EXCEPTIONALLY PRESERVED FOSSIL ASSEMBLAGES THROUGH GEOLOGIC TIME AND SPACE

Exceptionally preserved fossils of non-biomineralized tissues provide key insights into anatomies and communities of ancient organisms. Assemblages of such fossils are not evenly distributed through geologic time or space, suggesting exceptional fossil preservation is controlled by factors operating on global scales. Establishing the influence of global factors, however, requires documentation of temporal and spatial trends in the occurrences of such assemblages through the geologic history of complex life. To this end, we compiled and analyzed a dataset of 694 globally distributed fossil assemblages from ~610 to 3 Ma (Mega anna). Our analyses show that clusters of exceptional fossil assemblages decline in number and shift from open marine to restricted (transitional and non-marine) depositional settings through the Ediacaran-Silurian (635–420 Ma) interval in concert with increasing oxygenation of the ocean-atmosphere system and development of bioturbation. Thereafter, clusters of exceptional fossil assemblages generally rise in number through the Devonian-Neogene (420–3 Ma) interval with increasing non-marine sedimentary rock quantity and improving geologic sampling. Secular environmental transitions and rock record biases, thus, overprint the distribution of exceptionally preserved fossil assemblages in geologic time and space. Overall, our study affirms the importance of low oxygen and bioturbation levels in the conservation of non-biomineralized tissues, demonstrates the role of rock record bias in the exceptional fossil record, and provides fundamental bases for understanding occurrences of exceptionally preserved fossils through time and space.