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During and her coworkers noted the cataclysmic sequences of events as part Publication of a paper in Nature, which pinpoints the Chicxulub impact to the middle of springIn the Northern Hemisphere. The researchers analyzed fish fossils as well as tektites lodged in the animals’ gills that show “they were buried alive,” said coauthor Jeroen van der Lubbe, a geochemist at Vrije Universiteit Amsterdam. However, not all experts agree with the doomsday scenario outlined in the new paper.
Paleontologists not involved in the research applaud the team’s approach and general conclusions about what killed the fish, but also voiced concern that it’s built on the assumption that the material from the Tanis bone bed was deposited in the immediate wake of the end-Cretaceous event; lead author During went so far as to say she’s confident the animals died within an hour of the distant impact.
Other researchers who study what happened at the K-Pg boundary—shorthand for the moment in geological time when the Cretaceous ended (with a bang) and the Paleogene period began—are less certain. They don’t question the mass death and seiche that piled the bodies, but believe it could have been the result of a smaller, more localized catastrophe. Their concern over the new findings is that they rest on another paper—a controversial one that has not yet been fully accepted by the field.
“I totally buy that these fish died in the spring. I think the authors of this paper did a really good job on that,” says Tyler Lyson, a vertebrate paleontologist at the Denver Museum of Nature and Science. Lyson isn’t part of the new paper’s team, but he is familiar with it. Lyson has also been involved in extensive fieldwork in Hell Creek Formation. This famously fossil-rich area is located at the intersection of two Dakotas. Montana, Wyoming, and includes layers from K-Pg’s boundary.
Melanie During, lead author, excavates a paddlefish at Tanis site.
Melanie During/Atlas Obscura
The Tanis site is part of Hell Creek, but Lyson, whose research focuses on the extinction of the dinosaurs and subsequent proliferation of other animals, is concerned that the new paper assumes the Tanis bone bed represents the K-Pg “kill layer,” that moment of mass death on, he says, “the single worst day for multicellular life on Earth.
“I think there’s still a lot of doubt about that,” says Lyson, who believes the fish and other animals may have been killed in a regional event not related to the Chicxulub impact. “It could be [from Chicxulub], but we’re still all waiting for more data…. Because it’s either the fish died in the spring, or the fish died in the spring when the asteroid struck. Those are two very different conclusions.”
The new research is not the first to suggest the dinosaurs’ doom came in the Northern Hemisphere springtime—another team’s paper, Published in late 2021 Scientific Reports, a sister journal to Nature, made a similar suit based upon similar material from Tanis.
Van der Lubbe said the two teams arrived at their conclusions independently, and that his team’s work is unique because it includes analysis of osteocytes, tiny pores or cells within the fish bones, that reveal additional information about the animals. The regular growth patterns preserved in their bones like tree rings indicate that the fish from Tanis were in good health and had not suffered drought or famine before their sudden deaths.
Modern paddlefish is little different from its relatives 66 million years back.
Ryan Hagerty/ USFWS/Public Domain
However, both papers and other research on Tanis site are based on a 2019 article Published in Proceedings of National Academy of Sciences that confidently claimed Tanis was a “snapshot … of the immediate effects of the Chicxulub impact.” The lead author of that paper, and of the 2021 Scientific ReportsRobert DePalma was a paleontologist and the central character of a paper. Long story published by The New Yorker a day before his bombshell 2019 paper. Numerous paleontologists worried that DePalma’s bold claims had not yet been vetted with scientific rigor; the young researcher’s apparent reluctance to open Tanis to more scrutiny by other teams only heightened that skepticism.
Lyson and some colleagues have examined other blocks of fossilized fish, taken from the Tanis site before DePalma began work there a decade ago, and they failed to find a single impact spherule, the tiny, telltale tektite upon which much of the mass extinction “snapshot” theory rests. Summing up what other researchers have said privately, Lyson says that the initial 2019 paper is “a really good paper,” but, “everything about this (Tanis) locality is just bizarre. What I would like to see is more evidence that this is the K-Pg to begin with.”
He adds that he understands the desire for the core Tanis team, including DePalma, to protect their own research interests, but that “it would be nice for other scientists to go to this locality and have a look and collect their own samples. To have different folks with different eyes, because we’ve all seen different things from different K-Pg boundaries all around the world and we’re all experts in different areas.”
“It’s just independent verification,” he adds. “It’s the way science works.”
Lyson is also skeptical about some of the conclusions in the new paper, including the suggestion that the Chicxulub event’s occurrence in Northern Hemisphere spring—when many animals would be “out and about,” as During put it, actively foraging and reproducing—played a role in which species survived the mass extinction.
“I don’t really buy that,” Lyson says, adding that the pattern of the species around the world that survived the mass extinction has nothing to do with seasonality. Smaller animals, with slower metabolisms and who lived underground or under water, had the best chance of surviving, regardless of where they were located. These animals were protected from most of the initial devastation caused by the asteroid impact.
They also had lower energy needs, allowing them to survive a period of harsh cold and limited resources that resulted from particles blocking out the sun in what During called “a nuclear winter of unknown duration.” Species that did make it through this grim period included several mammals, and the end of the dinosaurs’ reign is widely accepted as leading to the rise of mammals, which quickly evolved to fill vacant ecological niches.
Lyson hopes that more researchers can access Tanis and conduct their own analysis to verify DePalma’s work. If proven to be a snapshot of the K-Pg boundary, Lyson says, “I think it’s really cool. I think it’s amazing to think that we could know what season this extinction was.”
“It’s such a critical interval of time,” he adds. “If it hadn’t been for that fateful day, we wouldn’t be here … there’s no doubt about that.”
Robert DePalma, paleontologist, stated that several institutions had conducted fieldwork on the Tanis site after the story was published. All research has been done in accordance with the field’s standards.
