Late Pleistocene bats from Arkenstone Cave, Arizona

A small, late Quaternary deposit of degraded bat guano in Arkenstone Cave, Colossal Cave Mountain Park, Pima County, Arizona, yielded thousands of fossil bat bones. The bones primarily represent an attritional accumulation of dead bats beneath a maternity colony of Myotis thysanodes, a species that no longer roosts at the elevation of the cave. Rarer bones in the deposit represent a smaller species of Myotis and the extinct vampire Desmodus stocki. Due to leaching in the alkaline cave environment, the bones could not be dated by radiocarbon, but the fossils probably date to the late Pleistocene. Myotis thysanodes, a species that frequently forages in the desert but typically day-roosts at higher elevations in pygmy conifer woodland or higher vegetative zones, is consistent with the occurrence of conifer woodland at similar elevations in nearby mountain ranges in the late Pleistocene. This is the first record of D. stocki in what is now the Sonoran Desert and the second locality of occurrence for the species in Arizona.