What was life like for Tyranossaurus rex?

T. rex may be the most famous prehistoric predator, but life wasn’t always bone-snapping chomps and food chain scaremongering.

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  Hey, it's Kathleen Davis, and you're listening to Science Friday. While most of the monsters that come out of the woodwork for Halloween are supernatural, there was once a very real and terrifying creature that prowled the earth over 65 million years ago. That's right, I'm talking about the T-Rex.

• 1:14Speaker 02

  While Tyranossaurus Rex has reached celebrity status in our minds, thanks to movies like Jurassic Park and famous fossils, it can be difficult to imagine what everyday life was like for this charismatic, prehistoric predator. Well, acclaimed science writer Riley Black has investigated and reimagined life of the T-Rex in her new book, Tyrant Lizard Queen. And as a dinosaur enthusiast myself, I can't wait to learn more about the dino that scared the living daylights out of me as a kid. So, welcome back to the show, Riley. Thanks for being here.

• 1:44Speaker 03

  Oh, thank you so much for having me back on.

• 1:47Speaker 02

  Okay, so we just played this clip from Jurassic Park, where a T-Rex famously roars. Did T-Rex actually roar, though?

• 1:55Speaker 03

  We don't know for sure. I wish that we did. I wish that they had really cool, like, throat bones, like we have for some fossil mammals, like dire wolves. They've got the hyoid bone that, you know, controls the tongue. We can see how they howl, but for T-Rex, we don't quite have that. And yet, if we look at alligators and crocodiles today, for example, they're, they can be loud creatures, they bellow and make sounds, maybe not a roar of that cinematic intensity, but especially around springtime, when these reptiles are getting amorous, they, they bellow and roar. And I think T-Rex could have done something quite similar. It would have been very bassy, very bass notes. That's what their ears were tuned to. So, if you're one T-Rex wanting to talk to another a few miles away, it'd probably be, you know, a relatively deep roar.

• 2:37Speaker 02

  Okay, but maybe not quite like the movies?

• 2:39Speaker 03

  Not quite like the movies. I mean, everything was for effect. This is the same film that, like, oh my goodness, like, whether you're a computer scientist, a theme park manager, a paleontologist, there's, there's something wrong for everybody, really. So, you know, grain of salt on Jurassic Park.

• 2:55Speaker 02

  I mean, why do you think we're so obsessed with T-Rex? I mean, not just you and me, but Steven Spielberg and, you know, other people out there, too.

• 3:03Speaker 03

  I think at this point, you know, in the 21st century, T-Rex is popular for being popular. If we go back to when the dinosaur was initially discovered, so we're talking about the early 20th century, there weren't all that many dinosaurs known yet. We had Triceratops, and Stegosaurus, and Brontosaurus, and dinosaurs like that. But T-Rex at the time, you know, 1905, it is the largest carnivorous dinosaur that's ever been found. There's a particular skeleton, Amin H5027, which is my personal favorite. You can go visit this one on the Upper West Side of New York at the American Museum of Natural History. It's the one that I saw when I was five years old and inspired, like, scores of paleontologists at this point. It had a relatively complete, relatively unsmushed skull.

• 3:45Speaker 03

  So, this was our first look at what one of these gigantic carnivorous dinosaurs was like. The hype for this animal was so great that only its legs and its hips were up on display as they were reconstructing it. And the New York Times still ran an article calling it "The Prizefighter of Antiquity." It's just like, big, meat-eating, this was a thing that you wouldn't want to run into in the past. So, there's just something about this dinosaur that latched into our imaginations early and has stayed with us ever since, where you, you have to have a T-Rex, whether it's a Jurassic Park film, museum, dinosaur book, whatever, T-Rex has to at least be mentioned in there somewhere, as if it's getting, like, royalties off every mention.

• 4:22Speaker 02

  Our understanding of what dinosaurs look like has evolved a lot in the past few decades, right? I mean, now we know a lot more about feathers and colors. What did T-Rex look like?

• 4:34Speaker 03

  One of the things I love about adult T-Rex skeletons is each and every one is different. So, often we look at dinosaurs, and they're like, oh, they look more or less the same, right? But like, T-Rex, each and every one has a little bit different personality. And that's partially because they had ornaments on their skull, they had horns on their nose and over their brow ridges. We think that they were likely fuzzy, maybe not extensively covered. It doesn't look like a gigantic cardinal or something like that. But other tyrannosaurs that we found have these almost hair-like, kind of shaggy coats of feathers. We think T-Rex had something like that. And it would have been this, you know, very bulky animal. If you look at T-Rex and you do the full walk around, not just from the side, but especially

• 5:14Speaker 03

  from the front, you can just see how broad and muscular this animal was, like, how much everything was invested into those jaws that were not only powerful, but especially sensitive. We have fossils, for example, that show us how, like, T-Rex delicately scrape away flesh at bone, like, very delicately and intentionally. We know it could have just chomped through the whole thing, but it was also capable of handling things in this more graceful sort of manner. So, it's this, you know, up to 40 foot long or above, nine-ton carnivorous creature. You probably wouldn't see the teeth, they're probably covered by lips. It's kind of giant murder bird, for lack of a better term, but it was still graceful for, for as bulky as it seems.

• 5:54Speaker 02

  So, in your book, we follow Snaggletooth, who is a T-Rex that you've, you've made up, and you really follow Snaggletooth from birth to adulthood. And we see through that telling that T-Rexes were quite vulnerable for a lot of their lives. I mean, why was life so tough even for the tyrant lizard queen?

• 6:18Speaker 03

  I mean, nature just did not like baby dinosaurs. You know, if you've seen The Land Before Time, it was kind of like that back in the Mesozoic, based upon what we know from other dinosaur species that we have good population data for. It could be up to 90% mortality in the first year.

• 6:33Speaker 02

  Wow.

• 6:33Speaker 03

  For hatchling dinosaurs, because, right, they're all, you know, hatching out of eggs, eggs that are no larger than a grapefruit in most cases. They're these small animals that were relatively underdeveloped, that they had big eyes and were kind of like gawky and gangly. We've know from small tyrannosaurs that they weren't just miniature versions of the adults, that they're quite different, probably chasing after bugs and things like that. But there are just so many things that a baby dinosaur, even a baby T-Rex, whatever to worry about, including, you know, larger tyrannosaurs, all sorts of smaller carnivores, you know, the, the raptors and meat-eating pterosaurs, things like that, natural disasters like droughts and floods, you know, even the really heavy rain that would soak their feathers and make it hard to regulate their body temperature.

• 7:15Speaker 03

  You know, the Mesozoic world really was a dangerous place for many of these animals. This is why we don't find many baby dinosaurs at all. We really tend to see them in the fossil record, once they're hitting their teenage years and above. But that first part of life, they're kind of absent in much of the fossil record, and that speaks to how rough life was, even for what we think of as, you know, the most powerful carnivorous animal.

• 7:39Speaker 02

  What did baby T-Rex look like? Was it particularly fearsome for a baby?

• 7:45Speaker 03

  We're still getting fossils, they're very fragmentary, but it seems that they're relatively leggy, that they're these gangly little things, that their heads were almost wedge-shaped, that they had these relatively shallow snouts that weren't especially long, yet their teeth were a little bit more blade-like, they weren't these kind of railroad spiked serrated teeth that the adults have. Their eyes would have been relatively big. We know there's some other dinosaur species as well, that they look quite different from the adults. They're often, you know, they look like baby puppies and kittens and things like that. They look cute, they have that big-eyed, kind of stubby-nosed sort of look about them, and T-Rex would have been no exception whatsoever. We know from a few other fossils, you know, as they got older, as they started to hit

• 8:30Speaker 03

  those teenage years, that's when they started sort of getting muscular, packing on the pounds, getting that deep-skulled, kind of bone-crushing sort of look. But, you know, they were cute little babies and had an awkward teenage phase, just like we do. There's actually a lot to relate to, I think, in terms of life of a T-Rex.

• 8:47Speaker 02

  We have to take a break, and when we come back, we'll talk about how scientists are piecing together what T-Rex's life was like from modern animal analogs. Stay with us.

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• 10:14Speaker 02

  What did the social life of a T. rex look like?

• 10:18Speaker 03

  So it's funny because we often don't think about T. rex as being a social animal, right? The emphasis is often, was it a pack hunter or not? And that's a very complex and difficult thing to get to. It seems not. However, even animals that we think of as being solitary are still social. Big cats, for example, we think of them as being these solitary predators, and yet they encounter each other. They can smell and notice each other on the landscape. They certainly come together to court and mate. And tyrannosaurs like T. rex itself are probably very, very similar. So we know a lot of young dinosaurs sometimes group together just because it's easier to look out for danger or, you know, just more eyes to see if they need to run away from something. And then as these animals get towards adulthood and get larger, they become much more solitary.

• 11:03Speaker 03

  But even then, we have, for example, bite marks on T. rex snouts that were made by other T. rex. So we know that they met sometimes and didn't always agree with each other. And they settled these disputes by biting each other on the face, as many modern animals still do today, like alligators and crocodiles. And we know that they must have courted and mated as well. This is how they existed for more than 2 million years, right? So the social life of T. rex was kind of sporadic. They were kind of loners for, you know, a great deal of their time, but they did notice and interact with each other, whether it was either in more friendly or agonistic ways, you know, throughout their lives.

• 11:39Speaker 02

  I mean, how much of T. rex's life is, is put together by the experts based on what we know from fossils versus like potential analogues that still exist?

• 11:51Speaker 03

  It really takes both. From the very beginning of paleontology, the science has really relied on both geology and comparative anatomy. And we're always looking for resonance between the past and the present. So in terms of T. rex's social lives, for example, we have bitten bones. And we can say, okay, this was definitely a fight between these two animals. And they seem to exist on a lot of these fossils. In fact, it might even be a sort of disease transmission that we know tyrannosaurs got these infections in their mouths of this parasite. And that might be one way that this parasite got transmitted and why we see it on so many of these fossils. So things like that are tangible and we can feel relatively sure about. In terms of, you know, how they would have reacted to one another, you know, catching the scent of another T. rex

• 12:36Speaker 03

  or, you know, during some of these times of the year where they might have courted or mated, that's when we have to start looking at other analog animals or parental care. For example, we don't know what the parental care life of T. rex exactly was, but we know, for example, that birds, very species throughout their family tree, have a lot of different forms of parental care. Alligators and crocodiles have this as well. Chances are it goes back to their last common ancestor. And this was a common thing that we find amongst many other non-avian dinosaurs. So we can at least form a kind of hypothesis. To put it another way, this isn't behavioral, but you know, T. rex must have had a heart, right? We've never found a fossil of a T. rex heart, but it must have had one. It's a vertebrate, it had a cardiovascular system. We can see all the openings for blood vessels.

• 13:18Speaker 03

  So we can start to hypothesize and guess about the shape of what that was and narrow down an image that helps us look for it. So it really is this combination of what the fossil record directly tells us and looking for modern equivalents to kind of guide our questions and investigations.

• 13:34Speaker 02

  Yeah. I mean, obviously we have this idea in our heads of T. rex as this, you know, apex predator. But what role did they play in the ecosystem? I mean, was it more than just, you know, top of the food chain?

• 13:48Speaker 03

  I mean, T. rex was like garbage disposal head of staff, really, for a lot of these large carcasses that wound up on the landscape. Because as hard as things were for them, it was also hard for many other species of dinosaurs. So in the book, I set it in prehistoric Utah rather than Montana, a more familiar T. rex kind of place. And the reason I did that is because there's a long-necked dinosaur called Alamosaurus that lived in the same habitat, grew to be more than twice as long as T. rex, you know, weigh more than 40 tons, you know, hatched out of an egg, started relatively small, and then, you know, if they're able to get large enough, became these, these giants on the landscape that were more or less impervious. When one of them passes away from some other cause, T. rex is basically recycling all that nutrient back into the ecosystem

• 14:31Speaker 03

  and often opening up those large, tough-skinned carcasses that many other living things, whether it's toothed birds or insects or what have you, can access all that and kind of do this deconstruction project together. And T. rex really occupies this precarious place in its ecosystem. It wasn't dominating anything. It only existed because of the biodiversity and the abundance that existed below it. So all these other organisms that we normally don't even think about in terms of T. rex, like, you know, like fungi in the soil and microorganisms, the plants that the herbivores ate, all of these things basically built this habitat that then T. rex changed through its behavior. We know from modern herbivores, for example, that they will tend to avoid places where they might be ambushed. And we think that T. rex was kind of an ambush hunter.

• 15:15Speaker 03

  It wasn't a pursued predator, it wasn't racing after things that would try and hunt by surprise. So we know these herbivores changed the vegetation around them by what they ate, where they walked, all that sort of stuff. So basically, the fear of T. rex changed the landscape. And this is another way in which it interacted with its ecosystem, these top-down and bottom-up forces that basically go out, like, you know, ripples in the pond from a big carnivorous animal like this.

• 15:40Speaker 02

  Huh. So last month, there was some new research from UCLA where scientists used portions of fossilized teeth to figure out a T. rex's body temperature. And they figured out it was about 97 degrees Fahrenheit, which like is pretty similar to humans. We're at about 98.6. What does this tell us about T. rex? Is this important? How, where do you fall on this?

• 16:03Speaker 03

  Yeah. The thing that I love about that study is that they looked at the implications of that body temperature, and it mimics what we're able to do with our relatively elevated, constant, high body temperatures. Like, well, where do humans live? We live just about everywhere. Where did T. rex live? Just about everywhere it could reach. That having this high, constant body temperature, they looked, I think, at the sort of outer limits, how cold a habitat could T. rex withstand and how hot? And it was similar to some of our own taunters and covers a broad swath of the planet. So it wasn't just a matter of this determines the dinosaur's energetic needs, that it can't just have one big meal like a crocodile and, you know, you know, just relax for the next month

• 16:45Speaker 03

  or something like that, had to eat relatively constantly. And then those warm internal temperatures gave it better responsiveness, allowed, allowed it to move more quickly, allowed it to be a very active animal. But even just more broadly ecologically, it kind of answers part of that question of like, why was T. rex so incredibly abundant and successful when we see other tyrannosaurs in these more constricted ranges? And it's likely partially because that body temperature and being able to maintain it so constantly, let it basically cross within reach of the Arctic Circle and still proliferate down like as we're starting to approach, you know, like semi-tropical habitats as well. T. rex was everywhere in Western North America. It, either it or its direct ancestor evolved in ancient Eastern Asia,

• 17:30Speaker 03

  came over the Bering Land Bridge, and then just spread through Western North America. So if the age of dinosaurs had continued, if that asteroid had missed, you know, who knows what, you know, the future would have held for, for this dinosaur? It was really capable of living just about anywhere on the continent.

• 17:46Speaker 02

  Riley, what do you want people to take away from our T. rex palooza here?

• 17:51Speaker 03

  I really hope that when people look at a T. rex skeleton or any dinosaur, they think about what we share in common with that animal. You know, we're able to understand their skeletons because they have many of the same parts that we do. They're in different shapes and different sizes. They, they lived in a different way. But there's so much that's held in common, the way that they sense the world, that they still smelled things, they felt things, they itched at insect bites, they felt shades slide over them, they probably felt the wind kind of ruffle their feathers like we feel the breeze in our hair. I, I don't really care if people take away like what the bite force was, the walking speed or any of those technical points whatsoever. I really hope that this is an exercise in empathy, rather than looking at this animal and saying like, wow, I wonder what it would be like if one tried to eat me or how monstrous it is.

• 18:34Speaker 03

  Thinking about what we share in common with a big reptile that's been dead for 67 million years. Because if we can do that, then we can start to engage with a different relationship with nature. Everything is so busy all the time. I know it hurts my brain. And really, this is an invitation to get people to just slow down a minute and think about how wonderful it is that something like T. rex exists because all the other lives around it, those ripple effects that we see because of ecology. And we can bring that perspective to how we relate to the nature that's around us now.

• 19:07Speaker 02

  Riley Black is a science writer and author of several dinosaur books, based in Baltimore, Maryland. Her new book, Tyrant Lizard Queen, is out now. Riley, thanks so much for being back on the show.

• 19:19Speaker 03

  Always a pleasure. Thank you.

• 19:27Speaker 02

  This episode was produced by Iman Moyn. And if you have a fun dino story you'd like to share, please leave us a voicemail, 8774-CY-FRY. You can also leave us a question or a comment about any other science story. Until next time, I'm Kathleen Davis.

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