Dave Hone: T-Rex, Dinosaurs, Extinction, Evolution, and Jurassic Park | Lex Fridman Podcast #480

- 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.

- I mean, this is a Velociraptor skull. There are some carnivores

that are a bit bigger than this, but not enormously

so which were knocking around as T. rex. The skull's the same type.

...toothed crap. But, like, you think about that.

And that's like going to Africa and

going, "Okay, there are lions. What's the next biggest

predator? And it's like, well, there's a weasel about this big.

Like, it's that kind of size difference and

you don't get that normally in ecosystems.

- It would eat those, the juvenile of the herbivores, but not...

- Oh yeah, it's gonna be eating Triceratops and Edmontosaurus and Parasaurolophus.

There's even a couple of giant sauropods knocking around.

- Got it.

- In some places it's gonna be hoovering them up, but like,

how often is it gonna eat... Again, Velociraptor isn't there, but how often

is it gonna eat something the size of an adult Velociraptor?

I mean, they're a fraction of our size and we're probably too small.

This is like lions hunting mice. Like, you're just not gonna bother,

unless one, like, virtually runs into your mouth, you're not gonna try and eat it.

- 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. Let's start with the T.

rex dinosaur, possibly the most iconic predator in the history of

Earth. You have deeply studied and written about their evolution, biology,

ecology, and behavior, so let's first maybe put

ourselves in the time of the dinosaurs and imagine we're standing in front of a T.

rex. What does it look like? What are the key features of

the dinosaur in front of us?

- It's gigantic. It's almost trite now

because everyone knows T. rex is massive. But yes, if you actually

stand in front of one, you would be seriously impressed just how

absolutely vast they are. So I've got a copy of a T. rex

skull in my downstairs from my office and yeah, I could fit comfortably through its mouth.

So it would be just about capable of swallowing me whole, and I'm a pretty big guy.

- Your body, you could fit- ... in it's, its mouth?

- I can fit through, I can fit through it.

- Wow.

- Yeah, yeah, yeah. And it's not even a particularly big one. It's a copy of the one that's

in the Smithsonian, and they get bigger than that.

- You have a to-scale copy.

- Yeah, it's a cast, so it's just a giant mold made and then-

- Nice.

- ...pulled out like the dentist do your teeth, but very, very big. So yeah,

they are 12-ish meters long, so what's that? 14 yards. Four and a half, maybe five

to the top of the head, standing up. So another six yards high.

And then seven-ish metric tons. What's that?

About eight and a half short tons. So a colleague of mine, Tom Holtz,

described them as an orca on land, but that's it. It is a

killer whale-sized animal but on legs, on

land. And those are massive predators. So you're

looking at something absolutely colossal, and I think that is what will

stun you. I think people don't realize how big a lot of

animals are, which sounds weird, but I used

to work in a few zoos, and something I think you notice is when you go and see things like

elephants or giraffes or rhinos, everything's built to the scale of

the animal. The elephant house is huge. The doors are huge. The

bars are huge. The food is huge. And so you don't

see them in the context of something that you have a good

frame of reference for. And I learned this, yeah, when I was at London

Zoo and was going into the basement of the

old elephant and rhino pavilion, and a rhino stuck its head out from like this gap in

the wall, and the head was twice the size I thought it was

once you stood next to it. And the same with an elephant. I once stood next to an

elephant closer than you are to me now, and you go, "Oh, they

are so much bigger than I thought." And I think it's similar in

museums. Like even when you get up relatively close to a T. rex

skeleton, there's a bit of space between you and it, and then some

bars. And then it's usually raised up a little bit on a mount, on a little mount

to hold the platform. And then you stand back from that, and you don't

actually get to stand like under them. And when you do

that, you realize that, yeah, the foot finishes at my knee.

- So is a T. rex bigger than an elephant? That'd be fair to say?

- Yeah, I mean, a very large savanna African

elephant is five to six tons, and we're looking at seven plus.

And a biped and a carnivore. So

yeah, you know, a big lion. A big lion is 200 kilos. So 430 pounds. Yeah.

- Well, that's what, that's why I mean, it's why they consider it to be probably the

most epic predator in the history of Earth.

- Yeah, I mean, and I think more than that, it's I think it's one of the most iconic animals

period. I mean if you, if you're listing things that the average person has

heard of: lion, elephant, giraffe, tiger, hippo,

rhino. There's a few more, but T. rex is coming somewhere up in that

list. That, that's how prominent it is as an animal.

So yeah, it's, it, it's almost inescapable as a

paleontologist. And then doubly so for me, who works on dinosaurs, and doubly so again,

'cause I do work on tyrannosaurs. But yeah, it just dominates conversations.

- Well, some of the other features, maybe we can go through.

- Yeah, sure.

- So big skull, big head, small hands.

- Massive head. Very kind of boxy. It's very robust. Big forward-facing

eyes. Massive eyes. Massive. I mean, tennis

ball-sized eyes. These things had amazing eyesight.

Yeah. Giant teeth. There's a cast of a-

- What?

- ...Tyrannosaurus rex tooth.

- What?

- Yeah, I know. So-

- How...

- It, it looks a bit bigger than it is. So this is all root, so this would be stuck in the jaw. This would be supporting it.

- Right. But that tip part is-

- But that-

- ...that's the tooth?

- The tip, as you call it.

And, yeah, you know, so that would comfortably go through pretty much any part.

- Wow.

- And then you realize just how thick it is. So this is a cast of a

thing called Carcharodontosaurus from Africa. You get it down in

Niger and a few other places like that.

And they're very, very big. Not as big as T. rex, but not a

million miles away. And then if you look at the teeth in profile, they're a

surprisingly similar shape and not far off in size as

well. And then you look at them that way on, and you realize it's

a third of the width. So this isn't just massive,

it's thick. And of course, being thick, it makes it strong. And with

that giant head, with all that extra bone and then all the extra musculature

attached to that giant head, they've got this uber-powerful

bite and the ability to just chomp through basically anything it wants to.

So yeah, they are truly unusual in that regard, even actually compared to a lot of the

other very big tyrannosaurs, they're often a kind of step above

in their proportions.

- So, incredible crushing power in the jaw?

- Yeah. And then, as you say, like this really short, bull neck, 'cause you've got this

massive weight of this head up front that you need to hold it up and not tip

forwards. Really quite a massive body. Again,

there's two or three other big carnivorous dinosaurs which

people argue, oh, maybe they're a little bigger than T. rex, maybe they're a little smaller, but it's

always in terms of length, which is one way of looking at things. You know,

pythons are very long but

they're nothing like as massive as, yeah, a lion or a tiger. Same

thing. T. rex is massive. It is built. So really

big kind of barrel-shaped chest, making the body very, very big

as well. And so that's why, yeah, there's things like Giganotosaurus and

Mapusaurus from South America. Maybe they get a bit longer, another

meter or so in length. But in mass, we're talking about maybe

only two-thirds, three-quarters. So T. rex is just massively bigger

than basically any other big carnivore we know of.

And then, yeah, little arms, as you say. So this is a, not great, but

it's a cast of a T. rex arm. It's not the biggest animal.

They do get a bit bigger than this. But as I love showing, it's not a

million miles off the size of my own. And

I could do with a diet, but I don't weigh seven tons. So

yeah, it really is really pretty small.

- Two claws, two fingers.

- Yeah, so two fingers. You will see sometimes that they say there's a third.

This is a slight misnomer. So you do see this extra little bone here?

This doesn't turn up in all of them, and it's an extra hand bone.

So it's these, the metacarpals. But it's not supporting an extra digit.

- So mostly functionality-wise, it wasn't very functional.

- They're not doing very much at all. This is what's called the

deltopectoral crest. It's really important for big

arm movements because it's deltoids and pectorals. The radius and

ulna are really quite thin, thinner than ours. The fingers are pretty stocky.

The claws look big and curved, and they are, but

other tyrannosaurs, and indeed other carnivores generally,

have much more curved claws. And then they have these

little things, oh, where can I say it? There, there you can see there's a little mark.

That's a ligamentous pit. And so what you can imagine is,

if you're trying to hold onto something and something's wriggling, you want grip.

And there's a risk that you'll just dislocate your fingers. So we have

ligaments that hold bone to bone. And if you just put it

flat to flat surface area, there's only so much you can attach. Whereas if you turn

that into a little hemispherical dip, you get a lot more surface area for your area.

If that makes sense.

- Yeah.

- So if you have a really big ligamentous pit, it means there's a really big ligament,

which means your fingers are really strong and they're really resistant to being

wiggled around and pulled, as if you've grabbed something that doesn't want you to kill

it. Well, T. rex has probably the smallest ligamentous pits of any

tyrannosaur. So that kind of suggests it's not doing very

much. And again, when you look at the claws, proportionally, they're not that big and

they're not that curved. So even though it looks like quite a wicked

thing to us, remember, put this on a seven-ton animal

whose individual teeth are the size of entire fingers.

Suddenly that arm doesn't look like it's doing very much.

- What about the feet?

- So massive. Again, not surprisingly, you're supporting a

colossal amount of weight. But they have this beautiful

adaptation in the foot. So the equivalent bones in the foot, the

metatarsals, for us make up the flat of the feet. But these animals walk

like birds. They got three toes on the ground and then the metatarsals stick nearly

vertically. That overall extends the length of the leg, so you can walk a

little bit faster. You get a slightly bigger stride length. Don't worry,

I've got the right bone here.

- Nice.

- But they also have... Yeah, there's a good one. That one's a great one. But

they also have this really neat adaptation in the middle bone. So you

can see it on this one quite well, and that this is actually not a

tyrannosaur, this is an ornithomimosaur. So one of the really

ostrich-like ones, Gallimimus from the first Jurassic Park. It has the

same thing. You can see the normal bones would be really quite long and

square and then flat at the top. And instead, this thing shrinks in the