Laramidia Emerges as Island Continent

During the Late Cretaceous, the Western Interior Seaway split North America into two landmasses. The western portion, Laramidia, stretched from modern-day Alaska to Mexico. Formed by subsidence driven by the Farallon oceanic plate subducting beneath the North American Plate, this isolation persisted for roughly 34 million years. The seaway acted as a biological barrier, restricting east-west terrestrial dispersal and fostering distinct dinosaur provinces with latitudinal climatic gradients that promoted regional endemism among tyrannosaurs, ceratopsians, and ankylosaurs.