by Dion Stewart
“Water water everywhere but not a drop was rain!” had to be the moto for our successful fossil collecting trip in Stewart County on Saturday, April 19th. Even though the rainy weather predictions scared away most of the 24 persons who signed up for the trip, the heavy rains from the previous day did not dampen the spirits of the hearty eight people who wadded into the swollen streams in search of Cretaceous fossils in the Blufftown and Ripley Formations.
Participants filled their buckets with the major discovery of the day, Exogyra ponderosa, an extinct oyster. Although many were found in the embankment, some of the larger specimens were collected from the stream by feeling them with your feet first then reaching down through a foot or more of water to blindly dig them out of the stream bed.
Alex, who became known as “Shark Man,” felt a rough area with his feet, reached down and dug up a handful of the gravely mudstone to find a shark tooth sticking out of the rock (see picture to right), the tooth was an anterior tooth that belonged to the species Scapanorhynchus, the extint predecessor to the modern Goblin Shark. Four of us waded up another stream where a dinosaur tooth was found by a CCGMS member on a previous trip; this locality has also reported findings of both Pterodactyl bones and Mosasaur vertebrae. Unfortunately the water was too high and this Cretaceous rock unit was covered.
Geologically the Blufftown Formation was deposited in a near shore marine environment, likely an estuary where rivers coming off the Appalachian Mountains near Atlanta reached the coast line that would have been in the vicinity of Columbus about 75 million years ago. The large Exogyra oysters would have made a great seaside meal for those dinosaurs, which soon faced mass extinction when the asteroid hit further offshore in the same gulf. The Exogyra had a bottom shell that was very large, distinctly coiled and tapered down to a beak on one side. This larger shell was buried in the muddy sediment, with the smaller flat upper shell flush with the bottom of the bay. This oyster had no brain, no heart, and fed by lifting the upper shell and filtering the micro-organisms out of the passing seawater.
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