PROGRESS AND CHALLENGES IN ASSESSING PROTEROZOIC EUKARYOTIC DIVERSITY

Over the past half-century, the number of fossils described from Proterozoic rocks has increased exponentially. These discoveries have occurred alongside an increased understanding of the dynamics of the rest of Proterozoic Earth system. The fleshing out of the Proterozoic record has allowed us to begin to form hypothesis about the relationships between abiotic and biotic events, including “Snowball Earth”, dramatic changes in the redox state of global oceans, and the rise of metazoans. However, these efforts are hampered by our lack of an adequate understanding of the myriad factors that lead to fossil diversity in the Proterozoic rock record. Here, I will attempt to quantitatively and qualitatively address the biases present in the Proterozoic fossil record of eukaryotes and present new data compilations of eukaryotic fossil diversity.

The past decades have seen significant progress towards a view of Phanerozoic marine diversity that takes into consideration various potential biases such as sampling, rock volume, and preservation, enabling us to begin to answer essential questions about the Earth-life system. Such interpretations are not yet possible in the Proterozoic, where we face specific challenges when attempting to analyzing diversity, including the relative paucity of exposed strata, the lack of a large amount of fossil data to create statistically significant correlations, fossil specimens with few taxonomically meaningful character traits, and the challenges of “telling time” in a world with little meaningful biostratigraphy.

In order to move towards a more comprehensive view of the Proterozoic Earth system, I have dissected the current Proterozoic fossil record of eukaryotes in an attempt to account for major biases. Initial analyses show that assemblage changes through Proterozoic are robust, as is an increase in the number of functional groups and modes of recalcitrance. Overall, there is an increase in both alpha and beta diversity through the Proterozoic, however, smaller-scale patterns are difficult to discern through the lens of lithological, taphonomic, and geographic biases. Further quantifying and addressing these biases will be an essential step towards future paleontological and geobiological work in the Proterozoic.