Open Access Kent State (OAKS)

Identification of 8640 specimens of bryozoan, mollusk, decapod, and vertebrate fossils from the Paleocene Clayton Formation in southern Illinois has resulted in recognition of 44 species-level taxa of which 40 have been identified to genus or species. The fauna is less diverse than other Clayton Formation faunas which may be a result of its having formed in an area of reduced salinity at the head of the Mississippi Embayment. One bryozoan, seven mollusk, and one shark species comprise 93% of the individuals. Thirty-nine of the taxa identified have been known previously from occurrences in Cretaceous rocks of the Atlantic and Gulf Coastal Plains and the Upper Midwest documenting a high percentage of survivors in this fauna. The area, although connected to the Gulf of Mexico, may have served as a refugium.