BLACK BUTTES FOSSIL MOLLUSCAN SECTION, WYOMING: ANOTHER HISTORIC LYNCH-PIN IN INTERPRETING THE LATEST CRETACEOUS CONTINENTAL MOLLUSCAN RECORD OF NORTH AMERICA

Modern studies of critical continental molluscan fossil localities in the Western Interior (USA) are commonly quite minimal. The Lance Formation’s historic “Black Buttes" fossil locality, Sweetwater County, is a good example. In the 1870s a number of new fresh and brackish water species were named (represented by line drawings), and subsequently widely referenced.

With track laid by the Union Pacific Railroad, Meek (1873) with Bannister (1873) initiated geological and paleontological field studies in 1872 on easterly dipping strata on the east flank of the Rock Springs uplift on bluffs of Bitter Creek and tributaries. White (1877) followed their efforts with field work in 1876 that included description of a number of new species placed in geologic section. In 1896, Stanton and Knowlton (1897) restudied White’s section south of Black Butte depot. That study and those by Stanton (1909; 1909 field work), Knowlton (1909; with Peale, 1909 field work), and Lee (1916; 1914 field work) were less interested in molluscan continental paleontology and focused more on the “Laramie” problem and correlation of taxa (Meek’s Bitter Creek series ~ Lance Formation) throughout the northern Great Plains. Bannister, Meek, White, and Stanton described a complicated section of intertonguing brackish and freshwater mollusks dominated both in abundance and diversity by cyrenid, corbulid, and unionoid bivalves and thin beds of important snails (e.g., viviparids and others). Roehler’s (1993) 200 measured (surface/subsurface) sections provide invaluable paleoenvironmental context for past and ongoing fossil studies.

Current Black Buttes fossil section studies (senior author) began in 1982, with major coal mine operations well underway. Current work on this collection includes selection of lectotype specimens, their illustration, and recognition of the potential endemic nature of many of the Black Butte area species. Examination of Smithsonian Institution type lots shows important variation within a given species (syntype lots), making determination of a species concept difficult for some, if not all, of the "Black Buttes" species. New collections from the type area are needed to better describe and diagnose unionoids from the Black Buttes area and clarify taxonomy continental molluscan taxonomy near the end of the Cretaceous.