CAREER: Toolkit, Innovation, and Natural History of Fossil Ichthyoliths and their Sedimentary History

About This Grant

Fish are the most diverse group of vertebrates on our planet and the main source of protein for a large portion of the world’s population. Therefore, understanding how fish respond to changing environmental conditions is essential to mitigating future human impacts on marine ecosystems. This research effort explores fish evolution and ecology by leveraging microfossil fish teeth and shark scales (together called ‘ichthyoliths’) found in deep-sea sediments to evaluate the ecological and evolutionary responses of fish to major transitions in Earth’s history. Ichthyoliths are the most numerically abundant marine vertebrate fossils, as each fish can produce dozens to hundreds of teeth, and a shark may produce tens to hundreds of thousands of scales in its lifetime, presenting the potential for high-fidelity studies of paired biological-environmental records to explore the impact that changing environmental conditions have on fish populations and biodiversity. However, ichthyoliths are extremely small – most are less than the width of a human hair – and are typically found separately from the animals that produced them, making these valuable fossils a challenge to work with. This research project will be the first to develop a robust, open-source, and freely available toolkit for ichthyolith studies, combining modern fish biology, machine learning, and high-resolution digital imaging, and then to use this toolkit to explore how fish and sharks responded to several major environmental perturbation events in Earth’s history. This framework will be a transformative tool, allowing for a wide range of research into fish and shark evolutionary and ecological dynamics far beyond the case studies of this research. Finally, this award supports a unique summer research program for undergraduate students to develop skills as researchers and science communicators, providing professional development and unique fully accessible research experiences, while also developing accessible education and outreach materials that will make these small, near-invisible microfossils accessible to a wide audience of K-12 students and the wider public. The highly robust ichthyolith microfossil record has the potential to unlock fish and shark evolutionary and ecological dynamics going back millions of years on an unprecedented scale. However, these microfossils are typically found in isolation from the animals that made them, making precise taxonomic identification a challenge. Further, their small size and large morphological diversity have been barriers to developing a robust morphological or taxonomic framework for the group, limiting their utility for evolutionary and paleoecological studies. This research will develop a robust taxonomic, ecological, and morphological framework for ichthyolith classification, by leveraging a machine-learning ensemble model-based approach to classify ichthyoliths using a repeatable morphological framework. This framework will be grounded in the modern with a catalog of extant fish species, allowing for taxonomic and ecological identification of different fossil tooth morphologies. Finally, the researchers will use this analytical toolkit to test hypotheses about fish abundance, biodiversity, paleoecology, and evolutionary trajectories across major climate events in Earth’s history including the Mid-Pliocene Warm Period, the Cretaceous-Paleogene Boundary, and the Early Eocene. The framework and toolkits developed through this work will be shared as an open-source, image and morphological database, R package, and online platform to support national and international collaboration on ichthyolith work, providing a common language, analytical toolkit, and structure to support widespread, diverse ichthyolith-based research going forward, unlocking the potential of ichthyoliths to better understand – and protect – the fish in our oceans. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.