Surviving a mass extinction: Lessons from the K-Pg fern spike

Emily Sessa

The K-Pg asteroid impact and its aftermath profoundly disrupted life across the planet. While this event is usually associated with the loss of dinosaurs, its impact on plants, which form the foundation of ecosystems across the globe, was also profound. In north temperate latitudes, regions close to the impact site were denuded of all life, forests were leveled, and four out of five species of plants went extinct. Analysis of North American K-Pg sediments indicate that generalist ferns were the first plants to recolonize these sites. Over time, this “fern spike” was noted as a biomarker in K-Pg localities around the globe. Surprisingly, the attributes that imparted ferns with such astonishing resilience to stress have not been investigated. This is non-trivial because the immediate post-impact climate was stressful enough to largely eliminate competition from both flowering and non-flowering plants, which today are the dominant plant groups on Earth with respect to species numbers, biomass, and economic significance. Post-impact devastation and climate disturbance re-shuffled the structure of the planet’s vegetation. The impact released megatons of particulates into the atmosphere, along with climate-altering gases from the carbonate and sulfate rich rocks at the impact site. Global dimming, cooling, and acid rain characterized an environment that has been described as a nuclear winter. There is also evidence for massive fires around the globe, which would have added soot and compounded the loss of sunlight. The duration of this post-impact winter is unknown, but the pollen/spore record indicates that ferns were dominant for at least 30,000years following the strike. The goal of this research project is to combine fossil and phylogenetic analyses with physiological experiments to understand why ferns responded differently than other plants to the post-impact environment.