Laramidia

Laramidia was an island continent that existed during the Late Cretaceous period (99.6–66 Ma), when the Western Interior Seaway split the continent of North America in two. In the Mesozoic era, Laramidia was an island land mass separated from Appalachia to the east by the Western Interior Seaway. The seaway eventually shrank, split across the Dakotas, and retreated towards the Gulf of Mexico and the Hudson Bay. The masses joined to unite the North American continent.

The name was coined by J. David Archibald in 1996.

Laramidia stretches from modern-day Alaska to Mexico. The area is rich in dinosaur fossils. Tyrannosaurs, dromaeosaurids, troodontids, hadrosaurs, ceratopsians (including Kosmoceratops and Utahceratops), pachycephalosaurs, and titanosaur sauropods are some of the dinosaur groups that lived on this landmass.

Vertebrate fossils have been found in the region from Alaska to Coahuila.

From the Turonian age of the Late Cretaceous to the very beginning of the Paleocene, Laramidia was separated from Appalachia to the east. As a result, the fauna evolved differently on each land mass over that time. Geological conditions were generally favorable for the preservation of fossils in Laramidia, making the western United States one of the most productive fossil regions in the world. Less is known about Appalachian biodiversity in the Cretaceous as few fossiliferous deposits exist in the region today and half of the fossil beds in Appalachia were destroyed during the . However, fossil beds which haven't been discovered yet could exist in areas of the former Appalachian continent.

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