Dinosaur extinction is an unsolved mystery. This ancient fish may have swallowed some crucial evidence.

To some extent, fossils are like photographic images of the past. A still from millions or even billions of years ago becomes preserved within the bedrock of the Earth, underneath layers that have accumulated over time. If you’re lucky, you can use these specimens as a snapshot into the past. By that logic, a new set of fossils found in North Dakota could potentially give us our best pictures yet of the extinction event that wiped out the dinosaurs 66 million years ago—assuming the findings hold up to what’s already amounting to some serious scrutiny.

In a new study published in the Proceedings of the National Academy of Sciences on Monday and first announced in The New Yorker last week, a group of scientists analyze a huge cache of exquisitely preserved animal and fish fossils that lived and died in the moments surrounding the Chicxulub meteor impact. Scientists have long theorized that the rock that slammed into the Yucatan Peninsula in Mexico and created a 93-mile-long, 12-mile deep crater near the town of Chicxulub, led to the eradication of 75 percent of all plant and animal life on Earth. While Chicxulub was probably not solely responsible for the death of the dinosaurs (climate change and increased volcanic activity were also stressing the environment out at the time) it’s the moment that ended the Cretaceous period and heralded the rise of mammals.

“If dinosaurs were betting creatures, they’d probably be fairly upset with those odds,” says Phil Manning, a University of Manchester paleontologist and coauthor of the new study. “It was just bad timing for the dinosaurs, and great timing for the mammals.”

Nothing like this has ever been found before. The fossils “are the only concentrated assemblage of articulated [complete] carcasses at the K-T boundary known anywhere in the world,” says Robert DePalma, a doctoral student in geology at the University of Kansas and the lead author of the new study. “Elsewhere others have found isolated bones at the boundary, but never any articulated carcasses.” While the immediate effects of the Chicxulub impact vary from region to region, DePalma describes the site as illustrating the “first bloody nose” hit the meteor’s crash had on a region 2,000 miles away.

“As far as we know,” says Manning, “and I stand to be corrected if I’m wrong, this is the first time we have actual debris from the impact itself raining down onto an ecosystem, with organisms from that ecosystem found interacting with that debris.”

The K-T boundary (better known as the K-Pg boundary these days) is short for Cretaceous–Paleogene boundary, the geologic transition of the former period into the latter. There are sites all around the world that scientists have studied to better understand how this change occurred, but the Tanis site in North Dakota, located within the Hell Creek Formation, was not necessarily thought to be one of them. When DePalma and his colleagues first approached the Tanis site, there didn’t appear to be anything particularly special about it. “It was just another Hell Creek outcrop that we were visiting,” says Manning.

Eventually, however, the team was finding scores of fossilized paddlefish in the site—a rarity for Hell Creek. Other fossils included other marine creatures, terrestrial vertebrates, trees, branches, and plants. The 1.3-meter-thick sedimentology didn’t look like the Hell Creek or Fort Union formations; it was something that looked sandwiched in between, deposited very rapidly, like something you’d expect from a tsunami. The geochemistry of the area included pieces of ejected material associated with impact events, like shocked quartz and iridium-rich matter. Iridium is only found either deep in Earth’s core, or within meteorite materials. Subsequent dating techniques confirmed the ejecta matched well with the expected timing of a seismic shockwave to hit the region.

Here’s the picture the research team paints: 66 million years ago, marine bodies lived in some kind of water channel that existed within a deep valley. Suddenly, a six- to-seven-mile-long rock pummeled the planet at 40,000 miles per hour. Debris moving at ballistic speeds started to rain down onto the site. Seconds or minutes later, a massive shockwave thrust this water 10 meters high and dumped its contents (i.e. the marine organisms living in that channel) onto another bank, several times over in quick succession. “Literally throwing the baby out of the bathtub,” says Manning.

But the findings aren’t without dissenters. The New Yorker article that first broke the news quotes DePalma describing dinosaur specimens that are not at all discussed in the PNAS paper. In fact, only one dinosaur bone is mentioned by the researchers, in the supplement section. The connection of the Tanis findings to the death of the dinosaurs is not part of the published literature so far, making it difficult for paleontologists to really assess what the findings mean for the famous megafauna.

And DePalma is already a lightning-rod figure within the scientific community. He’s previously been criticized for misidentified a piece of a turtle shell as a wishbone of a newly discovered velociraptor genus (though it should be noted that misidentifications are not horribly uncommon, and don’t mean a scientist is acting in bad faith). He has an unusual reputation for retaining the rights over his specimens even after they’ve been made part of university and medium collections, which is controversial since scientists are supposed to study these objects objectively and dispassionately. He’s been called out for selling replicas of his findings, purportedly as a way to fund his research.

Manning pushes back on many of those criticisms—especially regarding past errors, which Manning calls “petty”—and is pretty enthusiastic about his work with DePalma. “I dock my hat to Robert,” says Manning. “He’s been a fine field geologist and paleontologist. Over the last seven years or so, he’s really gotten to know the site. Robert thankfully is inviting people very openly to work at the site, across multiple disciplines and from multiple countries.”

Manning also believes the team’s conclusions are supported by the data itself. “The absolutely most beautiful and elegant part of all of this is the geochemistry,” he says. Some of the tektites found at the site (glassy materials formed from molten crust, such as during impact events) had a “perfect chemical fingerprint” that Manning says matches them with other K-Pg boundary sites with material blasted out from the Chicxulub impact. “There is absolute evidence matching this site to the K-Pg impact” that created the Chicxulub meteor impact. The fossilized paddlefish (Acipenseriform) actually inhaled (and maybe choked on) tektite materials as debris rained down into the water. One of Manning’s favorite parts was finding fossilized amber that had managed to preserve some of the microtektite material almost perfectly, recording the chemistry from this event.

The findings also help us to understand how vast the Chicxulub impact really was, in ways we were just about clueless about before. “The deposit preserves the immediate aftermath of the impact in great detail, with minute-by-minute clarity, which is important for us to understand how exactly the impact affected Earth’s ecologies,” says DePalma. Bodies of water elsewhere in the world could have experienced similar surges after impact, giving scientists some clues about where else they may find sites similar to Tanis.

Mark Norell, the chair and Macaulay Curator at the American Museum of Natural History’s division of paleontology (who was not involved with the study) thinks the paper at least succeeds in demonstrating how vibrant and fascinating the Tanis site is from a paleontological and geological point of view. We’ve never before encountered a site with so much to unravel: preserved specimens of so many plants and animals, tektites, impact debris, and iridium concentrations of these levels. He thinks the findings are another step in helping to characterize what happened after impact, including the intense amount of heat generated, whether there was a tsunami or a swelling displacement of water created by shockwaves propagating through the ground, and more. The work being done at other K-Pg boundary sites ought to help confirm or dispute what’s been raised by the latest findings.

Norell does caution, of course, that the study is still quite preliminary. “Just like some of the other KT boundary stuff that exists, this is something that will need lots and lots of work—decades to really realize the full implications of it.” But based on the impressive list of authors attached to the new study, he’s confident the follow-up is going to be done at the highest levels of scientific scrutiny.

Still, it’s not really fair to ask the public to be cautious after researchers allowed the New Yorker to write 10,000 words on an unpublished study. Manning acknowledges there’s a significant margin for error in the findings. “I’ll be honest: if we’re wrong, I’d embrace it,” he says. “It’s part of the scientific method. My ears open to it. But we’re confident what we’ve put together is correct.” With only about 10 percent of the site’s fossils properly excavated and studied, and many other scientists expressing interest in visiting Tanis to do their own research, there’s plenty of heavy lifting left to do. Hopefully, it leads to some published insight into what Tanis might tell us about dinosaurs in particular. “We’re going to be working on it for a good many years,” Manning says.

a large rocky landscape
The Tanis fossil site in North Dakota’s Hell Creek Formation.

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