Taphonomy of ground squirrel remains in a Late Pleistocene ichnofabric, Nebraska, USA

The burrows and skeletal remains of Late Pleistocene ground squirrels are present within the “Citellus zone”, a bioturbated interval that includes the base of the Gilman Canyon Formation and the top of the Loveland Formation of the central Great Plains, USA. To determine the spatial relationship of the ground squirrel remains to the “Citellus zone” ichnofabric, the author screen-washed 0.67 tonne of sediment sampled from burrow fill and from adjacent sediment matrix at 104 outcrops in 10 major canyons in the study area. Within the upper, pedogenically altered, portion of the zone, 14% of the remains are in burrow fill and 86% are in adjacent matrix. All of the remains in the lower portion of the zone are in burrow fill. All of the weathered remains are found in the pedogenically altered upper portion of the zone. Published behavioral observations of Spermophilus richardsonii explain this phenomenon. Upon emergence from hibernation, the animals eject skeletal remains from burrows. The bones are left on the surface in the vicinity of burrow entrances to be incorporated into the soil. Morphometric analysis of their postcranial remains confirms the conclusion of an earlier study of cranial remains that the S. richardsonii represented in the “Citellus zone” were intermediate between two modern subspecies. This relationship is consistent with phylogenetic conclusions of genetic studies.