The Lost Continent of Laramidia

Tuesday, February 13, 2018

North America, 76 million years ago

In this article, we discuss the nature of North America in the Late Cretaceous Period. Between 100 and 70 million years ago, the entire continent was divided by a shallow sea. This sea was once filled with colossal marine lizards, long-necked plesiosaurs, toothed birds, and the occasional diving Pteranodon. The sea divided the land into two smaller continents: Appalachia in the east and Laramidia in the west. As residents of the eastern United States, we are saddened by the meager dinosaur fossils (so far) discovered in the east. However, the vast and exposed formations in the west tell an amazing story.

Fossil-bearing formations dot the landscape of Laramidia, from the North Slope of Alaska down into Mexico. Each formation exhibits a similar ecosystem to the other: there are always tyrannosaurs, horned dinosaurs (ceratopsians), duck-billed dinosaurs (hadrosaurs), and raptors (dromaeosaurs) among other creatures. However, there are always different species belonging to each group. Even formations of the same age, or nearly the same age, differ in their species when they occupy different latitudes on the continent. This suggests that there were multiple “mini-ecosystems” throughout Laramidia some seventy-five million years ago.

Around seventy million years ago, as continents shifted and climates grew colder, the sea began to dry up. This linked the mini-continents of Laramidia and Appalachia once again and opened vast new regions for land animals to inhabit. The fossils of this age suggest that the divided mini-ecosystems began to blend together. It was into this great new world that Tyrannosaurus rex appeared on the scene, occupying the role of top predator until the extinction of the dinosaurs sixty-five million years ago.

The divided continent of North America. Note that the column on the left displays only a small number of the dinosaurs in each ecosystems. Also note that the Kirtland Formation is slightly younger than the others displayed.