The extinct oyster Exogyra (Ostreoida: Gryphaeidae) thrived during the Cretaceous Period. The Genus was especially abundant in the southern parts of the United States, as these areas were once covered under a shallow sea. Left (lower) valves of the species Exogyra costata (Say, 1820), show different variations of the shells including differences in size and scarring of the scar remaining from the point of substrate attachment. The scars are often created by attaching to another organism, leaving an impression of it via a process called bioimmuration. This research analyses specimens from three sites within two different geological formations (Owl Creek Formation, Prairie Bluff Formation). Statistical analysis of attachment frequencies of collected specimens, as well as the analysis of the overall substrate availability reveals certain patterns of attachment, in addition to variations in lithologies of the study areas.