Bulletin of the Mizunami Fossil Museum, no. 32 (2005), p. 97–108, 7 figs., 1 table. © 2005, Mizunami Fossil Museum The fauna of the Clayton Formation (Paleocene, Danian) of southern Illinois: a case of K/P survivorship and Danian recovery

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