BUG IN A JAR: TAPHONOMIC EXPERIMENTS ALTERING BURIAL CONDITIONS OFFER INSIGHTS INTO SOFT-BODIED PRESERVATION

Fossils of soft-bodied organisms can offer taxonomic and paleoecological insights not available elsewhere in the fossil record, yet the mechanisms of their preservation are often elusive. Taphonomic experiments can help decipher the soft-bodied fossilization process by tracking the decay of freshly deceased organisms under different burial conditions. In this study, insects—specifically soapberry bugs (Jadera sp.)—were used to test two potentially critical burial environment variables: burial sediment mineralogy and sediment permeability.

In the sediment mineralogy alteration experiment, insects were buried in quartz sand, crushed illite sediment, or crushed iron-rich Green River Formation marlstone, and were then submerged in either distilled water or natural creek water. It was hypothesized that sediments with a low interactivity potential (i.e. the sand) would not protect the buried insects from microbial attack like sediments with higher interactive potential would (i.e. the illite, and especially the marlstone). Unexpectedly, soapberry bugs buried in sand showed little decay, while those in marlstone or illite with distilled water showed extensive decay.

In the permeability barrier experiment, insects were buried in sand beneath a synthetic barrier made of neoprene, a natural barrier of montmorillonite clay, or no barrier at all, while the water column above was continuously amended with creek water and metabolites (sulfate and acetate). The synthetic barrier treatment soapberry bugs were predicted to show the least decay, followed by the natural barrier and no barrier treatment bugs. While insects without a barrier decayed more than the synthetic barrier treatment bugs, insects with a clay barrier displayed the most degradation.

Surprisingly, there were few differences in tissue preservation quality between treatments at a microscopic scale. This concurs with the fossil record, where seemingly poor quality specimens can reveal local patches of fine detail upon close inspection. The many unexpected results of this study highlight the importance of experiments in testing taphonomic hypotheses, and offer a template for similar future studies with more advanced chemical analyses. Of particular interest is determining how clays react with the buried insects to promote macroscopic decay.