A new specimen of shark from the Monte Postale locality (Eocene, Bolca) and the rise of the Triakids in ancient ecosystems

This thesis focuses on the description of a fossil shark found in the Museo di Storia Naturale di Pavia during a complex restoration project started in 1989. The specimen represents one of the rarest shark taxa from the world–renown Eocene Bolca locality. Unlike the Ypresian taxa Galeorhinus cuvieri and Eogaleus bolcensis, the specimen partly disarticulated and lies in a limestone matrix, suggesting its provenience from the Monte Postale site. The dataset of measurements for body parameters, vertebral centra, teeth and placoid scales was compared to both fossil and extant taxa in order to discuss the overall systematic assessments of the Bolca sharks at higher taxonomic levels. Overall body measurements collected from all Bolca specimens were combine in order to estimate the size of the examined specimen. Statistical approach performed on body measurements and preserved vertebrae support a largely sharing of these characters among the extant taxa of the order Carcharhiniformes. SEM analysis on dermal denticle support that the Pavia specimen is an individual of Eogaleus bolcensis. A comprehensive dataset of teeth was used to compare dental morphologies of the living species Galeorhinus galeus and Galeocerdo cuvier, considered here as standards. The general clustering is primarily based on qualitative characters and ratios between selected measurements. The comparison between fossil and extant taxa based on newly defined tooth morphotypes increase our knowledge on taxonomic identifications of Bolca’s sharks. The morphometrical measurements for each fossil specimen indicates three distinct ontogenetic classes, further supported by estimated ages following standard Von Bertalanffy growth curves. As the present–day Galeocerdo, Eogaleus was most likely a mesopelagic, top predator. The combination of biological and abiotic proxies suggests the Bolca setting as a possible nursery area for the juvenile–schooling individuals of G. cuvieri.