Tackling the 99%: Can We Begin to Understand the Paleoecology of the Small and Soft-Bodied Animal Majority?

Abstract

Not all organisms have an equal chance of entering the fossil record. Previo—us attempts to quantify this percentage suggest that for megascopic marine organisms (megafauna), ∼30% would be predicted to leave no identifiable fossils. Here, that exercise is repeated for marine macrofauna, for which ∼80% are predicted to leave no identifiable fossils. The percentage will be far higher for meiofauna, the numerically most dominant marine animals. The organisms which are often most abundant in marine sediments, such as small polychaetes and nematodes, have essentially no fossil record. Yet such organisms are ecologically important in the modern oceans, and almost certainly were in ancient environments as well, so it is useful to consider the roles they play in different ecosystems. Insight into the evolution and paleoecology of these groups can be gained by using molecular divergence estimates to infer temporal origins combined with modern distributional and ecological data. As a case study, this approach is applied to the small and soft-bodied early animal fauna living under low levels of atmospheric oxygen that likely characterized the Precambrian.