After death, bone is exposed to various abiotic and biotic processes. Microbial bioerosion has been reported from recent, archaeological and palaeontological bones and is deemed to have been caused by fungi, cyanobacteria or bacteria. It is recognizable as microscopic tunnelling, caused by microbial enzymes. However, fossil (i.e., fully permineralized) bone exhibits strikingly few signs of bioerosion. Fossilization only happens if bone is preserved long enough to allow diagenesis by mineral uptake and loss of collagen.Upper Jurassic sauropod dinosaur long and girdle bones from Kenton quarries 1, 5, and 6 (Oklahoma, Morrison Formation) present abundant and distinctive filamentous microstructures. This kind of preservation is absent in hundreds of other Morrison Formation dinosaur bone samples studied.Methods used to evaluate the nature of microstructures include literature research (comprehensive review of palaeontological and archaeological literature) and thin section analysis. Polarized light microscopy was used to describe the general bone histology, ontogeny, and density and distribution of bioerosive microstructures. The aim of this work is to identify bioerosive microstructures and to elucidate possible causative agents, bioerosive mechanisms and invasion patterns. The conclusion is that the filamentous microstructure are most likely Wedl tunnels caused by fungal attack. Presence of tunnelling seems to be unrelated to the specific quarry, ontogenetic stage, taxon, and bone type.Further research on the taphonomic and depositional environments of the Kenton quarries are needed to identify the cause of these unique microstructures. Heavily bioeroded bone and its rarity allows to constrain hypotheses regarding bone fossilization.