Date of this Version
There is an abundance of the fossilized remains of the genus Spermophilus in the "Citellus Zone" of the Late Quarternary of the Central Great Plains and adjacent regions. Many of these fossils have been identified as belonging to the S. richardsonii complex, and appear to differ morphologically from their Recent descendants. The forms from the "Citellus Zone" appear to date back at least 28,000 years before present and may represent a new species. Among the specimens studied is a single complete skeleton including the baculum. The baculum seems typical of members of the complex. A close comparison of the baculum of the fossil specimen with the bacula of the Recent S. r. elegans and S. r. richardsonii suggest that the Recent forms are somewhat derived from the more primitive fossil form.