The microtine rodents from the Pit locality in Porcupine Cave, Park County, Colorado
Abstract
This report presents the results of an analysis of the microtine rodents from the Pit locality, one of four localities within Porcupine Cave that have a relatively long stratigraphic sequence. At 2900 m elevation. Porcupine Cave is the highest elevation site in North America to have produced a diverse microtine rodent assemblage. At least 11 species are distributed through 14 stratigraphic levels: Phenacomys gryci, Phenacomys sp., Mimomys (Cromeromys) cf. M. virginianus, Ondatra sp., Allophaiomys pUocaenicus, Terricola meadensis, Mictomys cf. M. meltoni, Microtus paroperarius, Microtus sp. (not M. paroperarius), Lemmiscus curtatus, and Lemmiscus sp. All but one of these {Phenacomys sp. not P. gryci) occur within a single stratigraphic level (level 4), making the assemblage of microtines unique in species composition and among the most diverse known from any fossil deposit. The diversity of the assemblage probably results from the location of the site within a topographically diverse ecotonal region that allowed sampling of a wide range of nearby microhabitats by the carnivores and raptors that initially collected the bones. The unique species assemblage is likely related to the high elevation of the site, which differentiates it physiographically from any other fossil deposit that has produced microtine rodents in abundant numbers, and perhaps because the Rocky Mountain backbone served as both a dispersal corridor and refugium as taxa adjusted biogeographic ranges in response to glacial-interglacial transitions and other climatic changes.
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