[1][2] Geologists employ biostratigraphy, the use of index fossils, for dating sedimentary rock units like the Coon Creek.

Index fossils are species of plants or animals that existed over a wide area for a geologically short period of time .

[3] The cephalopod Jeletzkytes nodosus is a time-sensitive fossil found in rocks a little younger than 70.6 million years old in the western United States.

When the continent moved west past the hotspot, the cooled land minus the eroded 2 kilometers created a deep trough.

The embayment gradually filled with sand, clay, and gravel brought in by rivers on uplands to the north, east, and west .

[3] A couple of miles to the east lay a marshy lowland bordering the limestone bluffs of the Western Highland Rim of the Nashville Basin, home to duckbill and theropod dinosaurs.

Sluggish rivers annually washed tons of driftwood, along with the occasional dinosaur carcass, from this heavily forested area into the bay .

Crabs, snails, lobsters, clams, scallops, whelks, nautilus, sharks, and other familiar animals lived in the warm, shallow sea, eating, reproducing, and being eaten Sohl 1960Sohl 1964.

Giant reptilian mosasaurs, highly ornamented cephalopods, and other less familiar sea creatures lived in the water.

Their shells, bones, carapaces, teeth, and other hard parts were constantly being buried in the sandy mud of the seafloor.

Periodic hurricanes may have brought in heavy loads of river sediment to bury the plants and animals living there.

Huge plesiosaurs, marine crocodiles, sea turtles, and mosasaurs shared the waters with sharks and fierce fanged-tooth fishes.

The clay in the sediment at Coon Creek sealed off the fragile fossils from the corrosive action of water and the hard parts of the clams, snails, crabs, and shrimps were well preserved.

[11] • Because the Coon Creek Formation sediment is unconsolidated, it makes it very easy to collect and prepare the fossils.