[LARGE ANIMAL INHALES, EXHALES]
>>MARK NORELL: When people hear the word “Tyrannosaurus rex,”
they think, like, big,
vicious,
[THUNDERING FOOTSTEP]
apex predators.
But I like to change people’s preconceptions.
Welcome to the family.
[LIGHT MUSIC]
>>NORELL: Tyrannosaurs first appear 150 million years or so ago.
T. rex was the most advanced, the most specialized and the biggest tyrannosaur of all.
As a paleontologist, one of the big hard things to look at has always been growth.
Because baby dinosaurs and young dinosaurs are just so incredibly rare.
And largely that has to do with their bones are extraordinarily fragile.
So, it’s only been in the recent maybe 20 years when more and more juvenile and baby
dinosaurs have sort of been found.
Which we’re getting a window into what the early life history of these animals was.
Whenever, like, we work on any fossil group, and we’re making models and that kind of
thing, there is a good deal of speculation.
But it’s informed speculation from looking at closely related animals.
>>JASON BROUGHAM: I think this is the first time we’ve ever made the same species of
dinosaur at three different stages of its growth and development.
>>REBECCA MEAH: I’m assigned to make the adult T. rex.
>>HANNAH RAWE: I was assigned first to make the hatchlings.
And then Jason and I decided to switch because
I was more interested in making the four-year-old T. rex.
>>JASON BROUGHAM: And I wanted to do the babies.
In our show, we’re going to have the hatchling be very densely fluffy,
sort of like down feathers.
Sort of like what you see on a baby ostrich or a baby emu.
>>NORELL: From all the inferential evidence we have, these animals would have hatched
out of an egg, just the way a modern chick does.
They would have been covered with a fluffy covering.
It just would have looked like a really weird looking big bird when it came out of the egg.
We don’t really have any direct evidence for parental care in Tyrannosaurus rex.
However, we do have some indirect evidence.
Most living birds, including, you know, primitive birds like ostriches and emus
and cassowaries, they have some level of parental care, whether it’s nest guarding or bringing
food to their young.
Similarly, crocodiles guard their nests.
So, at least at the nest guarding level, we would predict, then, that tyrannosaurs would
have the same kind of thing.
When a little tyrannosaur was born, the teeth were a lot different than the adults.
In lots of living animals, especially big reptiles like Komodo dragons, they also go
through an ecological shift of what they eat from the time that they’re hatchlings and
juveniles to full adulthood.
They have different diets.
So, the smallest ones feed on insects and small reptiles.
But then when they’re adults they can even take down large animals, like animals that
weigh almost as much as they do.
As adults, the primary way in which the big tyrannosaurs hunted is that they have these
really deeply rooted, very stout teeth.
So, they’re able to bite into things with such force
that it wasn’t like a lion or a leopard.
They would actually cause the thing to explode because they’re able to bite so hard, and
their teeth could just go through bone.
They could crush everything.
>>RAWE: You know, you think of the teeth as being crescent moon-shaped, but in fact, it’s
not as much of a curve.
I decided to sculpt the four-year-old T. rex with his mouth closed.
Because I just kind of thought it was maybe more interesting as a study of nature that,
you know, the majority of the T. rex’s time spent alive, I’m sure, was with their mouth closed.
And I’m actually working off of a really new discovery and very little fossil evidence.
>>NORELL: There’s been a lot of speculation about what Tyrannosaurus rex used its miniscule
arms for when it was an adult.
But when a Tyrannosaurus rex first hatches, the arms would have appeared quite a bit longer
than they do in an adult.
Basically, the body grows faster than the arms do.
So, it’s not like the arms diminish in size.
They just don’t grow as fast as the rest of the body does.
>>RAWE: One of the main things I think that we sort of used each other’s reference points
on were the hands and feet.
>>MEAH: We copied an emu-slash-ostrich.
If you look at, like, the footprint left by a T. rex, it looks almost identical
to an emu footprint.
So-
>>BROUGHAM: But much bigger.
>>MEAH: But much bigger, yeah.
>>NORELL: When the animal was young, it was a really kind of, like, gangly animal.
And it would have had a much more cursorial gait, meaning it was a fast runner.
As opposed to the adult, which was probably just a stealth predator.
I mean, that’s the way tigers, for instance, hunt today and stuff.
Is that they’re not like cheetahs.
They don’t go running forever and run stuff down.
They hide in the bushes and they’re ambush predators.
A lot of people really wonder what the skin of Tyrannosaurus rex looked like.
And a lot of them equate the skin of a tyrannosaur to be just like the skin of a lizard or a snake.
And they were scaled, but scaled in a very different kind of way.
The skin would be more like a leathery covering—what the leg of a turtle looks like, or even the
foot of a chicken.
Also, you know, we feel that even adult tyrannosaurs were feathered.
There’s an animal from China called Yutyrannus,
which is a fairly close relative to Tyrannosaurus rex,
and spectacular fossils of it show that the animal’s completely covered with feathers.
>>BROUGHAM: When we don’t have specimens that preserve the skin texture, we have to
sort of infer what it could be.
So, for each model, there’s a few choices that you have and you- you run them past the
curator and see if they think they’re plausible.
>>MEAH: I think where we like to do our best work is making it convincing to the audience.
>> NORELL: Since its discovery, Tyrannosaurus rex has been the most iconic, the biggest,
the meanest, probably by far the best-known dinosaur.
And you know, we want to give people a very different look and appreciation for what a
remarkable animal Tyrannosaurus rex was, and the evolutionary steps that its ancestors
went through to get there.