Love Fruit? Thank (Dinosaur) Mass Extinction

Move over, TikTokers. It's time to shine a spotlight on some of the earliest influencers around: dinosaurs. When these ecosystem engineers were in their heyday, forest canopies were open and seeds were small. But around the time most dinosaurs were wiped out, paleontologists noticed an interesting shift in the fossil record: Seeds got bigger — much bigger. There was a fruit boom. Did the death of these dinosaurs have something to do with it? And who are the modern day equivalent of dinosaur influencers? To find out, host Emily Kwong https://www.npr.org/people/767284140/emily-kwong talks to Chris Doughty https://www.cdoughty.org/people, an ecologist at Northern Arizona University. Tell us what other tales of dino past you want us to regale you with by emailing us at [email protected] mailto:[email protected]! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Emily Kwong?

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• 0:18Emily Kwong?

  You're listening to Short Wave from NPR.

• 0:24Emily Kwong?

  Today, we are going back in time, all the way to the Cretaceous period. Here's what it looked like.

• 0:30Speaker 01

  It would have been a very bright forest. They would have been very open. You have a lot of pine trees.

• 0:34Emily Kwong?

  A time that Christopher Doty loves because of this one kind of dinosaur.

• 0:39Speaker 01

  The sauropods are the biggest terrestrial animal that's ever walked the earth.

• 0:44Emily Kwong?

  Chris uses big data sets to understand ecosystems. He's an associate professor of ecoinformatics at Northern Arizona University. And he told me that sauropods were so big, they acted like ecosystem engineers.

• 0:58Speaker 01

  They can knock down trees, they can distribute nutrients, they can move seeds. They do a lot of really important things. And big animals tend to do that differently than than small animals.

• 1:07Emily Kwong?

  And the way sauropods move nutrients and seeds around was through their poop.

• 1:11Speaker 01

  Yeah, and their bodies.

• 1:13Emily Kwong?

  The decaying corpse of a sauropod.

• 1:15Speaker 01

  That's true. That's not quite as fun to think about, but yeah.

• 1:17Emily Kwong?

  The circle of life. Maybe there was like a Mufasa sauropod who was like, my son, you'll be the grass someday.

• 1:25Speaker 01

  That's right, yeah. You were, those, the same elements have cycled through your son that were in a sauropod someday.

• 1:29Emily Kwong?

  Probably. Those sauropods were herbivores, eating plants. And the plant seeds from this time were actually kind of small, like a centimeter across. And that was fine for them because of all this light in the understory.

• 1:42Speaker 01

  And so there was no evolutionary reason for seeds to get big. But what happened was, after the dinosaurs went extinct, the forest got really dark.

• 1:51Emily Kwong?

  When the asteroid hit, it wiped out as much as 75% of all life on Earth. And suddenly, there were no longer these big dinosaurs to knock down the trees. So the trees grew lush and tall, and the understory between the forest floor and the tree canopy got roughly 20% darker.

• 2:09Speaker 01

  For a little seed, that's trouble. You know, these little seeds, they need light.

• 2:13Emily Kwong?

  And paleontologists observed something weird in the fossil record around this time. Not long after the asteroid hit, seeds suddenly got bigger, much bigger. And there was this sudden boom in fruit, the edible plant ovaries we love today. But why? And what did the death of the dinosaurs have to do with it? Today on the show, how the mass extinction of the dinosaurs may have led to the fruit and vegetable aisle you see today, and how we're living in another time of mass extinction where the dinosaurs are us. I'm Emily Kwong, and you're listening to Shore Wave, the science podcast from NPR.

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• 3:24Speaker 04

  On the next Throughline from NPR, Finding Catharsis Amid the Trauma of World War II.

• 3:30Speaker 05

  I crept into an unbelievable world where everything was natural and benign and possible.

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  Finnish artist Tove Janssen and her children's classic, The Moomins. Listen to NPR's Throughline in the NPR app or wherever you get your podcasts. In the much-talked-about new movie, Wicker, Olivia Colman plays a woman who commissions a husband literally made of wicker. Yes, wicker.

• 3:56Emily Kwong?

  We'll tell you why the silly and bawdy new movie is also a nice, cozy fall watch. Listen to Pop Culture Happy Hour via the NPR app or wherever you get your podcasts.

• 4:08Emily Kwong?

  So, Chris, let's talk about mass extinctions. The world has gone through five of them. How do you know something is a mass extinction?

• 4:15Speaker 01

  That's right. So species go extinct all the time and it's not unusual. It's just part of nature, but certain things happen that drastically accelerate this process that make it so, you know, 80, 90% of species go extinct. So what distinguishes a mass extinction from just a normal extinction is many more species are going extinct and it's global.

• 4:37Emily Kwong?

  All right. So you have this theory that the mass extinction got rid of these dinosaurs that were changing the forests and knocking down trees and that meant that the forest understory was getting darker.

• 4:49Emily Kwong?

  How did you go about testing this idea that that dark understory then led to bigger seeds and fruits?

• 4:57Speaker 01

  Yeah, so you know.

• 4:58Emily Kwong?

  It's not like you can go back and check. You can't set up a wildlife cam.

• 5:01Speaker 01

  No, no, no. Yeah, it is difficult to try to piece these together. So the first starting point was we had colleagues that literally scraped off fossils from leaves right before the extinctions and pretty much right after the extinctions. And we could test the chemistry of those leaves and we could actually say how much light these leaves got. And so for one of the first times, we were able to accurately quantify, you know, how much less light, you know, was in this understory after the dinosaurs went extinct. And then what we were able to do was go into rainforests and study how plants grow. And so, you know, from that perspective, we could see how tall would you get at a given seed size? And it's a very strong correlation. So if you're small, you develop into a tiny little seedling. And if you're a big seed, you develop into a big seedling.

• 5:46Emily Kwong?

  Wow.

• 5:47Speaker 01

  And then, then we can go even further and look at modern megafauna like forest elephants and see, you know, how do they open up the understory? And so then what we do is we take, you know, all this information going from fossil records to how plants grow, to how seeds grow, to how forest elephants affect forests, and we put it into a model. You can think of it like a computer simulation.

• 6:08Emily Kwong?

  It's like roller coaster Tycoon.

• 6:11Speaker 01

  I don't know that one, but yes, like, you know, like, you know, SimCity or something. Sim dinosaurs.

• 6:16Emily Kwong?

  Same genre of, you're taking all this real world data and you're putting it into a model and you're saying like, what if?

• 6:21Speaker 01

  Exactly. Yeah. And then you just allow. You know, millions of years of ecology to happen. And so basically you just kind of input this into our model and then you see what happens.

• 6:30Emily Kwong?

  So yeah, what's the verdict?

• 6:32Speaker 01

  The verdict is, yeah, it worked. So, you know, basically what we saw was the darker understory basically created an evolutionary advantage for bigger seeds. And so those bigger seeds then created fruit that would entice bigger animals to eat them. And these bigger animals would distribute the fruits farther. And the trees that are moved farther away from their mother tree are very happy because you don't have to put up with the same diseases that your mother has. You don't have to be under her shade. And so that's an evolutionary incentive as well. So basically they're bribing these animals with fruit to move them around.

• 7:05Emily Kwong?

  In the time immediately following the mass extinction of the dinosaurs, did that eventually give rise to the ancestors of primates?

• 7:12Speaker 01

  Yes, our primate ancestors developed because they were good at climbing trees and eating fruit. And so had there not been fruit, you wouldn't have this incentive to climb up in the tree and eat fruit. So.

• 7:26Emily Kwong?

  So the death of the dinosaurs was our boon?

• 7:30Speaker 01

  It was, it was, yes.

• 7:33Emily Kwong?

  Well, I feel bad for them. Okay. Did the model ever show this trend happening in the other direction?

• 7:37Speaker 01

  Yes, at one point, all the seed sizes were getting bigger. And then about 35 million years ago, these seed sizes started getting smaller. And it was a big mystery as to, you know, what's driving this? You know, and what our model explained was that it was actually the evolution of these really large mammals now.

• 7:55Emily Kwong?

  Like, like who? Who were the new influencers?

• 7:58Speaker 01

  You know, you had all sorts of like, you know, weird looking mammal groups that, you know, grew enormous that are kind of the, some of the relatives of what we see now out on the African savanna. So they'd get really big and then they'd start opening up these understories as well. And so long those big seeds were no longer way better than the small seeds. And so the small seeds, the seed size started to decrease.

• 8:20Emily Kwong?

  But then, you know, boom, seed size goes up again several million years after that. Woolly mammoths, saber tooth tigers, giant sloths. What happened to those mammals and what happened to the plants?

• 8:33Speaker 01

  That's right. So that's another really interesting extinction event because it overlaps with us. So this is commonly referred to as the sixth extinction. There is a lot of tree species that co-evolved with these these big animals to have them move their seeds around. So think of the avocado, think of chocolate, two of our favorite plant species. You know, those co-evolved with these, you know, now extinct South American elephants. So that's why you kind of see this this increase in seed size over time more recently.

• 9:03Emily Kwong?

  Yeah, I mean, animals are clearly such a huge factor in shaping ecosystems as engineers, as influencers in a way. And we are currently in another mass extinction, the Holocene. Who are the influencers of today?

• 9:19Speaker 01

  That's right. Yeah. So, you know, I I'm really interested in trying to predict the future with some of these models, not just thinking about the past. And so, you know, one of the fun things we did in this paper was say, all right, we went through another mass extinction recently of these really large, important animals. What do we predict for future seed size? And without these large mammals, like, you know, the Gompheferes, mammoths, giant ground sloths. You know, these forest understories are a lot darker. And so our model would say, OK, well, it's dark, this the seeds want to grow bigger again. But the interesting thing was, we couldn't actually say that because, you know, there's another enormous ecosystem engineer that, you know, is dominant on the planet now, which is us.

• 9:59Emily Kwong?

  Ah, we're a we're quite a variable to add to the model.

• 10:03Speaker 01

  Exactly. Yeah. So we've taken on the ecological roles of of some of these now extinct animals.

• 10:08Emily Kwong?

  Oh, how so?

• 10:09Speaker 01

  Through logging and, you know, creating farms, creating grasslands, like, you know, it's not uncommon for, you know, larger animals to create grazing lawns. We just call it agriculture. You know, they're excellent at distributing nutrients across the landscape. We're not so good at moving nutrients, but we dig up a lot of, you know, elements and, you know, spread it across the planet. And so a lot of these big animals used to consume a lot of this vegetation that, you know, when they went extinct, you got a big increase in fire.

• 10:37Emily Kwong?

  Right.

• 10:38Speaker 01

  So there, yeah, there's a lot of interesting ecological changes that occurred once these. Animals went extinct.

• 10:44Emily Kwong?

  Yeah.

• 10:44Speaker 01

  And I actually have a, I have an interesting little, little tidbit for, you know, we're, we are King Kong. And I don't mean that as a metaphor. I mean that we're metabolically King Kong.

• 10:53Emily Kwong?

  Wait, what do you mean by that?

• 10:54Speaker 01

  Humans, you know, use other energy. We heat our houses, you know, we have fires.

• 10:59Emily Kwong?

  Oh.

• 10:59Speaker 01

  Um, and so if you figure out how much energy we use, like by burning oil on top of like everything we eat, you could predict what size animal would be.

• 11:08Emily Kwong?

  Oh.

• 11:09Speaker 01

  And so we would be eight billion King Kongs, uh, we're metabolically eight billion King Kongs running around the planet. And so, you know, we in the Western world consume a lot more energy than typical global citizen. We, that we might be the ultrasaurus, you know, that's, that's, I haven't done that actual calculation. We might even be bigger than King Kong. So we're really changing this long-term evolutionary trajectory, um, of, of the planet in interesting ways. But of course, you know, who knows where we're going to be in, you know, a thousand years versus a million years. Like, that's something that our models cannot predict, unfortunately.

• 11:41Emily Kwong?

  And considering the way the dinosaurs went, I just, I don't feel great about this. So, um, with all this in mind, how do you hope people think about the kind of like wax and wane of the understory in relationship to mass extinctions? Cause we're in one right now.

• 11:59Speaker 01

  Yeah. I mean, I, I'd like people to reflect on our, our ecosystems co-evolved with these big animals. They're used to having these, these big animals, both as nutrient distributors, you know, affecting forest structure. They play really critical roles and now they're missing. And so that's kind of like our motivating factor for creating these models is to, you know, say something about our future world on big spatial scales over long periods of time.

• 12:23Emily Kwong?

  Thank you so much for coming on the show.

• 12:25Speaker 01

  Oh, yeah. Thank you so much for having me.

• 12:29Emily Kwong?

  This episode was produced by Burley McCoy and edited by our showrunner Rebecca Ramirez. It was fact-checked by Tyler Jones. The audio engineer was Robert Rodriguez. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave, the science podcast from NPR.

• 13:00Speaker 02

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