Spatial resolution in subfossil molluscan remains: Implications for paleobiological analyses

Abstract

The ability of paleobiologists to draw paleoecological inferences based on spatial faunal variability within a single stratigraphic interval depends ultimately on the spatial resolving power of the fossil record. This paper evaluates the potential spatial resolution of fossil assemblages by examining modern skeletal remains of molluscs on a benthic transect, along which there is a marked decrease in seagrass cover, in Smuggler's Cove, St. Croix, U.S. Virgin Islands. The sampling transect began in a Thalassia-covered area approximately three meters deep, extended into slightly deeper water with lighter seagrass cover, and ended on an open, bioturbated sandy tract at a depth of nearly six meters.Two-way cluster analysis and polar ordination of 37 samples of molluscan remains, taken at 10-meter intervals along the 360-meter transect, reveal patterns of variation that are shown by correlation analyses and consideration of the autecologies of individual species to be related to measured changes in vegetation. There is a transition from dominance primarily by epifaunal gastropods living on seagrass blades to dominance by infaunal, burrowing bivalves as grass cover becomes lighter. Some non-systematic variability exists in faunal distributional patterns within areas where the environment does not vary systematically, but this does not mask the regular faunal transitions related to environmental changes. Correspondence between the dead and live faunas is difficult to ascertain because of the scarcity of live fauna in collected samples.The results suggest that spatial faunal transitions in fossil remains at even the fine scale evaluated in this study are potentially preservable in the fossil record.