ECOLOGICAL RECYCLING AND TAPHONOMIC BIAS THE FOSSIL RECORD

Ongoing paleontological discoveries, new technologies, attention to taphonomic biases, and the growth of quantitative methods for assessing patterns in the geological record have built increasingly confident generalizations about evolution and paleoecology based on fossils. But how well do these samples of past biodiversity actually represent life’s long and complex history? Causes of incompleteness of the fossil record include geological forces that consumed large parts of the earth’s crust, chemical and physical destruction via diagenesis, and ecosystem processes that controlled early post-mortem decomposition and nutrient recycling. Recycling maintains ecosystem function by returning organic materials to circulation, imposing a strong initial filter on potential fossil preservation. Paleontologists study the limited samples of remains that survived destructive processes associated with ecological recycling. We can use this perspective and an accounting of modern biomass across marine and terrestrial organisms (Kingdoms) to take a fresh look at how fossil samples represent the much larger story of life over time. Today, 80% (450 Gt C) of Earth’s biomass consists of Plantae (mainly terrestrial) and Animalia represent only 0.36 % (2/550 Gt C) (Bar-On et al. 2018). In contrast, fossil plants make up only ~8% of the occurrences in PaleobioDB (5/5/21), and animals constitute ~92%. Assuming that these biomass estimates from the Recent can be applied to the Phanerozoic, this provides one measure of the tiny fraction of past life represented in the fossil record, which consists mainly of animals with biomineralized skeletons. These preserved life forms are used to reconstruct local to global biodiversity trends, extinctions, and ecological change through time. The vast majority of other organisms that lived on Earth over the past ~3.5+ byr, including nearly all microbes and soft bodied eukaryotes, were reduced to elemental components and/or rapidly recycled into new life. If the unrecycled organic remains preserved as fossils fairly represent evolutionary processes and interactions with environmental processes over geological time, then the fossil record provides a faithful chronical of the history of life. It is conceivable, however, that the more abundant and easily recycled life forms important to ecosystem functioning represent different evolutionary histories. Ecological theory and modern analogue studies could be brought to bear on such questions to build a more inclusive understanding of the history of life.