ECOLOGY AND TAPHONOMY OF PLEUROCERID GASTROPODS AS A MODEL FOR ANCIENT FLUVIAL FAUNAS, MUKWONAGO RIVER, WAUKESHA COUNTY, WISCONSIN

The Mukwonago River in Waukesha County, Wisconsin is designated as an Exceptional Resource Water (=high water quality with minimal human/pollution impact) by the state Department of Natural Resources. Biweekly benthic surveying in the stream reveals an abundant and diverse macro-fauna, dominated by bivalve mussels and the gastropods Pleurocera acuta and Elimia livescens of the Family Pleuroceridae, among a myriad of arthropod larval forms. This abundance, coupled with the (relatively) unaltered physical habitat, makes the Mukwonago River an ideal ecologic and taphonomic model for the numerous fossiliferous deposits containg Pleurocerids. Preliminary live-dead results include: very poor preservation of all arthropod fauna, high rates of fragmentation, encrustation, periostracum loss, and corrasion among both Pleurocerid species, and the preferred preservation of larger size classes. The common presence of numerous gastropod individuals among the dead collections that are not present among the living fauna points to a complex taphonomic history that includes exhumation of long-dead shells from multiple environments. Such results suggest once again that caution must be taken when interpreting paleoecology from faunal lists of ancient fluvial deposits.