A STUDY OF VARIATION IN SHELL MORPHOLOGY OF FLEMINGOSTREA (OSTREA) CRETACEA AND OTHER OYSTERS FROM THE UPPER CRETACEOUS OF ALABAMA

Measurements of Late Cretaceous fossil oyster specimens from the Geological Survey of Alabama’s paleontology collection were analyzed for morphological analysis, and variation compared with stratigraphy. Species measured included Flemingostrea cretacea, Exogyra costata, E. cancellata, E. ponderosa, and Pycnodonte mutabilis from Santonian and Campanian strata. Morphological measurements included scar length and width; shell length and width; and convexity depth. Of all species, F. cretacea showed the greatest variation in shell morphology, and all F. cretacea specimens were from the Eutaw Formation in eastern Alabama. Morphological patterns with respect to stratigraphic position and lithology indicate a correlation between marine environment and shell morphology. It is interpreted here that these morphological differences were influenced, in part, by water depth and population size in two differing depositional environments within the Eutaw. This is not unlike the relationship between environmental factors and oyster morphology observed in modern environments.