Shapeshifting dinosaurs Jack Horner

are asked for a show of hands or

clapping of people in different

generations I’m interested in how many

are three to twelve years old

none ah all right well I’m going to talk

about dinosaurs do you remember

dinosaurs when you’re that age dinosaurs

are kind of funny I mean you know we’re

gonna kind of go in a different

direction right now I hope you all

realize that right so I’ll just give you

my message up front try not to go

extinct that’s at

people ask me a lot when in fact one of

the most asked questions I get is why do

children like dinosaurs so much I mean

what what’s the fascination and I

usually just say well you know dinosaurs

were big different and gone they’re all

run well that’s not true but we’ll get

to the goose in a minute so that’s sort

of the theme big different and gone the

title of my talk shape-shifting

dinosaurs the cause for a premature

extinction now I assume that we remember

dinosaurs and you know there’s lots of

different shapes different lots of

different kinds a long time ago back in

the early 1900s museums were out looking

for dinosaurs they went out and gathered

them up and this is an interesting story

every museum wanted a little bigger or

better one than anybody else had so if

the museum in Toronto went out and

collected a Tyrannis for a big one then

the Museum in Ottawa wanted a bigger one

and a better one and that happened for

all the museum’s so everyone was out

looking for all these bigger and better

dinosaurs and this was in the early

1900s by about 1970 some scientists were

sitting around and they thought what in

the world

look at these dinosaurs are all big

where are all the little ones

and they thought about it and even wrote

papers about it where are the little

dinosaurs well go to a museum you’ll see

see how many baby dinosaurs are people

assumed and this was actually a problem

people assume that if they had little

dinosaurs if they had juvenile dinosaurs

they’d be easy to identify you’d have a

big dinosaur and a littler dinosaur but

all we had were big dinosaurs and it

comes down to a couple of things first

off scientists have egos and scientists

like to name dinosaurs don’t like the

name anything everybody likes to have

their own animal but they named and so

and so every time they found something

that looked a little different they

named it something different and what

happened of course is we ended up with a

whole bunch of different dinosaurs in

1975 a light went on and somebody’s had

dr. Peter Dodson at the University of

Pennsylvania actually realized that

dinosaurs grew kind of like birds do

which is different than the way reptiles

grow and in fact he used the castle area

as an example and it’s kind of cool I

mean if you look at the cassowary or any

of the birds that have crests on their

heads they actually grow to about 80%

adult size before the crest starts to

grow

now think about them I mean they they’re

basically retaining their juvenile

characteristics very late into what we

call untidy so allometric cranial

ontogeny is relative skull growth okay

so you can see that if you actually

found one that was 80% grown and you

didn’t know that it was going to grow up

to a cassowary you would think there

were two different animals all right so

so this was a problem and Peter Dotson

pointed this out using some duck-billed

dinosaurs thing called hypocracy Saurus

and he showed that if you were to take a

baby and an adult and make an average of

what it should look like if it grew in

sort of a linear fashion it would have a

crest about half the size of the adult

but the actual sub-adult the 65% had no

crest at all so this was interesting so

this is

this is where people went astray again

I mean if they’d had just taken that

take computer Dotson’s work and gone on

with that then we would have a lot less

dinosaurs than we have but scientists

have egos they like to name things and

so they went on naming the dinosaurs

because they were different now we have

a way of actually testing to see whether

a dinosaur or any animal is a young one

or an older one and that’s by actually

cutting into their bones but cutting

into the bones of a dinosaur is hard to

do as you can imagine because museums

bones are precious

all right you go into a museum and they

take really good care of them they put

them in foam little containers and I

mean it’s they’re very well taken care

of they don’t like it if you come in and

want to saw them open and look inside so

they don’t normally let you do that

but I have a museum and I collect

dinosaurs and I can saw mine open so

that’s what I do

so if you cut open a little dinosaur

it’s very spongy inside like a and if

you cut it into an older dinosaur

it’s very massive that’s very I mean you

can you can tell it’s a mat or bone so

it’s real easy to tell them apart so

what I want to do is show you these in

North America and the northern plains of

the United States and the southern

plains of Alberta and Saskatchewan

there’s this unit of rock called the

Hell Creek Formation that produces the

last dinosaurs that lived on earth and

there are twelve of them that everyone

recognizes I mean the twelve primary

dinosaurs that went extinct and so we

will evaluate them and that’s sort of

what I’ve been doing so my students my

staff we’ve been cutting them open now

as you can imagine cutting open a leg

bone is one thing but when you go to a

museum and say you don’t mind if I cut

open your dinosaur skull do you they say

go away

so so here are 12 dinosaurs and we want

to look at these three first so these

are dinosaurs that are called

pachycephalosaurs and everybody knows

that these three animals are related and

the assumption is is that they’re

related

you know like cousins or whatever but no

one ever considered that they might be

more closely related in other words

people looked at them and they saw the

differences and you all know that if you

are going to determine whether you’re

related to your brother or your sister

you can’t do it by looking at

differences all right you can only

determine relatedness by looking for

similarities so people were looking at

these and they were talking about how

different they are

Pachycephalosaurus has a big big thick

dome on its head and it’s got some

little bumps on the backs of its head

and it’s got a bunch of gnarly things on

the front of its nose and then

Stygimoloch another dinosaur from the

same age lived at the same time has

spikes sticking out the back of its head

it’s got a little tiny dome and it’s got

a bunch of gnarly stuff on its nose and

then there’s this thing called Draco

wrecks Hogwarts I guess where that came

from

dragon so here’s a dinosaur that has

spikes sticking out of its head

no dome and gnarly stuff on its nose

nobody noticed that gnarly stuff sort of

looked alike but but they did look at

these three and they said these are

three different dinosaurs and Draco Rex

is probably the most primitive of them

and the other one is more primitive than

the other it’s unclear to me how they

actually sorted these three of them out

but if you line them up if you just take

those three skulls and just line them up

they line up like this Draco Rex is the

littlest one

did you Moloch is the middle sized one

Pachycephalosaurus is the largest one

when one would think that should give me

a clue

but it didn’t give them a clue because

well we know why scientists like to name

the thickness so if we cut open

Drako racks I cut open our draco Rex and

look at it was spongy inside really

spongy inside I mean it is a juvenile

and it’s growing really fast so it is

going to get bigger if you cut open

Stygimoloch it is doing the same thing

that dome the dome that little dome is

growing really fast it’s inflating very

fast what’s interesting is the spike on

the back of the Draco rex was growing

very fast as well the spikes on the back

of the Stygimoloch are actually

resorbing which means they’re getting

smaller as that dome is getting bigger

and if we look at Pachycephalosaurus

Pachycephalosaurus has a solid dome and

it’s little bumps on the back of its

head we’re also resorbing so just with

these three dinosaurs you can easily you

know as a scientist we can easily

hypothesize that it is just a growth

series of the same animal which of

course means that stigma lock and

Dracorex

are extinct

which of course means we have ten

primary dinosaurs to deal with so a

colleague of mine at Berkeley he and I

were looking at Triceratops and before

the year 2000 now remember Triceratops

was first found in 1800s before 2000 no

one had ever seen a juvenile Triceratops

there’s a triceratops in every Museum in

the world but no one had ever collected

a juvenile and we know why right

does everybody wants to have a big one

so everyone had a big one so we went out

and collected a whole bunch of stuff and

we found a whole bunch of little ones

they’re everywhere they’re all over the

place so we have a whole bunch of at our

Museum

and everybody says because I have a

little Museum where you have a little

Museum you have little dinosaurs so if

you look at the Triceratops you can see

it’s changing its shape-shifting as the

juveniles are growing up their horns

actually curved backwards and then as

they get older the horns grow forward

and that’s pretty cool if you look along

the edge of the frill they have these

little triangular bones that actually

grow big as triangles and then they

flatten against the frill pretty much

like the spikes do on the

Pachycephalosaurus and then because the

juveniles are in my collection I cut

them open and look inside and the little

one is really spongy and the middle

sized one is really spongy but what was

interesting was the adult Triceratops

was also spongy and this is a skull it

is 2 meters long it’s a big skull but

there’s another dinosaur that is found

in this formation that looks like a

triceratops except it’s bigger and it’s

called Torosaurus and Torosaurus when we

cut into it ESMA tore bone but it’s got

these big holes in that shield and

everybody says a triceratops and a

Torosaurus can’t possibly be the same

animal because one of them’s bigger than

the other one

and it has holes in the frill and I said

well do we have any juvenile Toro

sources and they said well no but it has

holes in his throat so one of my

graduate students John’s Cannella look

through our whole collection and he

actually discovered that the hole

starting to form in Triceratops and of

course it’s open in Torosaurus so he

found the transitional ones between

Triceratops and Torosaurus which was

pretty cool so now we know that that

Torosaurus is actually a grown-up

Triceratops now when we name dinosaurs

you know when we name anything the

original name gets to stick and the

second name is thrown out so Torosaurus

is extinct Triceratops if you heard the

news a lot of the newscasters got it all

wrong they thought Torosaurus should be

kept and Triceratops thrown out but

that’s not going to happen

all right so so you know we can do this

with a bunch of dinosaurs you know I

mean here’s Edmontosaurus and the natto

Titan a natural titan giant duck so

giant duck-billed dinosaur so here’s

another one so we look at the bone

histology the bone histology tells us

that edmontosaurus is a juvenile or at

least a sub adult and the other one is

is an adult and we have an ontogeny and

we get rid of an adult Titan so we can

just keep doing this and the last one is

t-rex so there’s these two dinosaurs

t-rex and Nanotyrannus

yeah it makes you wonder

but they had a good question I mean they

were looking at and they said one’s got

17 teeth and the biggest ones got 12

teeth and that doesn’t make any sense at

all because we don’t know of any

dinosaurs that gain teeth as they get

older so that must be true

they must be different so we cut into

him and sure enough Nanotyrannus

has juvenile bone and the bigger one has

more mature bone looks like you couldn’t

still get bigger and at the Museum of

the Rockies where we work I have 40

Rex’s so if I can cut a whole bunch of

them but I didn’t have to cut any I’m

really because I just lined up their

jaws and it turned out that the biggest

one had 12 teeth and the next smallest

one had 13 and the next smallest had 14

and of course Nano has 17 and we just

went out and looked in other people’s

collections and we found one that has

sort of 15 teeth so again real easy to

say that Tyrannosaurus ontogeny included

nano tyrannous and therefore we could

take out so when it comes down to our

end Cretaceous we have 7 left and that’s

a good number

that that’s a good number to go extinct

I think now as you can imagine this is

not very popular with fourth graders

fourth graders love their dinosaurs they

memorized them and and they’re not

they’re not happy with this

thank you very much