DISCUSSION

A survey of the literature pertaining to the late Pleistocene small mammals of Kansas and adjoining states, including the excellent reviews of Stewart (1987), Wells and Stewart (1987a, 1987b) and Davis (1987), provides an interesting view of climatic change at the end of the Pleistocene in this region. Table 1 reinforces the conclusion from many other studies that late Pleistocene climate was considerably different from that of today, bringing extralimital modern rodent species, mostly of boreal affinities, into the central Great Plains. These records include ground squirrels, gophers, arvicolids and dipodids. The faunas represented in Table 1 range in age from about 31,000 to around 11,000 radiocarbon years B.P. The invasion of a group of species including the red-backed vole (Clethrionomys gapperi), yellow-cheeked vole (Microtus xanthognathus), boreal lemming (Synaptomys borealis) heather vole (Phenacomys intermedius), northern pocket gopher (Thomomys talpoides), motane vole (Microtus montanus) and the western jumping mouse (Zapus princeps) onto the Great Plains seems to have mostly occurred after the deposition of the Jones l.f. of Meade County, Kansas, dated at 27-29,000 years B.P. and also, at least in central Oklahoma, subsequent to the deposition of the Washita l.f. with radiocarbon dates ranging from 16-18,000 years B.P. (Kirkland et al. 2000). However, some of these boreal indicators were present in the Coon Creek l.f. of northern Kansas 18,000 years ago (Stewart 1987), and may simply not have reached central Oklahoma at this time. Twelve thousand five hundred years ago, the association of rodents at Golliher B in southwestern Kansas indicates that cold steppe conditions were likely present at this latitude. Assuming that M. parmaleei had environmental requirements similar to that of the modern diminutive subspecies M. o. minor, the "area of sympatry," or area where most of the rodents of the Golliher B l.f. all overlap today, is in southeastern North Dakota. The western harvest mouse, Reithrodontomys montanus, is restricted to the northern Great Plains, but does extend into southern North Dakota.

Patterns indicated from the mammals are generally substantiated by molluscan and pollen studies on the Great Plains covering the same time periods and, in the case of the Golliher B l.f., from the same outcrop. Miller (1975) compared the molluscs from a sequence of radiocarbon-dated sites in southwestern Kansas and northwestern Oklahoma, including our level A of the Golliher sequence. A radiocarbon date of 16,100 + 250 years B.P., about 4,000 years older than level B, was obtained for this unit. The molluscs from Level A were dominated by cold-adapted species with southern distributions controlled by high summer temperatures (42%, as compared with 7% in that category today). According to Miller (1975), there was a gradual decrease in these species and an increase in species of southern affinities through the late Pleistocene, with a particularly emphatic shift in the last 10,000 years. Both the Jones and Robert l.f.s also maintain a high percentage of northern mollusc species, testifying to the presence of cool summer temperatures through the latest Pleistocene.

Pollen profiles are unfortunately not available for the Golliher sequence, but published reviews of late Pleistocene palynology for the Great Plains and Missouri Ozarks (King 1973; Fredlund and Jaumann 1987) clearly demonstrate the presence of boreal conditions during "Woodfordian" time (~22,000-10,000 years B.P.). White spruce has been recovered from a peat dated at 19,340 + 200/210 years B.P. near Wichita, Kansas. Spruce and arboreal pollen dominate in the North Cove site in southern Nebraska (Table 1). Wells and Stewart (1987a) reported Rocky Mountain limber pine (Pinus flexilis) and spruce from sites in Graham (Coon Creek; see Table 1) and Logan Counties (unnamed; no small mammals-- 10,245 + 335 years B.P.), northwestern Kansas. Wells and Stewart (1987a, 1987b) also confirmed changes in the land snail fauna first observed by Miller (1975). As they note (p. 131):

"Perhaps the outstanding event of the North American molluscan history in the late Quaternary was the virtual disappearance of this [northern, "pleniglacial"] landsnail fauna from upland habitats of the Great Plains."

Further, on the same page, they observe:

"Aside from the deciduous-forest species, all of the landsnails that suffered extinction on the Plains survived in the Rocky Mountains..."

In their review of the history of cotton rats, genus Sigmodon, in the Meade Basin, Peláez-Campomanes and Martin (2005) noted that cotton rats were absent from the known Wisconsinan-age assemblages. As mentioned above, the extant hispid cotton rat, S. hispidus, was apparently a Holocene immigrant into the Basin, characterizing the current interstadial warm period. The small mammal fauna at Golliher B 12,510 Years B.P. (= 14,826 calendar years ago) is consistent with these reports and provides further documentation of the considerable changes in climate and habitat that have occurred in southwestern Kansas since the deglaciation phase of the latest Pleistocene.

In summary, rodent, mollusc and botanical assemblages from the Meade Basin of southwestern Kansas and adjoining regions document a period of extreme climatic conditions and associated habitat modification on the Central Great Plains near the close of the Pleistocene. Further collecting from among a series of latest Pleistocene sections in Meade County may help reveal the intricacies of environmental and climatic change at the Pleistocene-Holocene boundary, thus providing important background data for comparison with global climatic changes during modern time.