Geology of Ohio terrestrial environment since the Permian. For instance, the main subdivisions of the Pennsylvanian: the Pottsville Group, Alleghany Group, Conemaugh Group and Monongahela Group, along with the Early Permian Dunkard Group, are each more terrestrial than the last. The region was situated inland, experiencing terrestrial erosion as the Proto-North American continent of Laurasia collided with Gondwana to form the supercontinent Pangaea. Rocks from the end of Paleozoic are best exposed in road cuts along I-77, between Canton and Marietta, I-77 from Cambridge to Bridgeport and cliffs on the Ohio River north of Marietta to East Liverpool. For 245 million years, spanning
Phanerozoic of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic-Cretaceous extinction. Sea levels rose, destroying fern prairies and creating shallows. Ichthyosaurs became extinct whereas sauropods, as a whole, did not; in fact, some species, like "Titanosaurus", lived until the K-T extinction. The increase in sea-levels opened up the Atlantic sea way which would continue to get larger over time. The divided world would give opportunity for the diversification of new dinosaurs. The Cretaceous is the longest period in the Mesozoic, spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous,