The trophic pyramid, where many plants are consumed by a large number of herbivores, which are, in turn, eaten by a smaller number of carnivores, is the foundation for land-based ecosystems today. In fact, it is one of the earliest features of ecology that students learn in school. This structure, despite its ubiquity, has not always been in place. Three hundred million years ago, during the Permian Period, carnivores were the dominant dietary ecology and herbivores were exceptionally rare. At some point, likely during the Permian, a key shift occurred from the carnivore-dominated ecosystem to the herbivore-dominated environments observed today. The fossil record of Oklahoma, which includes the most diverse and best-preserved fossil vertebrate assemblage from the Paleozoic, offers an exceptional opportunity to explore this change. The goals of this project are to track the evolution of herbivory in different tetrapod clades and assess the patterns and processes that lead to it becoming the foundational dietary ecology of terrestrial environments today. This project will directly support Oklahoma graduate and undergraduate students through scientific and technical skills training, as well as broader institutions by utilizing understudied resources, such as the vertebrate faunal collections at the University of Central Oklahoma and the Sam Noble Museum, Oklahoma’s Museum of Natural History. The establishment of the modern terrestrial ecosystem structure represents a profound