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Shall I ask for a show of hands

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or a clapping

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of people in different generations?

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I'm interested in how many

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are three to 12 years old.

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(Laughter)

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None, huh?

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All right.

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I'm going to talk about dinosaurs.

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Do you remember dinosaurs when you were that age?

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(Applause)

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Dinosaurs are kind of funny, you know.

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(Laughter)

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We're going to kind of go in a different direction right now.

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I hope you all realize that.

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So I'll just give you my message up front:

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Try not to go extinct.

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(Laughter)

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That's it.

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(Laughter)

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People ask me a lot --

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in fact, one of the most asked questions I get

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is, why do children like dinosaurs so much?

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What's the fascination?

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And I usually just say,

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"Well dinosaurs were big,

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different and gone."

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They're all gone.

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Well that's not true,

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but we'll get to the goose in a minute.

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So that's sort of the theme:

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big, different and gone.

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The title of my talk:

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Shape-shifting Dinosaurs:

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The Cause of a Premature Extinction.

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Now I assume that we remember dinosaurs.

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And there's lots of different shapes.

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Lots of different kinds.

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A long time ago,

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back in the early 1900s,

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museums were out looking for dinosaurs.

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They went out and gathered them up.

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And this is an interesting story.

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Every museum wanted a little bigger or better one

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than anybody else had.

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So if the museum in Toronto went out

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and collected a Tyrannosaur, a big one,

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then the museum in Ottawa wanted a bigger one

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and a better one.

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And that happened for all museums.

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So everyone was out looking

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for all these bigger and better dinosaurs.

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And this was in the early 1900s.

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By about 1970,

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some scientists were sitting around

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and they thought, "What in the world?

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Look at these dinosaurs.

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They're all big.

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Where are all the little ones?"

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And they thought about it

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and they even wrote papers about it:

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"Where are the little dinosaurs?"

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(Laughter)

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Well, go to a museum, you'll see,

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see how many baby dinosaurs there are.

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People assumed -- and this was actually a problem --

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people assumed

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that if they had little dinosaurs,

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if they had juvenile dinosaurs,

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they'd be easy to identify.

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You'd have a big dinosaur

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and a littler dinosaur.

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But all they had were big dinosaurs.

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And it comes down to a couple of things.

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First off, scientists have egos,

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and scientists like to name dinosaurs.

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They like to name anything.

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Everybody likes to have their own animal that they named.

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(Laughter)

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And so every time they found something that looked a little different,

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they named it something different.

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And what happened, of course,

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is we ended up with a whole bunch of different dinosaurs.

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In 1975,

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a light went on in somebody's head.

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Dr. Peter Dodson

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at the University of Pennsylvania

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actually realized

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that dinosaurs grew

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kind of like birds do,

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which is different

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than the way reptiles grow.

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And in fact,

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he used the cassowary as an example.

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And it's kind of cool -- if you look at the cassowary,

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or any of the birds that have crests on their heads,

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they actually grow

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to about 80 percent adult size

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before the crest starts to grow.

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Now think about that.

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They're basically retaining their juvenile characteristics

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very late in what we call ontogeny.

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So allometric cranial ontogeny

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is relative skull growth.

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So you can see

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that if you actually found one

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that was 80 percent grown

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and you didn't know that it was going to grow up to a cassowary,

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you would think they were two different animals.

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So this was a problem,

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and Peter Dodson pointed this out

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using some duck-billed dinosaurs

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then called Hypacrosaurus.

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And he showed

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that if you were to take a baby and an adult

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and make an average of what it should look like,

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if it grew in sort of a linear fashion,

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it would have a crest

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about half the size of the adult.

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But the actual sub-adult

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at 65 percent

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had no crest at all.

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So this was interesting.

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So this is where

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people went astray again.

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I mean, if they'd have just taken that,

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taken Peter Dodson's work, and gone on with that,

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then we would have a lot less dinosaurs

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than we have.

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But scientists have egos;

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they like to name things.

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And so they went on naming dinosaurs

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because they were different.

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Now we have a way of actually testing

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to see whether a dinosaur, or any animal,

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is a young one or an older one.

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And that's by actually cutting into their bones.

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But cutting into the bones of a dinosaur

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is hard to do, as you can imagine,

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because in museums

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bones are precious.

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You go into a museum and they take really good care of them.

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They put them in foam, little containers.

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They're very well taken care of.

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They don't like it if you come in

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and want to saw them open and look inside.

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(Laughter)

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So they don't normally let you do that.

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But I have a museum

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and I collect dinosaurs

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and I can saw mine open.

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So that's what I do.

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(Applause)

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So if you cut open a little dinosaur,

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it's very spongy inside like A.

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And if you cut into an older dinosaur,

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it's very massive.

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You can tell it's mature bone.

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So it's real easy to tell them apart.

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So what I want to do

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is show you these.

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In North America in the Northern Plains of the United States

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and the Southern Plains of Alberta and Saskatchewan,

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there's this unit of rock called the Hell Creek Formation

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that produces the last dinosaurs that lived on Earth.

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And there are 12 of them

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that everyone recognizes --

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I mean the 12 primary dinosaurs

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that went extinct.

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And so we will evaluate them.

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And that's sort of what I've been doing.

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So my students, my staff,

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we've been cutting them open.

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Now as you can imagine,

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cutting open a leg bone is one thing,

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but when you go to a museum

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and say, "You don't mind if I cut open

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your dinosaur's skull do you?"

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they say, "Go away."

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(Laughter)

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So here are 12 dinosaurs.

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And we want to look at these three first.

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So these are dinosaurs that are called Pachycephalosaurs.

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And everybody knows

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that these three animals are related.

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And the assumption is

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is that they're related

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like cousins or whatever.

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But no one ever considered

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that they might be more closely related.

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In other words,

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people looked at them and they saw the differences.

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And you all know

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that if you are going to determine

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whether you're related to your brother or your sister,

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you can't do it by looking at differences.

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You can only determine relatedness

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by looking for similarities.

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So people were looking at these

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and they were talking about how different they are.

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Pachycephalosaurus has a big, thick dome on its head,

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and it's got some little bumps on the back of its head,

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and it's got a bunch of gnarly things on the end of its nose.

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And then Stygimoloch, another dinosaur

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from the same age, lived at the same time,

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has spikes sticking out the back of its head.

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It's got a little, tiny dome,

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and it's got a bunch of gnarly stuff on its nose.

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And then there's this thing called Dracorex,

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Hogwart's Eye.

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Guess where that came from? Dragon.

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So here's a dinosaur

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that has spikes sticking out of its head, no dome

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and gnarly stuff on its nose.

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Nobody noticed the gnarly stuff sort of looked alike.

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But they did look at these three

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and they said, "These are three different dinosaurs,

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and Dracorex is probably the most primitive of them.

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And the other one is more primitive than the other.

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It's unclear to me

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how they actually sorted these three of them out.

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But if you line them up,

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if you just take those three skulls and just line them up,

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they line up like this.

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Dracorex is the littlest one,

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Stygimoloch is the middle size one,

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Pachycephalosaurus is the largest one.

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And one would think,

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that should give me a clue.

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(Laughter)

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But it didn't give them a clue.

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Because, well we know why.

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Scientists like to name things.

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So if we cut open

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Dracorex --

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I cut open our Dracorex --

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and look, it was spongy inside,

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really spongy inside.

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I mean, it is a juvenile

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and it's growing really fast.

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So it is going to get bigger.

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If you cut open Stygimoloch,

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it is doing the same thing.

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The dome, that little dome,

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is growing really fast.

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It's inflating very fast.

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What's interesting is the spike on the back of the Dracorex

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was growing very fast as well.

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The spikes on the back of the Stygimoloch

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are actually resorbing,

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which means they're getting smaller

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as that dome is getting bigger.

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And if we look at Pachycephalosaurus,

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Pachycephalosaurus has a solid dome

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and its little bumps on the back of its head

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were also resorbing.

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So just with these three dinosaurs,

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you can easily -- as a scientist --

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we can easily hypothesize

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that it is just a growth series

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of the same animal.

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Which of course means

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that Stygimoloch and Dracorex

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are extinct.

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(Laughter)

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Okay.

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Which of course means

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we have 10 primary dinosaurs to deal with.

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So a colleague of mine at Berkley,

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he and I were looking at Triceratops.

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And before the year 2000 --

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now remember,

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Triceratops was first found in the 1800s --

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before 2000, no one had ever seen

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a juvenile Triceratops.

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There's a Triceratops in every museum in the world,

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but no one had ever collected a juvenile.

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And we know why, right?

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Because everybody wants to have a big one.

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So everyone had a big one.

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So we went out and collected a whole bunch of stuff

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and we found a whole bunch of little ones.

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They're everywhere. They're all over the place.

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So we have a whole bunch of them at our museum.

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(Laughter)

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And everybody says it's because I have a little museum.

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When you have a little museum, you have little dinosaurs.

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(Laughter)

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If you look at the Triceratops,

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you can see it's changing, it's shape-shifting.

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As the juveniles are growing up,

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their horns actually curve backwards.

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And then as they grow older,

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the horns grow forward.

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And that's pretty cool.

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If you look along the edge of the frill,

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they have these little triangular bones

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that actually grow big as triangles

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and then they flatten against the frill

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pretty much like the spikes do

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on the Pachycephalosaurs.

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And then, because the juveniles are in my collection,

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I cut them open

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and look inside.

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And the little one is really spongy.

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And the middle size one is really spongy.

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But what was interesting

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was the adult Triceratops was also spongy.

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And this is a skull that is two meters long.

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It's a big skull.

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But there's another dinosaur

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that is found in this formation

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that looks like a Triceratops, except it's bigger,

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and it's called Torosaurus.

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And Torosaurus, when we cut into it,

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has mature bone.

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But it's got these big holes in its shield.

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And everybody says, "A Triceratops and a Torosaurus

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can't possibly be the same animal

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because one of them's bigger than the other one."

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(Laughter)

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"And it has holes in its frill."

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And I said, "Well do we have any juvenile Torosauruses?"

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And they said, "Well no,

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but it has holes in its frill."

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So one of my graduate students, John Scannella,

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looked through our whole collection

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and he actually discovered

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that the hole starting to form

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in Triceratops

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and, of course it's open, in Torosaurus --

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so he found the transitional ones

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between Triceratops and Torosaurus,

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which was pretty cool.

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So now we know

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that Torosaurus

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is actually a grownup Triceratops.

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Now when we name dinosaurs,

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when we name anything,

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the original name gets to stick

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and the second name is thrown out.

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So Torosaurus is extinct.

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Triceratops, if you've heard the news,

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a lot of the newscasters got it all wrong.

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They thought Torosaurus should be kept and Triceratops thrown out,

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but that's not going to happen.

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(Laughter)

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All right, so we can do this with a bunch of dinosaurs.

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I mean, here's Edmontosaurus

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and Anatotitan.

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Anatotitan: giant duck.

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It's a giant duck-bill dinosaur.

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Here's another one.

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So we look at the bone histology.

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The bone histology tells us

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that Edmontosaurus is a juvenile,

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or at least a sub-adult,

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and the other one is an adult

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and we have an ontogeny.

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And we get rid of Anatotitan.

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So we can just keep doing this.

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And the last one

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is T. Rex.

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So there's these two dinosaurs,

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T. Rex and Nanotyrannus.

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(Laughter)

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Again, makes you wonder.

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(Laughter)

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But they had a good question.

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They were looking at them

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and they said, "One's got 17 teeth, and the biggest one's got 12 teeth.

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And that doesn't make any sense at all,

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because we don't know of any dinosaurs

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that gain teeth as they get older.

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So it must be true --

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they must be different."

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So we cut into them.

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And sure enough,

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Nanotyrannus has juvenile bone

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and the bigger one has more mature bone.

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It looks like it could still get bigger.

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And at the Museum of the Rockies where we work,

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I have four T. Rexes,

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so I can cut a whole bunch of them.

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But I didn't have to cut any of them really,

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because I just lined up their jaws

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and it turned out the biggest one had 12 teeth

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and the next smallest one had 13

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and the next smallest had 14.

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And of course, Nano has 17.

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And we just went out and looked at other people's collections

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and we found one that has sort of 15 teeth.

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So again, real easy to say

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that Tyrannosaurus ontogeny

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included Nanotyrannus,

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and therefore we can take out another dinosaur.

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(Laughter)

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So when it comes down

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to our end cretaceous,

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we have seven left.

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And that's a good number.

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That's a good number to go extinct, I think.

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Now as you can imagine,

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this is not very popular with fourth-graders.

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Fourth-graders love their dinosaurs,

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they memorize them.

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And they're not happy with this.

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(Laughter)

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Thank you very much.

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(Applause)