Terror Birds

Introduction to Prehistoric Predators

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0:30They are the biggest birds to have ever lived. Apex predators that roamed the plains of South America for millions of years. Mega carnivores that followed the dinosaurs, flightless yet monstrous. Scientifically, they are known as forest rackets. We know them simply as terror birds. So what do we know about these monster birds? What do we know about this prehistoric age where they thrived, when South America was an island isolated from the rest of the world?

1:04And what ultimately led to their downfall, to their extinction?

The Discovery and Naming of Terror Birds

1:09Welcome to the Ancients. I'm Tristan Hughes, your host. And this is the story of the terror birds. Our guest is Dr. Steve Brissati, Personal Chair of Paleontology and Evolution at Edinburgh University and the author of The Story of Birds.

1:38Steve, it is so good to have you back on the show. Tristan, it's always a pleasure. I've always loved talking to you guys and bridging the science and history worlds and talking about the deep prehistory that I study as a paleontologist. We love doing prehistoric animal episodes once in a while, whether it's the dinosaurs or from this period right after the dinosaurs. Maybe not right after, but a few million years after. Yeah. And as we'll see, it still kind of was the age of dinosaurs because birds are dinosaurs. We can get to that, of course.

2:09And these are the terror birds. That's right. They seem and sound so bizarre to have ever existed, but they did. They did. They did. And this is really the lesson of the fossil record, that sometimes we find fossils of things that don't live anymore. We would have no idea they ever existed, but we have the fossils. And the fossils are totally bizarre, totally wacky, sublime. The terror birds are a great example of that. These were birds that would have been terrified. The nickname suits them.

2:40They were top predator birds. They were basically birds that gave up the ability to fly. They traded flight in order to get bigger, in order to grow to large sizes. They were bigger than us. Not all of them, but many of them were. And they were the top predators in South America for tens of millions of years. Not just millions of years, tens of millions of years. And I probably butchered the naming of it, the pronunciation of its scientific name in the intro. How do we say it?

3:10Oh, you're asking. Oh, my God. That was the one thing I was hoping you wouldn't ask. I don't know. So it's a name that goes way back. The Amagino brothers in Argentina. These were basically the family. There are three brothers. They were the founders of paleontology as a science in Argentina. They were immigrants. Their family came from Italy, and they established themselves in Argentina. One of them ran a bookshop. One of them did expeditions and explored and collected fossils.

3:42And one of them wrote scientific papers about the fossils. And they came up with this name based on this little jaw. It was just, you know, a few inches long. At first, they didn't really know what it was. Now, this was way back in the 1800s. Okay. So this was long before we knew a lot about the different types of dinosaurs and saber-toothed tigers and woolly mammoths and all these amazing fossils that we now know about. And so they found this thing. It looked like a jaw. It had no teeth in it. But they thought it was a mammal jaw that had just lost the teeth.

4:16The teeth had fallen out when it was fossilized. And they thought it could have been something kind of like an anteater or, you know, a sloth or an armadillo, something like that, which makes sense because these kind of animals, mammals live in South America. But as it turned out, a few years later, their mistake was corrected. And yes, it was a jaw. Yeah, it didn't have teeth. The reason it didn't have teeth was because it was a beak and it came from a bird. Now, as you'll see, I'm stalling. So I don't have to pronounce the name. I don't actually, I must say, I've never actually been sure of the correct pronunciation.

4:50It's one of these long words. I think it comes from Greek. I can't remember. Forest. Yeah. So it's for us or rackeds or something like this. Forest racked. Okay. Yeah. And so P-H-O-R, you know, but there's a reason why they're called the terror birds because they're terrifying. Obviously it's a great nickname, but the nickname is really stuck because the scientific name is such a tongue twister that it's so hard to pronounce. Then we will stay with terror birds for the rest of this chat. We will stay with terror birds. My God. I should have been better prepared. No, you- This is why. So, you know, the book, you mentioned the story of birds. I think it's behind me there. Absolutely. So I have a whole chapter on these things.

5:21And that's what I love about writing is that it doesn't matter. I don't record the audio book, so I don't have to say some of these words. That's for some other poor soul to do. Well, okay. So the terror birds.

The Eocene Origins in South America

5:32Yes.

The Eocene Origins in South America

5:33When are we talking? If they're apex predators for tens of millions of years, which tens of millions of years should we be thinking of? So, as always with the fossil record, we don't exactly know when the very first terror birds lived, but we can say that the oldest fossils come from what's called the Eocene time. And this is one of the subdivisions of the beginning of the age of mammals, basically the time after most dinosaurs went extinct. So we're talking about probably between 50, 55 million years ago, we know there were terror birds, but those first fossils are really fleeting little glimpses.

6:07They are rare clues. There's just not a great fossil record in South America at that time. So it's likely they went back even earlier. Maybe they originated soon after T-Rex and Triceratops and the classic dinosaurs went extinct. That would have been 66 million years ago. But we can be confident, I think, that sometime between about 66 million years ago and about 50 million years ago, that's when terror birds entered the scene. And they would continue to live, to diversify, to evolve, to adapt.

6:39For many tens of millions of years more. The last ones went extinct really just a few tens of thousands of years ago, just before the very first humans reached South America. So we didn't cause their extinction, by the way. This is one we're absolved of blame. This was a natural thing. We don't know exactly why, but there were big waves of immigrants from North America, other types of animals that came down when North America and South America finally docked together.

7:10We'll explore that extinction part. But so we have, let's say, roughly 50-some million years of terror birds. They only lived in South America except for this one species that did make its way northwards across the Isthmus of Panama. It may have actually even migrated even a little bit before North and South America touched. And this one got into Florida, got into Texas, made its way to California, but it didn't last very long. So there was a rare American terror bird.

7:40We have other terrors in the United States of America. This terror bird never quite gained a foothold. I'm jealous you've got terror birds compared to here where we didn't. But that's another story. But you also make an important point. So the age of the terror birds, the real time when they are really at the top, this is a time when South America is an island. That is exactly right. So think about Australia today. It's a continent, you know, it's a big slab of land, but it's an island. It's not connected to anything else. South America was like that for many tens of millions of years, 60 million years, maybe even 80 or 90 million years.

8:16So it used to be part of what was called Gondwana. That was the southern half of Pangaea, which was the single supercontinent. So Pangaea was around for a long time. Then it basically split from east to west and from north to south. South America was in the south. It remained connected to Africa for a long time. That's why they look like puzzle pieces that fit together, because they did for a long time. But Australia was part of that Gondwana continent. So was Antarctica. So was Madagascar. So was India. India used to be part of the south. It's only very recently moved northwards.

8:49Then that Gondwana continent, it broke apart. And somewhere between probably 70 and 90 million years ago, South America went off on its own. A large chunk of land, a continent in its own right, but an island divorced from everywhere else. And so because it was isolated, the animals there, the plants there, they evolved in splendid isolation, as the biologists like to say. So you get all kinds of wacky creatures living there that are pretty much disconnected from the bloodlines on other continents.

9:21And it remained that way until South America and North America made their connection. So we set the scene. So it's South America for the story of the terror birds, largely when it was an island. So now let's explore kind of getting to terror birds and the story, that evolution story is so interesting. And I feel we should probably start with the extinction of the dinosaurs.

The Asteroid Impact and Mass Extinction

9:44So 66 million years ago, what happens? Oh, the worst day in the history of the earth happens. I know I mean that actually. I mean, it sounds hyperbolic, but I think it really is true. Because 66 million years ago, one random day, this rock fell out of the sky. This was an asteroid. It was about six miles or about 10 kilometers wide. So basically a rock the size of Mount Everest or a rock the size of the city of Edinburgh, where I live. So you look at Edinburgh on the map, that's basically the size of this rock.

10:17It was hurtling through the emptiness of outer space. It was basically a leftover crumb from the formation of our solar system, a piece of space junk. And it could have gone anywhere, but it just so happened to make a beeline for the earth. And it smashed into what's now the Gulf of Mexico, very close to Cancun, the very popular tourist town on the Yucatan Peninsula. And it exploded. It detonated with a force that was bigger than a billion nuclear bombs put together.

10:48So just unimaginable fury. I mean, it punched a hole in the face of the earth more than 100 miles wide. And that crater today is mostly covered by the water of the Gulf of Mexico, but you can still see some traces of it on land. So this was catastrophic. This was the biggest asteroid to hit the earth in at least the last half a billion years. And it triggered earthquakes and wildfires and volcanoes. And all the dust and the dirt and the grime from that collision, the soot from the fires, went up into the atmosphere.

11:19The atmosphere has currents like the ocean does. So that stuff spread around the world. And before long, the earth was plunged into darkness. It was a global nuclear winter. The earth went dark and cold, maybe for a few years, maybe for up to a decade or so. And that was the real agent of doom. 75% of species went extinct. If you were alive the day the asteroid hit your entire species, a one in four chance of survival. Really? And it's in those following years, months and years that the extinctions really happened because of entering that nuclear winter time period.

11:55That's right. I mean, I don't really want to imagine it because it's so grim. But I mean, imagine if the earth, the entire earth basically was dark and cold. There was no sunlight or very little sunlight that could get through. Plants could not photosynthesize. They couldn't make their own food. So those ecosystems on land where there were forests and jungles, they would collapse. And so the plants would die, the plant eaters would die, the meat eaters would die. You know, these ecosystems would collapse like a house of cards. Same in the ocean. The ecosystems in the ocean are based on what are called phytoplankton, these little microscopic creatures that also make their own food using sunlight like plants do.

12:32So food webs just collapsed. There was very little food to go around. If you were a big animal, you were in trouble. There just wasn't much food to eat. And if you couldn't hide very easily, if you couldn't dig a burrow, if you couldn't move away from the danger very quickly, you'd be in trouble as well, especially when there were the fires and the earthquakes and the tsunamis. And if you grew slowly, you'd be in trouble. Imagine if it took you, you know, many months to lay eggs and raise your babies. And if as a baby, it took you many years to become an adult, I mean, that would not be a good strategy for getting through this sort of destruction.

13:06So it's those types of animals that really died. That's probably why most of the dinosaurs died. T-Rex, Triceratops, the long neck ones, they were big. They needed to eat a lot of food. They couldn't hide very easily. They didn't grow very quickly. So they had dominated the world for 150 million years. Now, suddenly things had changed so quickly, so profoundly that they were on the back foot and they didn't make it through. But some animals did. Oh, yes. Who are the great survivors? Who are the great survivors?

13:37So there were many victims. The big dinosaurs were among them, the pterodactyls, you know, those reptiles that were flying around over the heads of dinosaurs. Not quite true dinosaurs, cousins, but they died as well. All of those reptiles living in the oceans, the mosasaurs, the plesiosaurs, they died as well. The ammonites, those beautiful fossils, they're so common here in Britain. Those coiled shells, you know, that so many of us collect, they died. But some things did survive or else we wouldn't have life today. And one of the survivors was this group of small, furry little creatures that could eat lots of different types of food but didn't need to eat huge volumes of food because they were small.

14:18They could dig burrows. They could keep themselves warm with their hair. They could raise their babies really quickly, turn over the generations quickly. Those animals were mammals. They were our ancestors. So we had ancestors that stared down the asteroid. And again, if we didn't, we wouldn't be here. You know, our whole evolutionary family had to get through that bottleneck. But there were other survivors too. And some of them were also small, but they didn't have hair. They had feathers. And they could fly with those feathers so they could move around quickly.

14:50They didn't need to eat a whole lot of food. They grew super quickly. And they had beaks, which means they could eat seeds. And when forests collapse and ecosystems collapse, we see this today. If there's a volcano that obliterates an island or a big forest fire, seeds will remain. Seeds will really be the last thing that remains. So if you could eat seeds, it wouldn't keep you alive forever, but you would at least be able to eat the last surviving food. You could stick around for a while. Now, these animals, of course, were birds. And so it was probably because that hand of cards, that was the winning hand of cards, being small, growing fast, being able to fly, being able to eat seeds.

15:28Those were the things that helped them stare down that asteroid alongside our mammal ancestors. So these small birds, we'll focus on the birds. So obviously mammals are there as well. Oh yeah, we do mammals another day. I think we have done it as well. But these small birds, they survive the nuclear winter. And so they emerge as, you know, into this brave new world. I mean, how do they then get very big?

Surviving the Nuclear Winter

15:51How do we then get to things like the terror birds from really small survivors? Well, imagine what it would have been like to be one of these animals that did survive. That you endure this nuclear winter for a few years or a decade or so, and then the sunlight starts to trickle through the clouds. It must be quite something. It would be eerie. You'd look out on this devastated world, this desecrated planet. But this was also, of course, a world of opportunity. T-Rex is gone. This triceratops is gone. Those enormous long-necked dinosaurs that would crush you with a single footfall, they were gone.

16:26So if you could survive, you now had the opportunity. And evolution, of course, doesn't like a vacuum, and it will fill that vacuum. If there's opportunity, evolution by natural selection will shape organisms to take advantage of those opportunities. So what we see is both birds and mammals start to proliferate. From those few survivors, you get lots of new species really quickly. And you start to see some of those species, yeah, they stay small and they stay doing what their ancestors did. But some of them start to do new things.

16:56They get bigger. They move to new places. They start to eat different foods. And they start to form these more complex ecosystems where now there's a lot of mammals and a lot of birds in many different roles in the food web. And that is how we say the age of mammals started. But really, this whole age of mammals thing, we say it because we're a mammal. But look, there's over 10,000 species of birds today. That's about double the number of mammal species. So in many ways, we should be talking about us being in the age of birds now or maybe even the age of dinosaurs if we want to be really cute about it.

17:32So how do we get from – so there's a lot of then diversifying of birds in that brave new world. Do we know much about the particular family line, the particular lineage that went to South America and started getting bigger and bigger? We know some things. We know that the birds that survived – we have fossils of some of these birds that are there right at the end of the Cretaceous, right before the asteroid. And some of these birds that survived were ones that were pretty small. They lived not in the trees, but they lived on the land.

18:04They were ground birds or water birds. And by that, I don't mean something like a penguin, but something more like a duck. And in fact, some of these birds were actually in the duck group on the family tree. Prehistoric ducks. Prehistoric ducks living with T-Rex, honking around, quacking around, annoying T-Rex.

18:24I'm just imagining Donald Duck now next to T-Rex. Oh, yeah. There you go. There you go. And so these were the birds that did survive. And then afterwards, they were the ones that had that opportunity to proliferate. We don't have enough fossils to know every detail of that story. And this is true, especially of birds, because birds tend to be small. Their bones are really, really light. In fact, most bird bones are hollow. They're full of air. You know, that helps birds be lighter so they can fly better. So it's hard to preserve something small, something delicate as a fossil.

18:58We do have fossils. It's just that we don't have loads of them. And a lot of times we need those really special opportunities where a whole bunch of fossils are preserved in the same place because of some weird contingency of prehistory where some volcano erupts and buries a bunch of stuff like Pompeii. That happens with fossils or there's some lake where a bunch of stuff falls in and it has just the right chemistry to preserve the bones. So we're always at the mercy of the fossil record. So what that means is we don't know exactly which birds got to South America to become the terror birds.

19:32We know from the bones of terror birds that they are very similar to birds that still live in South America today. And these are the Sariemas. Now, they look nothing like a terror bird. They're smaller, but they live on the ground. They don't fly a whole lot, or at least they don't fly, you know, they're not ace flyers like some other birds. And they can be quite ferocious. So we know that these Sariema birds must have got to South America at some point not too long after the extinction. I should say we can build family trees of modern birds using DNA.

20:05You know, DNA, you use it like a paternity test. You can build family trees of animals using their DNA. And we can tell that a huge amount of the diversity of modern birds was established soon after the dinosaur extinction, soon after the asteroid. There was this manic blitz of evolution. And so it seems like probably within the first few million years at most, that's when these Sariema birds and their close relatives would have diverged from the other birds that are rapidly evolving. And then somehow they got to South America. And then when they were there, some of them then gave up flying, traded flying for being able to get bigger.

20:43It's really an evolutionary trade-off because it's very hard to fly if you're big. I mean, it's one thing if you're an airplane. I mean, you have your fixed wings and big engines on it. But if you're an animal like a bird that has to flap wings and power those wings with muscles, really, once you get past a certain size, it's just not going to really work. So to be something as hefty as a terror bird, something that weighed hundreds of kilos, you couldn't really fly very easily with that kind of body weight. So these ancestors gave up flying, got bigger, basically supersized their bodies, became real true big birds, and moved into the top predator niche in the ecosystem.

21:23Wow. And we're now going to delve into the anatomy of a terror bird right after this.

Anatomy and Hunting Mechanics

21:29Yes. So, Steve, that's the story of how we get to terror birds and birds getting very big in South America, an island at that time, giving up flight to get big. The biggest birds to have ever lived, is that fair to say? They weren't quite the biggest birds. They were among them, but there are some other weird fossil birds that are even bigger. There were things that once lived in Madagascar that were called elephant birds. Right. I think you can see these things get great nicknames. And they weighed well over 1,000 pounds.

22:02You know, they were something like the 700 kilo range. They laid eggs the size of watermelons. Wow. Okay. They were the biggest birds. And there were some in Australia called demon ducks. Demon ducks. Which weren't quite as tall as an elephant bird. Elephant birds got to be like 10 feet tall. Wow. Demon ducks were a bit shorter, but they were heftier. Now, both elephant birds and demon ducks, though, were plant eaters. So we call them demon ducks, but they weren't really that demonic. Right. The biggest bird predator. The biggest bird predator. There you go. Okay. That's my correction. Thank you very much.

22:33But yeah, let's explore the body structure, what we know from the surviving fossils. So let's start with the head. And so they trade flight for incredible height and size. I'm guessing the skulls are pretty extraordinary, pretty ferocious. The skulls are insane. And we were just looking at not a real skull, but a cast copy of a skull in the National Museum of Scotland the other day. I was just looking at it with my students. And this thing is about this big. I mean, it's basically the size of a horse's head.

23:04Wow. And at the end of it, of course, there's a beak. You know, these things didn't have teeth. They didn't have steak knife teeth like T-Rex or a velociraptor. They couldn't. You know, birds don't have teeth. They've lost the ability to grow teeth. Actually, birds start to grow teeth in the egg, but then very quickly they're replaced by the beak. So what that means is if you want to be a bird and you want to be a predator, you've got to use your beak to do it. You can't just use teeth. And so these terror birds had ferocious beaks.

23:36Their beaks were hooked. Big, nasty hook. Kind of like, you know, eagle or a hawk or something like that, but a much bigger, much sharper, much nastier weapon at the end of the beak in terms of that hook. And then the sides of the beak are very, very sharp. And the skull as a whole is quite big. It's very robust. Most birds today have lots of bones in their heads that are linked together very tenuously by ligaments and by muscles. So birds have a lot of movement, different than us. We have kind of this bit of our head and our jaw, and that's it.

24:09The bones have fused together, but not most birds. Terror birds have kind of done what we've done. They've fused up a lot of those bones so they could make their skull extra strong, so they could bite harder with their muscles. It's all about the bite, is it? All about the bite. And there have been some scientists, people like Dino de Grange, Larry Whitmer, my colleagues, they study anatomy. They study what's called biomechanics, how animals move and feed and what they do. And they run these different tests, mostly using software, you know, the type of software

24:42that engineers use to build when they're building a bridge or building a skyscraper. You know, you don't want to just start building. You want to model it. You want to make sure the thing's going to be strong enough. And so there's software that does this. And these paleontologists, they've used the software and they've shown that these terror birds had really strong bites and that their skulls were really robust in order to accommodate that bite, you know, so the skull didn't break apart in order to give us a proper scaffold for the muscles. And probably, and this is based on these computational analyses, these modeling analyses, they think

25:17that terror birds use their head to basically batter their prey. They would go down and strike. Repetitively. Repetitively. Okay. Yeah. Repetitively. I mean, not like a crazy axe murderer or something, just going nuts, but strategically. And they all, because they also had other weapons. They had really powerful legs, really thick legs, really big claws at the end of their feet. And it looks like those legs had a wide range of motion and they could be used to kick and they could be used to also pummel prey.

25:49So it seems like they might have, best we can tell from the fossils, use their feet to, you know, get a little mammal or a big mammal or whatever into submission and then attack with the beak, pummel it. I mean, yes, before we kind of go down the body, I mean, what prey should we be thinking of? So small and medium sized mammals? What types? Yeah. So South America during this time when it was isolated as an island continent, it did not have all the same mammals as most of the rest of the world. A lot of the mammals there were marsupial mammals, like in Australia today, the ones

26:21that give birth to tiny little babies that they raise in pouches. So in Australia, that's kangaroos and wallabies and koalas. South America also still has a lot of marsupials. And it seems like they got there before South America was an island. And they just so happened to then have this opportunity to diversify when it became an island. There were some placental mammals. Those are the ones like us that can give live birth to well-developed young. There were a bunch of hoofed mammals in South America. But these were weird hoofed mammals.

26:53They were actually studied by Darwin. When Darwin sailed on the beagle, he went many times. The beagle dropped anchor. He would go inland. He would, of course, look at the plants and the animals and theorize about what they were doing, why there was such great diversity. But he would also try to find fossils, and he would try to understand the history of these places. And so he went inland with some indigenous South Americans, and they showed him these giant bones of mammals, mammals that seemed a little bit like a horse, a little bit like an elephant, a little bit like a rodent.

27:24They didn't really match any of the mammals in Europe or in North America. It turns out we now know, because some DNA is preserved in some of the bones of those mammals in South America, they are weird horse and rhino relatives. Okay. So they would have been like the biggest plant eaters at the time. Ungulates. They were ungulates. Yep. They were ungulates, and they were odd-toed ungulates, like a horse, rhinos, and tapirs. They would have been probably some of the primary prey of the terror birds. And they ranged in size basically the same way hoofed mammals do today, from little ones,

27:55like little species of deer and sheep, all the way up to rhinos and cattle and so on. And then there would have been crocodiles there. There would have been some rodents and some monkeys, which are placental mammals like us, that actually rafted over from Africa. Their closest relatives are African. So they must have survived these one in a trillion seaward voyages after a storm or something over the millions of years. So that's the world that terror birds lived in, this isolated island fortress of South America.

28:30They were the top predators. These strange hoof mammals were the biggest plant eaters. There were also a lot of marsupial mammals, and there were crocodiles, and there were some weird rodents and monkeys that had come from Africa. This was that world, very different from anywhere else. That was the world that terror birds ruled. Well, let's keep going down the body. So we've mentioned the massive head and the incredibly powerful beak and attacking the prey. But when you get images of terror birds, their neck is incredibly long, almost giraffe-like.

29:01So what do we know about the neck? It's cool, isn't it? I mean, this is one of those. There's so many things when you look at a terror bird, when you look at the skeleton, that it's just like, that's weird. That's wild. That's cool. And some of it are those extreme things like that big hooked beak, or like the really powerful feet, or the tiny little wings. It didn't need wings to fly, but it kept them. Probably the same reason an ostrich keeps them today, to use for display to attract mates and intimidate rivals, and maybe to help turn and break and slow down when they're running.

29:33Those things are weird. Other things about terror birds, though, are actually quite normal for birds. It's just when you see them at giant size, they look strange. And the neck is one of those things. Birds have quite elongate, quite gracile, gracefully curved necks. And if you look at the skeleton of a pigeon or a chicken, you'd see the same thing. And that's actually something they inherited from their velociraptor-type dinosaur ancestors. So that gracefully curved neck with the head at the end, you know, that's what allows birds

30:04to move their heads. You see birds moving their heads, bobbing their heads all the time. That's a normal bird thing. But when you look at a terror bird, it's so big, the neck looks so stretched, it kind of does look a little bit like a birdie version of a giraffe. And that adds, I think, to the charm, to the quirk of this animal. I mean, yeah, there must be incredibly muscly necks as well, you know, it's kind of all the movement. And then the body itself is its small wings, completely covered in feathers. And I am picturing almost like an ostrich today, that kind of oval-ish kind of body.

30:35I think it would look quite similar to an ostrich. Of course, the head would be much different. Ostriches have pretty small heads. Terror birds would have these enormous heads. Terror birds probably had all things considered smaller wings, but it's hard to tell because we don't get the feathers really preserved as fossils very commonly. Terror birds would have had bigger, more muscular legs. Ostriches are super fast. They're the sprinters of not really only the bird world, really the animal world. I mean, these things are out in the savannah in Africa. And they, I mean, they sprint like the fastest mammals sprint.

31:08So terror birds probably were pretty fast, not quite as fast as ostriches, probably because they were bulkier. But they had these more muscular legs and these big, powerful kickboxer feet capped with these nasty, gnarly claws. Almost like the claws of like a velociraptor. And do we know how they were able to walk and run with these massive claws? They would have held the claws off the ground, you know, like a velociraptor would. And there's even footprints of terror birds that show this as well.

31:38They kind of look in some ways like a velociraptor footprint. You know, you can tell the claws were held up so they wouldn't be damaged. So to me, that's incredible that these feet, I mean, they were like Swiss army knives. They could do so many things. They could run fast on these feet. Then they could use their feet as murder weapons. And I mean, that's just, it's just wild to think about it. Some birds today use their feet to catch prey. Some raptor birds, you know, birds of prey do it. But the terror birds probably really were like kickboxing with those feet and just jumping, leaping onto their prey, subduing it.

32:10And then if my friends, you know, the scientists that have done these biomechanical models, if they're correct, then once the prey was down, then the head perched on that powerful arched neck would have jabbed and jabbed and jabbed. But we think more like Muhammad Ali as a fighter, you know, just taking the opportunity, pulling back a little bit, you know, float like a butterfly, sting like a bee. So float like a hummingbird, sting like a terror bird. I don't know.

32:40But that's the idea they put forward, that it would have been like a Muhammad Ali prize fighter, not quite like a George Foreman or a Mike Tyson. It was much more like boom, boom, boom, boom, boom, more selective, more selective. Okay. I like you bringing it in with those sporting analogies. I wish I could say I came up with that analogy myself. But in the story of birds, I use that analogy. I credit Larry Whitmer, my good friend, the paleontologist who came up with it. I mean, that's been a lovely description. Actually, last thing, there's no tail or anything like that?

33:11No, so birds don't have tails. So the first birds did have tails. The first birds in the fossil record, which go back to about 150 million years old, back to the Jurassic period, they had feathers and wings, but they also had teeth. They had big claws on their hands and they had long tails. They really looked like little raptor dinosaurs, like a little velociraptor. Then over time, as birds became better flyers, their wings got bigger. Their tails got shorter just for aerodynamic reasons. And birds today have tail feathers. They have a big fan of feathers, but they don't have a long bony tail.

33:42They have this little stub, this little nubbin. It's called the pygastile. You see it when you roast a chicken or back home when we roast Thanksgiving turkeys in America. It's this fatty little bulge at the end of the body. There's this little nubbin of bone inside. It's called the parson's nose in some old cookbooks because it kind of looks like this twisted, you know, nose of like a parson in a medieval woodcutting. And it's really fatty, really glandular. It's not very good eating, but that's it. That's the remnant of the tail. So terror birds, because they were proper birds, because they evolved from birds that did fly,

34:17they had long lost their tail. So they didn't have a long tail. They couldn't use a long tail for balance, like say a velociraptor or a T-Rex could when they ran. So they must have balanced themselves in another way. And I don't really know how they did it. To me, that seems like a mystery. Gosh. Brilliant description of terror birds and the classic image we have of them today.

Diversity Among Terror Bird Species

34:40But as we're about to explore after this short break, there's much more to the story than just that initial design. There certainly is. See you in a second. So Steve, that's the classic image we have of the terror bird. Big, powerful, razor sharp claws. You know, really powerful beak as well for attacking. But diversifying. This wasn't the only type of terror bird that thrived in South America for tens of millions of years. That's exactly right.

35:11And we should think of terror birds similar to maybe how we think of cats. You know, there's so many cats in the world today. And yes, they're all predators of some description. But they range from small little cats, you know, all the way up through lynxes and so on. All the way up to jaguars and cheetahs and tigers and lions. And so there would have been a similar diversity of terror birds in South America. The biggest ones were absolutely terrifying to the core. They were the top predators. They literally were filling those niches left behind by the big meat-eating dinosaurs like T-Rex.

35:47But there were smaller terror birds as well. There would have been predators, but they wouldn't have been pummeling these hoofed mammals and devouring these, you know, interesting horse relatives and so on. They would have been going after smaller prey. Maybe some of the small marsupials, maybe some of the small rodents, the smaller primates. Do we know much at all? I remember asking you this about T-Rex when we've done previous episodes. I always like asking it. But I appreciate it's more difficult from the surviving archaeology, paleontology.

36:17Do we know much about their young? I don't think we do. I honestly don't know. So with terror birds, you know, I had to learn a lot about them to write about them. I'm not a specialist on them in the sense that I've never dug up terror bird fossils myself or studied them directly. I studied many other types of birds. I'd love to. This is now on my bucket list to go to South America and work with some of my friends down there and find terror bird fossils. I'd just love to be able to find one of these skulls. I don't know if we have eggs.

36:49Maybe some eggs have been reported. There definitely are eggs that are fossilized for some of these other large birds like the elephant birds and the demon ducks and so on. These demon ducks that I mentioned from Australia, these giant, corpulent, plant-eating birds, their eggs are actually found in archaeological sites in Australia. Humans, the first humans in Australia, were eating demon duck omelets for breakfast. Wow. Sadly, that's probably why the demon ducks went extinct.

37:20So we know the eggs of some of these large birds. Terror birds, I think, would have been pretty similar. We know, of course, a lot about how modern flightless birds raise their young, ostriches and cassowaries and emus and so on. They're very good parents. They differ in the details of how they do it. Some of them, the fathers raise the eggs, raise the babies, which I love. As the father of a little six-year-old, I love the fact that I see some of these father birds with their kids. So we don't know, I think, for terror birds.

37:52I might be wrong. There might be something out there that somebody's discovered or somebody's found quite recently. But I think this is probably something that needs to be discovered. We need to find terror bird eggs and terror bird nests and get a better idea of how they raise their young. And I'm sure the fossils are out there. Yeah, absolutely. And looking forward to seeing what comes out of the ground in the future. But come on, let's get to the end of the age of terror. So terror birds have been apex predators in South America as an island for tens of millions of years.

38:23But then what happens?

The Great American Biotic Interchange

38:25Something happened. Something big happened. And as is often the case in Earth history, you know, the Earth is four and a half billion years old and the Earth is always changing. And sometimes it's an asteroid that arrives from the heavens. Sometimes it's big volcanoes or other changes that happen to the physical Earth. Sometimes the big changes are just the simple side effects of the continents of the Earth slowly moving, as they always do.

38:55You know, continents are moving. Now, the ground beneath our feet is moving about at the pace our fingernails. I feel it shaking. But I feel it, yeah. But sometimes, yes, it does move more than others. And when there's a big earthquake, it might shift a lot more. But the Earth is always in motion. And South America became an island continent because it split away from the rest of those southern lands that were once part of Pangaea, the supercontinent. Then South America would cease to become an island continent because of those same processes of plate tectonics, of continental drift, of the Earth moving around.

39:30What happened was about two and a half million years ago, give or take, South America and North America approached each other, and ever so slightly, fingers of land from both, but especially from the north, touched at what is the Isthmus of Panama. And that's where the Panama Canal is today, the easiest place to, you know, dig a canal between the Pacific and the Atlantic. If there was no Isthmus of Panama, you need no canal. That's a very recent geological phenomenon.

40:01Now, when that happened, probably for a few million years before, the land was close enough that some species could maybe move from north to south, just hopping across islands, maybe even swimming. There's some evidence that terror birds may have actually gotten to North America before the land actually touched. Oh, okay. Not a long time before, but a little bit before. It all comes down to how accurately some of these bones and eggshells can be dated. Now that I say eggshells, I'm pretty sure there are terror bird eggshells from North America. Okay, fair enough. I think.

40:32See, I'm thinking this through. The gears are turning in real time. But about two and a half million years ago, North and South America properly connected. And that meant there was now a land corridor. And that land corridor acted like a superhighway. And there were animals that were streaming northwards from the south and animals streaming southwards from the north. This is when you get the ancestors of things like alpacas and llamas going down into South America. They've only been there for a little bit of time. They came from the north. There used to be camels in North America.

41:04That's what gave rise to these things. Jaguars and other big cats, bears, dogs. These kind of things that are now the top predators in South America. They came from the north. Meanwhile, there were things like some marsupials, possums that came from the south up north. And now we have them at home. They're all over the Midwest where I'm from. There are things like some of the really interesting mammals like armadillos. They're southern. Really? They came north. That's why they're across.

41:34The giant armadillos. And we get the giant armadillos later. And there were even giant ones as well. They went extinct during the ice age or at the end of the ice age. But there were armadillos the size of cars. I love that. And they came from the south and moved north. So you had animals moving both ways. And that was just a huge disruption. It was just a time of migration, a time of dislocation. And when all was said and done, the terror birds just melted away. And it's not clear if they were out-competed necessarily by jaguars or bears.

42:06They could have been on their way out otherwise. There was climate change happening, of course, as there often is. But there were some quite extreme climate changes around that time. That's when the ice ages proper were starting. So the earth was getting much colder. And some of these terror birds reached North America as well. And they died out there too. So it really is a bit of a mystery as to exactly how they died. A lot of people will say it was because they were out-competed by these cats and these bears and these dogs, these placental mammal carnivores. It's possible, but the story might be more complex.

42:38What we do know is that the very last terror birds did die. They disappeared from the fossil record really just a few tens of thousands of years or so before the first humans got to South America. So we did not kill them. This one wasn't our fault. Other bird extinctions, elephant birds and Madagascar, moas on New Zealand, dodos on malicious. That's because of us. But this one wasn't. But we ever, ever so slightly missed that opportunity to meet a terror bird.

43:09Maybe a good thing. But still, I know, but still a great story to tell. It would have been incredible. Could you imagine if there was something in human legend in the oral stories that passed down from somebody meeting a terror bird? I mean, we just missed that opportunity. You know, we just missed the opportunity for somebody to paint a terror bird on a cave wall. I mean, can you imagine? Oh, dear. Ice Age would have a whole host of new characters. Yeah. And I always have that image of like, I mean, saber-toothed tigers meeting a terror bird.

43:40Yeah. And they would have. Yep. They would have. There were saber-toothed tigers that lived in the north that came south when that interchange happened. So there would have been some overlap there. God knows if they came into a combat. I don't know. Yeah. I don't know. That's for the movie makers. Well, exactly. That's the image you sometimes get of the saber-toothed and the terror bird, don't you?

The Story of Birds and Penguins

44:00Steve, this has been absolutely brilliant. Yes. A lovely introduction and explanation of the weird and wonderful world of terror birds, you know, and for how long they dominated South America from. They are just part of your brilliant new book, which is called. It's called The Story of Birds, and it is a pop science book. It's not an academic book. It's not a textbook. It is the story of what birds have done for the last 150 million years, how they evolved from dinosaurs, how some dinosaurs got feathers and wings and started to fly, how these feathery

44:34winged ones were the only ones to survive the asteroid, and then the amazing things they did afterwards, including things like terror birds, but also the evolution of cognition in crows and beautiful songs and many songbirds and the long migrations that birds have, all the amazing things birds do today. So it's similar to my previous books, The Rise and Fall of the Dinosaurs, The Rise and Reign of the Mammals. These are pop science books that try to tell these grand stories about evolution. And of course, for our next episode, penguins. Yes, penguins. Maybe even more terrifying than terror birds.

45:06I'm just leaving that hanging. That's a great end. You wouldn't think so, but stay tuned. Stay tuned, indeed, for that. Right. Yes, we'll see you in a bit. Steve, this has been absolutely brilliant. Thank you, Tristan. Always a pleasure. Thanks so much for joining us on The Ancients today. I hope you enjoyed the episode. And if you are loving The Ancients, then why not become a History Hit subscriber? As a subscriber, you will have access to hundreds of hours of original documentaries with a new release every week, plus early access and ad-free podcasts.

45:38You can sign up at historyhit.com slash subscribe. See you in the next episode.