Science Friday
Hosted by Flora Lichtman
Scientists look inside the fossilized stomach contents of a massive dinosaur. And, why some birds listen for prairie dogs’ alarm calls.
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Hi, I'm Flora Lichtman, and this is Science Friday.
Today on the show, how did a huge plant-eating sauropod eat its dinner? Some insightful crumbs about dinosaur diets from a fossil tummy.
They're not really chewing it at all. They snip with their teeth, and then they more or less swallow and let their gut bacteria do the rest.
There are a lot of dinosaur fossils and a lot of plant fossils. But just exactly how the plants and the plant-eating dinos came together, you know, the eating part, is somewhat of a mystery. It turns out that paleontologists hadn't ever found the fossilized gut contents of a sauropod. That's the group of massive plant-eating dinos that includes the Brontosaurus, the Apatosaurus, the Diplodocus. We knew they ate plants, but not exactly which ones or how. But now researchers report that they have found what's called a cololite. That's a hunk of fossil gut contents in the remains of a sauropod from about 95 to 100 million years ago.
Dr. Stephen Poropat is a paleontologist and deputy director of the Western Australian Organic and Isotope Geochemistry Centre at Curtin University in Perth, Australia. He recently wrote about this discovery in the journal Current Biology. Stephen, welcome to the show.
Thank you very much, Flora.
First, what is a cololite, and what does it look like?
Well, a cololite is the fossilized gut contents of an animal. And I guess depending on what that animal had eaten, a cololite would be quite different in appearance between animal to animal. For a plant-eating animal, you would expect it to be full of plants. For a carnivorous animal, say something like Tyrannosaurus, we'd expect to find crunched-up bits of bone and maybe mineralized bits of flesh.
Tell me about your cololite.
Well, our color light, it actually, it it sort of doesn't look that impressive in some ways. It it's a really weird piece of rock. When we encountered it, all it looked like to us was an iron-rich rock layer that had some very weird shapes and and patterns in it. On one side, it had a hexagonal sort of pattern repeated all over it. And on the other side, we saw marked in different colors or marked as basically voids or hollows in the rock, what looked to our eyes like fossil plants.
How big are we talking?
So I guess the size of a small desk, maybe a medium-sized kitchen table at largest extent, and thickness only about ten centimeters or about three inches.
Did you know right away, oh yeah, this is a tummy?
We didn't. We had to really convince ourselves that that was what it was. And that's because there have been reports of gut contents in herbivorous dinosaurs before, where it's been shown that, well, actually, those plants were washed into the belly rather than having been interred because they were eaten by the animal. And so we really needed to prove to ourselves that those were genuine gut contents. And that's why the specimen was found in twenty seventeen. It's taken us best part of eight years to actually get this this work published. We were fairly confident because, for one thing, this skeleton was very much arranged in very close to life position. So all the neck vertebrae, or many of the neck vertebrae, were all in alignment, all in the position they would have been when this sauropod was alive.
Immediately behind them was a jumble of vertebrae and ribs, but still partially arrayed, I guess, in in life position. And then, slightly further back from that, we found the pelvic region of the animal as well. And the gut contents are right between the torso and the pelvis, exactly where we would expect to find them if they were genuine gut contents.
It was in the right spot, and so was everything else.
Exactly. And and the other thing is, of course, that that hexagonal pattern that I mentioned before was on the underside, and we realized later on that that was mineralized skin. So what this meant was that plant-rich layer was sitting inside the skin. The scales were facing towards the ground.
Oh, cool. That's awesome. Okay, so it sounds like there were plants in there. Were there any surprises?
Uh, I guess not really. We would expect, based on a hundred and fifty years of of good science from from paleontologists around the world, we would expect sauropods to be herbivores. Uh, it's hard to envisage them eating anything else, mainly because they were so big and and not terribly bright, that they really wouldn't have been able to pursue anything that could move faster than a plant. Well, I guess the the main surprise was that when we'd looked at skeleton of this animal before, and especially in light of the new skeleton, which has the most of the neck and the torso, we'd realised that it was very likely that we had a specialist high browser or something that was at least approaching a specialist level of of high browsing as an adult. But in the gut contents of this sauropod,
whilst we did find evidence of plants that certainly did grow up high, uh, like bracts from conifers and plants from aracharias or monkey puzzle trees, we also found leaves from flowering plants, angiospherms. And when these dinosaurs were around, those plants were relatively small and and low growing and didn't really have terribly woody stems. And so that suggested to us that this sauropod dinosaur was feeding at multiple different levels above the ground.
So they weren't just a high browser, they were they're eating high and low.
Yes, exactly. And and we wondered, and we speculate this, um, that because the sauropod that we have found the cololite or the gut contents for was a subadult, so it's still growing, it's not quite reached adulthood, some of its bones are still yet to fuse together. We have speculated that this sauropod is sort of halfway between its diet as a as a hatchling or a youngster and its diet as an adult. So it's basically eating everything that it can possibly come across because it's growing rapidly and excreting relatively regularly. It needs to basically feed itself and and so it can keep growing big enough to be able to evade predators effectively. And it would seem that this particular sauropod was, as it grew, changing which plants it was targeting.
Hmm. You know, to me, it's surprising you could pick out the plants at all. Like, did they not chew?
No, that was one thing that was, again, verifying an ancient hypothesis in many ways. Because people have looked at sauropod teeth and seen that there's no evidence of a tooth anywhere near like our own molars or the molars of plant eating mammals. They realized that if they were herbivorous, they certainly weren't doing much processing of their food in their mouth. They're not really chewing it at all. They snip with their teeth and then they more or less swallow and let their gut bacteria do the rest. So they're basically giant fermenting vats, probably keeping any given meal on board for up to two weeks before finally digesting what's left of that meal.
Do they have multiple stomachs like cows? Like, how do they make that work?
It's probable that they actually used a process called hind gut fermentation. So not what cows use, that's what that's foregut fermentation. But we do have animals that today use a hind gut for that fermentation process. So things like elephants, rhinos, horses, they are hind gut fermenters. So they will swallow often large quantities of pretty low quality vegetation and then basically try and keep it inside themselves for as long as possible so that they can then use that fermentation process to extract as much nutrition from that plant matter as they possibly can before they finally excrete what is left.
So my mental image of a sauropod is, you know, not small. How much would they have to eat to sustain their massive size?
That's a really good question, and I guess fundamentally it depends exactly what their physiology looked like. If they were homeotherms and endotherms, so warm blooded, then they would have needed to eat a lot more food than if they were cold blooded. I suspect that they probably weren't the highest metabolism dinosaurs out there. If they had, they probably would have eaten themselves out of house and home in short order. But also, the fact of the matter is that that fermentation process would have actually generated quite a lot of body heat. So it's entirely possible that as youngsters, they had a pretty Warm internal furnace and then as they matured, it kind of slowed down, cooled down and let their gut bites bacteria basically warm them up from the inside out.
And so maybe they were extremely plant hungry when they were young, but then after that, they they might not have needed to sort of keep that that level going and they might have not needed as much food relative to their size as as you'd expect.
Hmm. So if this is the first sauropod cololite, does that mean that when we heard about plant eating dinosaurs in the past, we didn't really know for sure what plants they were eating?
Pretty much. Yeah. I mean, while we while we were very confident for many, many reasons that sauropods were herbivorous, the specifics of sauropod herbivory were still a little bit unknown. And I guess if you look at any given sauropod, or even a bunch of sauropods altogether, they can kind of look all the same. But when you look at them in detail, their head shapes are different, their tooth arrangements different, their neck lengths will vary and and as will the length of the individual vertebrae and also the supporting ossified tendons, the cervical ribs that run underneath the neck, the proportions of the limbs will vary. So for a long time, sauropod workers have looked at the sort of nitty gritty of sauropod anatomy and suggested
that there was quite a disparity in the kind of plants that they ate, that not all of them fed right up high in the trees, but some actually fed relatively low to the ground as a habit. And so those inferences have all been based on anatomy and comparisons with modern day herbivorous mammals. It's nice to finally have a way to test those hypotheses that have been based in anatomy in the form of this cololite.
That's really cool. It does feel like it gives you a different view of this ancient life that we that feels so remote in a lot of ways. I mean, for you, what's the, you know, whether this sauropod ate this type of plant or this type of plant, like, is there a big picture here that interests you?
Absolutely. One of the things that particularly interests me about sauropods that were living around 100 to 95 million years ago is that they were living in a time where you're actually approaching the warmest time in Earth's history in the last 120 million years or so. And you're also at the point in time where flowering plants are becoming co-dominant with things like conifers and sea ferns in flora around the world. What this means is that we're seeing sauropods that are kind of under environmental stress from multiple different angles in terms of floral change, in terms of climatic change and global warming, naturally reduced in this case. And to be able to understand which
sauropods benefited and did not from that process. For me, it's exciting to see how plants and sauropods influenced each other throughout their evolutionary history. Because sauropod dinosaurs were the biggest herbivorous animals on land throughout the world for 130 million years. And during that time, they witnessed much floral change and somehow still managed to stay on top despite that. And to me, it's remarkable that they were so evolutionarily malleable, even though they weren't terribly brainy or rapid in terms of their movement.
Everyone likes a survival story.
Exactly.
Can I see this somewhere?
You certainly will be able to see the skin and the gut contents of our sauropod dinosaur on display at the Australian Age of Dinosaurs Museum in Winton, Queensland. It's a privilege to have any specimen that I work on on display so that everyone can enjoy it. And this one's going to bring more joy than most.
I hope you find another one.
Me too, because the one last thing that I would probably bring up is, of course, we are not sure that this cholelite and the plants that are preserved within it are representative of this dinosaur's average diet. It might be the sort of last meal of a stressed animal or a diseased animal. And so we would love to find more to basically see, well, what sort of plants were other dinosaurs versus eating other sauropods as well.
Good luck.
Thank you.
Dr. Stephen Poropad is a paleontologist and Deputy Director of the Western Australian Organic and Isotope Geochemistry Centre at Curtin University in Perth, Australia.
Coming up after the break, how birds are eavesdropping on prairie dogs to protect their chicks.
There's been all this cool work on prairie dog vocalizations, but not as much work on who's listening to who and how are they able to use that information?
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In prairie dog towns, there's a lot of chatter. Barks to signal danger is near, yips for the all-clear, even specific calls for specific threats. And it turns out that prairie dogs aren't the only ones tuning in. A new study in the journal Animal Behavior suggests birds called long-billed curlews are eavesdropping on these prairie dog conversations to learn when predators are lurking. How did the researchers figure this out? The study involved a taxidermied badger on wheels. I'm not joking. Here to tell us more is Andrew Drelin, lead author on the paper. He studies birds with the Smithsonian Conservation Biology Institute and is a PhD candidate at Northern Illinois University. Andrew, welcome to Science Friday.
Thank you so much for having me, Flora.
What brought you to this research question?
Yeah, so my very first day on the prairie, I was a Smithsonian intern for my supervisor, Andy, who was the senior author on the paper. And we're walking across the short grass prairie and... Start to hear these barks from, from prairie dogs. And this was even before we got to the prairie dog town they had spotted us. And then when you're on a prairie dog town and they're barking at you, there's just this feeling that you're triangulated by the prairie dogs at all times. You can really feel your presence like kind of ripple out through nature.
Like they're watching you.
Oh, absolutely. And Andy explained that that curlew nest that we were checking had been particularly hard for him to catch because the prairie dogs were barking at him as he went up to it. And he thought it was giving the curlew an extra warning. And I was the one who was just crazy enough to say, I think I should make this a chapter of my dissertation and, you know, kind of dive in more.
Why did your experiment require a Hot Wheels Badger Cadaver?
Totally, yeah. So we picked a badger because badgers famously eat prairie dogs. And they also eat curlew eggs and chicks. First off, we needed to do the experiment in a way where we could be a long way away without disturbing the curlews. And so that's why we needed to put the badger on the RC cars. With that built, we would basically go out and look for curlew nests. And then when we finally found one, we would essentially flag out a little race course for the badger to follow to approach the curlew nest. And then we would drive the badger at the curlew nest.
And in one version, we would have a speaker that was not playing anything by the curlew nest. And in the other version, we would have a speaker that's playing the prairie dog alarm calls.
Okay, so not only do you have this badger cadaver on a car, you have a visual signal, but you also put a speaker in the field to test whether the curlews respond differently if they hear the prairie dog saying, "Badger, badger, badger," in prairie dog language.
Exactly, exactly.
Let's hear a clip of that.
Okay, so how did the curlews respond when they heard the alarm?
Yeah, so the curlew that's incubating on the nest, normally she'll be sitting on the nest on the ground, but when she spots a predator, regardless of what it is, she's going to flatten herself out on the ground and become essentially invisible. You can be standing right next to one, and you can even have GPS coordinates for the nest, and you're still going to have a hard time spotting it. And so when the curlews didn't have the help of the prairie dog alarm calls, the badger could typically get about 16 meters from the nest on average. But when those alarm calls were present from the prairie dogs, the badger was only getting
around 48 meters from the nest. And so it was a three times difference in their response.
Okay, so it certainly seems like the curlews are understanding this call. What about prairie dogs? Can they speak curlew?
That's a great question. And truthfully, someone would have to go out and test it. I don't know the answer.
Andrew, it's your next chapter.
Oh, I am very happy to be done with my dissertation at this point. But there's been all this cool work on prairie dog vocalizations, but not as much work on who's listening to who, and how are they able to use that information to mutually make a living in a predator-rich environment. And so, yeah, to me, this is just like, starting to like pry open the lid on a Pandora's box of cool ecological interactions.
We love a Pandora's box of cool ecological interactions on this show.
Yes, yes, totally. Positive Pandora's boxes only.
Andrew, thanks so much for joining me today.
Thank you so much for having me, Flora. It was an absolute pleasure.
Andrew Dreelin is a research fellow with the Smithsonian Conservation Biology Institute and a PhD candidate at Northern Illinois University in DeKalb, Illinois.
And before we go, shark alert. Our chums over at Radiolab put together a week of sharks on their podcast. It is Sharkapalooza over there. And today's episode, you really don't want to miss. It is about the shark inside all of us. And I don't mean that metaphorically.
These sharks.
These are like swimming fossils.
They're ancient. Ooh. They come from a line of sharks that date back.
400 million years ago.
Ooh. And hidden inside of them, scientists like Aaron believe there is this very ancient key. A key that could unlock our ability to fight off some of the deadliest threats we face on Earth.
This is a new series from Radiolab called Swimming with Shadows. Check it out on the Radiolab podcast feed or at radiolab.org/sharks. Thanks for listening. Don't forget to rate and review us wherever you listen, but only if you like the show. It really does help us get the word out and get the show in front of new listeners. Today's episode was produced by Charles Burquist and Rasha Aridi. I'm Flora Lichtman. Thanks for listening.
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