© Chona Kasinger for The New York Times
A gray wolf has been confirmed roaming California’s Mendocino National Forest, marking the first verified sighting there since the species made its comeback to the state 15 years ago. Wildlife officials say the discovery signals the predator’s continued expansion across California’s wild landscapes.
The sighting was reported in late August in the far northern reaches of Lake County, roughly two hours north of San Francisco. After receiving multiple reports from residents and observers, the California Department of Fish and Wildlife investigated and officially verified a wolf’s presence in the area, according to a statement from county officials.
Gray wolves were once hunted to extinction within California’s borders, disappearing from the state for nearly a century. Their return began in earnest around 2011, when a lone wolf known as OR-7 crossed into California from Oregon, reigniting hopes for the species’ natural recovery. Since then, small numbers of wolves have gradually reestablished territory across parts of Northern California, with packs forming in areas such as Lassen and Siskiyou counties.
The latest sighting in Mendocino National Forest suggests the animals are pushing further into new territory, a development conservationists view as an encouraging sign of ecological resilience. Wolves play a critical role in maintaining balanced ecosystems by regulating prey populations and influencing the behavior of other wildlife. Wildlife officials say they will continue monitoring the region to better understand the wolf’s movements and determine whether it may be part of a larger pack venturing into unfamiliar terrain.
The post Gray Wolf Spotted in Mendocino National Forest for First Time in 15 Years first appeared on EnviroLink Network.
A contentious plan allowing major polluting industries to use carbon credits generated from a new koala national park in New South Wales to offset their emissions will proceed, after a deal was struck between the governing party and the Greens. The agreement means the Greens declined to join a Coalition-backed effort to block the arrangement in the Senate.
The plan has drawn criticism from environmental advocates who argue that using a protected wildlife sanctuary to generate offset credits undermines the conservation purpose of the park and allows heavy emitters to continue polluting rather than cutting emissions at the source. Supporters of the deal counter that it secures funding and formal protection for critical koala habitat that might otherwise remain vulnerable to logging or development.
The agreement did not have unanimous support within the Greens party room. Three senators — two from Tasmania and one from Western Australia — broke ranks to cross the floor and vote against the deal when it came before the Senate on Thursday afternoon. Their dissent highlights ongoing tension within the party over how far to compromise on environmental protections in pursuit of broader legislative wins, and raises fresh questions about the long-term ecological trade-offs of carbon offset schemes tied to national parks.
The koala park itself has been championed as a landmark conservation project, aiming to protect one of the last strongholds of the vulnerable species amid ongoing habitat loss from land clearing, bushfires, and climate change.
The post Great Koala National Park Carbon Credit Deal Clears Senate Despite Internal Party Revolt first appeared on EnviroLink Network.
Across the stories today, a common thread emerges: the gap between what protects us on paper and what protects us in practice. Again and again, communities are discovering that designations, promises, and permits only matter when someone is willing to enforce them — and that when systems fail, it’s ordinary people, and often the most vulnerable, who absorb the shock.
Nowhere is that clearer than in Jackson, Mississippi, where a federal appeals court ruled this week that the Constitution guarantees no right to clean water. For residents who have lived through years of contaminated taps and boil-water notices, the decision lands as a gut-punch reminder that legal frameworks haven’t caught up to environmental reality. A similar tension runs through the Guardian’s reporting on datacenter wastewater in Wyoming, where testing turned up a rare, potentially hazardous bacterium, and on English golf clubs, where one in twelve have quietly broken water extraction rules amid growing drought stress. Behind the numbers are real communities adapting in real time — often without knowing what’s actually flowing through their pipes or being pulled from their aquifers.
That same gap between promise and delivery surfaces in the UK’s datacentre boom, which new analysis suggests will produce only a quarter of the jobs once advertised, even as it strains the national grid. It echoes in Georgia, where a once-booming EV manufacturing corridor is hitting turbulence under shifting federal policy — a reminder that industrial transitions built on incentives can be as fragile as the politics that fund them.
Yet the day’s coverage also points to growing momentum around care, restoration, and reckoning. Hurricane Lowell’s damage across Hawaii’s western islands — toppled trees, flooded roads, thousands without power — sits alongside quieter stories of renewal: Gloucestershire’s proposal to reintroduce beavers as a defense against drought and flooding, Douglas Head’s new conservation status on the Isle of Man, and Coventry’s investment in Longford Nature Park. These are small, deliberate acts of stewardship, the kind Wendell Berry spent his life advocating for. His death last week, at 92, feels newly resonant this week — a farmer-poet who insisted that loving a place well was itself a form of environmental action, long before it became policy language.
Farther afield, the human cost of extraction runs deep. In Peru and Brazil, mercury from illegal gold mining is showing up in children’s blood and in fish that families have eaten for generations, forcing painful dietary changes in communities that did little to cause the contamination. In Indonesia, El Niño-fueled fires are pushing orangutans out of burning forests, while in Uttarakhand, India, women — who gather firewood and fodder — are bearing the brunt of increasingly long fire seasons. In Colombia, the Wiwa community’s decision to relocate their village down the mountain is less retreat than adaptation, a recognition that sacred land is changing faster than tradition can hold still.
It’s a reminder that progress and pressure often arrive together — a new spaceport investment in Shetland, a badger vaccination program under scientific scrutiny, a push for a Natural History GCSE to reconnect children with the outdoors. Each represents a small bet on the future, even as larger systems strain under climate and economic pressure.
As the week unfolds, watch whether the Jackson ruling prompts congressional attention, whether Britain’s Green Party succeeds in forcing transparency around ecosystem collapse risks, and whether Gloucestershire’s beavers get their chance to prove that sometimes the oldest solutions are still the best ones.
The post Hurricane Lowell Floods Western Hawaii, New Forest Wildfire Threatens Woodland — Today’s Environmental Briefing for Wed, Sep 9 2026 first appeared on EnviroLink Network.
On June 19, the Aquarium of the Pacific took in almost 500 animals in one go. Fish, marine invertebrates, and sharks were all brought into the facility in Long Beach, California, but the aquarium hadn’t just gone on some big marine shopping spree.
These animals were rescued from animal trafficking, and were in urgent need of a home. At the aquarium, the staff worked through the night to stabilize and care for them.
“Every animal that arrives at the Aquarium, whether through a carefully planned acquisition or a last-minute confiscation, receives the same high standard of care. What can differ is the condition in which those animals arrive,” Johnathan Casey, Aquarium of the Pacific curator of fish and invertebrates, tells Popular Science.
Many trafficked animals have been traveling in stressful or poor conditions, so the aquarium’s experts immediately check their physical condition, water quality, and individual needs. They usually know little about an animal’s origin or history, so the team needs to be prepared for anything. The rescued animals are also quarantined to avoid the potential spread of diseases, according to Alyssa Tillman, the assistant curator of fish and invertebrates.
The species included brownbanded bamboo sharks (Chiloscyllium punctatum), ocellaris clownfish (Amphiprion ocellaris), and Banggai cardinalfish (Pterapogon kauderni). The IUCN Red List classifies brownbanded bamboo sharks as Near Threatened and Banggai cardinalfish as Endangered.
While the arrival of almost 500 animals was a standout event, the Aquarium of the Pacific has received rescued animals from over 30 confiscation events since September 2024. This means they saw one confiscation event every three weeks, though the first eight months of 2026 have already seen over a dozen cases. Overall, the aquarium has taken in over 3,600 rescued trafficked animals in the past two years.
The Aquarium encourages “the public to become informed consumers to help avoid wildlife trafficking of exotic pets. This includes researching the protected status of the species and ensuring purchases are through a reputable vendor,” Casey explains. “If the vendor cannot provide proof of where the animal came from, refraining from purchasing it is a way to help.”
The post Nearly 500 animals rescued from trafficking arrive at a California aquarium appeared first on Popular Science.
Queensland open-cut Saraji mine will be able to keep digging until 2055 as Anthony Albanese denies tensions with Pacific leaders over fossil fuels
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Australia’s new national agency for environmental protection has approved its first coal project, allowing a Queensland open-cut mine to keep digging until 2055 while clearing threatened woodland and koala habitat.
The confirmation of the extension of the Saraji mine, which digs and exports coal for steel making, comes after the prime minister, Anthony Albanese, denied this week there was tension over Australia’s fossil fuel exports during talks with Pacific leaders.
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© Photograph: Wikimedia/Lock the Gate Alliance
© Photograph: Wikimedia/Lock the Gate Alliance
© Photograph: Wikimedia/Lock the Gate Alliance
Australia’s extinct thylacine, also known as the Tasmanian tiger, was not the powerful predator European settlers had assumed based on experiences with the dogs and wolves of their homeland, scientists say.
In a recent study of the skull of this creature, famously hunted to extinction, researchers from Flinders University and the University of Melbourne found something unexpected: the thylacine likely hunted only small prey. The team presented these findings in a paper published in Nature Communications, challenging the assumption that the Tasmanian tiger targeted large animals like sheep.
According to the new research, false European assumptions brought to a new land led to the overhunting and extinction of the thylacine species.
The primary discovery in the work was that the thylacine’s long, deep jaw shape would be poorly suited to holding down large animals. Instead, it would be more effective at delivering a powerful snap to a much smaller animal.
“Our latest findings on their feeding adaptations counter the myths that drove the thylacine to extinction,” said lead author Professor Vera Weisbecker, from the College of Science and Engineering at Flinders University. “Thylacines were often compared to Northern Hemisphere predators such as wolves, jackals and foxes from the dog family Canidae. This resemblance gave them their species name ‘cynocephalus’, meaning ‘dog-head.’”
While the animal may have had some superficial resemblance to a wolf or dog, they followed a quite different evolutionary trajectory. Instead of being closely related to canines, they were more similar to kangaroos. Thylacines were marsupials, pouch-bearing mammals that separated from the broader mammalian lineage in the time of the dinosaurs.
The researchers say the thylacine skull combines a set of features seen in no other living carnivorous mammal, making it a true outlier. At a glance, the team noted the extinct animal’s large skull, with its long, tall upper jaw that protrudes and ends in a wide snout—an unusual feature that is worthy of more detailed study.
“Even though the average thylacine may have weighed only half as much as the average wolf, its vastly oversized skull is about as large as a grey wolf’s skull,” said co-author Dr Douglass Rovinsky. “But while it was big, it wasn’t really shaped like the skull of a big predator. Instead, the thylacine’s snout was long and slender, almost delicate – not robust like the snout of a grey wolf. It very much looks like the snout of a fox or jackal, which can be much smaller than thylacines.”
Instead of holding down large animals, the researchers say these jaws would be better suited to capturing bandicoots, an animal similar in size to a rabbit, with a powerful snap.
“The longer a jaw is, the faster its tip moves when an animal bites. This increases the impact of the strike. We think that the thylacine’s huge skull size allowed it to withstand these bite forces,” says Professor Weisbecker.
Intriguingly, while this skull configuration is not seen in carnivorous mammals, large-headed hunters with powerful snapping jaws are common outside of the mammal group. This shape is particularly useful in aquatic environments, where fast, slippery fish are a primary target for predators.
Long, tall jaws with a wide tip are frequently found in crocodiles and some predatory fish. While the shape is conducive to hunting, it is typically used to capture smaller, highly agile prey.
“Thylacines were hunted because of myths that they were ferocious predators of livestock, when there was little evidence for this. Their extinction is a story of ignorance and lack of respect for Australia’s unique wildlife and its Indigenous custodians,” Professor Weisbecker concluded. “As a country at the global forefront of mammal extinctions, we need to do all we can to safeguard equally irreplaceable surviving species.”
The paper, “Skull Morphology of the Extinct Tasmanian Tiger Suggests Unique Biting Style,” appeared in Proceedings of the National Academy of Sciences on August 31, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
Scientists at the University of Colorado at Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES) have discovered that some microbes in Antarctica’s soil don’t exist anywhere else on Earth, upending the long-held belief that microbes move freely around the planet and inhabit many regions.
The researchers behind the discovery said understanding that some microbes are endemic to Antarctica’s soil challenges previous assumptions and offers valuable insights for future research and present-day conservation efforts.
Announcing the findings, study leader and postdoctoral researcher Nick Dragone and co-author Noah Fierer, a CIRES Fellow and Director of the Center for Microbial Exploration, noted that scientists have always assumed that microbial species were widespread.
“There is a long-standing assumption in microbiology that ‘everything is everywhere,’” Dragone explained.
That’s because, unlike plants and animals, which are generally restricted to certain global zones or latitudes, microbes are highly mobile. For example, a simple updraft could propel microbes into an atmospheric jet stream, then deposit them hundreds or even thousands of miles away.
Still, Dragone and Fierer propose that, given Antarctica’s remote location, if there were a spot on Earth containing species unlike the rest of the globe, it would be on the planet’s southernmost continent.
“If we do find we’re looking for endemic microorganisms, a good place to start is Antarctica, because it’s an entire continent that is geographically isolated, ” Fierer said.
The study coauthor also noted that the unique conditions found in Antarctica’s soil aren’t usually found in other soil environments. “[Being] cold is the obvious one,” Fierer said, “but also super dry; Antarctica is a desert.”
Instead of starting with any microbial species, the CIRES team focused on bacterial strains within the Arthrobacter group. First, these strains grow well in lab conditions, which was critical to the team’s experiments. Second, Arthrobacter group bacterial strains are found in diverse environments ranging from the tropics to Colorado, and most critically, to Antarctica’s soil.
Byron Adams, professor of biology at Brigham Young University and a co-author of the study, said the species is widespread, but also diverse.
“Arthrobacter as a group may be found all over the planet, but when we look closely at individual strains, just like penguins, Antarctica clearly has its own distinctive biological history,” the professor explained.
To start, the team collected soil samples from Antarctica. They also collected comparison samples from similarly cold, arid regions like the Tibetan Plateau, Svalbard in the Arctic, and Chile’s Atacama Desert.
When examining the sampled soils, the team tested over 100 Antarctic bacterial strains and 500 worldwide strains.
Dragone and Fierer both noted that the research was made possible by “long-term collaborations among international research teams who have spent decades collecting samples across the continent for various projects.”
After sequencing the genomes of the Arthrobacter strains found in samples from Antarctica’s soils, the team compared them with worldwide strains. For the worldwide species, the team obtained genomes from international research databases.
As hoped, the genetic comparison found species in Antarctica’s soil that were not found anywhere else in the world. Perhaps even more shocking, 90 percent of the Antarctic strains they’d sequenced were completely endemic, with no matches anywhere in the world.
Fierer said previous studies had identified “a few endemic microbes found in very specific environments.” However, the researcher also noted that finding such a large and unexpected number of endemic microbial species “does suggest there could be some in other locations.”
“[Determining] whether other microbial groups show these patterns is a good direction to go,” Fierer added.
Next, the team ran a follow-up experiment to see whether the endemic Antarctic strains showed signs of adaptation to the local, extreme environment. This included growing strains of the collected Antarctic Arthrobacter strains in the laboratory. Critically, the team mimicked the continent’s harsh environmental conditions.
First, the experiments showed that the strains collected from Antarctica’s soil were extremely resilient. They also grew more slowly than non-endemic strains. The team suspects these results show that Arthrobacter strains “are uniquely adapted to Antarctica.”
“We already knew that a broad diversity of microbes can survive the inhospitable conditions of Antarctica,” Fierer said. “Now we know that some of those microbes are also unique to Antarctica and are uniquely adapted to life on the southern continent.”
When discussing the implications of their findings, Adams pointed to a potential shift in public perception of what species diversity means.
“We tend to think of biodiversity in terms of penguins, seals, and whales, the researcher explained, “but this shows that some of Antarctica’s most distinctive species are microscopic.”
Along with the study’s scientific and public relations value, the team said it “sets the stage for future research on microbial life in Antarctica.” They also noted that the findings will aid efforts to preserve Antarctica’s biological diversity, including its microbial species.
“Protecting Antarctic biodiversity also means protecting the biological history contained in a handful of soil,” Adams concluded.
The study, “Evidence for endemism and local adaptation in Antarctic soil bacteria,” was published in the Proceedings of the National Academy of Sciences.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.
Scientists have discovered China’s first known freshwater cave snail, an eyeless species so rare that only three living adults have been found. Deep inside a mountain cave in southwestern China, scientists found an animal that appears built for a world where sunlight never reaches. The tiny freshwater snail has no eyes, almost no color, and [...]Scientists and citizen volunteers discovered two new snail species in northwestern Montenegro, revealing the region’s hidden biodiversity and strengthening calls to protect Komarnica Canyon within the Durmitor World Heritage Site rather than build a hydropower plant. Two previously unknown snails have been added to Europe’s documented wildlife. Named Cochlostoma komarnica and Cochlostoma dobrido, the species [...]
© American Bird Conservancy
An ichthyosaur fossil found in Australia's outback may preserve a rare snapshot of a prehistoric food chain. Around 100 million years ago, the enormous marine reptile swallowed a flying pterosaur before being attacked by a giant ocean predator, new research suggests.
The fossil set, nicknamed "BOB" or "Bag of Bones," belonged to a 20- to 23-foot-long (6 to 7 meters) ichthyosaur, an animal that belonged to a group of dolphin-shaped marine reptiles that lived alongside the dinosaurs during the Mesozoic era, from about 250 million to 90 million years ago. But in a new study, researchers discovered fragments of a pterosaur's jaw — along with fish and cephalopod remains — preserved inside the animal's body cavity.
The finding is the first confirmed evidence that ichthyosaurs ate pterosaurs, an extinct group of flying reptiles that ruled the ancient skies, according to the new study, published July 28 in the journal Gondwana Research.
The fossils may also hint at the ichthyosaur's violent end. Its skeleton — discovered in 2019 in Queensland's outback — contains shattered bones, missing ribs and large crushing injuries. Researchers think the gruesome wounds may have been inflicted by Kronosaurus queenslandicus, a colossal crocodile-like apex predator that lived 120 million to 100 million years ago in the ancient Eromanga Sea in Australia.
Fossilized stomach contents are a rare find because they can be preserved only under very specific conditions.
"Rapid burial after death is essential to prevent decay and scattering of remains," study co-author Matt White, a research associate at the University of New England in Australia, told Live Science in an email. "The animal must have died soon after its last meal so stomach acids don't fully digest the prey."
Researchers used advanced neutron imaging to peer inside BOB's stomach contents without breaking any of the fossilized formations. The scans revealed hidden bones and helped scientists determine that the remains were likely associated with the ichthyosaur's digestive system.
White said that advances in imaging technology are making it possible to uncover evidence that would previously have remained hidden inside fossils.
"Scanning techniques have also improved, which has enabled us to see inside specimens and reveal what they potentially ate," White said. The methods can also reveal "the shape of various organs" and internal bone structures, he added.
The pterosaur remains were found near the front of the ichthyosaur's body cavity rather than in their expected position as digested prey, which White and his colleagues think may be because the ichthyosaur struck the seafloor headfirst shortly after its last meal, shifting some of its stomach contents forward.
"We believe the animal died in the water column — perhaps from a pliosaur (Kronosaurus) attack or natural causes — and then sank," White said. "It impacted the seafloor with its rostrum, and connected soft tissues kept most of the body in sequence."
The fossil offers a rare glimpse into the food web of the ancient Eromanga Sea, which covered much of central Australia during the early Cretaceous period around 145 million to 100 million years ago.
Although ichthyosaurs are known to have eaten fish and squidlike animals, evidence that they ate pterosaurs, a common predator of the ancient skies, has been elusive. The new fossil suggests that at least some ichthyosaurs may have fed on flying reptiles that landed on the water or died and floated to the surface.
"Such discoveries yield valuable information about trophic interactions and allow us to reconstruct ancient ecosystems in greater detail," White said.
© Fernando Llano/Associated Press
© Joel Sartore/National Geographic Photo Ark
When the famous Chicxulub asteroid struck what is now Mexico's Yucatán Peninsula 66 million years ago, it ended the reign of the nonavian dinosaurs. As ecosystems recovered, small, adaptable mammals rapidly spread into newly vacant niches, evolving new diets, larger bodies and more diverse ways of life until they dominated the land within a few million years.
Now, new evidence suggests that even before the asteroid hit, Earth was already beginning to rot.
A study published May 12 in the journal PNAS found evidence of environmental fungal blooms before and after the Cretaceous-Paleogene (K-Pg) mass extinction event. Looking at microscopic fossils from rocks dating to the K-Pg event in North America, a team of researchers led by Dr. Arturo Casadevall, chair of the Molecular Microbiology and Immunology Department at Johns Hopkins University, identified an earlier fungal bloom dating to roughly 30,000 to 100,000 years before the asteroid hit, during a period of cooling linked to intense volcanic activity in the Deccan Traps in what is now India.
The researchers also found a fungal spike immediately after the Chicxulub impact exactly when dead plants and animals would have littered devastated ecosystems. The finding adds to earlier evidence from New Zealand that suggests the fungal bloom wasn't just a local event.
This idea feeds into a controversial idea called the fungal infection-mammalian selection (FIMS) hypothesis. First proposed two decades ago by Casadevall and subsequently updated in 2018 and 2026 papers, the FIMS hypothesis suggests that the abundance of fungus before the asteroid impact may have helped mammals gain an evolutionary advantage over the dinosaurs that remained after that cataclysm.
The hypothesis doesn't argue that fungus wiped out the dinosaurs. Instead, it proposes that mammals' live births and immune systems may have helped them withstand the rise of fungus in ways egg-laying reptiles and nonavian dinosaurs could not, thereby giving them the upper hand in disrupted ecosystems full of rot, cold, starvation and polluted air.
"The fungal infection mammalian selection hypothesis is focused on how the mammals became the dominant land animals," Casadevall told Live Science via email, "not dinosaur extinction."
But not all experts are convinced. Mary O'Connell, the Chair of the Zoology department at the University of Manchester told Live Science via email that the hypothesis doesn't fit all the evidence and that "it emerges from a chain of plausibility arguments rather than direct evidence, and the links in the chain are weaker than the framing may suggest."
To find this pre-asteroid fungal bloom in their new study, Casadevall and Rosanna Baker, who researches fungus at Johns Hopkins, focused on palynomorphs — tiny fossilized organic remains, including fungal spores, fungal hyphae and plant pollen — preserved in ancient sediment layers from the Denver Basin in Colorado dating back to the K-Pg extinction.
Baker counted between 100 and 500 microfossils per sample across sediment layers spanning about 60,000 years before the K-Pg mass extinction event to 30,000 years after it. Most samples were dominated by plant material, but some layers contained 50% or more fungal spores. The researchers interpreted this high proportion of fungal spores as a sign of ecological disturbance — more dead material and more fungi feeding on it, especially after the dinosaur-killing asteroid.
Baker and Casadevall also found an earlier fungal bloom dating to roughly 10,000 to 30,000 years before the asteroid impact.
"What surprised us was the proliferation in association with Deccan volcanism, which implies ecological disruption prior to [the] meteor impact," Casadevall told Live Science via email.
In other words, ecosystems may have already been under stress — and faced with a fungal overgrowth — before the asteroid delivered the final blow.
When Casadevall first proposed the FIMS hypothesis, it rested on a simple observation: Mammals are unusually resistant to invasive fungal diseases.
Fungi are major pathogens of plants, insects, amphibians and many reptiles, but life-threatening systemic fungal infections are relatively rare in mammals with healthy immune systems. Casadevall argued that mammals' relative resistance to fungi came from their sophisticated immune systems. In mammals, first-line, relatively nonspecific defenses such as neutrophils recognize fungal cell walls, engulf spores and attack invasive filaments, while the adaptive arm of the immune system excels at building customized antibodies that selectively target specific fungi, and then creating immune memory so the invaders are recognized the next time they're encountered.
Casadevall also initially believed that mammals' high, stable body temperatures — generally around 97 to 104 degrees Fahrenheit (36 to 40 degrees Celsius) — could prevent many environmental fungi from growing well enough to establish an infection.
"The success of mammals made no sense given their high energy needs and this idea provided a plausible mechanism for their success," Casadevall said.
After the asteroid hit, forests burned, plants died, darkness fell and dead matter piled up, providing a feast for fungi. If fungal spores filled the air, surviving animals may have inhaled enormous, possibly dangerous doses.
However, the FIMS hypothesis proposes that mammals had several possible adaptations against these fungal invaders that other animals did not. In addition to having warm body temperatures and complex immune systems, mammals who could maintain stable body temperatures could forage during the cold "impact winter," when ash and dust blocked out the light of the sun. Meanwhile the dinosaurs, who were originally thought to be the "cold-blooded," would have struggled to stay active and find food, leading them to become weaker and more susceptible to disease.
Differences in gestation may have mattered, too. Many mammals protect developing embryos inside the mother's body, where warmth and immunity could shield them from fungi. In contrast, all dinosaurs laid eggs. Those eggs developed in nests, which were often in contact with soil and decaying plant matter — the exact environments where fungi thrive. Modern fungi can invade reptile eggs, and fossilized hyphae, a type of fungus, was described in dinosaur eggshells in a 2008 study.
That does not prove fungi wiped out dinosaur nests. Fossilized hyphae could suggest either that fungi invaded a living egg, or that fungi colonized the egg after death. Still, eggshells provide one clue that fungi were a problem for the survival of dinosaur young..
Another potential line of evidence to buttress the FIMS hypothesis came from dinosaur bones that showed evidence of fungal infection.
In 2022, a team led by Cary Woodruff, curator of vertebrate paleontology at the Phillip and Patricia Frost Museum of Science in Miami, described a Late Jurassic sauropod fossil from Montana with unusual lesions in its neck vertebrae. The dinosaur, an immature diplodocine known as MOR 7029, lived roughly 150 million years ago, long before the asteroid impact.
Sauropods had long, air-filled neck bones connected to their respiratory system. In fossils of healthy sauropods, the places where air-sac tissue met bone are smooth, sometimes glass-like, Woodruff told Live Science.
But in this animal, the normally smooth sockets were rough and irregular. "Coming out of the socket — like imagine coming out towards you —it looked like fossilized heads of broccoli florets," Woodruff said. "And I had never seen that."
Unsure what he was looking at, Woodruff posted a photo online and asked whether anyone had seen anything similar. Other anatomists and paleontologists quickly weighed in. Their response, he recalled, was essentially, "That's exactly what we would have predicted a respiratory infection to look like," he said.
By comparing the fossil lesions with respiratory diseases in modern birds, which are living dinosaurs, the team tentatively flagged the condition as airsacculitis with associated osteomyelitis — air-sac inflammation that had spread to nearby bone.
However, the researchers could not identify the exact disease that caused the inflammation. In modern birds, airsacculitis can be caused by fungal infections such as aspergillosis, but also by bacterial infections. Without preserved soft tissue or fungal structures, they stopped short of confirming a fungal infection diagnosis.
Either way, Woodruff thinks the sauropod was probably sick enough that the infection contributed to its death. It may have become too weak to keep up, too ill to eat or drink properly, or too vulnerable to escape predators.
Even so, many experts remain skeptical of Casadevall's hypothesis. For one thing, the asteroid and its aftermath already explain a tremendous amount. The impact triggered tsunamis, earthquakes and a global food-web collapse. Those disasters alone would have killed off large dinosaurs at the top of disrupted food chains.
Another problem revolves around body temperature. In 2005, when Casadevall first proposed his hypothesis, dinosaurs were often thought of as "cold-blooded," while mammals were "warm-blooded." But over the years, research has uncovered that many nonavian dinosaurs, such as Velociraptor, T. rex and Brachiosaurus, were likely warm-blooded, too — so body temperature wouldn't explain why fungus would have been a big problem for many dinosaurs.
Complicating the picture, birds — the only surviving dinosaurs — often have higher body temperatures than mammals do. So the FIMS theory rests on an assumption that living examples of dinosaurs don't support, Flynn said.
If everything we know that suggests dinosaurs are more susceptible to fungal infections is based on living dinosaurs (birds) and they survived, doesn't that rather undermine this hypothesis?
Jingmai O'Connor, paleontologist at the Field Museum in Chicago
Around the time of the asteroid impact, cold-blooded creatures like turtles and crocodilians that lived in the water "don't really suffer as severely as other groups, even including mammals," Andrew Flynn, an assistant professor of paleobotany at New Mexico State University, told Live Science. "Clearly this fungal thing is not probably what's causing mammals to rise up and go on to dominate the ecosystem."
The FIMS hypothesis also has a contradiction at its heart, said Jingmai O'Connor, a paleontologist at the Field Museum in Chicago.
"It's just a hypothesis I had vaguely heard about but was not popular, not often mentioned, and I guess I would say 'out of favor,'" O'Connor told Live Science via email. "If everything we know that suggests dinosaurs are more susceptible to fungal infections is based on living dinosaurs (birds) and they survived, doesn't that rather undermine this hypothesis?"
Dr. Isabel Jimenez, an assistant professor at Johns Hopkins University and a proponent of FIMS, agrees that this discrepancy must be explained.
"For the FIMS hypothesis to still hold water, we have to consider alternative mechanisms by which dinosaurs could have been more susceptible to fungal diseases than mammals," Jimenez told Live Science in an email.
Modern-day birds are avian theropods — the surviving branch of the dinosaur family tree — and likely faced the same fungal pressures as their extinct relatives. More recently, in 2026, Jimenez and Casadevall have suggested a tweak to their theory: that some of the small-bodied, beaked, flying or semiflying theropods may have been able to pull through, despite some baseline higher susceptibility to fungal disease. That's because they were small, had feathers to better insulate their bodies, and maintained generalist diets that enabled them to use more food sources than the dinosaur lineages that died out.
Working with Jimenez, Casadevall outlined an updated version of the FIMS hypothesis in a paper published earlier this year. In it, they propose that dinosaurs' respiratory systems may have made them more at risk than their mammalian counterparts.
Whereas mammals breathe by expanding and contracting flexible lungs filled with blood-rich alveoli, modern birds — and probably many dinosaurs — have rigid lungs ventilated by a network of thin-walled air sacs. The air sacs act as bellows, maintaining one-way airflow through the lungs, but they perform little gas exchange and have relatively poor blood supply. This system could have also carried inhaled fungal spores deep into the respiratory tract, where they may have settled in air sacs that are harder for circulating immune cells to reach and clear.
While birds have a similar sophisticated immune system as mammals — including macrophages and antibodies — their air sacs extend throughout the body and sometimes into the bones, making fungal infections easier to spread beyond just the respiratory system.
This possible weakness is what Jimenez and Casadevall suggest is what made air-sac-bearing dinosaurs vulnerable to fungal infections, similar to modern birds.
After the asteroid strike, there would have been soot and sulfur polluting the air and dinosaurs would have been nutritionally stressed. "So secondary fungal infections are certainly possible," Jimenez said, referring to infections that take root after the body's defenses are weakened.
But skeptics argue that even with these updates in the FIMS hypothesis, more evidence is needed to show it's not just possible but likely.
The idea that their air-sac respiratory systems made them more vulnerable to fungus is "a more testable claim," but its likely impact on dinosaurs would also be more limited, because of competing environmental factors, O'Connell said.
And because only a handful of fungal species actually cause disease in animals, to show that fungi worsened dinosaur deaths, researchers would need to find evidence of elevated fungal disease in dinosaur fossils from right after the asteroid struck, O'Connell said.
"We would also need to be able to identify elevation of pathogenic fungal spores in the sedimentary record at that boundary, rather than just more spores," she said.
Overall, "the fungal infection-mammalian selection hypothesis feels like a conjecture in search of any supporting evidence," paleontologist and science writer Riley Black, told Live Science in an email.
How much do you know about the king of the dinosaurs? Test your knowledge with our T. rex quiz!
Science word of the day: Coprolite
Pronunciation: KAHP'-ruh-lite
What it means: Coprolites are fossilized poop. Scientists have found coprolites from animals as diverse as fish, dinosaurs and saber-toothed cats. Teeth in the saber-toothed cat poop indicated that it had been eating baby sloths, which frankly feels a bit unfair from a creature with 11-inch-long (28 centimeters) teeth.
These fossils form when poop gets rapidly buried and mineralized instead of rotting away. Coprolites can be hard to match to the animal that produced them, but undigested bones and teeth in the fossilized poop can often provide clues to the kinds of animals that other animals eat.
How to use it in a sentence: If you're ever in a science museum and a volunteer, with a twinkle in their eye, asks you what you think a chunky, rock-looking thing is, the answer is always coprolite.
Can you crack our science word of the day puzzle, Chain Word?
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