Microbiologists from Johns Hopkins University, through meticulous examination of fungal microfossils within 66-million-year-old rock strata sourced from Colorado’s Denver Basin, have not only substantiated the theory of a global fungal proliferation following the dinosaur-annihilating asteroid impact but have also identified an antecedent, previously unrecognized ecological crisis.
The terminal Cretaceous mass extinction was characterized by the dual catastrophes of the Chicxulub asteroid impact and persistent Deccan Traps volcanic activity.
“A surge in fungal presence within geological archives can serve as an indicator of significant ecological upheaval,” stated Rosanna Baker and Arturo Casadevall, researchers affiliated with Johns Hopkins University.
“Such pronounced increases are documented globally in relation to the Permian-Triassic extinction event; however, for the end-Cretaceous extinction, they had previously been reported exclusively from New Zealand.”
“Our endeavor involved re-evaluating the proposition of a worldwide fungal proliferation subsequent to the conclusion of the Cretaceous period and its associated mass extinction event, utilizing specimens procured from North America.”
Within the scope of this investigation, the research team concentrated their efforts on analyzing rock samples extracted from several paleontological localities situated in Colorado’s Denver Basin and North Dakota’s Williston Basin.
These samples underwent rigorous processing and detailed analysis to ascertain the quantity of fungal microfossils present and to differentiate them from pollen grains and other microfossils originating from plant matter.
The analytical results derived from the Colorado samples revealed a distinct and significant augmentation in the prevalence of fungal microfossils, in comparison to microfossils of plant origin, within the geological layers precisely corresponding to the period of the asteroid impact.
This discovery provides the inaugural direct corroboration of the findings from New Zealand, lending substantial support to the premise that the close of the Cretaceous era was not solely marked by a cataclysmic impact but also by a pervasive global proliferation of fungi.
Remarkably, the investigation unearthed evidence of an additional, more protracted phase of fungal dominance that occurred approximately 30,000 to 10,000 years preceding the asteroid impact.
The scientists demonstrated a correlation between this elevated fungal activity and a recognized interval characterized by comparatively cooler terrestrial temperatures at the study site—an interval that succeeded a period of intense volcanic eruptions in the geographical region now known as western India.
“Existing evidence within the fossil record suggests that certain species were already experiencing decline during this earlier period,” remarked Baker.
“It is conceivable that the volcanic events in Asia placed considerable stress on planetary ecosystems, thereby predisposing them to succumb to the eventual catastrophic impact of the asteroid.”
The analytical process also identified another period of fungal overgrowth, lasting approximately 2,000 years and of indeterminate origin, within the Early Paleocene epoch, roughly 10,000 years subsequent to the asteroid event.
“Fungi are biological entities that frequently flourish in the wake of environmental catastrophes,” observed Professor Casadevall.
The rock samples from North Dakota did not exhibit a comparable surge in fungal proliferation concurrent with the asteroid impact; however, the researchers posited that this discrepancy might be attributable to variations in the lithological composition of the rock when contrasted with the Colorado samples.
Nevertheless, their analysis of the North Dakota samples did corroborate the observations pertaining to the Late Cretaceous period, tens of thousands of years prior to the asteroid impact, and the Early Paleocene findings, approximately 10,000 years post-impact.
“These outcomes lend credence to the hypothesis that the pervasive proliferation of fungi following the Cretaceous period bestowed a crucial evolutionary advantage upon mammals—possessing their elevated, more fungally resistant body temperatures—over reptiles, ultimately enabling them to ascend to planetary dominance,” the researchers concluded.
These groundbreaking discoveries have been published in the esteemed journal Proceedings of the National Academy of Sciences.
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Rosanna P. Baker & Arturo Casadevall. 2026. Fungal proliferation before and after the Cretaceous-Paleogene mass extinction event in North America. PNAS 123 (20): e2536899123; doi: 10.1073/pnas.2536899123
