Western Interior Seaway

Because the Earth has seen saw warmer global temperatures than today, at different points in the planet’s history, much of North America was under water. The sea levels during the Mesozoic were so high, in fact, that a shallow sea split North America in half. Therefore, many fossils found in landlocked states like Tennessee are marine including mosasaurs, plesiosaurs, ammonites, and sea turtles. Elsewhere, in the same rock layer fossils of dinosaurs and other land animals are found. The Coon Creek Formation in West Tennessee is full of marine reptile and invertebrate fossils.

AllisonBarbato, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

The Western Interior Seaway changed shape with rising and lowering global temperatures. With the highest sea levels, nearly all but the Appalachian and Rocky Mountain Ranges were submerged.

A World Under Water

The Mesozoic was not the first time land was covered by shallow seas. Throughout our planet’s long history, sea levels have risen and fallen many times. For example, during the Ordovician period, what would become Tennessee was completely submerged under a shallow sea. This is why you can find marine fossils like crinoids, brachiopods, trilobites, and nautiloids in Middle Tennessee.