SUSTAINED SHIFT IN ACRITARCH MORPHOLOGY OVER THE EDIACARAN-CAMBRIAN TRANSITION

The early (approximately 1800 – 540 million years ago) history of eukaryotes was punctuated by several major environmental perturbations that potentially had an outsized influence on the evolution of the Proterozoic biosphere, and the changing structure of Earth systems leading up to the Cambrian Explosion of animals. Reconstructing how early microbial eukaryotes responded to these events has not been extensively quantified. Here, we evaluate trends in acritarch size and morphology across potential environmental perturbations during the Ediacaran-Cambrian transition. We illustrate a sustained decrease in vesicle diameter and pronounced shift in morphology beginning in the late Ediacaran following the ‘Shuram’ carbon isotope excursion. This shift in morphology may have been driven by nutrient stress enhanced by environmental change and/or the increased importance of planktonic lifestyles, highlighting the expansion of microbial eukaryotes into the plankton at this time and the establishment of modern marine food webs.