D3028: Biological and geological processes governing insect fossilization

Insect soft tissues are rarely found in the fossil record because their susceptibility to decay leaves only a short time for preservation. Decay experiments can examine the early chemical environments that might lead to soft-tissue fossilization. Experiments have been designed to analyze the role of bacteria-mediated mineralization in the soft-tissue preservation of insects. Bacteria are agents of decay and preservation: anaerobic respiration consumes organic matter while also creating the precursors to minerals that preserve organic structures. The molecules and ions that dictate which bacterial process are most efficient are found in the surrounding sediment, pore water, and insect itself. Decay experiments with crickets (Acheta domesticus and Telogryllus oceanicus)and locusts (Locusta migratoria) have explored the effects of water salinity and sediment on insect decay and bacterial growth. All insects were euthanized by freezing and placed in individual containers filled with either freshwater or artificial seawater. Some specimens were also buried beneath mixed-composition sand to limit the diffusion of oxygen and ions. Decay progress was monitored through periodic photography and measurements of bulk acidity and reduction-oxidation potential. Decay progress and bacterial growth were compared across sediment-water conditions to determine which conditions bias preservation most prominently, and to set realistic timelines for the fossilization of insects in deep time.