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Laramidia was an island continent that existed during theLate Cretaceous period (99.6–66Ma), when theWestern Interior Seaway split the continent ofNorth America in two. In theMesozoic era, Laramidia was an island land mass separated fromAppalachia to the east by the Western Interior Seaway. It was home to many dinosaurs includingankylosaurs,ceratopsians, andtyrannosaurs. The seaway eventually shrank, split across theDakotas, and retreated toward theGulf of Mexico and theHudson Bay. The masses joined, forming the continent of North America.
Laramidia is named after theLaramide orogeny. The name was coined by J. David Archibald in 1996.[1]
Laramidia stretched from modern-dayAlaska toMexico.[2] The area is rich in dinosaur fossils.Tyrannosaurs,dromaeosaurids,troodontids,hadrosaurs,ceratopsians (includingKosmoceratops andUtahceratops[3]),pachycephalosaurs, andtitanosaursauropods are some of the dinosaur groups that lived on this landmass. A strong latitudinal climatic gradient existed on the landmass in the final 15 million years of the Cretaceous, helping drive regional provincialism of dinosaur faunas.[4]
Vertebrate fossils have been found in the region from Alaska toCoahuila.[3][5][6][7]
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From theTuronian age of the Late Cretaceous to the very beginning of thePaleocene, 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 thewestern 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 thePleistocene ice age. However, fossil beds which haven't been discovered yet could exist in areas of the former Appalachian continent.
In western North America, during the Cretaceous, the dominant theropods were thetyrannosaurs, huge predatory dinosaurs with proportionately large heads built for tearing flesh from their prey. In Laramidia, there were the theropods ofTyrannosaurinae such asTyrannosaurus rex,Nanuqsaurus hoglundi,[8]Daspletosaurus,Teratophoneus, and theropods ofAlbertosaurinae such asAlbertosaurus andGorgosaurus, all being included under the same family ofTyrannosauridae, although not all are contemporary.
Another common group of North American dinosaurs were thehadrosaurs, the so-called "duck-billed" dinosaurs. The fossil record shows a staggering variety of hadrosaur forms in Laramidia.
Other differences in genera appear between the island land masses.Sauropods roamed Laramidia during the Cretaceous after apparently dying out in Appalachia.Nodosaurs, though, appear to have been more plentiful in Appalachia. Nodosaurs were large, herbivorousarmored dinosaurs which lacked the giant club tail of theirwestern relatives. They were scarce in Laramidia by the late Cretaceous, existing only in specialized forms likeEdmontonia andPanoplosaurus while nodosaurs were thriving in Appalachia.
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Media related toLaramidia at Wikimedia Commons
