The Western Interior Seaway was a large inland sea that existed from the early Late Cretaceous to earliest Paleocene, splitting the continent of North America into two landmasses, Laramidia to the wes
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The Western Interior Seaway was a large inland sea that existed from the early Late Cretaceous to earliest Paleocene, splitting the continent of North America into two landmasses, Laramidia to the west and Appalachia to the east. Tanis in North Dakota was the northern end of the seaway where the catastrophic events occurred.