The distribution and composition of Holocene benthic assemblages of suspension and deposit-feeding trophic types are primarily controlled by (1) food availability, (2) sedimentation rate, (3) bottom stability and turbidity, (4) salinity, and (5) dissolved oxygen. Diverse and abundant fossil bivalve faunas from the Upper Cretaceous (Maestrichtian) marine deposits of South Dakota are used to evaluate the usefulness of trophic group analysis in paleoenvironmental reconstruction.

The recessional history of the Late Cretaceous sea in northwest-central South Dakota is recorded in an offlap sequence in the upper Pierre Shale and Fox Hills Formation representing offshore-shelf, bar-influenced-shelf, offshore-bar, and deltaic environments. Well-preserved molluscan assemblages from most of this sequence permit trophic comparison with assemblages from analogous Holocene environments.

Trophic groups reconstructed from the bivalve assemblages closely reflect the hydrographic and sedimentary conditions reconstructed for these paleoenvironments from independent lithologic and stratigraphic evidence. Recognition of fossil trophic groups can provide a useful tool in environmental reconstruction and analysis of fossil community structure.