PALEOECOLOGICAL AND PALEOGEOGRAPHIC SIGNIFICANCE OF NEW SELACHIAN PALEOFAUNAS FROM LATEST CRETACEOUS AND PALEOCENE MARGINAL MARINE FACIES, HANNA BASIN AREA, WYOMING

Several new selachian paleofaunas have been recovered from distributary channel, estuarine and interdistributary bay fill deposits of the Lancian-Puercan Ferris (66-64 Ma) and lower Hanna (Torrejonian-Wasatchian: ~62-55 Ma) formations of Wyoming’s Hanna and Carbon basins. In addition to common latest Cretaceous selachians like Myledaphus, Lissodus, and Cretorectolobus, several less abundant taxa have been recovered from Lancian strata of the Ferris (e.g., Cederstroemia, Brachaelurus, and ?Chiloscyllium). The most diverse paleofauna occurs ~5 m below the local K-T boundary. Based on calculated sedimentation rates, and estimated duration of local 3rd- and 4th-order sea level fluctuations, this paleofauna probably existed < 100 k.y. before the terminal Cretaceous. What is probably a new species of Dasyatis occurs in sandy estuarine deposits preserved as components of incised valley fills of the middle Ferris (Puercan: ~64 Ma). In estuarine strata of the basal Hanna Formation (early-middle Tiffanian: ~63-58 Ma) in the Carbon Basin, cf. Myledaphus and an unidentified lamniforme are represented, but are extremely rare (two teeth of each). In addition to being the first selachian teeth collected from terminal Cretaceous and Paleocene strata of southern Wyoming, these specimens, coupled with ichnofossil data and bed-by-bed facies analysis are important paleoenvironmental proxies for documenting local transgression-regression cycles in a previously unrecognized southern embayment of the Western Interior Sea.