SILICIFIED MIOCENE MAGGOTS FOUND IN A GOMPHOTHERE SKULL PROVIDE A MODEL FOR SOFT-TISSUE PRESERVATION IN TERRESTRIAL SETTINGS

Here we describe silicified blow fly larvae (Calliphloridae) which were discovered in the sinus cavities of a Miocene gomphothere (Proboscidea). The preservation of these soft tissue organisms appears to be a novel occurrence. This discovery was made in the Miocene Esmeralda Formation of Esmeralda County, Nevada, USA. Blow flies are carrion scavengers and can be used in modern forensic science for determining timing of death of organisms. The developmental stage of the blow fly larvae in this situation implies that the gomphothere must have been dead between 6 and 11 days prior to burial. Subsequent silicification of the soft-tissue larvae had to have outpaced necrolysis, or the processes of decomposition. This type of situation of rapid silicification of organic matter is known to occur in the presence of decay microbes and in the presence of abundant silicic acid. The latter situation has been artificially created in a laboratory setting by other studies. This kind of preservation was made possible by the environmental conditions of the Miocene Esmeralda Basin. Volcaniclastic deposits were common during this period, providing an abundance of silica that later mobilized throughout the region. The poorly drained floodplain and paludal depositional environments of the Esmeralda Formation led to the rapid sedimentation necessary to preserve fossil remains. Our study provides for a taphonomic mode of soft-tissue preservation in other tectonically active, terrestrial basins through geologic time and shows that callophoriid flies have been active carrion flies since at least the Late Miocene.