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