the remains in the lower portion of the zone are in burrow fill. All weathered remains are in the upper portion of the zone. Published behavioral observations of Spermophilus richardsonii explain this. Upon emergence from hibernation, the animals eject skeletal remains from burrows, leaving the bones on the surface to be incorporated into the soil. The area of maximum sympatry (based upon eight of the nine extant species) of the "Citellus zone" local fauna is a small portion of eastern Colorado. The paleoecology suggested is the short grass prairie ecosystem and an arid paleoclimate. ^

Subject Area


Recommended Citation

Tobin, Robert J, "Ichnology of the late Pleistocene "Citellus zone" ichnofabric, the taphonomy of its ground squirrel remains and the paleoclimate during its development" (2005). ETD collection for University of Nebraska - Lincoln. AAI3201783.