Determining Taphonomic Controls and Rates of Decay in Cave Environments Using Microcosms

Caves are important sites of fossil preservation. It is therefore critical to understand taphonomic processes operating in these environments. Since bat guano significantly impacts environmental chemistry and serves as the base of the food chain in cave ecosystems, its presence or absence should be a major control on preservation potential. This impact has not previously been experimentally examined. Microcosm experiments were used to determine the impact of guano presence and composition, moisture, temperature, and time on preservation potential of small mammal bones, leaves, and crickets. Guano came from insectivorous and frugivorous bats. DNA was extracted from the guanos to survey their microbial communities. Lab studies were supplemented with field experiments at Crumps Cave, Kentucky. The guano of insectivorous bats has an acidic pH, while the guano of frugivorous bats is close to neutral. Leaves and crickets preserved better in the guano of insectivorous bats, while bones showed recrystallization after burial. Leaves and crickets buried in the guano of frugivorous bats were quickly colonized by fungi and mostly destroyed, while only a few bones showed signs of fungi and degradation. Wet microcosms showed greater degradation, while time and temperature had less of an effect. Bones in either guano decayed much more rapidly than in sand. Bones buried in situ in cave sediments showed little degradation over three months. The oldest bats are Eocene and so bat guano should have influenced cave preservation only during the Cenozoic. This is a probable megabias of the cave fossil record.