Pleistocene (Irvingtonian, Cudahyan) vertebrates from the Texas Panhandle, and their geographic and paleoecologic significance

Abstract

The Cudahy “Fauna” was named by C.W. Hibbard for a fossil assemblage recovered from silty clays beneath the “Pearlette” volcanic ash at the type Cudahy ash pit and other sites in Meade County, Kansas. The “Pearlette” ash comprises several variously dated Yellowstone ashes. The Cudahy (=Lava Creek B) ash is most recently dated at 0.639 ± 0.002 Ma and is an important geochronologic marker in the Great Plains. The term Cudahy Ash Pit local fauna is now used for that of the type locality, although other Cudahy-type (Cudahyan) local faunas have been described. From 1968 to 1971, 30 tons of silty clay and diatomite were collected from below outcrops of Lava Creek B ash at elevations of 988–1058 m (3240–3470 ft) in the High Plains of the Texas Panhandle. Screenwashing yielded about 30 mammal taxa and numerous small amphibians, reptiles, birds, and mollusks. Four local faunas (Woody Draw, Bull Draw, Deadman's Creek, and Mayfield Ranch) are recognized. These faunas, dominated by shrews and microtine (arvicoline) rodents, are compositionally similar to each other and to the Cudahy and Sunbrite ash pit local faunas of Meade County even though the Panhandle sites are 300–340 km (186–211 miles) southwest of the Kansas sites and are 213–280 m (700–920 ft) higher in elevation. The Panhandle faunas contain two new species of Sorex as well as Sorex cf. cinereus, Sorex cudahyensis, Sorex lacustris, Sorex ( Microsorex) pratensis, Sorex megapalustris, Blarina, Cynomys, Spermophilus, Geomys tobinensis, Thomomys cf. talpoides, Peromyscus cragini, Reithrodontomys moorei, Ondatra annectens, Mictomys meltoni, Microtus llanensis (rare), Microtus paroperarius, and Microtus meadensis. The large sample size of the latter two taxa permits statistical comparisons of teeth with those from Kansas. The Texas faunas further substantiate the Cudahyan as a subage of the Irvingtonian between the older Sappan and younger Sheridanian subages and equivalent to Irvingtonian II based on microtine (arvicoline) rodents. Local habitats consisted of ponds or playas with marshy areas suitable for shrews, muskrats, and bog lemmings. Moist grassy meadows nearby would have been inhabited by voles, mice, and some of the shrews; the less abundant gophers, ground squirrels, and prairie dog would have preferred drier, grassy uplands with well-drained soils. Several mammals (e.g. bog lemming) show affinities with extant boreal species that range through Canada and the northern United States The collective evidence suggests that the Texas Panhandle enjoyed cooler summers with more effective rainfall during Cudahy time.