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 common mechanism by which skeletal remains become concentrated over time, leading to the formation of modern and fossil prey death assemblages. Skeletal element representation and breakage patterns within such death assemblages can be used to infer the identity of the responsible predator. However, assemblage-level metrics cannot be used to infer if a single fossil specimen is predator-derived. Microscopic digestive etching on individual bones can also indicate past predation events because acidic gastric fluids create distinctive micrometer-scale fissures in cortical bone. Here we establish a quantitative approach to predator identification from small mammal prey remains using microscopic digestive damage patterns. To do this, we collected mandibles from rodents digested by 13 predator species from local wildlife rehabilitation centers, and imaged them using an FEI Quanta 200 SEM. Results indicate that bones exposed to gastric fluids show clear digestive fissures, and that owl-digested specimens can be readily distinguished from specimens that were digested by diurnal raptors and mammalian carnivores. Specifically, owl-digested specimens are characterized by a high density of small and short digestive fissures. Within the owls, digestive fissure patterns appear to scale with owl body size. Finally, we used linear discriminant analysis to build a classification scheme from our modern data and applied it to Holocene mouse fossils from Two Ledges Chamber, Nevada. We found that the fossil specimens display the digestive fingerprints of owls. Quantification of microscopic digestive fissures thus offers a promising new approach for elucidating the taphonomic history of individual fossil specimens.