Late Pliocene and early Pleistocene rodents from the northern Borchers Badlands (Meade County, Kansas), with comments on the Blancan-Irvingtonian boundary in the Meade Basin

Abstract

New fossiliferous localities in the Borchers Badlands of southwestern Kansas add to our knowledge of rodent community change across the Plio-Pleistocene and Blancan-Irvingtonian boundaries. We report fossil rodents from ten local faunas in the Badlands that range stratigraphically from beneath the Huckleberry Ridge ash (2.10 Ma [million years ago]) to a level just beneath the Cerro Toledo B ash (1.23–1.47 Ma). The late Blancan Borchers local fauna (l.f.), includes the Meade Basin highest stratigraphic datum (HSD) for the following taxa that characterize or are found in earlier Blancan faunas:Alilepus, Geomys quinni, Sigmodon minor, andGeochelone. Borchers currently also has the HSDs forReithrodontomys pratincolaandOndatra zibethicus lidahoensis, but the prior temporal distribution of these taxa in the Meade Basin is unknown. The stratigraphically lowest Pleistocene (Irvingtonian) l.f. in the Badlands, Nash 72, includes the lowest stratigraphic datum (LSD) forCynomys, Reithrodontomys moorei, Microtus, andMictomys kansasensis, all of which are found above Nash 72 and beneath the Cerro Toledo B ash.Prodipodomysis last seen at Nash 72, andSigmodon curtisiis first encountered at Short Haul, a locality slightly younger than Nash 72. A preliminary hypothesis of age based on stratigraphic position places the Nash 72 l.f. at about 1.80 Ma, suggesting that this fauna and the genusMicrotusmay characterize both the Plio-Pleistocene and Blancan-Irvingtonian boundaries in the Borchers Badlands.