About 65 million years ago, after dinosaurs died, a giant fungus may have risen as forests filled with dead plants left behind by the mass extinction

When a mass extinction transforms an ecosystem, the organisms that survive can find themselves in a very different world. The asteroid impact at the end of the Cretaceous Period disrupted ecosystems and left large amounts of dead organic material. Following the event, fungi could have thrived in environments where there was an abundance of food.Fossil remains reveal a fungal bloom after the asteroid impactIn a study published in the Proceedings of the National Academy of Sciences, researchers Rosanna P. Baker and Arturo Casadevall examined fossil evidence from three boundary sections, one in the Denver Basin in Colorado and two in the Williston Basin in North Dakota. Their paper, Fungal proliferation before and after the Cretaceous-Paleogene mass extinction event in North America, documented a sharp increase in fungal remains immediately after the Chicxulub impact. The researchers compared the share of fungal remains among palynomorphs before and after the impact and argued that the fungal spike appeared just after the K/Pg boundary. They noted that this was the first North American record of the bloom and suggested it supported a broader, possibly global, wave of fungal proliferation after major ecosystem collapse.Palynomorphs are microscopic organic remains preserved in sediment, including pollen and spores and the US Geological Survey explains that they can preserve evidence of past environmental changes over millions of years. They show that fungi were present, but not how many living organisms there were. The Denver Basin findings are consistent with earlier evidence from New Zealand and suggest that the post-extinction fungal increase may have occurred across multiple regions, although further evidence is needed to establish how widespread the phenomenon was. The results are consistent with a broader ecosystem response to the extinction.The above-mentioned study also identified a prolonged interval of elevated fungal abundance in the Late Cretaceous, which its abstract dates to roughly 30,000 to 10,000 years before the impact. The authors note that this interval coincided with climatic cooling at the site and with the Poladpur phase of Deccan Traps volcanism in India, but a coincidence in timing does not establish a causal link.Dead vegetation may have favored decomposing fungiDamage to terrestrial ecosystems was brought about by the asteroid impact and its effects. The death of plants and decline in vegetation resulted in accumulation of dead organic matter, which could provide nutrients to some organisms that derive nutrients from decomposition of dead matter. Saprotrophic fungi are decomposers that feed on dead organic matter, including dead plants. The authors say it is likely that abundant decaying biomass after the mass extinction favored saprotrophic fungi, though they could not match the fossil forms to living fungal genera.However, the findings of the researchers were based on fossil records and not on direct estimates of dead biomass available to the fungi. This is an important distinction since an increase in the fossil record of fungi shows a change in the abundance of fungi in the sample sediments, but not necessarily the ecological conditions that caused such a change.Earlier chemical evidence pointed to fungal activityA 2020 paper by Berry in Acta Palaeobotanica, Evidence for fungal proliferation following the Cretaceous/Paleogene mass-extinction event, based on chemostratigraphy in the Raton and Powder River basins, western North America, examined boundary clay in the Raton Basin of Colorado and the Powder River Basin of Wyoming. The paper focuses on the Aib horizon in boundary clay from the Raton and Powder River basins, arguing that Aib is unlikely to be extraterrestrial because impact conditions would have destroyed it.Alpha-aminoisobutyric acid is a chemical compound that is known as Aib in short. The study examined the presence of α-aminoisobutyric acid (Aib) in Cretaceous-Paleogene boundary clay deposits in the Raton Basin of Colorado and the Powder River Basin of Wyoming to investigate evidence of chemical changes associated with the extinction event. The author proposed that this chemical horizon tracked a fungal spike like the one detected in New Zealand. This was indirect evidence of higher fungal activity in the region at the boundary between the two periods, since Aib is a fungal product rather than a fossil. Unlike the above-mentioned study, which focused on fossilized fungi found in North American sediments, the Berry paper based its conclusion on chemical composition. Thus, both studies offer various types of evidence of the increased activity of fungi in the proximity of the extinction event.The fungal bloom was not a single giant organismThe idea that a giant fungus took over forests after the dinosaurs went extinct could be misleading. What the findings entail is the growth in the abundance of microbial parts of fungi and not necessarily the evolution of one single giant fungus that has covered the land. Prototaxites is sometimes raised in discussions of giant fungi, but it lived about 407 million years ago, more than 340 million years before the end-Cretaceous extinction, so it has no bearing on the post-impact fungal bloom.According to a 2026 study published in Science Advances, fossils of Prototaxites taiti from the 407-million-year-old Rhynie chert differ structurally and chemically from known fungi, casting doubt on its classification as a fungus. Some researchers argue that it belongs in an extinct lineage of eukaryotes. Its oddity in form does not mean that there was a giant fungus following the demise of the dinosaurs.Fungi may have played a role in post-extinction ecosystemsThis new information helps scientists better comprehend how these organisms reacted to one of the greatest biological catastrophes on Earth. The ability of fungi to break down organic matter could be useful after the impact and could contribute to the cycling of nutrients in the new ecosystem. The fossil record does not help to prove that fungi became dominant in all ecosystems after the extinction or help to determine their contribution to the recovery of the terrestrial ecosystems. What it does prove is that there was an increased amount of fungal fossils in the studied sediments. Instead of showing how a huge fungus took over the world, the fossil record suggests a wider ecological reaction. In a world where food chains had been disrupted and where organic material was abundant, fungi could have found ideal conditions for survival.You use AI every day. Now get your AI Quotient. Take the AIQ test.