Fungi Bloomed Twice Around End-Cretaceous Mass Extinction

Why It Matters

Understanding how fungi proliferated during and after the Cretaceous‑Paleogene extinction clarifies ecosystem resilience and helps explain why mammals, not reptiles, came to dominate the planet.

Key Takeaways

• Fungal microfossils spiked globally at Chicxulub impact layer in Colorado
• Earlier 30,000‑10,000‑year pre‑impact fungal bloom linked to Deccan‑related cooling
• A 2,000‑year Early Paleocene fungal surge occurred 10,000 years post‑impact
• North Dakota rocks lacked impact‑time fungi, likely due to lithology differences
• Fungal dominance may have favored warm‑blooded mammals over reptiles

Pulse Analysis

The end‑Cretaceous mass extinction is traditionally framed as a two‑pronged disaster: the Chicxulub asteroid and the Deccan Traps volcanism. While the asteroid’s immediate blast and firestorm are well documented, the ecological aftermath has been harder to quantify. Fungi, as opportunistic decomposers, leave a distinct microfossil record that can reveal ecosystem collapse and recovery. By targeting well‑preserved sedimentary layers in the Denver Basin, researchers leveraged this signal to map a worldwide fungal explosion coincident with the impact, providing the first direct confirmation beyond isolated New Zealand findings.

Beyond the impact‑time bloom, the study identified a prolonged pre‑impact fungal surge dating 30,000 to 10,000 years before the asteroid strike. This interval aligns with a documented cooling phase following intense volcanic activity in the western Indian subcontinent, suggesting that early climate stress already primed ecosystems for disruption. The researchers also detected a brief Early Paleocene fungal spike roughly 10,000 years after the extinction, hinting at lingering ecological instability during the planet’s recovery. Variations between Colorado and North Dakota samples underscore how rock composition can mask biological signals, emphasizing the need for multi‑site analyses in deep‑time studies.

These findings reshape our understanding of the Cretaceous‑Paleogene transition by highlighting fungi as a key driver of post‑extinction dynamics. The rapid fungal takeover likely created a niche where warm‑blooded mammals, whose higher body temperatures resist fungal infection, could thrive over ectothermic reptiles. This insight not only clarifies a pivotal evolutionary leap but also offers a cautionary parallel for modern ecosystems facing climate‑driven disturbances, where opportunistic microbes may reshape competitive balances.