A thorough understanding of how communities respond to extreme changes, such as biotic invasions, is essential to manage ecosystems today. Here we constructed fossil food webs to identify changes in Late Ordovician (Katian) shallow marine paleocommunity structure and functioning before and after the Richmondian Invasion, a well-documented ancient invasion. Food webs were compared using descriptive metrics and Cascading Extinction on Graphs models. Richness at intermediate trophic levels was underrepresented when using only data from the...