The northern and eastern portions of Mississippi are home to outcrops of Late Cretaceous chalk and sands that were deposited in the shallow sea known as the Mississippi Embayment, approximately 66 million years ago. The embayment included much of present day Mississippi and extended north into what is now southern Tennessee. The embayment remainded underwater from the early Cretaceous through the Paleogene period, a duration of approximately 122 million years.
As such, most of the fossils we find in this portion of the state are marine creatures such as oysters and clams (bivalves), snails (gastropods), urchins (echinoderms), fish, shark, mosasaur (aquatic reptiles), and other sea creatures.
In the "Cretaceous Vertebrates" section you will be able to see 3-D scans of three parts of Mosasaurus hoffmanii: the left maxilla (upper jaw), the left pterygoid (internal jaw), and the left scapula (shoulder blade). The link you see will take you to an external site called Sketchfab.
The placement of shorelines change as sea level rises and falls. This map shows how the coastline of the US Southeast has changed from the Cretaceous Period through the Paleocene/Eocene epoch. The Mississippi Embayment, responsible for creating the chalk that contains many of the fossils we find in Oktibbeha County, is bound by the blue dashed line.
CRETACEOUS SNAILS (Gastropods)
They phylum Mollusca includes creatures such as snails, bivalves, cephalopods, and ammonites. Many of the snails and bivalves we find in Cretaceous sediments are preserved as steinkerns (internal casts) of the original shell, but some are shells that have been replaced by other minerals.
Rostellites angularis (G. Conrad 1855) Snail Steinkern Fossil
CRETACEOUS OYSTERS and CLAMS (Bivalves)
Large, encrusting oysters and giant rudists were the reef forming organisms during the Cretaceous Period. They created ample habitat for many of the creatures that lived in the Mississippi Embayment 66 million years ago.
The cephalopoda class includes octopi, squids, cuttlefish, nautiloids, and ammonites. The soft-bodied octopus is rarely preserved in the fossil record, but we have many examples of nautiloids and ammonites, as well as the internal skeleton (pen) of Belemnite squids.
3D Models of parts of Mosasaur hoffmanii (DSM 10716) can be viewed here. This will take you to an external site called "Sketchfab".
Left Maxilla (click here) - this is the upper, left jaw of the Mosasaur, and was the first piece of the specimen to be found in the outcrop.
Left Pterygoid (click here) - because the Mosasaur could not chew its prey, it had specialized, internal jaws that helped it to move the prey into its mouth and down its throat.
Left Scapula (click here)- this shoulder blade shows clear evidence that it was scavenged by a shark called Squalicorax. The grooves left behind by the shark's teeth are visible on both sides of the scapula.
