For decades, the asteroid strike that ended the age of dinosaurs has stood as the defining catastrophe of the Cretaceous period.
But a new study of 66-million-year-old rocks suggests the dinosaurs' final chapter may have been even more chaotic than scientists had thought, with a broad fungal takeover after the impact and signs that ecosystems were already under stress tens of thousands of years earlier.
Johns Hopkins University microbiologists studied fungal microfossils preserved in ancient rock samples from Colorado's Denver Basin and North Dakota's Williston Basin. Their findings, published in Proceedings of the National Academy of Sciences, strengthen the case that fungi surged worldwide after the asteroid impact that ended the Cretaceous period, known as the Chicxulub impactor or Chicxulub asteroid.
In the Colorado samples, the team found fungi becoming far more common in rock layers associated with the impact event 66 million years ago. That gives North America its first direct support for the earlier New Zealand results, pointing to a post-impact fungal bloom that was worldwide rather than isolated.
The researchers also uncovered a surprise. Another, longer stretch of fungal prominence occurred about 30,000 to 10,000 years before the Chicxulub asteroid hit. They linked that interval to cooler temperatures that followed heavy volcanism in what is now western India.
"There is other evidence from the fossil record that some species were dying off already at this time," researcher Rosanna Baker said, raising the possibility that ecosystems were already weakened before the asteroid delivered what she called "the final blow."
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The findings suggest that mass extinctions are not always caused by a single dramatic event. Ecosystems tend to unravel in stages, with overlapping shocks that make life harder for plants, animals, and entire food webs before a tipping point arrives.
"Fungal proliferation in geologic samples can signify major ecosystem disruptions," Rosanna Baker and Arturo Casadevall said. "Fungi are life forms that often thrive on environmental calamities."
Human communities depend on stable, resilient ecosystems for food production, clean water, disease regulation, and a livable climate. Research like this helps scientists understand how environmental stress can ripple through the natural systems that support everyday life.
The fungal spikes also hint at what happens when ecosystems lose their balance. Fungi often thrive on decay and disruption, so their sudden rise can serve as a warning sign that forests, wetlands, and other habitats are under severe strain.
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Scientists are continuing to use the fossil record as a kind of deep-time early warning system. By comparing microfossils, plant remains, and climate clues from multiple locations, researchers can better understand how sudden cooling, volcanic emissions, and other disruptions affect life on Earth.
The findings also sharpen a long-running idea about why mammals were able to rise after the dinosaurs disappeared. The researchers said a fungus-rich aftermath may have benefited mammals because their warmer bodies were better at resisting fungal disease than reptiles were.
As researchers learn more about the chain reactions behind ancient die-offs, they can better recognize the pressures building in modern ecosystems.
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