E43: Okay, but how terrifying were terror birds?

Scott Taylor: Imagine you're standing in a grassland in South America 10 million years ago. The grass is past your knees. It's hot. It smells like dust and like rain that hasn't arrived yet. Out on the plain, there's a herd of grazers, long necks, slender legs, something between a camel and a horse, but neither. Past them, heavier animals, rhino-shaped, cropping grass with big rodent front teeth. At the tree line, something the size of a bull is standing up on its hind legs, hooking branches down with claws as long as your hand. Low in front of it, an armored thing roughly the shape and size of a Volkswagen. None of it is familiar because South America spent more than 30 million years as an island. No Panama, no land bridge, just open ocean between this continent and everything else alive on Earth.

Scott Taylor: Which raises the obvious question, something is eating all of that, but what? If you pictured a big cat, that's a reasonable guess, and it's wrong. There are no cats here, no dogs, no bears, no hyenas. The entire carnivore lineage is an ocean away. So evolution led to a different group of organisms filling the role that we typically think of big cats or wolves or bears filling. And one of the animals that got the job stood 10 feet tall, ran on two legs, wore coarse hair-like feathers, and carried a head the size of a horse's skull with a hooked beak on the front of it. And it was the apex predator of an entire continent for tens of millions of years.

Scott Taylor: Which brings us to the topic of today's episode. Okay, but how terrifying were terror birds? To help us explore this topic, I'm joined by paleontologist Dr. Federico "Dino" Degrange. After the break, Dino walks us through what a terror bird skull was actually built to do. Video on. These skulls are nuts. We also get into how many kinds there really were and what these animals looked like alive. And we talk about what happened when the ocean between North and South America finally closed. Stay tuned.

Scott Taylor: Welcome back to the podcast, everyone. I'm really excited to have Dino here today to talk all about terror birds. Thanks for joining us.

Federico "Dino" Degrange: Thanks for inviting me. Hi to everyone.

Scott Taylor: Yeah, of course. Well, before we get into the terror part of it can you just tell us what a terror bird is and when they lived and where you would have run into one?

Federico "Dino" Degrange: Well a terror bird is a group of Cariamiformes were highly diverse during most of the Cenozoic but they are only represented today by two species the seriemas the Black-legged Seriema and the Red-legged Seriema which is the most closely related bird to this family, Phorusrhacidae, the popularly known as terror birds. Most remains actually comes from Argentina, from my country. But there are remains from Chile, Uruguay, Brazil, Peru, Colombia, and from the states Texas and Florida.

Scott Taylor: Oh, cool. I didn't know that there were Texas and Florida fossils. That's really cool.

Federico "Dino" Degrange: Yes, those remains actually belong to a larger terror bird called Titanis walleri, which is one of the youngest terror birds known. And terror birds actually live from the middle Miocene, we are talking about 45, between 45 and 50 million years ago, to actually only years. And they were characterized by having narrow slender hind limbs, reduced forelimbs, and probably what is the most characteristic feature is the skull. The skull of a terror bird looks like this. This is a real size skull. This is a 3D printing of a terror bird skull, Andalgalornis. From Catamarca province and basically you what you can see here is that the big is it's quite long it's narrow and it's sorry tall and it's tall and it's hollow also but What is actually the main feature of a terror bird, of a phorusrhacid, as we call it here in Argentina, is the lack of cranial kinesis is I have here a skull of an eagle it's basically the possibility to flex upward and downward the beak regarding I don't know if it's possible to see it there regarding the.

Scott Taylor: Yeah, I can see it moving a little bit. Yeah, the upper mandible moves a little bit up and down. Yeah, But one thing I want to ask about that skull that you have. So that's a 3D printed replica of an actual fossil. Is that one of the larger species or is that like medium-sized?

Federico "Dino" Degrange: No, actually it's a medium size. The largest skull known for a bird belongs to a terror bird Kelenken called the skull size about is 71 centimeters long.

Scott Taylor: Wow. 71 centimeters. That's like. Three quarters of a meter long. That's so big. Wow, okay. Well, the name terror bird, as I understand it, came from a paleontologist in 1978 and it really stuck. So now, you know, when I teach ornithology, I mentioned the terror birds. Often my students are like, can we talk about terror birds? Because it's such a, It's a very popular name, and it strikes a certain thought into your head. And you've said the popular image does not match the actual fossils. So what's wrong with the picture in people's heads? And tell us a bit more about this name, Terror.

Federico "Dino" Degrange: Based on what we know based on morphology and isotopes terror birds lived in a spaces with open savannas, spaces with rivers and wetlands, and more enclosed areas and shrubs.

Scott Taylor: Okay, cool. I mean, often when you see a drawing of a terror bird in some setting that, you know, that an artist has created, they're on grasslands. But it wasn't just grasslands. There were grasslands, wetlands, and then small trees and shrubby areas as well. Cool. Okay.

Federico "Dino" Degrange: Yes And this goes to the question that you made regarding Larry Marshall. Larry Marshall was the paleontologist that called terror birds based on actually this guy, Andalga.

Scott Taylor: Okay. I mean, that is terrifying. That skull is...

Federico "Dino" Degrange: It is terrifying. Yes. It is terrifying. And he actually... he had a point of what they were should be named terror birds and this is because we are talking that this animal Andalgalornis is about 140 one meter 40 centimeters one meter 50 centimeters tall that's a medium-sized terror bird.

Scott Taylor: Yeah. Medium size, a meter and a half.

Federico "Dino" Degrange: Medium size about 40 kilograms, though that is a medium-sized terror bird. A small-sized terror bird or for at the moment let's call it phorusrhacids actually, a small size phorusrhacids is about 90 centimeters tall and about 10 kilograms. And the really small ones, we think were maybe capable of clumsy flights, like seriemas. The medium and largest were fully flightless, right?

Scott Taylor: Flightless. Yeah.

Federico "Dino" Degrange: And also they have compared to this smaller phorusrhacid medium size and especially largest terror birds have highly reduced forelimbs what about the large size well this is where the thing comes it gets terrorific because actually large to gigantic terror birds are about two meters and three meters tall and 100 120 150 kilograms and it is.

Scott Taylor: That's huge.

Federico "Dino" Degrange: Huge it is huge but Larry Marshall actually thought that these animals were... These animals WERE fast runners. Terror birds were undoubtedly fast runners. But he actually thought at the moment that terror birds kill using their legs. So his hypothesis was that terror birds run... pursue prey, and once they reach the prey, actually they kick the prey in order to subdue them. Sorry for my English audience. And based on this animal which clearly had like a.

Scott Taylor: No, you're great. I mean, if we were doing this in Spanish, no one would be able to understand me at all. So you're awesome.

Federico "Dino" Degrange: A head that looks terrorific he thought oh these animals had to be like very scareful and scary sorry scary and terrorific so the terror birds that's and actually it's a name that stuck because it really stuck because actually he Marshall, I mean, he didn't consider the small terror birds, which doesn't look so terrorific. You can, if you see this, actually it's a huge skull for a bird, but smaller terror birds, the psilopterins, are actually even smaller. A skull of a psilopterin is about this size. We have a say here that it's like all terror birds are phorusrhacids, but not all phorusrhacids are terror birds. It's important to notice that actually when Marshall actually named Terror Birds, named the Forrest Rasset as Terror Birds were already known for almost 90 years. The first phorusrhacid species thought to be a mammal is actually Phorusrhacos longissimus, the species that give the name to the family. In 1887 by one of the main paleontologists of the Argentinian paleontological history, Florentino Ameghino. Phorusrhacos actually was one of these gigantic, really large-sized terror birds.

Scott Taylor: Yeah, I guess it also makes sense that those fossils would attract a lot of attention and someone would want to describe them and try to figure out what they were from because they are quite astounding. You put a terror bird skull through a CT scanner and ran physics on it. So you've been talking about the kinesis of the skull, the fact that these larger terror birds, their bill doesn't move up the way a lot of other bird bills can. What did the bite tell you about how these birds actually killed their prey?

Federico "Dino" Degrange: We use these scans to work on biomechanical 3D modeling using an engineering technique called finite element analysis. Which we had to estimate bite force. We didn't get the bite force from the scans. We had to, using bite data available of extant species, make regressions and estimate bite force. And we discovered that actually terror birds bite quite hard. But the most interesting thing that we find using this finite element analysis is that terror birds couldn't do like this. They couldn't grab a prey and shake it laterally. Terror birds didn't kill using the legs. The legs may work as a tool for... pressing the prey against the ground once the terror bird and had to but to kill the prey first they had to use very precise hatchet-like strikes so basically the terror bird was chasing you and once it was close to you it just opened the mouth this acts like movements in order to kill the prey this tall beak which is very tall actually compared with other birds it's highly resistant to forces directed upward.

Scott Taylor: Okay, mean, I can understand the original hypothesis about kicking because some contemporary birds of prey, like I think of secretary birds kicking snakes to death. So I can understand thinking that, but it's very cool that it probably was they were using these massive bills to take out their prey. And what kinds of things were they eating then? I mean, mammals or other birds, all of the above?

Federico "Dino" Degrange: We think that probably mammals, running mammals, because clearly terror birds are suited for chasing. Santa Cruz Formation is important because actually it's the only place where we can find four species of terror birds.

Scott Taylor: Okay, so multiple species of terror bird were occurring in the same places, eating different things, and.

Federico "Dino" Degrange: Species, one medium-sized species, and a large So we know that based on body size, there is a niche separation terror birds were considered as apex predator during the Cenozoic together with crocodiles and marsupials, we think that based on this body size differentiation between species allow a clear separation of the niche.

Scott Taylor: From the fossil record then, it seems unlikely that there were any vegetarian terror birds. They were all predatory, just predators of different sizes of other things. Yeah. All predators. So, I mean, still, that's still terrifying, depending on what size you are. If you're a little mouse, one of the small terror birds would still be pretty scary. In 2010, so there was this nearly complete terror bird skeleton discovered in Argentina, and you were able to work out what it could hear. Can you tell us more about that?

Federico "Dino" Degrange: That is actually this guy. It's the most complete skeleton of a terror bird ever found. My friend who discovered it called me from the outcrops.

Scott Taylor: Oh, really? Oh, that must have been a great phone call. Yeah.

Federico "Dino" Degrange: Yes he called me he was in the outcrops taking skeleton out of the rock and he called me like we found the terror bird we found the first terror bird the skull is so beautifully preserved that allow us to make CT scans. And with those CT scans, we were able to reconstruct the real size brain of a terror bird and the inner ear. Based on inner ear morphology, we know that semicircular canals of the ear this part of the ear that are related spatial orientation and equilibrium are quite long and slender indicated a fast animal part of the inner ear related with hearing allow us to estimate hearing range us that basically all terror bird birds have low hearing range frequency suffer less modifications during transportation in the air they are less modified so they you can hear further.

Scott Taylor: Right yeah elephants use low frequency sounds to communicate across really long distances in similar you know open habitats as maybe terror birds we're living in right yeah cool.

Federico "Dino" Degrange: Yes exactly so what it's important to say here that this doesn't mean that we know exactly what they eat or how was the sound production of terror bird except if you can hear low frequency range obviously you produce low frequency sounds so.

Scott Taylor: Yeah. Interesting to think about what we can and can't infer. Mean, it's frustrating to me as a population geneticist. I can't go back and watch what happened. I just have to infer what happened from the genomes of the things I sequenced. And just like same with paleontology, can make educated guesses about these things. But it's really cool that just based on the inner ear, you can have a pretty solid hypothesis that these things could run really fast, that they could hear these low frequency sounds. Maybe because that was a way to detect prey or maybe because that's how they were communicating like open savannah species a few years ago a bone turned up in Colombia that might be the biggest terror bird ever found and it had bite marks on it can you tell us a little bit about that discovery.

Federico "Dino" Degrange: Yeah, actually, there are two bones from that area. We published a more recent paper with an even larger terror bird than the one that you are mentioning same area in Colombia. And these tooth marks indicate us, terror birds suffer predation.

Scott Taylor: From the same area in Colombia?

Federico "Dino" Degrange: So there were things eating terror birds.

Scott Taylor: Even the big ones, which is impressive. Yeah.

Federico "Dino" Degrange: Even the big ones but it's important to state that in the area where in La Venta locality where this animal was found also there are large crocodiles known fossil crocodiles known And those marks are actually from one of those crocodiles. What we don't know is if the turtle was dead when it was bitten or it was directly hunted by this crocodile.

Scott Taylor: Mm-hmm. What have people been able to figure out about why we don't have terror birds anymore? What happened to them?

Federico "Dino" Degrange: We still don't know.

Scott Taylor: No, that's, I mean, that's the thing. I think there are a lot of these outstanding questions and it should motivate more research for sure. Yeah.

Federico "Dino" Degrange: Nevertheless, we have some ideas. Probably it is a combination of things one is related to environmental change terror birds were apex predator but terror birds probably were not any apex predator were highly specialized apex predator late myosin, early pliocin, great American biotic interchange occurred.

Scott Taylor: Yeah I was wondering about the great biotic interchange between when North America and South America finally were connected together by the Isthmus of Panama. You had this movement of certain... Well, the camelids went down, right? Because camelids evolved elsewhere and then colonized South America. So now you have guanacos and vicuñas and other things. And some predator mammals also moved into South America, which I was wondering exactly about this.

Federico "Dino" Degrange: Not only camelids most ungulates and in canids felids Procyonids a lot of a lot of carnivore placental mammals environmental so changing prey disappearance and competition with another less specialized, let's say, predators, were probably the driving of turtle bird extinction. It is not weird, actually, that our last record of a turtle bird, it's one of the smallest species. It's about five kilograms. It's Scatornis aterradora, the... from the very late Pleistocene especially from the very late Pleistocene of Brazil which is considered one of these terror birds that probably were more generalist based on body size it was able to reach not only prey but probably carrion or take advantage of feeding resources that medium to large terror birds were not able to.

Scott Taylor: Yeah, it makes sense that the generalist would maybe survive longer. And it's also interesting that there, you know, it wasn't just that all these organisms invaded South America where terror birds were. They also seem to have moved north, right? Like that's how they would have, they would have crossed the isthmus of Panama as well Is there any evidence that any of those canids or cats, ophelid predators that invaded South America preyed directly on terror birds? There's no evidence from the fossil record, at least, yeah. But maybe, I guess. Although I wouldn't want to go up against a two and a half meter tall bird with a giant beak that cut into me. But you never know, I suppose.

Federico "Dino" Degrange: No we don't have direct evidence.

Scott Taylor: All right. We've reached the part of the show. We call That's B.S.. So that's bird stuff where we give our guests an opportunity to debunk a myth that ruffles their feathers. So Dino, what do you want to call BS on?

Federico "Dino" Degrange: Want to call two bs actually one about terror birds and one about seriemas because there are not too many bs about terror birds but I have read somewhere that actually there are still terror birds in Amazonia.

Scott Taylor: All right, go for it.

Federico "Dino" Degrange: So people don't worry there are no terror birds on Amazonia living there so I mean, if you want to get lost in Amazonia rain forest, go for it. But don't worry, probably you will get killed by another thing and not a terror.

Scott Taylor: Not a terror bird. All right.

Federico "Dino" Degrange: And the other one is about seriemas. Actually, When I was doing my PhD, I was looking for seriemas, since they are the most related extant bird to terror birds, to phorusrhacids. I wanted to see how they live. I wanted to see a living seriema, not in zoos, in the natural environment. And you hear a lot of myths about this. Beautiful birds and amazing birds actually a farmer from there told me that they taste really good with noodles and they also said he must like noodles I They like noodles and they taste good. You can cook them with noodles. Honestly, I couldn't check any of those, so sorry. And the other one is that they actually like to run. The seriemas are really fast. They can run up to 40 kilograms an hour. So apparently they like to run. With the cars so if you go to dirt into dirt streets apparently if you go fast the seriema must have this like this instinct of going and oh there's a car I have to run with it and sorry no it doesn't work I tried several times and I didn't see any seriema actually It took me like a long, they are hard to see here in Argentina. In Brazil, it's more common. So it took me a long time to see several seriemas in the field.

Scott Taylor: That is a myth that is a myth yeah.

Federico "Dino" Degrange: In the area where I was. So those, I hope that you enjoy my BS.

Scott Taylor: Yeah, no myths busted. Don't try to feed seriemas noodles. And if you want to find them, don't drive a car fast. Cause that's not going to attract them. Well, thanks so much for joining us on the podcast, Dino. It's been really awesome to learn more about terror birds, and I appreciate you taking the time to talk to us.

Federico "Dino" Degrange: Again, thank you for inviting me. It was a pleasure. And if I say some last words. I suppose that you are going to use the bird sound here because I have to say it, sorry. I have to take this out of my system. For all the people who is hearing this amazing podcast, I have to tell you that Cherubi, it's not only the best group of vertebrates that they ever live, that ever live. They are just amazing.

Scott Taylor: They are. They are. Yeah. No.

Federico "Dino" Degrange: They are insane! So you have to use the sound several times.

Scott Taylor: No worries. No, they're incredible birds and it's been awesome to learn more about them. I, there were a lot of things today I did not know. So I really appreciate it. Yeah.

Scott Taylor: Birds are dinosaurs, and around here we like our snacks, so we end each episode with a dinosaur nugget. Today's nugget is, terror birds are gone, but their closest living relatives are not. They're called seriemas. There are two species, both still walking around South America right now. They're just over two feet tall, they can fly, but mostly don't bother, and they look like a chicken that got stretched. They also still hunt like the family used to. A seriema grabs a lizard or a snake, picks it up, and beats it against the ground until it stops moving. Same continent, same grassland. Roughly 1/20th the size.

Scott Taylor: That's a wrap on this week's episode. Okay, but how terrifying were terror birds? If you liked this one, help us out. Leave a rating or a review of five stars, obviously. We'll catch you next time. Byeee.

This transcript was generated using AI-assisted transcription and may contain errors or omissions. Please refer to the audio or video episode for the most accurate representation.