0:00:00.000,0:00:03.000
Shall I ask for a show of hands

0:00:03.000,0:00:05.000
or a clapping

0:00:05.000,0:00:08.000
of people in different generations?

0:00:08.000,0:00:10.000
I'm interested in how many

0:00:10.000,0:00:12.000
are three to 12 years old.

0:00:12.000,0:00:16.000
(Laughter)

0:00:16.000,0:00:19.000
None, huh?

0:00:19.000,0:00:21.000
All right.

0:00:21.000,0:00:23.000
I'm going to talk about dinosaurs.

0:00:23.000,0:00:26.000
Do you remember dinosaurs when you were that age?

0:00:26.000,0:00:31.000
(Applause)

0:00:33.000,0:00:36.000
Dinosaurs are kind of funny, you know.

0:00:36.000,0:00:38.000
(Laughter)

0:00:38.000,0:00:40.000
We're going to kind of go in a different direction right now.

0:00:40.000,0:00:43.000
I hope you all realize that.

0:00:43.000,0:00:45.000
So I'll just give you my message up front:

0:00:45.000,0:00:47.000
Try not to go extinct.

0:00:47.000,0:00:49.000
(Laughter)

0:00:49.000,0:00:51.000
That's it.

0:00:51.000,0:00:55.000
(Laughter)

0:00:55.000,0:00:57.000
People ask me a lot --

0:00:57.000,0:01:00.000
in fact, one of the most asked questions I get

0:01:00.000,0:01:04.000
is, why do children like dinosaurs so much?

0:01:04.000,0:01:06.000
What's the fascination?

0:01:06.000,0:01:09.000
And I usually just say,

0:01:09.000,0:01:11.000
"Well dinosaurs were big,

0:01:11.000,0:01:14.000
different and gone."

0:01:14.000,0:01:16.000
They're all gone.

0:01:16.000,0:01:18.000
Well that's not true,

0:01:18.000,0:01:20.000
but we'll get to the goose in a minute.

0:01:20.000,0:01:23.000
So that's sort of the theme:

0:01:23.000,0:01:27.000
big, different and gone.

0:01:27.000,0:01:29.000
The title of my talk:

0:01:29.000,0:01:31.000
Shape-shifting Dinosaurs:

0:01:31.000,0:01:33.000
The Cause of a Premature Extinction.

0:01:33.000,0:01:36.000
Now I assume that we remember dinosaurs.

0:01:36.000,0:01:39.000
And there's lots of different shapes.

0:01:39.000,0:01:42.000
Lots of different kinds.

0:01:42.000,0:01:44.000
A long time ago,

0:01:44.000,0:01:46.000
back in the early 1900s,

0:01:46.000,0:01:49.000
museums were out looking for dinosaurs.

0:01:49.000,0:01:52.000
They went out and gathered them up.

0:01:52.000,0:01:54.000
And this is an interesting story.

0:01:54.000,0:01:57.000
Every museum wanted a little bigger or better one

0:01:57.000,0:01:59.000
than anybody else had.

0:01:59.000,0:02:02.000
So if the museum in Toronto went out

0:02:02.000,0:02:05.000
and collected a Tyrannosaur, a big one,

0:02:05.000,0:02:08.000
then the museum in Ottawa wanted a bigger one

0:02:08.000,0:02:10.000
and a better one.

0:02:10.000,0:02:12.000
And that happened for all museums.

0:02:12.000,0:02:14.000
So everyone was out looking

0:02:14.000,0:02:17.000
for all these bigger and better dinosaurs.

0:02:17.000,0:02:21.000
And this was in the early 1900s.

0:02:21.000,0:02:24.000
By about 1970,

0:02:24.000,0:02:26.000
some scientists were sitting around

0:02:26.000,0:02:29.000
and they thought, "What in the world?

0:02:29.000,0:02:31.000
Look at these dinosaurs.

0:02:31.000,0:02:33.000
They're all big.

0:02:33.000,0:02:36.000
Where are all the little ones?"

0:02:38.000,0:02:40.000
And they thought about it

0:02:40.000,0:02:42.000
and they even wrote papers about it:

0:02:42.000,0:02:44.000
"Where are the little dinosaurs?"

0:02:44.000,0:02:49.000
(Laughter)

0:02:52.000,0:02:56.000
Well, go to a museum, you'll see,

0:02:56.000,0:02:59.000
see how many baby dinosaurs there are.

0:02:59.000,0:03:02.000
People assumed -- and this was actually a problem --

0:03:02.000,0:03:04.000
people assumed

0:03:04.000,0:03:06.000
that if they had little dinosaurs,

0:03:06.000,0:03:08.000
if they had juvenile dinosaurs,

0:03:08.000,0:03:10.000
they'd be easy to identify.

0:03:10.000,0:03:12.000
You'd have a big dinosaur

0:03:12.000,0:03:15.000
and a littler dinosaur.

0:03:15.000,0:03:18.000
But all they had were big dinosaurs.

0:03:18.000,0:03:21.000
And it comes down to a couple of things.

0:03:21.000,0:03:25.000
First off, scientists have egos,

0:03:25.000,0:03:29.000
and scientists like to name dinosaurs.

0:03:29.000,0:03:31.000
They like to name anything.

0:03:31.000,0:03:34.000
Everybody likes to have their own animal that they named.

0:03:34.000,0:03:37.000
(Laughter)

0:03:37.000,0:03:40.000
And so every time they found something that looked a little different,

0:03:40.000,0:03:43.000
they named it something different.

0:03:43.000,0:03:45.000
And what happened, of course,

0:03:45.000,0:03:48.000
is we ended up with a whole bunch of different dinosaurs.

0:03:50.000,0:03:53.000
In 1975,

0:03:53.000,0:03:56.000
a light went on in somebody's head.

0:03:56.000,0:03:58.000
Dr. Peter Dodson

0:03:58.000,0:04:00.000
at the University of Pennsylvania

0:04:00.000,0:04:03.000
actually realized

0:04:03.000,0:04:06.000
that dinosaurs grew

0:04:06.000,0:04:08.000
kind of like birds do,

0:04:08.000,0:04:10.000
which is different

0:04:10.000,0:04:12.000
than the way reptiles grow.

0:04:12.000,0:04:14.000
And in fact,

0:04:14.000,0:04:17.000
he used the cassowary as an example.

0:04:17.000,0:04:20.000
And it's kind of cool -- if you look at the cassowary,

0:04:20.000,0:04:23.000
or any of the birds that have crests on their heads,

0:04:23.000,0:04:25.000
they actually grow

0:04:25.000,0:04:27.000
to about 80 percent adult size

0:04:27.000,0:04:30.000
before the crest starts to grow.

0:04:30.000,0:04:33.000
Now think about that.

0:04:33.000,0:04:36.000
They're basically retaining their juvenile characteristics

0:04:36.000,0:04:39.000
very late in what we call ontogeny.

0:04:39.000,0:04:43.000
So allometric cranial ontogeny

0:04:43.000,0:04:46.000
is relative skull growth.

0:04:46.000,0:04:48.000
So you can see

0:04:48.000,0:04:50.000
that if you actually found one

0:04:50.000,0:04:53.000
that was 80 percent grown

0:04:53.000,0:04:56.000
and you didn't know that it was going to grow up to a cassowary,

0:04:56.000,0:04:59.000
you would think they were two different animals.

0:05:00.000,0:05:03.000
So this was a problem,

0:05:03.000,0:05:06.000
and Peter Dodson pointed this out

0:05:06.000,0:05:08.000
using some duck-billed dinosaurs

0:05:08.000,0:05:10.000
then called Hypacrosaurus.

0:05:10.000,0:05:12.000
And he showed

0:05:12.000,0:05:15.000
that if you were to take a baby and an adult

0:05:15.000,0:05:18.000
and make an average of what it should look like,

0:05:18.000,0:05:21.000
if it grew in sort of a linear fashion,

0:05:21.000,0:05:23.000
it would have a crest

0:05:23.000,0:05:26.000
about half the size of the adult.

0:05:26.000,0:05:28.000
But the actual sub-adult

0:05:28.000,0:05:30.000
at 65 percent

0:05:30.000,0:05:32.000
had no crest at all.

0:05:32.000,0:05:34.000
So this was interesting.

0:05:34.000,0:05:37.000
So this is where

0:05:37.000,0:05:40.000
people went astray again.

0:05:40.000,0:05:42.000
I mean, if they'd have just taken that,

0:05:42.000,0:05:45.000
taken Peter Dodson's work, and gone on with that,

0:05:45.000,0:05:47.000
then we would have a lot less dinosaurs

0:05:47.000,0:05:49.000
than we have.

0:05:49.000,0:05:51.000
But scientists have egos;

0:05:51.000,0:05:54.000
they like to name things.

0:05:54.000,0:05:57.000
And so they went on naming dinosaurs

0:05:57.000,0:06:00.000
because they were different.

0:06:00.000,0:06:02.000
Now we have a way of actually testing

0:06:02.000,0:06:05.000
to see whether a dinosaur, or any animal,

0:06:05.000,0:06:08.000
is a young one or an older one.

0:06:08.000,0:06:11.000
And that's by actually cutting into their bones.

0:06:11.000,0:06:15.000
But cutting into the bones of a dinosaur

0:06:15.000,0:06:18.000
is hard to do, as you can imagine,

0:06:18.000,0:06:21.000
because in museums

0:06:21.000,0:06:25.000
bones are precious.

0:06:25.000,0:06:28.000
You go into a museum and they take really good care of them.

0:06:28.000,0:06:31.000
They put them in foam, little containers.

0:06:31.000,0:06:34.000
They're very well taken care of.

0:06:35.000,0:06:37.000
They don't like it if you come in

0:06:37.000,0:06:39.000
and want to saw them open and look inside.

0:06:39.000,0:06:41.000
(Laughter)

0:06:41.000,0:06:44.000
So they don't normally let you do that.

0:06:44.000,0:06:47.000
But I have a museum

0:06:47.000,0:06:49.000
and I collect dinosaurs

0:06:49.000,0:06:51.000
and I can saw mine open.

0:06:51.000,0:06:53.000
So that's what I do.

0:06:53.000,0:06:58.000
(Applause)

0:06:58.000,0:07:03.000
So if you cut open a little dinosaur,

0:07:03.000,0:07:05.000
it's very spongy inside like A.

0:07:05.000,0:07:07.000
And if you cut into an older dinosaur,

0:07:07.000,0:07:09.000
it's very massive.

0:07:09.000,0:07:11.000
You can tell it's mature bone.

0:07:11.000,0:07:14.000
So it's real easy to tell them apart.

0:07:14.000,0:07:16.000
So what I want to do

0:07:16.000,0:07:18.000
is show you these.

0:07:18.000,0:07:22.000
In North America in the Northern Plains of the United States

0:07:22.000,0:07:26.000
and the Southern Plains of Alberta and Saskatchewan,

0:07:26.000,0:07:29.000
there's this unit of rock called the Hell Creek Formation

0:07:29.000,0:07:32.000
that produces the last dinosaurs that lived on Earth.

0:07:32.000,0:07:34.000
And there are 12 of them

0:07:34.000,0:07:36.000
that everyone recognizes --

0:07:36.000,0:07:38.000
I mean the 12 primary dinosaurs

0:07:38.000,0:07:40.000
that went extinct.

0:07:40.000,0:07:43.000
And so we will evaluate them.

0:07:43.000,0:07:45.000
And that's sort of what I've been doing.

0:07:45.000,0:07:48.000
So my students, my staff,

0:07:48.000,0:07:51.000
we've been cutting them open.

0:07:51.000,0:07:53.000
Now as you can imagine,

0:07:53.000,0:07:55.000
cutting open a leg bone is one thing,

0:07:55.000,0:07:58.000
but when you go to a museum

0:07:58.000,0:08:00.000
and say, "You don't mind if I cut open

0:08:00.000,0:08:03.000
your dinosaur's skull do you?"

0:08:03.000,0:08:06.000
they say, "Go away."

0:08:06.000,0:08:11.000
(Laughter)

0:08:11.000,0:08:15.000
So here are 12 dinosaurs.

0:08:15.000,0:08:18.000
And we want to look at these three first.

0:08:18.000,0:08:21.000
So these are dinosaurs that are called Pachycephalosaurs.

0:08:21.000,0:08:23.000
And everybody knows

0:08:23.000,0:08:25.000
that these three animals are related.

0:08:25.000,0:08:27.000
And the assumption is

0:08:27.000,0:08:29.000
is that they're related

0:08:29.000,0:08:32.000
like cousins or whatever.

0:08:32.000,0:08:34.000
But no one ever considered

0:08:34.000,0:08:37.000
that they might be more closely related.

0:08:37.000,0:08:39.000
In other words,

0:08:39.000,0:08:42.000
people looked at them and they saw the differences.

0:08:42.000,0:08:44.000
And you all know

0:08:44.000,0:08:46.000
that if you are going to determine

0:08:46.000,0:08:48.000
whether you're related to your brother or your sister,

0:08:48.000,0:08:52.000
you can't do it by looking at differences.

0:08:52.000,0:08:54.000
You can only determine relatedness

0:08:54.000,0:08:56.000
by looking for similarities.

0:08:56.000,0:08:58.000
So people were looking at these

0:08:58.000,0:09:00.000
and they were talking about how different they are.

0:09:00.000,0:09:03.000
Pachycephalosaurus has a big, thick dome on its head,

0:09:03.000,0:09:06.000
and it's got some little bumps on the back of its head,

0:09:06.000,0:09:10.000
and it's got a bunch of gnarly things on the end of its nose.

0:09:10.000,0:09:12.000
And then Stygimoloch, another dinosaur

0:09:12.000,0:09:16.000
from the same age, lived at the same time,

0:09:16.000,0:09:18.000
has spikes sticking out the back of its head.

0:09:18.000,0:09:20.000
It's got a little, tiny dome,

0:09:20.000,0:09:24.000
and it's got a bunch of gnarly stuff on its nose.

0:09:24.000,0:09:26.000
And then there's this thing called Dracorex,

0:09:26.000,0:09:28.000
Hogwart's Eye.

0:09:28.000,0:09:31.000
Guess where that came from? Dragon.

0:09:31.000,0:09:33.000
So here's a dinosaur

0:09:33.000,0:09:36.000
that has spikes sticking out of its head, no dome

0:09:36.000,0:09:39.000
and gnarly stuff on its nose.

0:09:39.000,0:09:42.000
Nobody noticed the gnarly stuff sort of looked alike.

0:09:42.000,0:09:44.000
But they did look at these three

0:09:44.000,0:09:46.000
and they said, "These are three different dinosaurs,

0:09:46.000,0:09:49.000
and Dracorex is probably the most primitive of them.

0:09:49.000,0:09:52.000
And the other one is more primitive than the other.

0:09:52.000,0:09:55.000
It's unclear to me

0:09:55.000,0:09:58.000
how they actually sorted these three of them out.

0:09:58.000,0:10:00.000
But if you line them up,

0:10:00.000,0:10:03.000
if you just take those three skulls and just line them up,

0:10:03.000,0:10:05.000
they line up like this.

0:10:05.000,0:10:07.000
Dracorex is the littlest one,

0:10:07.000,0:10:09.000
Stygimoloch is the middle size one,

0:10:09.000,0:10:12.000
Pachycephalosaurus is the largest one.

0:10:12.000,0:10:14.000
And one would think,

0:10:14.000,0:10:16.000
that should give me a clue.

0:10:16.000,0:10:18.000
(Laughter)

0:10:18.000,0:10:21.000
But it didn't give them a clue.

0:10:21.000,0:10:24.000
Because, well we know why.

0:10:24.000,0:10:27.000
Scientists like to name things.

0:10:27.000,0:10:29.000
So if we cut open

0:10:29.000,0:10:31.000
Dracorex --

0:10:31.000,0:10:33.000
I cut open our Dracorex --

0:10:33.000,0:10:35.000
and look, it was spongy inside,

0:10:35.000,0:10:37.000
really spongy inside.

0:10:37.000,0:10:39.000
I mean, it is a juvenile

0:10:39.000,0:10:41.000
and it's growing really fast.

0:10:41.000,0:10:43.000
So it is going to get bigger.

0:10:43.000,0:10:45.000
If you cut open Stygimoloch,

0:10:45.000,0:10:47.000
it is doing the same thing.

0:10:47.000,0:10:49.000
The dome, that little dome,

0:10:49.000,0:10:51.000
is growing really fast.

0:10:51.000,0:10:53.000
It's inflating very fast.

0:10:53.000,0:10:56.000
What's interesting is the spike on the back of the Dracorex

0:10:56.000,0:10:58.000
was growing very fast as well.

0:10:58.000,0:11:00.000
The spikes on the back of the Stygimoloch

0:11:00.000,0:11:02.000
are actually resorbing,

0:11:02.000,0:11:04.000
which means they're getting smaller

0:11:04.000,0:11:06.000
as that dome is getting bigger.

0:11:06.000,0:11:09.000
And if we look at Pachycephalosaurus,

0:11:09.000,0:11:12.000
Pachycephalosaurus has a solid dome

0:11:12.000,0:11:15.000
and its little bumps on the back of its head

0:11:15.000,0:11:17.000
were also resorbing.

0:11:17.000,0:11:19.000
So just with these three dinosaurs,

0:11:19.000,0:11:21.000
you can easily -- as a scientist --

0:11:21.000,0:11:23.000
we can easily hypothesize

0:11:23.000,0:11:25.000
that it is just a growth series

0:11:25.000,0:11:28.000
of the same animal.

0:11:28.000,0:11:31.000
Which of course means

0:11:31.000,0:11:35.000
that Stygimoloch and Dracorex

0:11:35.000,0:11:37.000
are extinct.

0:11:37.000,0:11:42.000
(Laughter)

0:11:42.000,0:11:44.000
Okay.

0:11:46.000,0:11:49.000
Which of course means

0:11:49.000,0:11:53.000
we have 10 primary dinosaurs to deal with.

0:11:53.000,0:11:55.000
So a colleague of mine at Berkley,

0:11:55.000,0:11:58.000
he and I were looking at Triceratops.

0:11:58.000,0:12:00.000
And before the year 2000 --

0:12:00.000,0:12:02.000
now remember,

0:12:02.000,0:12:04.000
Triceratops was first found in the 1800s --

0:12:04.000,0:12:07.000
before 2000, no one had ever seen

0:12:07.000,0:12:10.000
a juvenile Triceratops.

0:12:10.000,0:12:13.000
There's a Triceratops in every museum in the world,

0:12:13.000,0:12:17.000
but no one had ever collected a juvenile.

0:12:17.000,0:12:19.000
And we know why, right?

0:12:19.000,0:12:22.000
Because everybody wants to have a big one.

0:12:22.000,0:12:24.000
So everyone had a big one.

0:12:24.000,0:12:26.000
So we went out and collected a whole bunch of stuff

0:12:26.000,0:12:28.000
and we found a whole bunch of little ones.

0:12:28.000,0:12:32.000
They're everywhere. They're all over the place.

0:12:32.000,0:12:34.000
So we have a whole bunch of them at our museum.

0:12:34.000,0:12:39.000
(Laughter)

0:12:39.000,0:12:41.000
And everybody says it's because I have a little museum.

0:12:41.000,0:12:44.000
When you have a little museum, you have little dinosaurs.

0:12:44.000,0:12:47.000
(Laughter)

0:12:47.000,0:12:49.000
If you look at the Triceratops,

0:12:49.000,0:12:51.000
you can see it's changing, it's shape-shifting.

0:12:51.000,0:12:53.000
As the juveniles are growing up,

0:12:53.000,0:12:55.000
their horns actually curve backwards.

0:12:55.000,0:12:57.000
And then as they grow older,

0:12:57.000,0:12:59.000
the horns grow forward.

0:12:59.000,0:13:01.000
And that's pretty cool.

0:13:01.000,0:13:03.000
If you look along the edge of the frill,

0:13:03.000,0:13:06.000
they have these little triangular bones

0:13:06.000,0:13:08.000
that actually grow big as triangles

0:13:08.000,0:13:11.000
and then they flatten against the frill

0:13:11.000,0:13:13.000
pretty much like the spikes do

0:13:13.000,0:13:16.000
on the Pachycephalosaurs.

0:13:16.000,0:13:20.000
And then, because the juveniles are in my collection,

0:13:20.000,0:13:22.000
I cut them open

0:13:22.000,0:13:24.000
and look inside.

0:13:24.000,0:13:27.000
And the little one is really spongy.

0:13:27.000,0:13:30.000
And the middle size one is really spongy.

0:13:30.000,0:13:32.000
But what was interesting

0:13:32.000,0:13:34.000
was the adult Triceratops was also spongy.

0:13:34.000,0:13:37.000
And this is a skull that is two meters long.

0:13:37.000,0:13:40.000
It's a big skull.

0:13:40.000,0:13:42.000
But there's another dinosaur

0:13:42.000,0:13:45.000
that is found in this formation

0:13:45.000,0:13:48.000
that looks like a Triceratops, except it's bigger,

0:13:48.000,0:13:51.000
and it's called Torosaurus.

0:13:51.000,0:13:54.000
And Torosaurus, when we cut into it,

0:13:54.000,0:13:56.000
has mature bone.

0:13:56.000,0:13:58.000
But it's got these big holes in its shield.

0:13:58.000,0:14:01.000
And everybody says, "A Triceratops and a Torosaurus

0:14:01.000,0:14:03.000
can't possibly be the same animal

0:14:03.000,0:14:05.000
because one of them's bigger than the other one."

0:14:05.000,0:14:10.000
(Laughter)

0:14:10.000,0:14:12.000
"And it has holes in its frill."

0:14:12.000,0:14:15.000
And I said, "Well do we have any juvenile Torosauruses?"

0:14:15.000,0:14:18.000
And they said, "Well no,

0:14:18.000,0:14:21.000
but it has holes in its frill."

0:14:21.000,0:14:24.000
So one of my graduate students, John Scannella,

0:14:24.000,0:14:26.000
looked through our whole collection

0:14:26.000,0:14:28.000
and he actually discovered

0:14:28.000,0:14:30.000
that the hole starting to form

0:14:30.000,0:14:32.000
in Triceratops

0:14:32.000,0:14:35.000
and, of course it's open, in Torosaurus --

0:14:35.000,0:14:38.000
so he found the transitional ones

0:14:38.000,0:14:40.000
between Triceratops and Torosaurus,

0:14:40.000,0:14:42.000
which was pretty cool.

0:14:42.000,0:14:44.000
So now we know

0:14:44.000,0:14:46.000
that Torosaurus

0:14:46.000,0:14:49.000
is actually a grownup Triceratops.

0:14:49.000,0:14:51.000
Now when we name dinosaurs,

0:14:51.000,0:14:53.000
when we name anything,

0:14:53.000,0:14:55.000
the original name gets to stick

0:14:55.000,0:14:59.000
and the second name is thrown out.

0:14:59.000,0:15:02.000
So Torosaurus is extinct.

0:15:02.000,0:15:05.000
Triceratops, if you've heard the news,

0:15:05.000,0:15:07.000
a lot of the newscasters got it all wrong.

0:15:07.000,0:15:10.000
They thought Torosaurus should be kept and Triceratops thrown out,

0:15:10.000,0:15:12.000
but that's not going to happen.

0:15:12.000,0:15:17.000
(Laughter)

0:15:18.000,0:15:21.000
All right, so we can do this with a bunch of dinosaurs.

0:15:21.000,0:15:23.000
I mean, here's Edmontosaurus

0:15:23.000,0:15:25.000
and Anatotitan.

0:15:25.000,0:15:28.000
Anatotitan: giant duck.

0:15:28.000,0:15:30.000
It's a giant duck-bill dinosaur.

0:15:30.000,0:15:32.000
Here's another one.

0:15:32.000,0:15:34.000
So we look at the bone histology.

0:15:34.000,0:15:37.000
The bone histology tells us

0:15:37.000,0:15:39.000
that Edmontosaurus is a juvenile,

0:15:39.000,0:15:41.000
or at least a sub-adult,

0:15:41.000,0:15:44.000
and the other one is an adult

0:15:44.000,0:15:47.000
and we have an ontogeny.

0:15:47.000,0:15:50.000
And we get rid of Anatotitan.

0:15:50.000,0:15:53.000
So we can just keep doing this.

0:15:53.000,0:15:55.000
And the last one

0:15:55.000,0:15:57.000
is T. Rex.

0:15:57.000,0:15:59.000
So there's these two dinosaurs,

0:15:59.000,0:16:02.000
T. Rex and Nanotyrannus.

0:16:02.000,0:16:04.000
(Laughter)

0:16:04.000,0:16:07.000
Again, makes you wonder.

0:16:07.000,0:16:10.000
(Laughter)

0:16:10.000,0:16:12.000
But they had a good question.

0:16:12.000,0:16:14.000
They were looking at them

0:16:14.000,0:16:17.000
and they said, "One's got 17 teeth, and the biggest one's got 12 teeth.

0:16:17.000,0:16:19.000
And that doesn't make any sense at all,

0:16:19.000,0:16:21.000
because we don't know of any dinosaurs

0:16:21.000,0:16:23.000
that gain teeth as they get older.

0:16:23.000,0:16:25.000
So it must be true --

0:16:25.000,0:16:28.000
they must be different."

0:16:28.000,0:16:30.000
So we cut into them.

0:16:30.000,0:16:32.000
And sure enough,

0:16:32.000,0:16:35.000
Nanotyrannus has juvenile bone

0:16:35.000,0:16:38.000
and the bigger one has more mature bone.

0:16:38.000,0:16:41.000
It looks like it could still get bigger.

0:16:41.000,0:16:43.000
And at the Museum of the Rockies where we work,

0:16:43.000,0:16:45.000
I have four T. Rexes,

0:16:45.000,0:16:47.000
so I can cut a whole bunch of them.

0:16:47.000,0:16:50.000
But I didn't have to cut any of them really,

0:16:50.000,0:16:53.000
because I just lined up their jaws

0:16:53.000,0:16:56.000
and it turned out the biggest one had 12 teeth

0:16:56.000,0:16:58.000
and the next smallest one had 13

0:16:58.000,0:17:00.000
and the next smallest had 14.

0:17:00.000,0:17:02.000
And of course, Nano has 17.

0:17:02.000,0:17:05.000
And we just went out and looked at other people's collections

0:17:05.000,0:17:09.000
and we found one that has sort of 15 teeth.

0:17:09.000,0:17:12.000
So again, real easy to say

0:17:12.000,0:17:14.000
that Tyrannosaurus ontogeny

0:17:14.000,0:17:17.000
included Nanotyrannus,

0:17:17.000,0:17:22.000
and therefore we can take out another dinosaur.

0:17:22.000,0:17:24.000
(Laughter)

0:17:24.000,0:17:28.000
So when it comes down

0:17:28.000,0:17:30.000
to our end cretaceous,

0:17:30.000,0:17:33.000
we have seven left.

0:17:33.000,0:17:36.000
And that's a good number.

0:17:36.000,0:17:39.000
That's a good number to go extinct, I think.

0:17:39.000,0:17:41.000
Now as you can imagine,

0:17:41.000,0:17:44.000
this is not very popular with fourth-graders.

0:17:44.000,0:17:46.000
Fourth-graders love their dinosaurs,

0:17:46.000,0:17:49.000
they memorize them.

0:17:51.000,0:17:54.000
And they're not happy with this.

0:17:54.000,0:17:56.000
(Laughter)

0:17:56.000,0:17:58.000
Thank you very much.

0:17:58.000,0:18:01.000
(Applause)