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To a certain extent, fossils are like photographic images of the past. A still dating back millions, if not billions, of years, is preserved in the bedrock of the Earth, under layers that have accumulated over time. If you are lucky, you can use these specimens as a snapshot in the past. According to this logic, a new set of fossils discovered in North Dakota could potentially give us our best images of the extinction that wiped out the dinosaurs 66 million years ago, in the event that discoveries hold up what we are already serious about.
In a new study published in the Proceedings of the National Academy of Sciences Monday and announced for the first time in New Yorker Last week, a group of scientists analyzed a huge cache of exquisitely preserved animal and fish fossils, which lived and died at the time of the consequences of the impact of the Chicxulub meteor. Scientists have long believed that the rock that struck the Yucatan Peninsula in Mexico and created a crater more than 12 km deep near the town of Chicxulub led to the eradication of 75% of plant life and animal of the planet. . While Chicxulub was probably not the only one responsible for the death of the dinosaurs (climate change and increased volcanic activity also threatened the environment at the time), it was the moment that ended Cretaceous and who announced the rise of mammals.
"If dinosaurs bet on creatures, they would probably be quite unhappy with these chances," said Phil Manning, a paleontologist at the University of Manchester and co-author of the new study. "It was just bad timing for dinosaurs and perfect timing for mammals."
Nothing like it has ever been found before. Fossils "are the only concentrated assemblage of articulated materials [complete] carcasses at the K-T limit known all over the world, "says Robert DePalma, a PhD student in geology at the University of Kansas and lead author of the new study. "Elsewhere, others found isolated bones at the border, but never articulated carcasses." While the immediate effects of Chicxulub's impact vary from one region to another, DePalma describes the site as illustrating the "first bloody nose" struck by the meteor crash a region at 3,000 km.
"As far as we know," said Manning, "and if I'm wrong, I'll be corrected if I'm wrong. This is the first time we encounter debris from the impact itself on an ecosystem, with organisms that interact with this debris. "
The K-T boundary (better known as the K-Pg boundary nowadays) is the abbreviation of the Cretaceous-Paleogene boundary, the geological transition from the first to the second period. Scientists have studied sites around the world to better understand the reason for this change, but the Tanis site in North Dakota, located in the Hell Creek Formation, was not necessarily considered to be one of them. When DePalma and her colleagues first came to Tanis, there seemed to be nothing special about it. "It was just another outcrop of Hell Creek that we were visiting," says Manning.
However, the team finally found a large number of fossilized fly fish on 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 did not resemble the Hell Creek or Fort Union formations; it was something that seemed stuck between the two, dropped off very quickly, like what you'd expect from a tsunami. The geochemistry of the region included pieces of ejected material associated with impact events, such as shock quartz and iridium-rich material. Iridium is found only at the bottom of the Earth's core or in meteorite materials. Subsequent dating techniques confirmed that ejection was consistent with the expected timing of a seismic shock wave to hit the region.
Here is the image of the research team: 66 million years ago, marine bodies lived in a kind of water channel that existed in a deep valley. Suddenly, a rock six to seven miles long hammered the planet at 40,000 miles at the time. Debris moving at ballistic speeds began to rain on the site. A few seconds or minutes later, a massive shock wave projected this water to a height of 10 meters and dumped its contents (that is to say marine organisms living in this channel) on another bank, several times in a row. "Throw the baby out of the tub," says Manning.
But the conclusions are not without dissidents. the New Yorker An article that first made the headlines quotes DePalma describing specimens of dinosaurs that are not discussed at all in the PNAS paper. In fact, only one dinosaur bone is mentioned by researchers in the Supplement section. The link between Tanis' discoveries and dinosaur death is not part of the published literature to date. It is therefore difficult for palaeontologists to really evaluate the meaning of these discoveries for the famous megafauna.
DePalma is already an emblematic figure of the scientific community. It has already been criticized for mistakenly identifying a piece of turtle shell as an essential element of a newly discovered genus (Velociraptor) (although it should be noted that misidentifications are not terribly unusual and do not mean not a scientist acting in bad faith). It has the unusual reputation of retaining rights to its specimens even after they have been incorporated into academic and medium collections, which is controversial to the extent that scientists are expected to study these objects objectively and impartially. He was summoned for selling replicas of his discoveries, ostensibly as a way to finance his research.
Manning rejects many of these criticisms – especially regarding the mistakes of the past, which he calls "small" – and is very interested in his work with DePalma. "I take my hat off to Robert," says Manning. "He was a field geologist and paleontologist. In the last seven years or so, he has really come to know the site. Fortunately, Robert very openly invites people to work on the site, in several disciplines and in several countries. "
Manning also believes that the team's findings are corroborated by the data itself. "Geochemistry is the most beautiful and elegant element of all of this," he says. Some of the tektites found on the site (vitreous materials formed from melted crust, as during impacts) had a "perfect chemical imprint" which, according to Manning, would make them correspond to other K-Pg boundary sites with materials. blown by the impact of Chicxulub. "There is absolute evidence linking this site to the impact of K-Pg" that created the impact of the Chicxulub meteor. The fossilized spatula-fish (Acipensériforme) actually inhaled (and perhaps smothered) tektite materials as debris rained in the water. One of Manning's favorite parts was the discovery of fossilized amber which had managed to retain some of the microtektite material almost perfectly, recording the chemistry of this event.
The results also help us understand the magnitude of the impact of Chicxulub, which we had no idea before. "The deposit preserves the immediate consequences of the impact in a very detailed manner, with minute-by-minute clarity, which is important for us to understand exactly the impact of the impact on it." ecology of the Earth, "explains DePalma. Water masses elsewhere in the world could have seen similar increases after the impact, giving scientists clues as to where they could find sites similar to Tanis.
Mark Norell, President and Curator Macaulay of the Paleontology Division of the American Museum of Natural History (who did not participate in the study) thinks the document at least demonstrates how much the site of Tanis is vibrant and fascinating from a paleontological and geological point of view. view. We have never before encountered a site with so much to clear: preserved specimens of so many plants and animals, tektites, impact debris and concentrations of iridium of these levels. He thinks the results are another step to help characterize what happened after an impact, including the amount of intense heat generated, that it's like a tsunami or a swelling water displacement created by shock waves propagating through the ground, etc. Work at other K-Pg border sites should help confirm or challenge what has been raised by the latest findings.
Norell warns, however, that the study is still rather preliminary. "Just like some of the other KT border elements that exist, it's something that will require a lot of work – decades to really understand all the implications." But based on the impressive list of authors attached to the new study, he is confident that the follow-up will be conducted at the highest levels of scientific review.
However, it is not really fair to ask the public to be cautious after the researchers have authorized the New Yorker write 10,000 words on an unpublished study. Manning recognizes that there is a large margin of error in the results. "I'll be honest: if we make a mistake, I'll accept it," he says. "It's part of the scientific method. My ears open. But we are confident that what we have put in place is correct. With only about 10% of the site's fossils well excavated and studied properly, and many other scientists wishing to visit Tanis to conduct their own research, there is still much to be done. Hopefully this leads to a published overview of what Tanis could tell us about dinosaurs in particular. "We will work there for many years," said Manning.
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