02/16/2026
Around 77 million years ago, during the Late Cretaceous period, North America looked very different from today.
The continent was split by a vast inland sea called the Western Interior Seaway, which stretched from the Gulf of Mexico to the Arctic Ocean, effectively dividing the landmass into Laramidia to the west and Appalachia to the east. The climate was warmer than today, with no polar ice caps, and sea levels were much higher.
The western landmass, Laramidia, featured mountain ranges forming along the edge of the seaway, along with lush forests, floodplains, and river systems. This region was home to a rich diversity of dinosaurs, including famous species like Tyrannosaurus, Triceratops, Edmontosaurus, and Ankylosaurus, as well as smaller theropods and early birds. The eastern landmass, Appalachia, is less well-known because fewer fossils have been preserved, but it also supported dinosaurs, crocodilians, turtles, and early mammals.
Marine life thrived in the seaway, including mosasaurs, plesiosaurs, giant sea turtles, ammonites, and early fish species. The flora consisted of conifers, cycads, ferns, and early flowering plants, supporting both terrestrial herbivores and insect populations.
