Controlled excavations in the Pesciara and Monte Postale sites provide new insights about the palaeoecology and taphonomy of the fish assemblages of the Eocene Bolca Konservat-Lagerstätte, Italy

The Eocene Konservat-Lagerstätte of Bolca, Italy, is famous for the abundance and exquisite preservation of its fossils. Although the Bolca sites have provided one of the most studied ichthyofaunistic fossil assemblages of the world, several aspects about the community structure and the biostratinomic processes that led to the accumulation of its fish remains have been neglected or underestimated. In order to improve our knowledge concerning the palaeoecology and palaeoenvironment of Bolca, a quantitative palaeoecological and taphonomic analysis of the fish remains collected during controlled excavations at the Pesciara and Monte Postale sites is presented herein. The results of these analyses concur to suggest that these two sites have different speciose fish assemblages and different depositional contexts. The high-quality preservation of the fishes from the Pesciara site has allowed for the species level identification of most of its specimens, providing a good resolution of its palaeoecological spectrum. The Pesciara fish assemblage is defined by a sharp oligarchic structure clearly dominated by planktivorous taxa. The taphonomic features confirm that the sediments were deposited in an intraplatform basin in which anoxic conditions at the bottom and the development of the biofilm acted as promoters of high-quality fossil preservation. On the other hand, the moderate preservation quality of the fishes from Monte Postale does not allow for most of the specimens to be identified at the genus or species level, making it difficult to interpret the ecological and trophic relationships within this assemblage. Nevertheless, the abundance of marine and terrestrial plants, coupled with the large number of invertebrates (including abundant corals), concur to suggest that the sediments of Monte Postale were likely deposited close to an emerged coastal area characterized by mangroves, seagrass, and coral reefs. The prominent disgregation of fish skeletons, coupled with the unimodal dispersion of the elements and bioturbations, clearly indicate a high degree of disturbance in the Monte Postale palaeoenvironment, suggesting at least periodic aerobic conditions at the bottom.