TAXONOMY AND PALEOECOLOGY OF RUDIST BIVALVES FROM UPPER CRETACEOUS STRATA, GULF COASTAL PLAIN, USA

Rudist bivalve taxonomy and paleoecology have been analyzed for many Upper Cretaceous localities within the tropical Caribbean Basin and temperate Western Interior Seaway (WIS), but the first investigations from a geographic midpoint, the Gulf Coastal Plain (GCP), are presented. This study provides an analysis of Campanian and Maastrichtian GCP rudists from the Selma Group in the eastern GCP, including the Mooreville, Demopolis, Ripley and Prairie Bluff formations, and the Taylor Group in the west, including the Ozan, Annona and Marlbrook formations.

Material consists of 146 Selma Gr. specimens from the Alabama Museum of Natural History, and 52 Selma and 9 Taylor Gr. specimens from the Mississippi Museum of Natural Science. Identified rudist fauna comprise Monopleuridae Munier-Chalmas, 1873, including Gyropleura Douvillé, 1887, as well as Radiolitidae d’Orbigny, 1847, including Biradiolites cardenasensis Böse, 1906, Biradiolites jamaicensis Trechmann, 1924, Durania Douvillé, 1908, Durania maxima (Logan, 1898), Radiolites Lamarck, 1801, Radiolites acutocostata (Adkins, 1930) and Sauvagesia Choffat, 1886. Rudists are preserved dominantly as partial lower (attached) valves; the only upper valves are from four Gyropleura specimens. Taxa preserved in groups include Biradiolites jamaicensis, ranging from three to twenty individuals, and Durania maxima, commonly with two to four individuals.

Rudist biodiversity in the GCP during the Campanian and Maastrichtian is higher than the WIS, which reports two families and two genera. Both regions are lower in biodiversity than the Caribbean, which has five families and 20 genera. The range of Durania maxima, which was previously unique to the WIS, was extended into the GCP. The GCP also marks the northern range of Caribbean genera including Biradiolites, Gyropleura, Sauvagesia and Radiolites, which were likely distributed via surface currents that traveled northward from the Caribbean into the GCP and WIS during this time. Reported microbiostratigraphy of the GCP is well documented and shows the interval in the nannoplankton zones CC18-CC25, indicating an age of early Campanian to middle Maastrichtian.

This research fills a gap in Western Hemisphere Late Cretaceous research and provides a regional perspective on the paleobiogeography of this unique group.