QUANTIFYING THE DIGESTIVE FINGERPRINTS OF PREDATORS ON THE BONES OF THEIR PREY USING SCANNING ELECTRON MICROSCOPY

Paleoecological reconstruction relies on accurately determining the taphonomic origin of fossil deposits. Predation is a significant mode of small mammal bone accumulation. While assemblage-level bone breakage patterns can be used to identify predator taxa, this approach requires large sample sizes and thus cannot be used to infer if a single fossil specimen is predator-derived. Here we establish a quantitative approach to predator identification from individual specimens using Scanning Electron Microscopy (SEM). The digestive process creates distinctive micrometer-scale fissures in cortical bone due to dissolution by acidic gastric juices. Owls, diurnal raptors, and mammalian carnivores differ in the pH of their gastric juices as well as in the length of time prey remains are held in the digestive system before regurgitation or excretion. We tested the hypothesis that quantitative differences in the size, area, and density of digestive fissures reflects predator type due to these physiological and behavioral differences. Specifically, we collected mandibles from rodents digested by a suite of predators from local wildlife rehabilitation centers, and imaged ~5 mandibles per predator using an FEI Quanta 200 SEM. At 50 x 50 μm resolution, bones exposed to gastric juices showed clear digestive fissures, with owl-digested mandibles exhibiting a significantly higher density of microfissures than diurnal raptors and coyotes. The owl-derived fissures were also small in area and relatively short compared to diurnal raptor- and mammal-digested mandibles. We then performed a linear discriminant analysis and applied this classification scheme to owl-derived Holocene mouse fossils from Two Ledges Chamber (TLC), Nevada, and 27 million year old Aplodontid fossils of unknown taphonomic origin from the John Day Formation (JODA) in Oregon. As suspected, the TLC specimens display the digestive fingerprints of owls. The JODA specimens, however, do not appear to be clearly predator-derived. Quantification of microscopic digestive fissures thus offers a promising new approach for elucidating the taphonomic origin of individual small mammal fossil specimens.