This project advances NSF’s mission and national interests by increasing our understanding of ecosystem functioning, ensuring continued national prosperity as a society dependent upon healthy natural resources. The research addresses a problem with broad implications: reconstructing ancient ecosystem food webs. Food webs represent ecosystem energy flow and are important to ecosystem functioning and services for human societies. Human influence on ecosystems is expanding rapidly, but data on ecosystems’ responses to rapid or extreme impacts is limited. The fossil record contains many examples. Generally, paleontological reconstruction relies upon modern food web properties, but this correspondence breaks down after mass extinctions. Recovering ecosystems deviate significantly from expectations of how ecosystems function. This project will examine marine ecosystems spanning the Permian-Triassic mass extinction, 251 million years ago, when 80% of species became extinct. The project will reconstruct the ways in which ancient ecosystems adapted to extreme disturbances by using fossils collected in the field and deposited in museum collections combined with high performance computing analyses. The project will support and train numerous students and an early career scientist in analytical and museum curation skills. Reconstructing ancient ecosystems relies on models of interspecific interactions, operating under a uniformitarian assumption that the principles determining int