EFFECTS OF EXPOSURE PRIOR TO BURIAL ON PRESERVATION OF DETAILED MORPHOLOGY IN FOSSIL NEREIS

Preservational bias is prevalent throughout the fossil record, with organisms with hard parts being favored for fossilization. Soft parts are less often preserved and mostly occur under conditions of anoxia and rapid burial. Our aim was to determine the importance and timing of rapid burial in for the preservation of soft bodied organisms. Nereis was used as an experimental subject because it is common in the fossil record, specifically obrution deposits. 21 individuals were buried at different times after euthanasia to observe how rapidly soft tissues decay prior to burial, and the resulting preservation of detailed morphologies of tissues. The specimens were excavated after 3 weeks, and analyzed using light and scanning electron microscopy. Controls were left unburied to to create a decay series to compare to the buried samples.

Samples buried immediately after euthanasia were better preserved, including a greater percentage of attached parapodia and integumentary layers. Nereis began to lose detailed macroscale morphology after 6 hours of exposure. After 48 hours, the specimen become gelatinous. Specimens buried after 48 hours were compacted due to their increasingly degraded support structures such as the cuticle and the overlying sediment applying pressure, while those buried immediately after death retained their rigid structure. Samples will be analyzed using SEM to reveal quality of preservation of the basal cuticular layer, epicuticle, extracellular matrix and any remaining internal soft parts. This experiment is a pilot project to provide information correlating time prior to exposure with fossil fidelity.