Fluctuation of body mass in cotton rats and pocket gophers during the late Cenozoic in the Meade basin of Kansas: possible influence of the Huckleberry Ridge Ash-fall

Abstract

Equations estimating body mass were used to depict a near 5-million-year history of size change in pocket gophers and cotton rats from the Meade Basin of southwestern Kansas. Although phyletic size decrease was noted in Sigmodon minor and Geomys minor and size increase in Geomys quinni, no long-term intra-basin size trends were observed. Immediately following the Huckleberry Ridge ash-fall at 2.11 Ma, the small Pliocene cotton rat S. minor became extinct, a large cotton rat entered the basin, two gophers became extinct, and two new ones entered the basin. Assuming the same rodent contingent at the Short Haul locality as at the Aries A site, between deposition of the Borchers and Short Haul assemblages, minimally about 0.12 million years, 40% of the Meade Basin rodent fauna turned over and Microtus dispersed into North America across Beringia. Geochemical environmental proxy data did not identify significant climatic events in the Borchers Badlands Pleistocene sequence; consequently it is possible that a super-eruption from the Yellowstone caldera was at least partly responsible for size shifts in cotton rats and pocket gophers and significant modifications to the Meade Basin rodent community.