Beyond fish: a comprehensive, multi-proxy palaeoenvironmental analysis of a diverse Eocene ecosystem from Florești, Transylvanian Basin, Romania

This study provides the first fully integrated, multi-proxy reconstruction of an Eocene marine ecosystem from the Transylvanian Basin (Florești site, Romania) combining vertebrate trophic structure with invertebrate assemblages and plankton-based palaeoenvironmental signals. Linking shifts in primary productivity and water-column conditions to changes in faunal composition and feeding strategies allows rare insight into ecosystem functioning in a marginal Paratethyan setting during a time of climatic and oceanographical change. The calcareous nannoplankton assemblage indicates a shift in the palaeoenvironment from meso-oligotrophic, cooler surface waters as documented in the lower part of the section, to eutrophic, warmer conditions in the upper part, while foraminifera confirm an oligotrophic seafloor environment with episodic nutrient intakes. The site’s diverse marine fauna supported a complex food web with multiple trophic levels. Piscivore and generalist sharks dominated the food web while the middle and lower ranks were dominated by fish with more complex diets. The ecosystem fostered various feeding strategies, including durophagy, planktivory, and piscivory, and exhibited environmental complexity with a diverse fauna of malacostracans, echinoids, bivalves, gastropods and ostracods. This research substantially expands the Romanian fossil record by reporting numerous first occurrences, including several fish species (e.g. Squatina prima, Pseudabdounia spp., Galeocerdo clarkensis, Archaeomanta hermani), and key invertebrate groups such as Stomatopoda and Leucosioidea. The Florești assemblage thus represents a key reference point for understanding Eocene marine biodiversity, trophic dynamics, and palaeoenvironmental gradients in Central and Eastern Europe.