How paleontologists know what life on Earth was like the day the asteroid killed the dinosaurs

How paleontologists know what life on Earth was like the day the asteroid killed the dinosaurs

Last month’s discovery of a fossilized leg from a dinosaur that died on the day that an asteroid wiped out all of its kind was hailed as the “ultimate dinosaur drumstick” (as one scientist called it) — the holy grail of paleontology, and a rare and astonishing discovery. Indeed, evidence suggests the dinosaur’s death was likely caused by the aftermath of the Chixclub impact event some 66 million years ago, which scientists believe led to the extinction of all its fellow dinosaurs as well.

The details of the discovery, and other amazing fossils found at the Tanis dig site in North Dakota, are discussed in more detail in a two-part special called “Dinosaur Apocalypse,” which airs on May 11 at 9pm ET on PBS. The documentary, narrated by David Attenborough, follows paleontologist Robert DePalma and his team at a thriving dig site hidden in the Badlands of North Dakota, where paleontologists have uncovered rare fossilized creatures that appear connected to the fateful day that ended the Cretaceous Period. Through their discoveries, humanity will be able to learn more about what happened during the last days of the dinosaurs— and more about what life was like at the Tanis site.

“That [triceratops] skin is a beautiful example of a research opportunity to look for original organic compounds… And along that line, we could potentially work out the pigmentation or the pigment patterns of an animal with those techniques.”

Until now, no fossils of a dinosaur killed on the last day of the Cretaceous period had ever been found. While the findings have yet to be published in a peer-reviewed scientific journal, scientists are very excited about the discovery and the prospect of what information it might hold. Salon caught up with DePalma to talk more about the discoveries made at the Tanis dig site, and what he and his team have learned since filming the documentary.

This interview has been condensed and edited for print. 

What were you thinking and feeling that moment you started to uncover the coveted dinosaur leg at the Tanis dig site in North Dakota?

Work at the site is always edge-on-your seat stuff. You’re always about to find something that you’ve never even anticipated, and it happens every time we go there. We always end up finding something that drives us crazy. But at the moment that we uncovered the dinosaur leg, we weren’t expecting to find anything like that. We’re digging up a fossil palm frond and then when the scales first appeared, they looked just like an animal that had just died. And we were like, ‘Oh my gosh, we just landed into one heck of a situation.’ Our hearts were literally pounding out of our chest as we’re finding this thing and uncovering it more and more. And when more of it came to light by the end of the day, we had this whole leg sitting there that is three dimensional. You’ve got all of the skin on it. You can see bones poking out here and there. And we’re thinking, wow, this is like this is actually like seeing a dinosaur that had died yesterday.

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We’re feeling like we’re the most fortunate people on the planet. And then they put that into context and it’s buried in a muddy deposit from the day of the impact. We were just beaming. So it is pure excitement. All the way through to when you do the research and afterwards. The whole process is just phenomenal.

Where is the leg now?

Right now [it] is at the lab space at Florida Atlantic University, where all of the primary research is taking place. And we might send it back over to the UK at some point in the near future, because we did preliminary work at the diamond light source synchrotron facility, high-tech work involving synchrotron radiation, and we were looking at organic compounds that are still preserved in the fossil material. So, that might be our next stop for this, because there’s about 10 analyses we want to do. Right now, we’re just going through that list. And we’re basically documenting every darn thing we possibly can, because this is a prime example of something that we can just learn from, endlessly.

In addition to the leg, there was the triceratops skin that you discovered.

Absolutely. There were several patches of skin from the triceratops and some scattered bones. And those are absolutely exciting as well. It’s a much larger animal. But you know, we have a couple of small patches from a partially decayed animal, so at the time of impact the triceratops had been dead for a maximum of a month or two, maybe as little as a few weeks. But it just missed the major event of the end of the Cretaceous. And we know that it died already, but it still can tell us a lot.

Have paleontologists discovered dinosaur skin so well preserved before?

Dinosaur skin is known in the fossil record. It’s somewhat rare, but dinosaur skin has been found before. The thing that makes this very special is the Triceratops remains at the site are from higher up in the stratigraphic section than anything else found before. So in other words, there haven’t been any dinosaur fossils found in the Hell Creek Formation within the upper, let’s just say, nine feet of the Hell Creek Formation. You just don’t find them. They’re just uncommon. It’s a presentational artifact. So just finding Triceratops skin at all is really unique. But to have this example come from that mass death layer from the day of impact, that muddy layer that locked it in time the day of the impact that really sets this apart and makes it exceptionally special. So yes, dinosaur soft tissue has been done in the past, but no one has ever found any from that layer of the impact.

Do we know what color the triceratops was?

There are a few things that we can potentially tell about skin and soft tissue preservation, and I can’t get into too many details because as a scientist, you really can’t jump the gun and talk about those in a media setting until they’re at least reported in a scientific conference. But what I can tell you is this: that skin is a beautiful example of a research opportunity to look for original organic compounds — for example, organically-bound sulfur, organically-bound zinc, things that are traced to the original animal and not an artifact of the preservation. And along that line, we could potentially work out the pigmentation or the pigment patterns of an animal with those techniques. And I can’t tell you anything specifically about that specimen, other than the fact that we are very, very excited and very, very hopeful. So if that’s any indication of what’s playing for the reserves coming from the skin, that’s pretty much the most I can say without getting in trouble with the research team.


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I know you can’t say with 100 percent certainty that these fossils are from the day a 10-mile-wide space rock struck the Yucatán Peninsula in the Gulf of Mexico. But can you walk our readers through the evidence you have to suggest that’s the case?

There’s actually a lot of evidence to suggest that many of those fossils are from that day, and you really have to bring your mind back to that day. So essentially, you know, we’re looking at late spring, early summer, basically the time that we’re in right now. And it was a subtropical to tropical paradise back then. There was tons of life at that time and it was really, really vibrant.

On that unsuspecting day, that area would have experienced — first — some seismic activity. You would have had the seismic waves which would have reached there from the impact site, so you would have had that jolt in the ground. And then at the same time, you would have had this rain that came down and these little tiny beads of glass that were glowing, red hot, coming out of the sky; they would have looked like tracer rounds from a battlefield and would have been streaking across the sky.

“It wouldn’t have been a pretty wave of water like you’d see at the beach. This would have been muddy water filled with logs, complete trees, animals, fish, everything. It’s sort of like a meat grinder wall of death.”

They’re only about a couple millimeters wide, each one, but if they hit you, they would definitely sting you and not really feel too good. They probably would have killed bugs if they ever hit them. But these things would have been pelting the ground all over the place. The setting of the Tanis site is in a river valley, a paleo river that had basically carved through the landscape, you had this little notch cut out in the ground and being out into the seaway. At that time, it split North America into the left and right halves. And this river would have emptied out there and animals would have been drinking, you would have had fish and turtles and everything else. And then without warning, you would have had this massive 10 and a half meter high surge of water just force up that river valley, backwards, you know basically going inland. And it wouldn’t have been a pretty wave of water like you’d see at the beach. This would have been muddy water filled with logs, complete trees, animals, fish, everything. And it’s sort of like a meat grinder wall of death in this wave of water that would come up and basically swallow everything in its path. That then locked all those animals in time and that happened starting maybe 15 or so minutes after impact, and at most, up to two hours after impact. That’s the moment locked in time.

A lot of these [fossils] we can tell are almost certainly victims of that day. The fish have those little blobs of glass jammed in their gills because as they were raining from the sky, those fish were sucking them in and they’re jammed in the gills. A lot of the plants that are there, and the trees, have leaves and needles still on the branches. So these are not things that would have died and been sitting on the ground and fallen apart and washed into the river. They were still fresh enough that the leaves were still on the branches so those would have died as a result of the surge.

The Triceratops died before the surge; sadly, it was already decayed, but the leg that is beautifully preserved does not match something that would have died long before impact. The leg is three dimensional. So if it had died before impact, it did so soon before impact because it would have not had time to decay. The muscles had not liquefied, everything was still three dimensional and beautifully preserved.

So let’s just say it did die before impact. We’re looking at a time frame of days to weeks at maximum. So that’s still essentially the end of the Cretaceous era, but most probably those animals did die as a result of the surge. I’ll never say 100 percent, but it’s almost certainly from that surge event.

The turtle discovered in the documentary died by being pierced by a stick. How could that have happened during the impact? Was that likely a common way dinosaurs and reptiles died that day, say, from flying debris?

I think that anything that would have been within the path of such a surge would have had the risk of something like that happening to it. If you were near a body of water that had that sort of phenomenon occurring, then basically you could have been really damaged or killed by it— and also the actual tsunami coming from the impact site. But think about it if you jumped into that roiling body of water and you had all that stuff, you know, floating around in there and then tumbling around the branches and everything else. I guarantee you your first thought would be “Oh, God, I hope something doesn’t jam through me.” So it’s dangerous. That poor creature, that’s exactly what happened to him.

In the science world, there are different theories about exactly what hit Earth on that fateful day — most believe it was either an asteroid or a comet. Is there any evidence from the recently discovered fossils at Tanis that it was either an asteroid or comet?

The ironic part about that is that literally the day before we had a session with Sir David Attenborough for the show, one of the specimens— a slide of objective squirrels — revealed a really really cool fact. These little blobs of glass that were flying through the air, on occasion, would have encapsulated little bits of unmelted rock. And most of the bits of rock that we found were pieces of limestone from the Yucatan Peninsula, when the impact occurred. And there was another example that had a little fragment that was so wildly different from compositions and the rest, we had to take a second look at it. When we examine what it was made of, we’re looking at chromium— which is very uncommon in the Earth’s crust — when you see high levels of chromium, and high levels of nickel, like you see in that piece, that’s a dead red flag for a cosmic body. And then when we look at other chemicals, or other elements that are present in that little fragment that’s inside the spherical, we see a signature that matches cosmic bodies.

And not only cosmic bodies — but you see a signature for a specific type of cosmic body. It’s called a carbonaceous chondrite, and people in the past have proposed that that’s probably what hit 66 million years ago. They either figured it was a comet or a carbonaceous chondrites. And in this case, the composition does not match what you would see in a comet; it matches a carbonaceous chondrite, and we’re even further defining the type of carbonaceous chondrite with the ongoing work that we’re doing right now. Walter Alvarez is actually on point helping us with this. We are consulting with him and other people, and we probably — almost certainly— have an example of a little tiny, smaller than a millimeter, fragment of the asteroid that we can now figure out exactly what it was that hit that day.

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