The Grube Messel in Germany (middle Eocene) is a unique and spectacular locality for fossil bats. Messel bat specimens are remarkably abundant (>700 individuals known) and are typically represented by complete ornearly complete skeletons. The most common taxon by far of the four bat genera known from Messel isPalaeochiropteryx. This taxon is represented by the largest number of individuals and shows the most variability in
body size and proportions. Recently, many exceptionally small specimens of Palaeochiropteryx have been found, suggesting the existence of at least one more “hidden” species besides the two already known (P. tupaiodon and P. spiegeli). Variation in dental morphology is a useful taxonomic indicator, however, until now it was not possible to easily examine teeth with conventional methods or to differentiate the two known species based on teeth because,dentitions are often in occlusion or are hidden by the plate itself. We addressed this problem with the help of highresolution micro-CT technology. CT scanning allows visualization of not only whole tooth surfaces but also their internal structures, which can be helpful for determining cusp homologies. Based on CT scans of Messel specimens of Paleochiropteryx, we have developed differential diagnoses for three species of Palaeochiropteryx based on dental structures. Until now it has been assumed that seven bat species existed at Messel, each filling a specific
ecological role. The occurrence of an additional, small species of Palaeochiropteryx suggests that habitat utilization by Messel bats was more complex than previously thought.