>>DANNY BARTA: Alright, hello everyone.
I'm Danny Barta. I'm a PhD candidate at the
American Museum of Natural History's
Richard Gilder Graduate School and I'm
here today to discuss a new study that
was published just a couple of days ago
in the scientific journal Nature that's
really causing some people to maybe
rethink our thoughts about the dinosaur
family tree. So, before I get into the-
to the details and implications of the
study I think I'll just start out very
basically with- kind of tell the story of
how we have figured out our traditional
idea of what the dinosaur family tree
looks like. So, right next to me this is
of course Tyrannosaurus Rex. This is a
carnivorous dinosaur. It belongs to a
group of dinosaurs called theropods and
this is the group of dinosaurs that
includes birds. And then across the Hall
from me here, this is a dinosaur called
Apatosaurus. It belongs to the group
of dinosaurs called sauropods.
And these are two of, really, the
three major groups of dinosaurs we're
going to talk about today. The others are
all in the Museum's Hall of
Ornithischian Dinosaurs. And so, these
three groups were all recognized very
early on in the study of dinosaurs.
Almost, you know, immediately after Sir
Richard Owen named dinosaurs we had
examples of all these three groups. And
in 1887 a scientist named Harry Seeley,
who was working in England, he came up
with this division of dinosaurs into
Ornithischians and Saurischians. And subsequent
work for the next, you know, 130 years
really confirmed his idea of dinosaur
relationships—that the sauropods and the
theropods were each other's closest
relatives within this group called
Saurischia or the Saurischians. And the
Ornithischians were their sister group.
That's what we call- When two
groups branch off from a root like this,
they are called sister groups.
So, this was really our traditional
picture that was supported by the
results of cladistic analysis, which is a
means of inferring animals' evolutionary
relationships based on patterns of
common descent. It's a system of
classifying animals according to their
common ancestor. A clade is a group of
animals that includes its common
ancestor, which is represented by these-
these nodes here, these points where the
branches join, and then all of its
descendants. So, all the animals that
descend from that point.
INTERVIEWER: So, Danny, tell us
how we got to- like, what were
paleontologists looking at when they-
when they came to, sort of, these three
groups, and how they're related?
>>BARTA: Yeah, so some of the major features that
paleontologists were looking at—
one of them is the arrangement of the
dinosaurs' hip bones. That's what these
groups are really named for. So, these are
all the the lizard-hipped dinosaurs and
then these are the bird-hipped dinosaurs.
And it's- and it's just the arrangement-
it just relates to the arrangement of
how their three hip bones all
connect with one another. And- But one of
the other major features that Harry Seeley
used to group, say, sauropods and
theropods together is that they both
have spaces for air sacs within their
vertebral column. This is much like
modern birds have today and so this may
have helped lighten the skeleton, may
have aided in respiration. And so, that
was- that's a major feature that these
groups shared that Ornithischians don't.
And so, there's many other features
besides this, but there was a great, you know,
weight of evidence supporting this
arrangement of the family tree.
>>INTERVIEWER: Danny, since we're here, can we maybe
point out the hip bone on T. Rex here. I'm sure people
would love to get a look at exactly what we're talking about.
>>BARTA: So, in Saurischian
dinosaurs, you have this bone right in
front here between the legs with sort of
this big boot shape on it. This is called
the pubis and in Saurischian dinosaurs, as in
lizards and other kinds of reptiles, the
pubis is pointing more forwards towards
the head, whereas in an Ornithischian
dinosaur- I have a picture of this
dinosaur called Heterodontosaurus here.
It's a very primitive Ornithischian.
It may be difficult to see, but the pubis is
actually pointing backwards in these
animals. So, that's probably one of the more
obvious differences between
these groups. So, maybe we'll walk down
this way and look at some early
examples of members of both the theropod
and sauropod groups,
and talk a little bit more about the new- the new findings.
>>INTERVIEWER: I was just going to ask.
Yeah, what's this new paper sort of suggesting?
>>BARTA: Yeah, so now that we've done our work of
introducing dinosaurs, this new paper is the
result of quite a comprehensive new
cladistic analysis that takes into
account a really greater number of
different dinosaur species and different
anatomical features than previous
studies have done. So, it's- I think it's a
very thorough piece of work in terms of
examining lots of different types of
dinosaurs and their anatomy. And so,
what this study has done- When they
built their data matrix of anatomical
features, basically transforming the
anatomy of the animal into a matrix of
zeros and ones- So, a zero we usually put
down in the matrix if an anatomical
feature is absent, and we'll put in a one
if it's present. And so then, we run this
this matrix
through a computer algorithm and
that will tell us what the most- sort of
what the best arrangement of the tree is
based on those features. And so, they ran
this through a computer and they got out
a result that no one has ever really
found before in cladistic analysis of
dinosaurs. So, this is the tree that they
uncovered. So ,remember we have our
sauropods, our theropods and our ornithischians.
Before, the theropod- [audio dropout]
-with the sauropods over here. Now, the
theropods are the sister group to the
ornithischians. And they name this group
Ornithoscelida. And this is
actually kind of a resurrection of an
old name that Thomas Huxley had applied
to some dinosaurs. He was Charles
Darwin's great supporter. He had come up
with that name that they sort of
resurrected this old name to refer
to this new grouping of theropods and
ornithischians. Which maybe on the face
of it seems somewhat counterintuitive or
contradictory based on things like the
hip bones that we looked at, but taking
into a lot of different features into
account, the authors found evidence that
this grouping is supported based on
characters in the skull, characters and
the limbs, other characters throughout
the body.
>>INTERVIEWER: Let's maybe get in front of
one of these specimens, talk about some of the features they took into account.
>>BARTA: This is an early member of the
sauropod lineage. So, this is- this is
Plateosaurus. And you can see it has
that typical Saurischian arrangement of
pelvic bones where the pubis is pointing
forward. But maybe- maybe that isn't such
a good character is what these authors
of the study in Nature might argue. But
yeah, there's many characters
throughout the body. Some of them relate
to the shape of the shoulder blade,
for example, the shape of the upper
arm bone, the humerus. There's
others that are present in the skull and-
and so these are- these are features that
would not be present in this dinosaur
that are actually separating out the
sauropod group from the theropods and
ornithischians. And so, these I
think- I think going forward some of these
anatomical features are going to be, you know,
heavily debated and sort of the
interpretations of them will be argued
about in the literature going forward.
But I think this study does a very good
job of maybe challenging us to rethink
some of our assumptions based on really
a wealth of new evidence.
But I would say it remains to be seen, you know,
whether this will become sort of the new
orthodoxy for the next 130 years or, who
knows, maybe there will be new dinosaurs
discovered, you know, later this year that,
you know, might overturn this whole thing.
We just don't know because any time you
find a new species and you put it into
an analysis like this, it has the potential
to change the arrangement of the
evolutionary tree. So, science is always
discovering new things, always moving-
moving forward. I think- I think one
important thing to keep in mind is that
all the things that we've learned about
dinosaurs previously, about their biology—
so, about the way dinosaurs grew, about
the way they reproduced, about their eggs,
about their behavior—all of those things
haven't haven't really changed. Maybe the
distribution of some of those things on
this tree has, you know, maybe changed, but
all the things we've been able to
infer about dinosaurs—you know, this
has not, you know, altered our perspective on
any of the biology of dinosaurs as
living animals.
>>INTERVIEWER: Danny, you mentioned that
this is- this is challenging sort of a
pretty long-standing way of thinking. Has
that- have these assumptions been
challenged before? Is this something
that's been sort of thought about a
lot, or something that was kind of, you know,
we thought we had this settled 130
years ago, and now
it's being brought up again?
>>BARTA: Yeah, so I think there's been,
you know, some challenges throughout the past
130 years to the traditional
arrangement of dinosaur relationships,
but these always kind of taken the
form of just observations of like,
"Oh, isn't this weird that the theropods
and ornithischians share a, you know, an
anatomical feature?" But no one has
really- had previously, you know, put some
of these features into an analysis and-
and really found on the weight of a
cladistic analysis that this new
picture of relationships might instead
be a more accurate depiction of the
relationships.
>>INTERVIEWER: Fantastic. We have a couple
questions coming in from Facebook, but
while we field those- we've got a fossil
over here that I think is pretty close to your heart.
>>BARTA: Yes.
>>INTERVIEWER: Maybe introduce us to this guy.
>>BARTA: Yeah, so, this is a very
primitive theropod dinosaur.
This is Coelophysis. So, Coelophysis is
one of the earliest members of this
group that includes Tyrannosaurus rex. And so,
I think one interesting thing when we
look at Coelophysis and when we think
about that Plateosaurus that we just saw,
and then we look at this Heterodontosaurus,
the primitive Ornithischian- So,
when we look at the sort of primitive
members of all these groups, they all
look relatively similar. And when
you go even earlier in time, and you find
even earlier theropods, and even earlier
sauropods, they start looking even more
similar. They- And this is one of the
reasons why this problem has been really
difficult to figure out, because all the
early members of these groups right down
towards their origins—all are quite
similar in the sense that they're all
small. They all walk on their hind legs.
They all have these grasping hands,
which you can
see on Coelophysis there, as well. They
share certain features throughout the
rest of their skeletons that- it's really
difficult to sort of sort out
relationships when these animals are so-
either sharing primitive features or
they're convergently evolving on similar
body types. And so, it's difficult to sort
out, you know, what exactly is going on. It would-
It's really, you know, easy to see that
the later representatives of these groups are
very different from one another, like a
Tyrannosaurus versus an Apatosaurus
versus a Triceratops. Those are all very
different looking dinosaurs. But when you
find their earliest ancestors they're
all pretty similar, and so it can be a
bit difficult to sort out. But-
>>INTERVIEWER: When we talk about an early ancestor,
Danny, what's the span of time
difference between, like, the
Coelophysis here and the T. rex we were
near earlier?
>>BARTA: Sure. So, Coelophysis
lived about 200 million years ago, and
Tyrannosaurus lived about 66 million
years ago. So, there is probably more-
There's more time between
Coelophysis and Tyrannosaurus rex than
there is between Tyrannosaurus rex
and you and I standing here today. So,
that just gives you a sense of just how
long the age of dinosaurs was, and you
can, you know, really think about how
successful dinosaurs were through that
whole time to have survived, you know, hundreds
of millions of years.
>>INTERVIEWER: And Danny, maybe- You brought
this up a little earlier, but I
wanted to sort of dig into it a
little more.
What other research might this
Nature paper- what might that sort
of prompt researchers to look at going forward?
>>BARTA: Sure. So, I think going forward
this study is going to be heavily
debated, and it's actually going to be a
very fun debate to watch because it's,
you know, it's not every day that
something that's really stood the test
of time since 1887 is being, you know,
rigorously challenged like this. And so-
and so, a lot of the studies going forward now
are going to focus on details of the
anatomy that were used to support the new
findings of the new analysis. They're
going to focus on the statistical methodologies that
the authors used to build their
evolutionary tree, the computer
algorithms. Probably new, different
statistical techniques will be applied
to this study. People will include,
invariably, more specimens and more
species of dinosaurs in an analysis like
this. And of course, we, you know, can't really
predict what, you know, may be discovered in the
future in terms of new dinosaurs.
I think, you know, this area of
dinosaur origins has always been a-
really a hot area of interest, but I
think that's going to be even more true
going forward that, you know, we need
really a lot more specimens of some of
these early primitive animals to
eventually really sort this out. So,
things might be a little unstable in
terms of figuring out this part of
the tree of life right now, but that
happens with many other groups of
animals all the time. This is certainly
not a- not a, you know, scientific question
or scientific problem that's unique to
dinosaurs. If you work on fish or mammals
or any other group it's- you know, things
are in flux, and, you know, eventually more
evidence will accumulate and we'll
probably be able to have a more, you know,
I guess, confident answer. Maybe at least
for the next 130 years. But yeah,
science is always, you know,
increasing our- the knowledge that we- the
knowledge that we have in terms of
specimens, in terms of techniques we can
apply to them. So, it's an exciting time
to be a paleontologist.
>>INTERVIEWER: Fantastic. And we
want to get at least one- We've got a
great conversation going on in
the Facebook thread here. We wanted-
It seems like we're leaving out one thing
that people think about when we think
about dinosaurs. And Rob Ruiz asks if
pterodactyls aren't dinosaurs than what
are they? Where do sort of the
flying dinosaurs we think about fit into this picture?
>>BARTA: Yeah, so, pterodactyls are not dinosaurs.
So, no matter which family tree of
dinosaurs you use, pterosaurs fall
outside of this grouping. So, pterosaurs
are a side branch. If I were to put pterosaurs on
this tree, they would be- they would be
right out here where my index finger is.
And so pterosaurs are best thought of as
close evolutionary cousins of the
dinosaurs. They both belong to a group
called Archosaurs, which also includes
crocodilians, and, of course, birds because
birds are dinosaurs. But pterodactyls are not
birds. They're not dinosaurs. They are
their own separate side branch of
Archosaur evolution.
>>INTERVIEWER: Fantastic. Danny, we'll
let you get back to what I'm sure is a
very busy day. Thanks so much for
joining us today.
>>BARTA: Yeah, thank you. It's great talking to you.