Science Friday - Were Dinos On Their Way Out Before The Asteroid Hit? Maybe Not

Episode Date: November 7, 2025

One of the biggest debates in the dinosaur world is what was happening right before they went extinct. Were they already declining, or would they have thrived if not for the asteroid? Two recent studies shed some light on this question: one that analyzes a trove of fossils from New Mexico and suggests there was more diversity in the Americas than previously thought, and another that reanalyzes a long-debated juvenile T. rex fossil and finds it’s likely a separate, smaller species.Host Ira Flatow is joined by authors on those separate studies, paleontologists Steve Brusatte and Lindsay Zanno.Guests: Dr. Lindsay Zanno is division head of paleontology at the North Carolina Museum of Natural Sciences in Raleigh, NC.Dr. Steve Brusatte is a paleontologist at the University of Edinburgh in Scotland.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

I'm Ira Flato, and you're listening to Science Friday. Today on the show, where dynos on their way out before the asteroid hit. New research says, maybe not. This is why paleontology is fun. It's a detective game, and sometimes new evidence comes along and tells us that some of our cherished ideas were incorrect. One of the biggest debates in the dinosaur world is what was happening right before they went extinct. Were they already declining or were? would they have thrived if it wasn't for that darn asteroid?

Well, two new studies shed light on this question, and we have their co-authors here with us now. Dr. Steve Broussadi, paleontologist at the University of Edinburgh, Dr. Lindsay Zano, Division Head of Paleontology, at the North Carolina Museum of Natural Sciences based in Raleigh, North Carolina. Their studies were published in the journal Science and Nature, respectively. Welcome back to both of you to Science Friday.

Thank you, Ira. Always a pleasure. Thank you. You're welcome. Steve, this ongoing argument in the paleontology world, whether or not dinosaurs were on their way out before their extinction. I think it's now rivaling. Do you come here often as a standard opening line when paleontologists get together? Where is the story?

What does that story come from? Give us the origins of that. I think in many ways it goes back 200 years to when the first dinosaurs were named, when the first giant bones were recognized by scientists working in universities and museums, recognizes belonging to these giant extinct reptiles. And then the question became, where did these things go? What happened to them? Why aren't they here anymore?

And for a long time, people debated about this. There wasn't a whole lot of evidence, really. Then in 1980, Walter Alvarez and his team presented this bombastic new theory that an asteroid came down and wiped out the dinosaurs and many other. species at the end of the Cretaceous about 66 million years ago. And this was, of course, met with skepticism at first. And for a whole decade, people debated this, not only paleontologists, but geologists and chemists and physicists and astronomers. And really, it was one of the biggest debates in science during the 80s. When the crater was found, as the 80s turned into the 90s,

that sealed the deal that there was an asteroid. But then the debate became, well, did the asteroid really do it? Or is the asteroid been wrongfully accused? And dinosaur paleontologists have been going back and forth on this. There's this longstanding idea that dinosaurs were already on their way out. They had been around for a long time. Climates were changing. They were wasting away to extinction. Or maybe even if they weren't wasting away, they were just declining. There were fewer species. They were not adapting very well. And the asteroid maybe just finish the job. Other scientists, though, have said, no, no, no, no, there's all these dinosaur fossils. They go right up to the asteroid layer in the rocks. It seems to have been sudden. The debate keeps going on. I'm glad it does

because we get to publish these studies where we bring new evidence to it and these studies get attention because it's just a question that people are very interested in. You know, that's always the punchline when you talk to scientists. More research needs to be done. And I know you're part of some new research based on a trove of fossils found in New Mexico. Tell us how, how do they play? How did these new fossils play into this? Well, I'll give away what we think is the answer. We think they support the idea that dinosaurs went extinct very abruptly, that dinosaurs were doing well up until that one random Friday, let's say, when the six-wildite asteroid fell out of the sky. And the reason that we think that, there's many reasons, but the fossils from New

Mexico, these dinosaurs, they're from up in the four corners region, near Cuba, Farmington, these cities in New Mexico in Navajo country. And they've been known for a long time. These dinosaurs, many decades people have known about these dinosaurs. We've collected a lot of them. My colleagues, Andrew Flynn, who led this study as a young geologist, and Tom Williamson, who's the curator in Albuquerque, they've been collecting these fossils for years.

But what we've done in this study for the first time is accurately date these fossils, date the rocks. And the surprise there was that these dinosaurs were there right at the very end of the Cretaceous. They were there within a few hundred thousand years at most before the asteroid. Probably basically they were there when the asteroid hit. And there's a lot of these dinosaurs. There's meat eaters and plant eaters. There's big ones and small ones.

There's tyrannosaurs and duck-billed dinosaurs and armored dinosaurs and horn dinosaurs. There's even a long-neck dinosaur called Alamosaurus that was one of the very biggest dinosaurs. In fact, the very biggest animals to ever live on land in the history of the earth. heavier than a Boeing 737 airplane. Wow. It was basically there when the asteroid hit. These were dinosaurs that were at the top of their game. That's what we think.

And so we think this provides evidence that dinosaurs were doing well. Of course, this is one part of the world. There's other fossils, which Lindsay will talk about, from up north, from Montana and Wyoming and the Dakotas. These also show dinosaurs doing quite well right to the very end. But we don't have a lot of fossils that are well-dazed. from other parts of the world from the end of the Cretaceous. So that's really where the research has to move next to see if this is a global story or not.

All right, Lindsay, give me your evidence. What's your take on this? Well, I think it's important to think about the fact that dinosaur diversity, that is the number of species and the ecological roles that they filled throughout Earth's history has fluctuated. And so there have been some studies that have shown that possibly diversity is decreasing, leading right up to the asteroid impact. But the question really is, does that mean dinosaurs were in decline? Does it mean they were vulnerable or susceptible?

And I think this is where the narrative gets a little bit complicated. And Steve and I are both presenting studies that suggest that we've not recognized the true amount of dinosaur diversity and the true richness of dinosaurs, not just in a new area that Steve is bringing to the table from the southern U.S., but in the case of my study, in an area in North. Western North America that's been hunted for dinosaurs for over a century, and we're still learning new information about that we've underestimated diversity in these ecosystems that have been known for a very, very long time. Well, tell me about that. What is this new evidence that you're talking about? Well, there's a longstanding controversy about small tyrannosaur fossils from this famous rock formation in Montana called the Hell Creek Formation. And this, formation is most famous for housing the bones of Earth's most famous predator Tyrannosaurus rex.

But in the past, paleontologists have found smaller Tyrannosaurus skeletons from the very same rocks that we find T-Rex fossils. And for about, oh, 30 or 40 years, we've been debating whether these fossils represent a new species of Tyrannosaur, a different type of animal, or actually just a growth stage or a juvenile form of Tyrannosaurus rex. And of course, this question is very important because it plays directly into the complexity of ecosystems in this area right before the mass extinction event and predator diversity at that time. So it was a lot more diverse then. Yeah, our evidence is showing that rather than representing a juvenile stage of T-Rex, in other words, T-Rex being the only predator to inhabit this ecosystem, that there was a smaller-bodied animal

that we call nanoturanus that was running around in the same ecosystems as T-Rex, and that predator diversity and ecological richness at the time was much greater in even these well-known ecosystems than we previously knew. Your study focuses on this really dramatic skeleton. Tell us about that. Yeah, well, one of the problems with figuring out whether nanotorans, was a valid species or not, was that we didn't have really excellent fossils to work with. And this is, you know, the lament of every paleontologist throughout time, right? We need more fossils.

Well, in this case, we actually did acquire an extremely important specimen. It's a 100% complete 3D articulated skeleton of a small-bodied Tyrannosaur from the Hell Creek formation. And when we acquired it, we were following the conventional wisdom that this was a juvenile Tyrannosaurus wreck specimen, but soon after beginning to study it, we started to see some serious red flags that led us to think that perhaps this specimen, which comes from a fossil known as the dueling dinosaurs, might actually reveal the answer in this very longstanding debate. How are you able to distinguish between this being a completely different species versus a

juvenile? Well, one way is to look at the inside of the long bones of dinosaurs because we have methods now for determining how old a dinosaur was when it died. And that's because dinosaurs grow effectively like trees. They leave rings down on the inside of their bone every year. And we can count up those rings and we can look at the relative spacing to figure out where these dinosaurs are in their growth stage. So the growth rings indicate it was almost its full size when it died. Wow, Steve, what's your reaction to this? I love it. I love it. And big congrats to Lindsay and her colleague, James Knoply, who publish this paper.

It's a fantastic paper. And the other big congrats to Lindsay and her team is securing this fossil for science. This was collected long ago, 15, 20 years ago, and it was commercially collected, and she was able to secure it for her museum in North Carolina. But look, I was a long time skeptic of nanotyrannis. I had thought that the evidence was really in favor that these smaller, let's say, SUV-sized Tyrannosaurus were just juveniles of the bus-sized T-Rex. But I'm very happy to say on radio across the country to the people of America, the people that were listening, I was wrong.

And many of us were wrong, and this new evidence shows that this is a distinct animal. It's much smaller than T-Rex. It's a mature animal, as Lindsay and James have shown, with the bones. growth and it has this long arm that's very different from T-Rex. So I just think it's wonderful. I think as an example of how one new fossil can give us a lot of information and can change the game. And I think we always just have to be humble in the face of the fossil record, even a dinosaur like T-Rex that is so well-known and so well-studied. We really only have maybe a few dozen fossils of it. So, I mean, we're like squinting at the night sky trying to form constellations out of a few stars to

understand the universe. That's what it's like with these fossils. And I just think science is wonderful. This is why paleontology is fun. It's a detective game. And sometimes new evidence comes along and tells us that some of our cherished ideas were incorrect. Yeah. Can we get to see it online someplace? DuLinkdinosaurs.org. We have to take a quick break, but don't go away. More on this when we can. come back. Okay, so for both of you, the big picture, this question of how much diversity there was or not at the end of the dinosaurs, why is this relevant to us now, considering the

asteroid and the mass extinction? Steve, let me start with you. We study fossils because fossils tell us how life has evolved over time. The Earth's four and a half billion years old. And the Earth is changing a lot today. We know it. We feel. it, in large part, that's because of us. But the Earth has changed a lot in the past. And it is especially changed during these extinction events, these mass extinction. So we want to understand how these extinctions played out. That is really relevant to understanding changes today. Also, maybe giving us some wisdom that can mitigate some of the things that are happening now. And the end Cretaceous extinction, when the asteroid hit, and we do think the asteroid was the main

reason for it, but other things were happening around the same time. There were big volcanic eruptions in India. There were changes in sea level, changes in temperature. So teasing all of this out is going to tell us a lot more about how real animals, real ecosystems responded to real instances of climate and environmental change. And this is the most recent mass extinction, 66 million years ago. Maybe we are going through one now. But this extinction in many ways is the best one for us to study because it's the last time the Earth has gone through something like this. And I think that this notion that dinosaurs were thriving, that they had been around for over 150 million years, they were still going strong. Some of the biggest ones were still around,

bigger than jet airplanes. T-Rex was still around. And then the asteroid comes down, changes things so quickly. Those dinosaurs that were so well adapted to their own world were now all of a sudden, at a disadvantage, the game had changed. They were big, they grew slow, they needed a lot of food. Now they were on their back foot, and now it was the smaller, adaptable animals that could eat lots of things and hide away, like these small, furry little creatures that were hiding away in their burrows, our mammal ancestors that stared down the asteroid, they would then have the opportunity to prosper afterwards. So really our story, the dinosaur story, is all related. Everything in the history of life is related. It's fun to talk about this stuff.

Lindsay and I have great passion for what we study, but we really do think it is relevant. There's a lot of lessons here in these mass extinctions. Lindsay, anything to add? Yeah, I would say that I think it's important for Steve and I and the researchers to work in this area to explore whether dinosaurs were healthy at the time of the impact, in part because maybe there's a disconnect in humanity with the idea that we might experience extinction ourselves. And we love and are passionate about dinosaurs, but this idea that they were evolutionary failures, that they were somehow maladapted or they were already in decline,

it maybe feels safer and more comforting to us. But to counter that with the idea that these ecosystems were robust and thriving when an asteroid hit, maybe that feels a little vulnerable for us, but it's an important step, I think, for humanity to take to start thinking about our own vulnerability, perhaps in a different way. They were one of the most successful creatures on Earth, weren't they? They certainly were and still are. Yeah.

Well, I want to thank both of you for taking time to be with this. Fascinating discussion. I hope lots of people go visit it on your website. Thank you so much, Ira. Cheers. You're welcome. Dr. Steve Brousotti is a paleontologist. at the University of Edinburgh and Dr. Lindsay Zano is division head of paleontology

at the North Carolina Museum of Natural Sciences. If you love this story, you can also head to Science Friday.com slash dino to check out other paleontology stories and free educational resources about dinosaurs that your kids can get into. And before we go, some very important election results that you may not have heard yet. Hello? Hi, Denise.

Yes. This is Flora from Science Friday calling with the results of our first annual spooky science Halloween costume contest. Yes. And I just want to say right off the bat, the competition was quite stiff, as stiff as a corpse. But Denise, the people have voted, and you are our winner. Hooray, thank you. Congratulations. And just so people can pick up.

picture it, you designed and made costumes for your grandkids a weatherman and an accompanying tornado. It's very well executed. The upturned umbrella and the weatherman, the tornado with objects in it. Thank you. I was difficult to do the tornado. I thought it would be easy, but then I was like, oh, no, what am I going to do? So I ended up putting it, I put a sweatshirt, I bought her a sweatshirt and put it over a giant

vase in my living room and I just worked on it and worked on it and I had to do it two or three times, but I finally got the house and the cow and everything to stay inside the tornado. Thank you for participating. People loved it online and were very excited to send you a swag bag of cyphrae goodies. Thank you. It was lots of fun. And a quick shout out to our runners-up, the Western blots, a mashup of gels, pipettes, and cowboy attire. It was perfect, A for effort, including the voter fraud campaign you launched on Instagram. We see you Western Blots. And thank you to everyone who submitted costume ideas and who voted.

We had such a blast with this. Hey, thanks for listening. If you have a comment or question or a story idea, our listener line, it's always open. Call 8774 SciFRI, 877, the number four, side fry. This episode was produced by Dee Petershmit. Lots of folks helped make this show happen this week, including Beth Rami, Jackie Hirschfeldt, Jordan Smudjik, Emma Gomez.

See you next time. I'm Ira Flato.