Nova (1974–…): Season 35, Episode 6 - The Four-Winged Dinosaur - full transcript

One day, long ago,

life in a forest came
to a sudden halt,

snuffed out and buried
by volcanic ash.

130 million years later,
fossils are all that remain,

and some are like nothing
ever seen before.

Strangest of all is a creature
called Microraptor.

It had wings like a bird,

but it had them on its arms
and its legs.

It was a four-winged,
feathered dinosaur,

and no one has any idea
how it worked.

What's this dinosaur doing



with these aerodynamic feathers
coming off their hind limbs?

Rival teams have been trying
to figure it out,

piecing together clues
about what it looked like

and how it functioned from
crushed and distorted fossils.

Each team has built a model,
with very different results.

When the animal

is squashed flat, as these are,

well, it leaves a little room
for interpretation.

Scientists have argued
for decades

over whether and how dinosaurs
evolved into flying birds.

Now they think Microraptor
could solve the puzzle,

but they still don't agree
on the solution.

You have just shown me

the death of the dinosaur origin
of birds.



Birds are dinosaurs.

That's why they look
like dinosaurs.

I'm getting whip-lashed
by two lines of evidence,

and I'm going to be disturbed
this evening,

thinking about this.

One team is about to fly
their model in a wind tunnel.

But who's got
the real Microraptor?

It's the battle
of the four-winged dinosaurs,

up next on NOVA.

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One day in 2002,
a courier made a delivery

to the Institute of Vertebrate
Paleontology in Beijing.

The dinosaur specialist,
Xu Xing, was unprepared

for what he saw
when he opened the box.

My first feeling is...
amazing, beautiful fossil.

It was a nearly complete
skeleton of a small dinosaur,

with a feature
he'd never seen before...

Long feathers attached
to the arms.

This animal has feathers
like feathers in flying birds.

I thought, "Oh, we have evidence

suggesting some dinosaurs
could fly.

For over a century,

scientists have searched for
the origin of birds and flight,

and the evidence keeps pointing

to the same
improbable conclusion.

Somehow, flying birds evolved
from earthbound dinosaurs

more than a hundred million
years ago.

Exactly how it happened is still
one of the great mysteries

in the history of life.

And the solution may be
in this box.

Mark Norell and Mick Ellison

are from the American Museum
of Natural History in New York,

but they spend much of their
time in China hunting dinosaurs.

They're on their way
to Liaoning Province

in the northeastern corner
of China,

a region that's produced

some of the most spectacular
fossils ever seen.

It's an overnight train ride

to the kind of place
paleontologists dream about.

Today, it's a harsh
and often barren landscape.

130 million years ago,
during the Age of Dinosaurs,

it was a forest teeming
with life,

some familiar...

and some not.

It was also a place
where volcanic eruptions

created a virtual Pompeii.

Now the trees are gone, but
remnants of ancient life remain

in the petrified layers
of volcanic ash.

Norell has spent much
of the past ten years immersed

in the history recorded
in these slabs of rock.

They open like the pages
of a book,

sometimes with exquisitely
preserved fossils inside.

These are more than snapshots
of the distant past...

They're high-resolution records
of life in a temperate forest

during the Cretaceous Period.

They're especially valuable
for the number and variety

of small animals they add
to the fossil record...

The fish, frogs, turtles
and reptiles that lived

in and around
the freshwater lakes.

It's the first look
at a forest like this

and the creatures that would
live in a forest like this,

where we have tremendous
diversity,

but it's 130 million years ago,

and it's the first time
we've ever had that.

Victims were buried quickly
in fine ash,

preserving detail rarely seen
in fossils...

Skin impressions on a reptile,

fur on a small mammal.

Wish I could find something.

You'll go through hundreds,
if not thousands, of layers

and you won't find anything.

But occasionally,
on some layers,

you'll find lots of stuff...

Either tons of fish
or lots of insects

or if you're really lucky,
you know, once in a while...

I mean, it's never happened
in my life,

but once in a while,
people find feathered dinosaurs.

The first turned up
more than a decade ago

with what looked like a feathery
fringe along its back.

Then came others,

with feather impressions
that were unmistakable.

These weren't giants like T.rex;

some were no bigger than crows.

But their skeletons showed
they belonged

to well-known dinosaur clans.

They were runners, not fliers.

Their arms were too short
to function as wings.

They were just what most
scientists had predicted

the ancestors of birds
would look like

before they evolved flight...

Small, carnivorous dinosaurs
with feathers.

The dinosaur-bird connection
first came to light

in the 1860s, when quarrymen
in Germany discovered a fossil

called Archaeopteryx.

It had the feathered wings
of a bird,

but the teeth and long bony tail
of a reptilian ancestor.

Some thought the ancestor
might be a dinosaur.

But the idea didn't catch on
until a century later,

when paleontologist John Ostrom
led an expedition to Montana

and discovered a new kind
of dinosaur.

It was a lightly built
meat-eater

with a killing claw
on each foot.

They called it Deinonychus,
"Terrible Claw."

A few years later, Ostrom
was studying Archaeopteryx

when it dawned on him
that the skeleton looked

like a miniature version
of Deinonychus.

He found dozens of similarities,

enough to convince
almost everyone

that dinosaurs like Deinonychus

were not only the ancestors
of birds,

they were very much like birds
themselves.

The new-look dinosaurs made
their widescreen debut

as the raptor villains
of Jurassic Park.

Playing the role
of cunning predators,

they forever dispelled
the old image of dinosaurs

as dim-witted,
cold-blooded reptiles.

That's a radical change

in the way we looked
at these creatures...

Big, slow, lumbering, now seen
as active, dynamic animals.

20 years ago, Jacques Gauthier
worked out the details

of the family tree based
on changes in anatomy

that appeared
as dinosaurs evolved

from their earliest ancestors.

Just by using the sequence

in which those characteristics
appear,

we reconstruct
the history of life.

Gauthier found that dinosaurs
and crocodiles parted ways

240 million years ago,

when the ancestors of dinosaurs
evolved the ability

to stand up and run

with their legs straight
under their bodies.

As the family branched out,

the meat-eaters,
called theropods,

became more and more bird-like,

acquiring traits like
a three-toed foot,

a three-fingered hand,

a wishbone, and many others.

Each new feature was passed
along to the descendants.

Finally, a branch led in one
direction to Deinonychus,

and in the other,
to Archaeopteryx and birds.

With birds nested at the top
of the dinosaur tree,

linked to their ancestors
by hundreds of inherited traits,

Gauthier says there can be no
doubt about the family ties.

Birds are dinosaurs.

That's why they look
like dinosaurs.

And some dinosaurs
looked like birds.

We now know there's one detail

the makers of Jurassic Park
got wrong.

The raptors should
have had feathers.

The fossils from China
proved it.

Since the first discoveries,
Liaoning fossil collectors

have turned up
feathered dinosaurs

from many different
dinosaur clans.

All are from branches
of the tree

close to birds
and Archaeopteryx.

Some are from the same clan
as Deinonychus;

others are from
more primitive groups

like Oviraptors
and Tyrannosaurs.

And that means all the dinosaurs
in this part of the tree

had feathers, wherever
they lived in the world.

We would assume
that an Oviraptor

that we find in Mongolia

or a Tyrannosaur that we find
in Montana

would also have had feathers.

So, everywhere you go
in the world,

all these advanced theropods
were covered

with feathery body coverings.

Feathers could have been useful
to the ancestors of birds

long before they took
to the air.

There's nothing better
for insulation,

which may have been
their original function.

They can be used to bluff
an enemy,

attract a mate,

or simply to show off.

But long feathers attached
to the arm and finger bones

are the signature
of flying birds.

And they were missing from the
feathered dinosaurs of Liaoning.

There were no clues

to how earth-bound dinosaurs
achieved flight

until the strange fossil arrived
on Xu Xing's doorstep.

As he examined it
that first day,

it looked like it could be
a missing link,

with a bird's wing and
a dinosaur's long tail and legs.

But it had something else
that he'd never seen

in any dinosaur or bird.

I noticed something strange...

Long feathers attached
to the foot.

This is so bizarre.

You don't know any thing,
any animal has this long feather

attached to the foot!

A two-winged dinosaur would be
a spectacular find,

but four wings border
on science fiction.

Nothing in the world today
has feathers on its feet,

and this was the first clue
that such a thing ever existed.

Xu named it "Microraptor."

And we started thinking
of what this means.

And then it brings the big story
about the origin of flight.

The origin of flight in birds
is a puzzle

that seems to defy solution.

The aerial skills of modern
fliers evolved in small steps

over millions of years,

and the fossil record provides
few clues to how it happened.

It's one of the oldest debates
in paleontology,

and for decades,
it's been a standoff

between two opposing theories.

One has argued that flight must
have evolved from the ground up.

The ancestors were
running dinosaurs,

already feathered, probably
to conserve body heat.

Over time, the feathers could
have been adapted for flight,

as bodies became smaller and
the running leaps of dinosaurs

evolved into the powered
flapping flight of birds.

But not everyone bought it.

It was always a hard sell

because with a terrestrial
origin of flight...

Flight that originated from
running fast on the ground...

You're always working
against gravity.

But an arboreal origin of flight
where you fall out of a tree,

you accumulate air speed
whether you want to or not.

In the arboreal scenario,

the bird ancestor was
a small climbing animal

that evolved flight by gliding
from the treetops.

And that seemed to rule out
dinosaurs,

which presumably
couldn't climb trees.

The ground-up origin of flight
didn't make good physical sense.

But it seemed to be essential
to the dinosaur origin of birds,

and that made us suspect

that the dinosaur origin
of birds was wrong, too.

Fossil bird expert Larry Martin

has been a thorn in the side
of dinosaur paleontologists

for decades.

People are going to simply

have to explain how you can
originate birds from dinosaurs,

which apparently can't get up
in trees.

Years later, he's still at it.

So if you really love dinosaurs,

then my arguing that birds
aren't dinosaurs

is sort of like taking away
Christmas.

I get really frustrated by this

just because we shouldn't be
having to deal with something

which has been settled
for 20 years.

I don't know when Magellan
got back

from sailing around the world
if he was frustrated, too,

by people who still said
the Earth was flat.

It was hard to imagine

what kind of evidence
could break this deadlock,

until Microraptor turned up.

A four-winged dinosaur is a clue
that no one expected.

For Martin, it's evidence
that he was right,

at least about the origin
of flight.

I think that Microraptor
completely destroyed all hope

for a terrestrial origin
of flight.

This is an animal that probably

couldn't even walk on land
comfortably, let alone run.

And so you're looking
at something

that was probably
completely arboreal.

Xu thought the same thing.

With feathers on its feet,

Microraptor must have lived
in the trees,

but he's also quite sure
that it was a dinosaur.

Numerous details
of the skeleton say so,

from the long bony tail
to the sickle claws on its feet.

Xu also believes it must
have been able to fly.

I noticed the feather shape.

This animal has feathers
like feathers in flying birds.

The wing feathers
are asymmetrical,

with veins wider on one side
of the shaft than the other,

which forms an airfoil contour,
like an airplane wing.

Only flying birds have
asymmetrical flight feathers.

But unlike modern birds,
Microraptor had not yet evolved

the specialized shoulder anatomy
for powered, flapping flight.

It was more likely a glider,
like a flying squirrel,

so Xu concluded that gliding
came before flapping

in the evolution of birds.

He presented Microraptor
to the world as a synthesis...

Flight began with gliding
from the treetops,

and the glider was a dinosaur.

Those feathers will change

the whole idea of how dinosaurs
evolved into flying birds.

It looked like Xu had finally
cracked the origin of flight.

But within days,
another scientist announced

that he'd solved it and come
to the opposite conclusion.

We think we have the answer

and we didn't make it up...
Birds told us.

Man, to be able to catch
these guys..

Ken Dial is a well-known
experimental biologist

and a strong believer in
the dinosaur origin of birds.

He's convinced that the powered,
flapping flight of modern birds

really did begin on the ground
with a running start.

Dial studies living birds
called chukars.

They can run
within hours of birth,

although they can't fly
until they're a few weeks old.

He found that long
before they can fly,

young chukars use
their developing wings

to scramble up inclined surfaces
to a safe refuge.

Over time, the wing beat
that helps them scramble

becomes the power stroke
that helps them fly.

There's no gliding involved...

Powered flight comes first,
even on the way down.

Dial believes this is
a primitive behavior

common to all birds, reflecting
their evolutionary history.

I think you're looking
at the evolutionary process

through this developmental
process.

And what these animals do,
we think,

is paralleling the evolution
of what transpired

between the theropod dinosaurs
to modern day birds.

It makes sense,

unless the ancestor couldn't run
because of feathers on its feet.

But Dial says speculation
about fossils is not enough

to prove him wrong.

If we're going to live

in a world of interpreting
fossils because it's just fun

to think of all the different
things they might have done,

well, that's great.

It's just I think you're
stepping out of the bounds

of reality 90-some-odd percent
of the time.

That doesn't mean you shouldn't
do it, you can't do it;

I just don't think
it's great science.

Science is built
on testable ideas,

and it's hard to run experiments
on a fossil.

But what if Microraptor
could be resurrected

from this slab of stone?

What would it reveal?

Xu wants to find out...

and so does Norell.

This is a really
spectacular animal,

and I want to figure out
as much as we can

about functions
that it might have had

and how this will relate

to the origin of flight
in modern birds.

It's a real juvenile.

Together they decide
to dig deeper

to see what they can learn,

and the process begins
at Xu's lab in Beijing.

There are now at least 30
specimens of Microraptor

in China.

Xu has one of the best
collections,

and they're going to need
all of them.

The skull here, I mean,
it's much more typical of...

They plan to build
a model to see

how four wings
might have worked.

To do that, they need
to understand its skeleton

and the range of motion
in the arms and legs.

Unfortunately, the fossils
were crushed

under tons of volcanic ash,
making it difficult sometimes

to interpret the true shape
of the bones.

We can't really make out
exactly how the hind limb
would have fit.

In the best
of all possible worlds,

we'd make our reconstruction
from a wonderful,

three-dimensionally preserved
specimen.

But this isn't the best
of all possible worlds.

We don't have that.

Many bones are
damaged, deformed,

and sometimes missing
altogether.

They'll need to work
with multiple specimens,

look for the best preserved
examples of each bone,

and combine them all
into a composite

that fills in the blanks
in the original fossil.

I think would answer
a lot of our questions.

The specimens have to remain
intact and stay in China,

so they'll use high-resolution
photographs for reference.

At the American Museum
of Natural History in New York,

where Norell is curator
of paleontology,

a scientific sculptor
starts work

on a bone-by-bone reconstruction
of the entire skeleton.

Jason Brougham is an artist
and a trained anatomist.

We had more than 16 specimens
to look at.

So, many of these bones I could
see from not only both sides,

but from end on and from
all different positions.

But in the text,
it describes it as squared off.

Some specimens have already
been analyzed in detail

by other scientists.

So I would just sit there
with my micrometer

and check and make sure
that what I was sculpting

not only looked
like the picture,

but that it met
those measurements.

Since the specimens are all
slightly different sizes,

each bone is scaled to match
the dimensions

of the original fossil,
a process that takes months.

It's hard work to sit down
and look at every bone

from every angle.

It's grueling, in fact.

My wife says I have a high
tolerance for tedium.

I guess that might be true.

By chance, Microraptor is
also under investigation

at the University of Kansas.

Larry Martin and David Burnham
have built their own model

based on a single specimen and
a unique method of preparation.

The specimen was found
with this side exposed.

I embed it in optically
clear plastic...

I flip it over...

I clean down through
the matrix on this side,

exposing the skeleton
from the other side,

ending up with a specimen that
can be examined from both sides.

Burnham made molds
of each side of the slab,

cast the exposed bones
and cut out the pieces.

Some had good preservation,
and some were crushed.

When he assembled the bones,

the result looked more like
a crocodile than a dinosaur.

What really surprised me

when I was mounting
this skeleton

is when I put the back leg
into the hip socket

it just popped right into joint,

and as you can see,
when that happened,

the leg was mounted
in a sprawl posture.

The only time it felt
like it was in socket

was in this position,
splayed out.

What I try to do is
follow the lateral edge.

A sprawling Microraptor
is the smoking gun

Martin has been looking for
all these years

to prove that dinosaurs were
not the ancestors of birds.

All dinosaurs have hip joints
that support the legs

more or less straight
under the body.

It's one of their defining
characteristics.

Sprawling posture
is the signature

of more primitive reptiles,

including the early
common ancestors

of crocodiles and dinosaurs.

Martin has long believed
that birds arose

directly from these
pre-dinosaur reptiles,

making them distant cousins, not
direct descendants of dinosaurs.

And he says Microraptor's
primitive sprawl

proves him right.

You have just shown me

the death of the dinosaur
origin of birds.

News of Martin's latest salvo
in the bird origin debate

does not surprise Mark Norell.

People who are on
the other side of it, uh...

creatively reinterpret all new
evidence that's put into it

to fit their own thing,
you know.

I knew that they would still be
at it for years to come.

And they are.

And as for the sprawling
Microraptor skeleton...

I haven't seen it.

I don't know.

Beyond that, though,
I would question

whether, if that's true, that it
actually is Microraptor,

because I have seen definitive
Microraptor specimens.

Those are the ones the American
Museum team has used

for its reconstruction.

What do you think of that?

This looks good.

The primary specimen is
not particularly well preserved,

but did you look at other ones?

One interesting thing
with this process has been

to see the artist take
those fossils and render

these often flattened elements
into three dimensions.

But you have to have
a great relationship

of trust and collaboration
between scientists and artists

to really have those three-
dimensional representations

kind of be trustworthy
and accurate.

So we're articulating
the whole hind limb

from these elements,
is that correct?

BROUGHAM and NORELL:
Yeah.

Norell doubts

that Microraptor was anything
other than a typical dinosaur

with legs
straight under the body.

But for a second opinion,
they send the bones

to Harvard's Museum
of Comparative Zoology.

You lost it.

So it won't work that way.

Anatomists Farish Jenkins and
Steve Gatesy are specialists

in the function of limbs
and joints in fossil animals.

What's interesting...

In climbing or...

In his first paper, Xu himself
assumed that Microraptor

would have to splay its legs
out to the side

to form the rear wings.

But Jenkins says
that doesn't fly.

It anatomically is not possible,
given this limb.

You can see the articular
relationships,

there's no question about it.

This is a normal hip socket,

and here's a good,
well-developed femoral head,

and in a normal
standing position,

it would be about like that.

You can abduct the femur
away from the body;

that would be normal.

But if you reach
about 45 degrees,

you begin to hit bone on bone,
the femur on the pelvis.

So beyond 45 degrees, this
trochanter here acts as a lever,

and out she comes.

It just has to come out.

It has to come out.

This animal doesn't work

like the cover showed it
to work.

Xu didn't have the benefit
of the three-dimensional model

when he wrote the paper,
and he concedes

that he was probably wrong
about the posture.

He never questioned the dinosaur
origin of birds,

and upright posture makes sense
for the ancestor,

given that all birds
are built the same way.

But back in Kansas,
Martin and Burnham

are standing by their conclusion

that Microraptor was
a flat-out sprawler

and that this puts the ancestry
of birds outside of dinosaurs.

Microraptor is absolutely deadly
to the dinosaur origin of birds.

It wasn't even a biped.

It was quadrupedal.

It was on all fours.

And it was arboreal.

And that probably
couldn't be a dinosaur.

They think the evidence
is clear.

When I put this leg
into the hip, you know,

I can visually look at it
and determine where it fits.

But there's a certain
tactile sensation.

I can feel when
this bone plugs into the socket.

So which model
is more reliable...

The cast made directly
from a fossil...

or the sculpture based
on 16 specimens?

My criticism of the sculpting
method is

that somebody is carving that.

You know, they're...
they may miss

a little process or a little
bump, or a little shape

that the computer doesn't
think is important

or the artist doesn't think
is important,

and it's probably not even
the scientists themselves

that are sculpting these things.

It's usually done by artists.

Granted, it's a sculpture.

It's a handmade, you know,
piece of art.

But it was held to pretty high
standards, you know,

and very exacting measurement,
and it was cross-checked

against multiple specimens.

As far as, uh, it being
a subjective process,

well, if you think that
measuring, you know, bones

down to the hundredth
of a millimeter is subjective,

you should have been
where I was, you know,

for all those months
working on it.

In a final showdown,
Martin and Burnham examine

the sculpted bones
from the American Museum team.

Mm-hmm.

The only difference from our
pelvis is this area right here.

You see what they've done,
this is pushed in?

Mm-hmm.

I would argue that
this is fudged for
vertical posture

as much as you can
possibly do it.

And you still don't have it.

Now, let's see
if they can get...

Guess what.

They can't sprawl.

If they try to sprawl it,
it pulls all the way out.

Mm-hmm.

I'll be doggone!

At Harvard, Farish Jenkins looks
at Martin and Burnham's cast.

What we've got is
a very well preserved femur

in three-dimensional
preservation.

So this is preserved quite well.

That's not the case here.

This pelvis has been crushed.

It's been squashed actually flat

and made much more shallow

by this crushing.

And so if I fit
the femoral head in there,

it doesn't even fit all the way
into the socket.

There's not enough socket left.

Now, even if you tried to splay
the leg on this animal,

the femoral head is now
out of the socket.

So even
in this deformed specimen,

there is no evidence that the
animal could put the hind limb

in a horizontal plane.

It simply doesn't work.

I want to make a movie of this.

Neither side trusts
the other's evidence,

so the standoff continues.

How would you get
an egg out of that?

And with crushed fossils
as the starting point,

people are more likely
to believe

what they already believe.

When the animal
is squashed flat,

as these are,

well, it leaves a little room
for interpretation.

And then, as I've said before,
science is objective,

but people are scientists
and they aren't.

Still the question remains.

If Microraptor couldn't splay
its hind limbs,

how did it use its leg feathers
in flight?

A wing deflects the air flowing
over the upper surface,

creating lower pressure above
than below,

which generates the lift
necessary for flight.

Microraptor could spread
its forelimbs out to the side

to make an aerodynamic wing,
just as birds do.

But if the hind limbs couldn't
do the same thing,

what did they do?

They certainly can't flap
with their hind limbs.

It has the same hook-up
as you do.

It goes up vertically,
turns 90 degrees

and goes into your hip bone.

Can you flap your hind leg
in that direction?

Try sticking your leg out
in that direction

and see what you do to it,
you know.

So yeah, there are these
feathers hanging off of it

and they're aerodynamic.

What are they doing?

Jenkins and Gatesy
can't figure it out.

Just try to put this together.

And you've got a wing
that's shooting down.

How's that work?

And we can lengthen it,
we can shorten it,

but I don't even know
whether to turn it
this way or this way.

This is very problematic.

Coming off the back?

You've got to be mad!

That's what I see, right?

Martin and Burnham think
they have the answer.

Microraptor has a fully
developed wing on its hind legs.

And what that means is the hind
legs have to be able to sprawl.

There is anatomically,
simply put, no way

that it could elevate the hind
limb into a horizontal position.

The question is,
could it fly any other way?

One way to find out is to create
a model that can be flown

in a wind tunnel
to see how it performs,

and for that they'll need
more than a skeleton.

Jason Brougham builds up the
body form one muscle at a time,

guided by published science
on dinosaur anatomy.

To estimate the animal's mass
and center of gravity,

the sculpture is CAT scanned
and computer modeled

with internal organs.

Mick Ellison reconstructs
the feathering

of the wings and tail.

He traces the feather
impressions

from eight different specimens,

scales them to the same size,

and makes a composite that
combines all the information

from all the fossils and reveals
the shape of the wings.

Then model builders John Allen
and Hall Train take

the knowledge accumulated
by the science team...

The arrangement of feathers
on the wings,

the range of motion
in the limbs,

the body shape,
its mass and center of gravity...

And build a jointed, feathered
model that can be posed

in the various postures
it might have used in flight.

It all comes together

at the Massachusetts Institute
of Technology

in the Wright Brothers
Wind Tunnel.

It's been the scene
of some unusual experiments,

but never anything
quite like this.

Some of the world's leading
figures in paleontology,

biomechanics, aerodynamics
and scientific reconstruction

have come together
for a rare collaboration.

No, extended legs...

and as...

The aerodynamics crew
from Brown University,

led by Kenny Breuer, specializes
in natural flight and gliding.

This is their first experience
with a dinosaur,

and it's the first experience
anyone's had with four wings.

Does it look okay?

I have colleagues who work only
on living animals that say,

"I can't even understand
the living animal

"sitting in front of me.

What makes you think you could
make sense of this fossil?"

And yet, you know,
how could you not want to try?

Xu Xing has the most at stake.

He's claimed that Microraptor
was a link

between dinosaurs
and flying birds.

But he needs to show
how four wings could work

without splaying the legs.

Those feathers must be related
to flight in some ways.

But some people disagree.

Norell, for one,
is reserving judgment

until he sees
some hard evidence.

I mean, I'm fairly conservative

in the way that I interpret
behaviors of extinct animals.

I wouldn't say that we know

that Microraptor even was
a glider, let alone a flier.

I mean, I don't think
we know that.

Birds fly with
a complex wing beat

that propels them through
the air and also produces lift.

But gliders,
like flying squirrels,

get the energy to generate lift
from falling.

The more lift they produce,
the longer the glide path

and the farther they can travel
before they have to land.

Assuming that Microraptor
was a glider,

they'll test the hind limbs
in different postures

to see what, if anything,
works best.

They decide to start
with something simple...

Legs down and spread
as wide as they go.

Yeah.

This is the one.

This is the one.

This is the one my money's on.

Your money's on this one?

Big money?

Like a betting game, yeah.

And I bet you're
a big bettor, too.

Is that ready?

Yeah, we're ready... it's just...

Yeah, we're ready.
Okay.

This was one kilogram,
so the lifting force

is about ten Newtons, right?

The legs are really stable.

Yeah, they're very stable.

That's ten meters a second.

That looks good.

That looks like
a natural glider.

In the wind tunnel,
the model is mounted

on a sensor that measures
the forces produced

by air flowing over the wings,

including the lift
that keeps the flier aloft

and the drag that slows it down.

During each test,
they'll gradually raise

the angle of the wing
into the airflow,

which produces more lift,
but also more drag.

They're still going up.

Wow.

So the blue dots on the left
curve is the lift.

The data shows up
in the control room

on a graphic display.

The blue dots indicate the
amount of lift being generated,

and the red triangles
are the drag.

The higher the lift climbs,
relative to drag,

the farther Microraptor could
glide in that position.

I like the way
these data come in.

They're fun.

It's kind of like
watching the horses.

I was going to say,

it's like slow-motion
horse racing.

Yeah.

Kiss three, baby, kiss three.

Get up.

Now I think this is
significantly plummeting

to the ground.

That's a lot of drag.

That's going to give
it a nice...

It's still going
to slow it's fall.

Smarty pants!

With too much drag
and not enough lift,

the best it could do
in this position

is not much better
than parachuting.

A variation with the legs
tucked up under the body

isn't any better.

It could produce more lift
if it flew faster,

forcing more air over the wing.

But gliders can't generate
their own power.

Okay, so we're ready to try
a new posture, right?

He has it in almost like
a brooding...

The front wing doesn't provide
enough lift on its own,

so the hind limbs will have
to contribute somehow.

One possibility is to form
a second set of wings

with the leg feathers
straight back

and the foot feathers spread
horizontally,

something like
an old-fashioned biplane.

If we get it like this,

I mean, that's clearly
a second lifting surface.

It could be the only way
to get more wing area

without splaying the legs.

If it doesn't work,

Xu's dinosaur might not be much
of a flier after all.

Right, but the wing
is pushed forward.

Yeah, right?

But the force is going
to transfer...

But the early returns are good.

Almost at three already.

We're coming out
of the gate fast.

It looks like four wings
are better than two.

We may have a winner, then.

That's it!

Slow down...

This is actually

a fairly stable configuration.

I mean, this would be a...
a pretty good way to travel.

The biplane generates
enough additional lift

to produce a longer, slower,
more gradual descent,

but still not enough
to travel very far.

Moving the legs forward is worse

and causes the body
to pitch nose up.

If Microraptor were
a full-time glider,

it would need a way to extend
its range through the air.

I'm not sure, but this is
kind of a possibility...

Xu Xing has been holding back
so far,

but now he pitches
an idea of his own.

Positions to here.

It's a bit unorthodox

and takes a while to sink in.

Goes toward the tail.

But eventually,
they come around.

Well, why didn't
you say this earlier?

This is a very bright idea.

Let's see... this
would be a little...

Xu's idea is to extend the
legs almost straight back,

allowing the leg
and foot feathers

to form a canopy over the tail.

That's your hypothesis?

It's a possibility.

It's possible.

But that would not be
a lifting surface.

Boy, that's an interesting one.

This is it.

Let's see.

Once again, all eyes are
on the lift numbers.

Starting low.

1.12.

That canopy's not necessarily

a lifting surface.

I mean, you really have
to have an airfoil

to make it a lifting surface.

Get up.

I like the drag staying low.

Yeah.

If it did leap out of a tree,

that would be its initial
posture, right?

It would push off
with its hind feet...

And they'd be back there.

And they'd be behind.

So it would sort of dive,

and that would be
a diving maneuver.

3.42.

Now the lift starts to climb.

3.51!

Wow.

Almost close to 4.

That's amazing.

I'm... so, I take back
everything I said

about it not acting
like an airfoil.

It's acting like
an airfoil in the back.

This is the highest lift
and the lowest drag.

But I realized this.

I kept tellin' you this.

I know you did.

You win.

Congratulations!

All right!

Nice goin'!

Beautiful...
beautiful glide, huh?

It works!

Very nice, a beautiful glide.

It works in that position.

That's the off-the-branch
position.

That's fantastic!

I'm happy.

Yeah, you called it!

Xu's posture makes
for a long, fast glide.

But when it's time to stop,
it needs help,

and that could be
where the biplane comes in.

So if this animal
jumps off of a tree,

as it jumps, its legs
are already behind it.

It's able to dive, it's got
a nice glide ratio going.

And then when it gets
ready to land,

it can start bringing
its legs gradually forward

through those biplane
configurations.

And then as it brings its legs
all the way forward,

it's able to pitch up
and land on a tree.

So the ultimate glide story
is going to be this transition

from the legs all the way back
to the legs all the way forward,

which gets you very nicely
from the top of the tree

to the bottom of the next tree.

The experiment says that
Microraptor could glide

very well without splaying
its legs.

But does that mean flight
evolved from the trees down?

Microraptor belongs
to the clan of dinosaurs

that includes Deinonychus,

and it's close to the branching
point that leads to birds,

which means it might represent
the body plan

of the common ancestor
from which both lines evolved.

If so, then bird flight
probably did arise

from four-winged dinosaurs
gliding from the treetops,

and Deinonychus could be the
dinosaur version of an ostrich,

the flightless descendant
of a flying ancestor.

But if another dinosaur is found
to be even closer

to the branching point, and
it was not a four-winged glider,

then flight could
have evolved twice...

One line leading to birds
and another to Microraptor,

making four wings a side branch
on the tree of life.

This is not a ladder;
this is a bush with twigs

that branch out
in different directions.

And some of them are, in fact,
terminal buds.

Over millions of years
of evolution,

feathered dinosaurs could have
experimented with flight

in different ways, with
some becoming flightless again

and some going extinct.

And they all might have been
perfectly adequate.

This Microraptor may have been
a better flier

than an Archaeopteryx,
but for whatever reason,

they went extinct,
either by chance

or... or because they weren't
as good a flier.

When you look
at all these efforts

to make the early
flying machines,

there are some pretty weird-
looking contraptions in there.

But that same sort of thing
went on, you know,

in the evolution of biological
flight in dinosaurs.

If Microraptor proves
to be a dead end,

then all bets are off
on whether flight evolved

from the ground up
or the trees down.

We don't have a lot of other
fossils that can speak

to that question right now.

Microraptor is a fine candidate;

it's also one
of our only candidates.

Ken Dial may be right that young
birds show how it all began,

scrambling to safety
with their proto-wings.

Or more fossils like Microraptor

could prove Martin
and Burnham right

about flight evolving
from arboreal gliders,

though they'll need
more evidence than that

to persuade other scientists

that those gliders
were not dinosaurs.

This is a question
about the origin of flight,

not the origin of birds.

Those are separate issues.

We just have the dinosaurs
getting in trees first

or running off the ground first,
but they're still dinosaurs

that are doing this...
Feathered dinosaurs.

We still don't know exactly
how it happened.

But Microraptor is changing
the way people think

about the origin of flight.

Microraptor has thrown

our understanding into a new
and productive chaos.

It doesn't solve the problem,

it doesn't give us an answer,

but it gives us another way
of thinking about the data.

And I think eventually,

we are going to get
to some answers.

Microraptor is a creature
no one expected,

but we know only a tiny fraction

of the dinosaurs
that once lived.

More than 400,000 species
may have come and gone

in their 175-million-year
history.

To date, we've found only 1,100,

not counting the ones
that are still with us today,

long after the extinction
of their ancestors.

After the, you know,
asteroid hit,

65 million years ago,

the only dinosaurs that came out
of it are today's birds,

and they seem to have survived
it well enough.

There are 10,000 living
species...

Only about 4,000 mammals,

so it's still
the age of dinosaurs.

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