EXPLORING THE IMPACTS OF PRESERVATION ON PALEONTOLOGICAL DATA: A LITERATURE-BASED SURVEY OF BODY SIZE AND BIODIVERSITY IN LATE MESOZOIC-PALEOGENE GASTROPODS

One major challenge in understanding the history of life lies in differentiating the effects of preservational biases from true ecological and evolutionary patterns occurring in the fossil record. For example, from the late Mesozoic through the Cenozoic, unlithified sedimentary deposits become more common, and on average the preservational quality of fossils (particularly aragonitic fossils) is expected to increase accordingly. Within the same time interval, the overall diversity and size range of aragonitic fossil gastropods also appears to increase. Here, fossil gastropods are used as a model to explore how preservational quality impacts the way we perceive biological patterns in the fossil record. More specifically, we examine relationships between preservational condition and the shell dimensions of previously recorded and described gastropods from the Cretaceous and Paleogene. Data were collected from plates and illustrations accompanying taxonomic descriptions in over 200 published monographs, journal articles, and books. This literature-based approach allows a broad geographic sampling and will complement more detailed analyses of specific faunal assemblages or geographic regions. For the most complete specimen of each species in each formation, we recorded the greatest length and width of the shell, the greatest dimensions of the aperture, and the quality of preservation. The mode of preservation was determined based on four factors: whether the specimen was a mold, how pristine the surface of the shell was, whether the aperture was infilled by matrix, and the approximate overall completeness of the fossil. Preliminary analyses suggest that the size-frequency distribution and overall diversity of fossil gastropod assemblages is related to preservational condition, suggesting that observed trends through time in these factors could be attributable at least in part to changes in preservation. Additional analyses will further explore the strength and potential impacts of these trends in the late Mesozoic and Cenozoic.