There are several small tributaries to the Tennessee River named Coon Creek. One located near Savannah in western Tennessee, however, has eroded down into bedrock to reveal a treasure box of fossils from an ancient sea. The exposed rock is called the Coon Creek Formation and is Cretaceous in age, having been deposited in a shallow sea some 70 million years ago. At this time sea level was much higher than at present, with ocean waves lapping shores in the present areas near Memphis and Columbia, South Carolina. Part of the reason the sea level was so high is that the Cretaceous was extremely warm. So warm, in fact, that no glaciers existed anywhere on planet Earth. All that water formerly tied up in ice therefore ran into the oceans, raising their levels substantially all around the globe.
Cretaceous paleogeography showing sea level.
In west Tennessee the ocean teemed with life, including crabs and other invertebrates. The waters were also inhabited by large marine reptiles – the ocean-going counterparts to the dinosaurs which roamed the land at this time. In the sediments of the Coon Creek Formation the remains of one particular marine reptile, the mosasaur, has been found.
Mosasaur attacking shark. (source: nationalgeographic.com)
This reptile basically looked like a streamlined monitor lizard and some species reached over 40 ft in length. They were formidable predators that had to return to the surface every so often to gulp air. In rock shops around the world, their impressive slightly curved, peg-like teeth are immediately recognizable.
Mosasaur jaw with teeth. (source: fossilguy.com)
For millions of years they dominated these shallow coastal waters until, like their land-based relatives, they went extinct at the end of the Cretaceous about 65 million years ago.
As we drift by the tributary confluence we don’t have to worry about an attack from these long-vanished creatures. It is possible, however, that some of the very same molecules of water we pass through once brushed against the leathery skin of these reptiles in the ancient Cretaceous sea.
