We May Have Found Fossils From the Dinosaurs’ Last Moments on Earth

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Paleontologists may have found fossil beds that preserve the last moments of the dinosaur’s existence as the dominant species on Earth in a breakthrough that could transform paleontology — if it proves true.

Paleontologist Robert DePalma has been researching a site he’s nicknamed Tanis for a number of years. It’s part of the fossil-rich Hell Creek Formation in Montana, though the exact location has been kept secret. What makes this particular site unique is the nature of the fossils within it and the speed with which they may have been laid down.

Any time we talk about geologic time scales, there’s an understood margin of error baked in. The fossil record only records a minuscule fraction of all the living things that walked the Earth. You never find a fossil that’s identifiable as the first or last of a species, because you can’t ever make a claim about a moment that precise in time. But if DePalma and his fellow authors are right, we do know when this particular fossil bed was laid down: within two hours of the meteorite strike at Chicxulub.

What They Found

The Tanis fossil bed is unique for two reasons. First, it appears to have been laid down extremely quickly. Objects within the field are oriented vertically, heavily mixed together, and oriented in a manner that suggests a single, massive deposit event with a mixed load of animal and plant material. Tanis was nowhere near the actual Chicxulub impact crater 66 million years ago, but the entire area is scattered with tektites — shocked glassy objects formed as molten debris from a meteorite impact shot through the air. By calculating the speed with which debris from Chicxulub would have moved, the scientists were able to calculate how quickly the tektites would have arrived.

The researchers analyzed the various types of meteor-related debris found at Tanis and discovered they would’ve arrived in multiple waves depending on their ejection angles. Debris would have fallen starting 13 minutes after impact and continued for roughly two hours. The fact that the tektite impacts are preserved in the same fossil beds and from the same time periods is one way researchers know the events occurred virtually simultaneously.

Image courtesy of Professor David Burnham, University of Kansas

The fish that inhabited the warm waters of the Western Interior Seaway, as this area of Montana was once known, wouldn’t have had time to notice, on account of being aggressively killed. The Chicxulub impact may have set off a global earthquake a thousand times stronger than anything humans have ever experienced, causing what’s known as a seiche — a standing wave in a body of water — in the waters that covered the Tanis area. The seiche could have produced 35-foot waves — more than enough to inundate the local area. Many of the trees DePalma has found in the chaotic, mixed fossil bed have trapped spherules of meteorite debris in amber along their branches. Impact glass preserved in this fashion has been compared with deposits retrieved from the Chicxulub impact and found to be nearly identical.

Tektites-Gills-Fish

Image courtesy of Professor David Burnham, University of Kansas

The fish fossils, meanwhile, have microtektites in their gills. The image is hard to shake. Minutes after the asteroid struck, the low-lying area would have been rocked by waves, even as the sky began to rain fire. As the lunatic sea pitched and heaved, trees would have toppled into the water or exploded in flame. Beneath the water, fish choked to death on stone, unable to breathe in the flood of sediment. The entire site is an absurd jumble of creatures — exactly what you might expect to see if the earth heaved, the sky fell, and a whole lot of unexpected ecological mixing suddenly occurred. Here’s the New Yorker:

DePalma listed some of the other discoveries he’s made at the site: several flooded ant nests, with drowned ants still inside and some chambers packed with microtektites; a possible wasp burrow; another mammal ­burrow, with multiple tunnels and galleries; shark teeth; the thigh bone of a large sea turtle; at least three new fish species; a gigantic ginkgo leaf and a plant that was a relative of the banana; more than a dozen new species of animals and plants; and several other burrow types.

Combining the timing of the event at Tanis, the known Chicxulub impact, and the state of the actual deposit, DePalma and his fellow researchers, including Professor David Burnham from the Department of Geology at the University of Kansas, have constructed a remarkable timeline for the site. The preservation of the tektites and their impacts, combined with the jumbled, chaotic, and quickly deposited fossil layers, indicates these two events occurred at the same time. And while other paleontologists and researchers will need to confirm this — expect the debate to rage for years — it means we may have found a precise geologic record of what happened within the very first hours on the day the Cretaceous ended and the Paleogene began.

The New Yorker piece notes that DePalma may have a reputation for overpromising and under-delivering, but also leaves room for the fact that his discovery may be as earth-shaking as he claims. A precisely dated fossil record of the actual impact event, even in just one area, could answer numerous questions about the conditions on Earth after the asteroid hit. If these findings bear out, it’s a discovery as profound as the identification of the Chicxulub Crater in the first place.

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