Jack Horner: Shape-shifting dinosaurs

1,668,617 views ・ 2012-02-09

TED


Please double-click on the English subtitles below to play the video.

00:16
Shall I ask for a show of hands or a clapping
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of people in different generations?
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I'm interested in how many are three to 12 years old.
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(Laughter)
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None, huh?
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(Laughter)
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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, 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 than anybody else had.
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So if the museum in Toronto went out and collected a Tyrannosaur, a big one,
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then the museum in Ottawa wanted a bigger one, and a better one.
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And that happened for all museums.
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So everyone was out looking 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 and they thought, "What in the world --
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Look at these dinosaurs, they're all big.
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Where are all the little ones?"
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(Laughter)
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And they thought about it 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 that if they had little dinosaurs,
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if they had juvenile dinosaurs, they'd be easy to identify.
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You'd have a big dinosaur and a littler dinosaur.
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(Laughter)
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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 at the University of Pennsylvania
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actually realized that dinosaurs grew kind of like birds do,
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which is different 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 grow to about 80 percent adult size 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 is relative skull growth.
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So you can see that if you actually found one 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 using some duck-billed dinosaurs
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then called Hypacrosaurus.
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And he showed 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 about half the size of the adult.
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But the actual subadult at 65 percent had no crest at all.
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So this was interesting.
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So this is where 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 than we have.
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But scientists have egos; they like to name things.
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And so they went on naming dinosaurs 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, 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 is hard to do, as you can imagine,
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because in museums, 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 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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(Laughter)
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But I have a museum 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, 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 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 that everyone recognizes --
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I mean the 12 primary dinosaurs 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, we've been cutting them open.
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Now as you can imagine, 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 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 Pachycephalosaurus.
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And everybody knows that these three animals are related.
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And the assumption is that they're related like cousins or whatever.
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But no one ever considered 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 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 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 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 hogwartsia.
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Guess where that came from?
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Dragon.
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So here's a dinosaur that has spikes sticking out of its head,
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no dome 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 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, 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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(Laughter)
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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 Dracorex --
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I cut open our Dracorex --
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and look, it was spongy inside, really spongy inside.
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I mean, it is a juvenile 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, it is doing the same thing.
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The dome, that little dome, 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 are actually resorbing,
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which means they're getting smaller 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 were also resorbing.
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So just with these three dinosaurs,
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as a scientist, we can easily hypothesize
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that it is just a growth series of the same animal.
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Which of course means
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that Stygimoloch and Dracorex are extinct.
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(Laughter)
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OK.
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(Laughter)
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Which of course means we have 10 primary dinosaurs to deal with.
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So a colleague of mine at Berkeley -- he and I were looking at Triceratops.
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And before the year 2000 --
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now remember, Triceratops was first found in the 1800s --
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before 2000, no one had ever seen 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, their horns actually curve backwards.
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And then as they get older, 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 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 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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(Laughter)
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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 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 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, has mature bone.
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But it's got these big holes in its shield.
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And everybody says,
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"A Triceratops and a Torosaurus 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, 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 that the hole starting to form in Triceratops
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and, of course it's open, in Torosaurus --
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so he found the transitional ones between Triceratops and Torosaurus,
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which was pretty cool.
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So now we know that Torosaurus is actually a grown-up Triceratops.
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Now when we name dinosaurs,
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when we name anything, 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, 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 that Edmontosaurus is a juvenile,
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or at least a subadult,
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and the other one is an adult, 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 is T. Rex.
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So there's these two dinosaurs, T. Rex and Nanotyrannus.
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(Laughter)
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Again, it 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 and they said, "One's got 17 teeth,
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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 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, 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, 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 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 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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(Laughter)
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Fourth-graders love their dinosaurs, 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)
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