Unravelling shark ecology across extinction events with novel isotope proxies

In the midst of the “sixths mass extinction event”, shark populations are declining with severe consequences for marine communities and ecosystem resilience. Diet is a key driver of shark evolution and a predictor of their extinction risk. Conservation efforts benefit from understanding past shark trophic ecology and how they coped with previous biotic crises. New analytical achievements in isotope proxy development allow the use of fossil teeth to reconstruct the trophic ecology of pre-Pleistocene animals. Using the novel Zn isotope proxy combined, for the first time, with other innovative trophic proxies (Ca and enameloid-bound N isotopes) on the same fossil and modern tooth samples, SHARKS will investigate the factor diet for a shark’s extinction risk, as well as food web changes across extinction events. Acknowledging the trophic position as an evolving trait, the project will pioneer a temporal approach, tracking trophic ecology of shark species through time. We will combine enameloid Zn, Ca and N isotopes with conventional dietary proxies (collagen C and N isotopes) in modern marine food webs to create a template for palaeoecological applications. Using this novel multi-proxy approach, we will investigate whether the emergence of serrated teeth in the Carcharodon lineage provided an ecological advantage for the modern great white shark (C. carcharias) over its now extinct ancestor with unserrated teeth C. hastalis. We will also test, from an ontogenetic perspective, the hypothesis of dietary competition between C. carcharias and the giant Otodus megalodon as potential factor of the latter’s extinction. Finally, we will explore the impact of the Cretaceous–Paleogene extinction event (66 Ma) on the trophic ecology of sharks and food web dynamics providing a hitherto unachievable view on one of the most devastating faunal turnovers in Earth’s history. The results will provide so far unattainable insights for conservation palaeobiology, ecology and palaeontology.