Palaeogeography. Palaeoclimatology, Palueoecology, 108 (1994): 55-73 5~ Elsevier Science B.V., Amsterdam Taphonomic processes in modern freshwater molluscan death assemblages: Implications for the freshwater fossil record Robert Hays Cummins School o[Interdisciplinary Studies, Miami University, O.,¢fbrd, Ohio 45056, USA (Received October 12, 1992; revised and accepted July 22, 1993) ABSTRACT Cummins, R.H., 1994. Taphonomic processes in modern freshwater molluscan death assemblages: Implications for the fresh- water fossil record. Palaeogeogr., Palaeoclimatol., Palaeoecol., 108:55 73. Unionid life and death assemblages in several streams and reservoirs in east-central Ohio were investigated to examine taphonomic processes in freshwater environments. Twenty-six species were collected. As in most marine environments, rnost living molluscan species were represented in the death assemblage. Fourteen species were found in both the life and death assemblage at at least one study site, one species was found only in the living community, and one species was found live at one site, dead at another Ten species were found only in the death assemblage. With one exception, the time-aw~'rageddeath assemblage was more species rich than the living molluscan community based on single-sample census data. The death assemblage preserves the rank orders (live/dead) of abundance and biomass of the preservable molluscan components in some environments but not iq those the most environmentally disturbed. Unionid live/dead fidelity is high and compares favorably with live/dead fidelity in marine and estuarine environments. In nine of thirteen within-study site comparisons of life and death assemblages, there were no significantsize differencesbetween the single-census life and time-averaged death assemblages. These results are in contrast to estuarine assemblages along the Texas coast where 13 of 15 comparisons of the death assemblage and the estimated mortality from the living community indicated little similarity between life and death assemblage size distributions. It is likely that death assemblage formation and associated taphonomic processes, coupled with the unique life- cycle of unionid molluscs, are distinctive in freshwater environments. Recognition of the unique taphonomic characteristics of unionids should prove useful in freshwater paleocommunity analyses. Introduction Most comparative analyses of living aquatic communities and death assemblages have been conducted in marine environments such as estuar- ies, lagoons, tidal flats, and bays (e.g. Cadee, 1968, 1982; Lawrence, 1968; Warme et al., 1976; Peterson, 1976; Cummins et al., 1986 a-c; Frey, 1987; Powell et al., 1986; Staff et al., 1985, 1986; Ffirsich and Flessa, 1987; Miller, 1988; Davies et al., 1989; Meldahl and Flessa, 1990; Miller and Cummins, 1990; Russell, 1991) and the continental shelf (Bosence, 1979; Carthew and Bosence, 1986; Staff and Powell, 1988; Callender et al., 1990). These studies provide valuable insights into the initial steps of fossil assemblage formation and the effects of taphonomic processes on numerical abundance, diversity, population dynamics, trans- port, taxon dominance, and community biomass. Kidwell (1986), and others, quite logically ques- tioned whether taphonomic processes are equiva- lent from one aquatic environment to the next. In Kidwell and Bosence's (1991) meta-analysis of a wide variety of data sets from marine environ- ments, they found an apparent lack of strong taphonomic distinctiveness among marine and estuarine environments when using a series of standardized metrics to examine fidelity of life and death assemblages. Freshwater systems have received far less attention than their marine coun- terparts in modern taphonomic studies. With some exceptions (e.g. Pip, 1988; Cohen, 1989), little is known of freshwater death assemblage formation. The freshwater fossil record is often charac- 0031-0182/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSD1 0031-0182(93)E0128-G