Morphologically derived ground squirrels from the Borchers local fauna, Meade County, Kansas, with a redescription of ?Spermophilus cragini

ABSTRACT

We provide a description of the complete adult and upper deciduous cheek dentition of ?Spermophilus cragini, previously known only from M1–M3, from the transitional Blancan–Irvingtonian Borchers locality, Meade County, Kansas. We also present evidence for two additional morphologically derived ground squirrels in the fauna. All three forms are united with the clade including Cynomys and Spermophilus, indicating early diversity in this clade on the Great Plains, but placement within the clade is less certain. ?Spermophilus cragini, the best represented of the three, is more derived in several features than known species of the subgenus Spermophilus but lacks some derived features expected in Cynomys. This fossil species resembled Cynomys in size and, likely, in biology. The other derived morphs from Borchers may belong to undescribed taxa but are too poorly represented to allow formal recognition; one (morph B) exhibits a derived structure of m3. None of the adequately known morphs from Borchers appear to be appropriate ancestors for the subgenus Spermophilus–Cynomys clade or for any extant supraspecific group within it.