INFLUENCE OF MICROBIAL BIOFILMS ON THE PRESERVATION OF SOFT TISSUE IN SNAILS

Konservat-Lagerstätten deposits contain exceptionally preserved fossils with both skeletal and soft tissues. Taphonomy experiments have shown that microbes, particularly biofilms, can play a vital role in the early mineralization of soft tissues, and may be responsible for their presence in the fossil record. One group, the Gastropoda, have been present since the early Phanerozoic but their soft tissues are generally underrepresented in these exceptional fossil deposits; generally, only their exoskeletons are preserved. It is unclear what taphonomic factors are responsible for the lack of these tissues in fossil-Lagerstätten, and was the basis for this study. Here we describe taphonomy experiments in which marine snails (Margarites pupillus) were buried for 6 weeks and sampled every 12 hours to examine the conditions of both the shells and soft tissues. Physical observations were made throughout the course of the experiment and pH and ORP data were collected at every stage of sampling. Control snails were left unburied but otherwise followed experimental conditions. Snails were excavated from the sediments and analyzed using light microscopy and SEM/EDS to monitor the decay of the tissues, as well as look for the development of biofilms and/or mineral films on the shells and soft tissues.

By the end of the experiment, the soft tissues of the control samples still preserved the majority of morphological detail. In contrast, the soft tissues of the buried snails were largely disarticulated, and morphological detail was lost. Biofilms formed rapidly on the soft tissues of the control snails, but were rarely present and not persistent in the buried snails. These experiments clearly demonstrate that sediments greatly delayed biofilm formation, resulting in the poor preservation of the soft tissues. These results may explain, in part, the lack of preserved gastropod soft tissues in the fossil record.