T-Rex's size & biomechanics

T. rex is definitely weird, even compared to all the other giant tyrannosaurs that are very closely related to it, because it is by far, ludicrously by far, the largest carnivore in its ecosystem. So it doesn't really have competition, actually.

The following is a conversation with Dave Hone, a paleontologist, expert on dinosaurs, co-host of the Terrible Lizards podcast, and author of many scientific papers and books on the behavior and ecology of dinosaurs. This was truly a fun and fascinating conversation. This is the Lex Fridman Podcast. To support it, please check out our sponsors in the description and consider subscribing to this channel. And now, dear friends, here's Dave Hone.

So let's zoom out. What did it eat? I mean, you could go for the classic joke of whatever it wanted, but the reality is the relatively big herbivores that are around at the time, it's probably largely leaving them alone because, again, just the classic dynamics of predators, even superpredators like Tyrannosaurus, they're still real animals. If you get injured and you can't hunt, that's probably the end of you. So you don't want to tackle an adult Triceratops that weighs the same as you and has meter, meter and a half long horns on its head and is potentially pretty aggressive. And then even the big hadrosaurs, the kind of classic duck-billed dinosaurs, they're not present with any obvious defenses. They don't have armor.

How far were they spread? Where did they live? So the ones we've found, you've got them from Alberta down to probably New Mexico. I want to say there's some tyrannosaurine, so very close to T-rex, teeth that may or may not be T-rex in New Mexico. There's similar teeth in Mexico proper, down in Coahuila, about halfway down Mexico.

Yeah. Wow. This is incredible. So, okay. Let's complete the journey of Stan to the museum to, like, you get, you get to the process of cleaning everything, stitching it all together. Yeah, like Mark suggested, this can be, even with an animal that size, Borealopelta is, you know, four or five meters long. We've only gone and got the front two-thirds of it. This can be needle-level stuff.

Hey, you take that back. There's nothing they can do wrong. All right. Quick pause. Bathroom break? We've taken a few tangents, but let's continue on the thread of T-Rex. Go- go to the skull. So the skull of T-Rex is iconic. You- you describe it as being incredibly robust and overbuilt. Yeah, there's a lot of bone on there. So we mentioned a couple of other things, like Giganotosaurus is this, you know, giant carnivore. If you put Giganotosaurus T-Rex in... That's the one. So that's, yeah, that's from my old blog. It's not my image. Um...

The size of a velociraptor was exaggerated by Jurassic Park. Oh, enormously. I mean, they get a bit bigger than this. ... In terms of the skull. But yeah, they're kind of thigh-high to me, like a meter or so to the top of the head, two meters long, whereas in the movies, they're standing taller than guys who are six feet. So it's just massively, massively scaled up, and then these kind of big, domey heads, and they're not the really long, narrow snout.

So there's pack hunting, but there's also sociality, which is such an interesting idea. It's, how did they live? And this is something you look at that paleontology doesn't often touch, is like, the lives. Yeah, because, you know, animals are doing complicated things. So, you know, in the case of lions, a large part of this is down to territoriality in that the males ultimately are defending the territory, and that's effectively protecting the females. But of course, what they're mostly protecting them from is other males. So there's a ludicrous bit of self-interest. But that's effectively how it's operating as a system. But it could just be predatory type. Cheetahs are my go-to example for this. So cheetahs are the weird ones compared to the other cats because females are solitary, but males are social. So brothers will... When, when, you know, if the female has five or six cubs, the brothers will stay together in a group, and then the girls will go off on their own.

We've got, oh, at least a dozen good specimens of it by now and multiple ones with stomach contents. There's one I've described with a little mammal foot inside it, there's one with a bird inside it, there's one with a lizard inside it, and there's one with a fish inside it. On their own, and this happened for at least two of the papers describing these things, it's like, "It ate fish. These are fish-eating animals." No, that one ate one fish once. That one ate one bird once, that one ate one mammal once, and that one ate one lizard once. So what have we actually got here? I suspect we've got a group of generalists and we just happen to have found them eating different things at different times. But equally, it's also possible, at least, that, yeah, this is one of these things and it had learned to eat fish when the others hadn't, and actually this was mostly fish eaters and the others ate whatever they could get. Maybe one caught a bird up a tree in a nest, maybe one found it dead on the ground. You don't really know what one of these things on its own is fascinating, but potentially misleading.

So that brings it back to the topic we touched on a little bit. What are ... You've mentioned a bunch of the stuff that the Jurassic Park- ... series gets wrong. Maybe you could speak to more things, but also, what does it get right? So a lot of very, in some level, generic, but quite important things it gets right. T-Rex is about the right size and shape and is massive, and you don't actually see it run. You see it power walk. If you watch the Jeep chase again, you'll see it only ever has one foot on the ground.

I don't think we quite touched on this. I really want to ask you about intelligence. What we know about... ...The intelligence of, let's say, T-Rex. We talked about his big head. What do we know about... Not much. There's a T-Rex brain, or at least a very rough cast of part of one.

Yeah, so one piece of behavior I forgot to ask you about— —so T-Rex engaging in cannibalism— Yeah, almost certainly. Well, certainly, I think we've got a T-Rex bone with a T-Rex embedded tooth in it— ... with o- with overgrowth.

Let's talk about a sad topic, extinction. Yep.

Strange question. So as everybody knows, dragons are obviously real. I've been asked that on live TV before. Only not with the sarcastic tone, so-

Gotta ask you the ridiculous question. We do have dinosaurs here on Earth today. They're birds. Yup. 10 and a half, 11,000 species of dinosaur.

I think it's hilarious and just perfect that there's a giant dinosaur head next to you, and you didn't mention it once during this conversation. Yeah, sure, yeah. Because I thought, I thought we'd get it. Well, I mean, giant is an absolute diddy one. So this is Protoceratops andrewsi, and I've done loads of work on Protoceratops. It's from Mongolia. This is a latest sized juvenile, so I've got a big head, and the big head's kind of like this, but I really couldn't fit it in the bag.