Triassic Period

Pterodactyl illustration by Heinrich Harder
Illustration of Pterodactylus by Heinrich Harder, circa 1916

252-208 Million Years Ago

By the end of the Triassic Period, Pangaea was breaking up. Perhaps because Illinois remained above sea level and suffered erosion, it preserves no Triassic rocks or fossils. Although we cannot determine the species that lived here, fossils in other parts of the world document the evolution of the first mammals and flying pterosaurs. Dinosaurs appeared during the late Triassic.