An often neglected aspect of many paleoecological studies is the effect of quality of preservation (e.g., original shell material versus molds; pristine versus degraded shape and ornamentation) on observed patterns. This is especially important given that preservational quality probably varies significantly over space and geologic time. For example, preservational quality almost certainly varies with latitude, but the potential bias of observed richness and evenness patterns at the assemblage-level has been largely ignored. To test for such effects, this project focuses on the relationship between preservation state and taxonomic identifiability as the key aspect of preservation in paleoecologic interpretation. Bivalves and brachiopods have been examined from a variety of environments and a number of geologic time intervals, including the recent, in order to determine (a) which features of bivalve molluscs and brachiopods need to be preserved in order for an individual to remain identifiable at different taxonomic levels, (b) what types of taphonomic damage are most responsible for rendering an individual unidentifiable, and (c) how the factors that reduce taxonomic identifiability vary over time and space. Preliminary results, from modern bivalves and Silurian brachiopods, indicate that shell modification due to fragmentation is most important in reducing taxonomic identifiability. If this result continues to hold for a variety of environments and geologic time intervals, documentation of fragmentation frequencies in assemblages may yield a useful system for grading preservational quality and identifying taxonomic bias in paleoecological studies.