PHYSICAL AND CHEMICAL CONTROLS ON THE SINKING AND DECAY OF INSECTS

Soft tissue preservation, such as muscle and chitin, is rare, but can greatly expand our understanding of ancient organisms and ecosystems. Soft tissues are highly susceptible to decay processes, leaving only a short window for preservation. Realistic controls on the timing and modes of soft-tissue fossilization can be determined by monitoring the early stages of extant organism decay under varying environmental conditions. Burial is essential for fossilization, and it is thus surprising to find that naturally buoyant organisms such as insects are fossilized with exquisite detail in offshore deep-lake depositional environments. Here, we assess how water salinity and surface disturbances influence the initial stages of decay and sinking rates of insects. Greater water salinity should improve buoyancy while reducing decay rate by inhibiting the growth of bacteria. Surface water disturbances have the potential to increase insect disarticulation while also decreasing the time before sinking by overcoming surface water tension. Decay experiments of crickets (Telogryllus oceanicus) were conducted to determine how water salinity and surface disturbances impact the preservation potential of insects. Crickets were euthanized by rapid freezing in a -86°C freezer and placed in individual containers filled with either artificial freshwater, seawater, or hypersaline water. Decay progress was monitored through periodic photography (once every four hours) and the timing of feature loss (e.g., deformation and limb loss) and sinking was recorded. A second set of experiments were subjected to a variety of surface disturbances: water drops, horizontal oscillation, tumbling, and forced insect submersion. Decay progress was compared across salinity-surface disturbance conditions to place realistic bounds on the biases exhibited by fossilized insect collections in deep time.