The Western Interior Seaway, which existed roughly 80 million years ago, split North America into North and South. It was a warm, shallow sea teeming with life from the Arctic Ocean to the Gulf of Mexico. Fish, squid, and marine reptiles—the lizards that hunted them—inhabited this bountiful marine desert. Some of these predators included large-bodied, or sometimes giant-sized, mosasaurs. These semi-aquatic reptiles re-evolved to live in the ocean, along with long-necked polycotylids. To date, how did so many large predators exist and thrive in the same aquatic space without exhausting their food supply? This has been the focus of an international research collaboration, yet only now is there a comprehensive biomechanical answer based on recent 3D scanning, engineering simulation, and experimentation. The results provide clear evidence of the biomechanical differences between mosasaurs and polycotylids. These distinct physiological configurations represent distinct ecologies and prey types rather than direct competitors. Bite performance of North American mosasaurs and plesiosaurs, showing the bite performance as optimal (bright colors) or suboptimal (darker colors). (CREDIT: Université de Liège / F.Della Giustina) …