A COMPREHENSIVE MODEL OF THE FOSSILIZATION OF SOFT-BODIED ORGANISMS

Soft-bodied organisms constitute an uncommon but important component of the fossil record. Any paleobiological or paleoecological insights these fossils may provide, however, must be understood in terms of the taphonomic processes that led to their preservation in the first place. However, a general theory of soft-bodied taphonomy has proven elusive. Here I propose a model that brings us closer to this goal, which accounts for the preservation of soft-bodied fossils in any depositional environment.

Built from a careful consideration of the soft-bodied fossil record, this model relates the preservation pathway and preservation quality of soft-bodied fossils to varying conditions of three taphonomic variables critical to the preservation of soft-bodied fossils: the original organic composition of a fossilized organism, the microbial community associated with the organism at the time of burial, and the physical and chemical context of the burial environment. The model consists of two parts. In the first, different preservation pathways are grouped together into three classes based on the role the microbial community plays in fossilization. In the second, for each class two-dimensional plots are filled with zones that relate shared values of the three primary taphonomic variables with levels of preservation detail of soft-bodied fossils, these zones having been calibrated by an analysis of a dozen lagerstätten in the soft-bodied fossil record. Fossils may be placed on these plots, or the progress of a hypothetical deceased organism, from burial to decay or preservation, can also be traced.

This model serves not only to describe our current state of knowledge of soft-bodied taphonomy, but also as a building block for future insights. The second part of the model, in particular, offers a predictive capacity as to the mineralogies and qualities of fossils that can be expected from a given set of burial conditions. In addition, the preservation zones of the second part of the model also have the potential to be more finely partitioned as our understanding of the specific taphonomic conditions conducive to soft-bodied fossilization evolves. Studies in soft-bodied taphonomy have made rapid progress in the past few decades, and this model will help keep the field advancing.