All language subtitles for NOVA S52E03 Dino Birds 1080p WEB h264-BAE_track3_[eng]

♪ ♪

NARRATOR:
Birds live across our
entire planet.

Around 50 billion of them

fill our skies, seas,
and landscapes.

Each of the 11,000 species
expertly adapted

for the environments
they inhabit.

But how did they come to
be such an evolutionary triumph?

The answer lies
with their ancestors.

Today's birds are dinosaurs.

They are every bit as
much of a dinosaur

as a T. rex is
or a Brontosaurus is.

NARRATOR:
But exactly how this spectacular
evolution took place,

is still somewhat a mystery.

Right now,
we have very little data.

I mean, that's how it is
with paleontology.

You have

hundreds of millions of years

and just a few fossils
scattered around the world.

NARRATOR:
Now, a new breed of scientist

is making spectacular
discoveries...

We scanned it.
And then what we found

was...
Whoa.

...a lot of skeleton

underneath the rock.

Holy cow!

NARRATOR:
...to fill in the gaps
of this evolutionary tale...

We thought it's just going to be
a simple thing.

They're like dinosaurs
or they're like birds.

And what we found is that,
they are like neither.

NARRATOR:
...and answer
one of paleontology's

biggest questions:

why were birds
the only dinosaurs

to survive
the asteroid impact

66 million years ago?

FIELD:
The development
of new technologies

has provided us
with a richer picture

of avian evolution than has
ever previously been possible.

NARRATOR:
"Dino Birds"--

right now, on "NOVA."
(animal screeching)

♪ ♪

(birds chirping)

♪ ♪

NARRATOR:
Birds are full of surprises.

They lay eggs like reptiles,

but have
warm blood like mammals.

Only birds have feathers

and it's one of their most
distinctive characteristics.

NARRATOR:
There are 11,000 species
across the globe,

dazzling in their variety--

size, shape and behavior.

We think
we know them well,

but beneath
those colorful feathers

lurks an enduring mystery.

Why are birds here?

Scientists have discovered

that they are the sole surviving
branch of the dinosaurs.

When an asteroid wiped out
nearly all animal life

66 million years ago,

birds somehow survived

while all other
dinosaurs disappeared.

Why?
Was it pure chance?

Or did they possess some special
advantage that set them apart?

♪ ♪

Now, new discoveries

in paleontology
and evolutionary biology

might finally
be providing answers.

♪ ♪

FIELD:
I think this is
going to be

a great place
to see some birds

GUILLERMO FERNANDEZ:
Oh, I agree.

NARRATOR:
Historically, it's fossils

that have
revealed the past to us.

But in the case of birds,

the record is patchy.

Their fossil remains

are notoriously rare
and fragile.

(bird screeches, wings flapping)
Hey, over there?

A Eurasian
griffon vulture.

(bird screeches)

FIELD:
So you've got...
two griffin vultures,

on top and then one below.

Oh, I can see it.
Yeah.

FIELD:
I think they're warming up
before they take off.

Do you see it
stretching its wings?

FERNANDEZ:
I think so, yeah!

I think that vulture
is about ready to go.

(bird screeches)

Oh, one just took off!
FERNANDEZ:
Oh wow, yeah.

One just took off!
Yeah!

FERNANDEZ: He's flying.
FIELD: Oh, Wow!

FERNANDEZ:
Beautiful.

FIELD: That is a huge bird!
FERNANDEZ: Beautiful.

FIELD:
Oh my goodness!

♪ ♪

This is such an
amazing place

to come bird watching.

But these birds are never

going to turn
into fossils, right?

It's not
the sort of environment

that is conducive
to fossil formation.

♪ ♪

The bird fossil record

is particularly sparse,

and that's
because birds are,

by their very nature,

fragile animals.

♪ ♪

And the very lightweight nature
of bird skeletons,

which tend to
be filled with air

to make them even lighter

as a specialization for flight,

and those are features

that tend to conspire against

their preservational potential

in the fossil record.

NARRATOR:
This left the story of
bird evolution

virtually unwritten for decades.

Barely a clue to tell us

where today's four main groups
of birds all came from.

But every now and then
fossils do appear,

and when that happens,

a new chapter of the story
is unlocked.

♪ ♪

One of the greatest of
these fossil finds

lies in the heart of London,

in the treasure room

of the
Natural History Museum.

FIELD (voiceover):
This is Archaeopteryx,

one of the most
amazing fossils in the world.

NARRATOR:
Found just two years after
Charles Darwin

published his ideas
of natural selection,

Archaeopteryx was one of

the many great 19th century
dinosaur discoveries.

Dinosaurs took over the Earth

some 220 million years ago,

evolving from
reptilian relatives.

They inherited from reptiles
the defining features

we associate
with dinosaurs today--

big claws, sharp teeth--

but with one
major difference.

Dinosaurs, whether
they walk on four legs or two,

have an upright stance--

their legs below their bodies.

In reptiles however,

the legs extend horizontally
from their bodies.

Over the 140 million years

that dinosaurs ruled the Earth,

countless species came and went.

The approximately
150 million-year-old

dino bird, Archaeopteryx,

has turned out to be
one of the most important

in the story
of bird evolution.

With the discovery
of Archaeopteryx

and some of
the first dinosaurs,

even then,
the earliest paleontologist

looked at these things
and are like

birds are dinosaurs.

I mean, the skeletal
similarity is enormous.

Archaeopteryx provides us
with an amazing glimpse

at a combination of features

that we expect to see
in living birds

in the present day--
like large feathered wings--

as well as
the kinds of features

that we associate with
dinosaurs:

like a long, bony tail,

jaws full of sharp,
pointy teeth

and strong claws.

NARRATOR:
It bore an uncanny resemblance

to a known dinosaur fossil.

♪ ♪

Hello, Dan!

Good morning Olivia!
Good to see you!

Should we go
look at some fossils?
Yeah, sure!

Great,
let's take a look!

♪ ♪

This is the skeleton
of Compsognathus,

which was a really important
theropod dinosaur

into the 19th century,

because it helped convince
Thomas Henry Huxley

that there might be
an evolutionary link

between birds,
like Archaeopteryx,

and theropod dinosaurs.

♪ ♪

NARRATOR:
Compsognathus and Archaeopteryx

have some surprising
similarities.

They would both have

walked on two legs,

had long arms,
long bony tails,

and teeth.

♪ ♪

Features that convinced Huxley

that birds were likely
descended from dinosaurs,

a controversial theory
in the 19th century.

This idea was rejected
for 100 years,

uh, primarily because dinosaurs
did not preserve;

or no known
dinosaur at the time

had a fossilized furcula--
that's the wishbone.

But then,
you know, in the '70s

the first dinosaur wishbone
was found.

♪ ♪

NARRATOR:
The discovery of dinosaurs
with wishbones--

a feature previously
only found in birds--

sealed the deal.

And we now recognize
without a doubt

that Compsognathus,
Archaeopteryx,

and modern bird

all belong to
theropod dinosaur,

the group of three-toed,

meat-eating dinosaurs
like T. rex.

NARRATOR:
Despite this evolutionary link,

there are still mysteries.

Creatures
with early feathers

that don't look
like modern birds,

and archaic birds--
ancient species,

whose evolutionary lines
are now extinct--

that have bird-like beaks,
but filled with teeth.

But when was the moment
one evolved into the other

when modern birds
first appeared?

How did dinosaurs take flight?

And why did some birds survive

when all other dinosaurs
died out?

♪ ♪

Today, new discoveries are
revealing important new clues.

FIELD:
It's an amazing time
to be studying bird evolution.

NARRATOR:
On the border of
the Netherlands and Belgium,

quarry excavations
have revealed the world

as it was 67 million years ago,

not long before
an asteroid killed off

75% of animal species
on Earth.

Welcome to the very last days
of the dinosaur era.

This is it.

JAGT:
So what we see here was
basically what was deposited

in a shallow sea, quite warm,

during the last days
of the era of dinosaurs.

We can really compare this

with the Caribbean

or the Indonesian Archipelago
these days.

FIELD: Sounds good.
JAGT: Yeah.

FIELD:
It's a good place for vacation.

NARRATOR:
These shallow seas
provide the perfect conditions

for fossilization to occur;

a wet environment where sand
and mud cover remains quickly.

Waters filled with
hungry mosasaurs

whose fossils would
come to light,

millions of years later.

FIELD:
So this begins somewhere
in the range

of about 67 million years?

JAGT:
67 and a half,
something like that,

and then going up.

NARRATOR:
These layers of rock protected

one of the most incredible
bird fossils ever found;

a chance discovery made
by an amateur fossil hunter

in the year 2000.

This is the level that produced
both bird fossils.
Right.

I think it's time
to unwrap the birds.

All right.
And here it is.

This is
the only known specimen

of Asteriornis maastrichtensis.

I still remember

what my first impression

of this fossil was like,

when I looked at it, uh...

(chuckles) and it wasn't
a very positive impression.

NARRATOR:
It wasn't until 18 years
after its discovery,

that Daniel Field
began studying the specimen.

FIELD:
This fossil clearly preserves

a few bird bones.

And those bird bones
are not well preserved.

You can see there's
a broken thigh bone on top

and there's a broken
shinbone underneath.

But these are clearly
the bones of birds.

And so even though
the fossil didn't look

very... beautiful at first,

we thought maybe it
would tell us something

about what birds were like

just before the asteroid
wiped out

the giant bird cousins,
the large dinosaurs.

NARRATOR:
Using a CT scanner,

Daniel and his team
were able to digitally remove

the rock, and reveal
what secrets it held within.

What he saw exceeded his
wildest dreams.

♪ ♪

FIELD:
When we removed

the low-density rock and saw
this skull staring back at us,

my PhD student Juan and I
could not believe our eyes.

It was a shock.
It was really exciting.

And we realized immediately
that this fossil was going to be

very important because
it could provide us

with information that no other
fossil ever discovered could.

It was very exciting and,

and one of the most exciting
moments of my scientific career.

NARRATOR:
This specimen
provides a portrait of a bird

that lived 66.7 million
years ago.

This fossil is extraordinary
because it shows

several features that tell us

that it is a member
of the modern bird group.

And the most obvious
of those features is the fact

that it does not have any teeth.

NARRATOR:
The remains of
ancient archaic birds

have beaks filled with teeth.

Losing them was a key stage
in the evolution

of dinosaurs into modern birds.

And the fact that this
fossil has a beak very similar,

uh, similar to living
generalist birds

suggests that it probably would
have been happy

eating almost anything
it could find.

NARRATOR:
Just like birds with
similar beak shapes do today.

FIELD:
In addition to that,

if you look at the leg bones
of this fossil,

they're relatively narrow

and relatively long,

and those
are features that we associate

with predominantly living on
the ground in the present day.

NARRATOR:
Around seven or eight inches
tall, with the beak of a chicken

and the head of a duck,

this creature is
one of the oldest

modern birds
ever to be unearthed.

Scientists named the 67 million-
year-old species Asteriornis

after Asteria, the Greek Titan
goddess of falling stars.

It confirms
that modern birds existed

alongside the dinosaurs
before their extinction.

This small bird bears
witness to a world

prowled by T. rex
and Triceratops.

Neither the largest
nor the most dominant,

its omnivorous feeding habits
mean that it's satisfied

with small shellfish and seeds.

It might also
scavenge leftovers;

perhaps even
a washed-up Mosasaur carcass.

(birds screeching)

With its toothless beak
and variety of food options,

Asteriornis is well-equipped
to survive

in the realm of the dinosaurs.

But with such evolved features,

it's unlikely that it was
the first modern bird.

♪ ♪

At Rockefeller University
in New York,

Erich Jarvis and his team

are taking a different tactic
to find the beginning

of today's birds,

using modern DNA to map
their evolutionary past.

JARVIS:
The way we dated
the origin of modern birds

is we took the genome
scale tree,

which is the alignment of DNA

from one species to another.

NARRATOR:
This reveals the genetic code

for certain traits
in modern birds

that they can then look for
in ancient fossils.

Then we took fossil data

that's been collected
from all around the world

and placed those fossil dates
on the tree for like 20 species.

NARRATOR:
This tree allows Erich
to see exactly where

different species of living
bird genetically diverged.

But what the team really
wants to find out

is when these divergences
took place.

What does DNA suggest about when

modern birds first appeared?

JARVIS:
You look at mutations that
occurred over time.

And from those mutations,

you can get what's called
the molecular clock.

How much time do you need
to have one mutations,

two, three, four, five?

NARRATOR:
By estimating
this rate of mutation,

Erich wound back the clock
and put a timestamp

on when certain
characteristics changed.

JARVIS:
So from the combination
of this molecular clock,

the tree structure,
and the fossil evidence,

all three of those combined,

we can date when modern birds
originally formed.

And that was
90 million years ago.

NARRATOR:
Fossils confirm
that modern birds

and their giant dinosaur cousins
co-existed,

and DNA indicates this
wasn't a short-term arrangement.

They lived alongside one another
for some 25 million years,

perhaps even longer.

And new research is showing
just how similar

the lives of ancient birds
would have been to birds today.

LIDA (translated):
This is the most complete

and best-preserved oviraptor

embryo skeleton in history.

NARRATOR:
This is the egg of a type
of dinosaur that lived in Asia

70 million years ago.

(translated):
They were arranged in a circle.

For some reason,

perhaps because floodwater
covered the entire nest

in sand, they died quietly
in this way.

STEVE BRUSATTE:
And it looks like it was
fossilized

right before
it would have hatched.

So in looking at this fossil,

we are glimpsing
the last moments

of a dinosaur's development
in the egg

before it would greet the world.

What we're seeing
with this fossil

is that these dinosaurs would
have developed in their eggs

and hatched from their eggs
just like birds do today.

♪ ♪

NARRATOR:
It's the remains of embryonic
dinosaurs and their shells

that have helped scientists
answer

one of the great questions

surrounding bird evolution.

Of all animals alive today,

there are only two groups
of animals

that are warm-blooded:
mammals and birds.

NARRATOR:
It's a key feature of
what makes flight possible.

You have more energy available
that allows you

to be more active,

which allows you to move
greater distances.

NARRATOR:
Dinosaurs were first assumed
to have cold blood.

O'CONNOR:
And so

we are very interested
in knowing

when this warm-bloodedness
evolved in birds.

♪ ♪

NARRATOR:
Scientists have been
investigating

the question for decades.

And recently, key evidence
came from dinosaur eggshells.

That eggshell formed within

the body
of the mother dinosaur.

NARRATOR:
Geochemist Robin Dawson
analyzed minerals

in the fossilized shells

to reveal what temperature
they formed at--

in other words,
the mother's body temperature.

DAWSON:
We looked at eggshell

from the major clades
of dinosaurs.

Major groups have body
temperatures that are warmer

than their environment,
which suggests to us

that they actually
had the capability

to have a high metabolism,
raise their body temperature

above their environment,

like their warm-blooded
relatives,

like living birds.

O'CONNOR:
For sure,

dinosaurs were warm-blooded,

but actually some dinosaurs,
like Stegosaurs

and duck-billed dinosaurs,

actually secondarily evolved
to be cold-blooded,

which I think why we were having
difficulty deciding

if dinosaurs
were warm-blooded or not,

because, you know,
there was a conflicting signal.

NARRATOR:
With warm blood, dinosaurs would
have a lot of energy to expend,

raising interesting questions.

Like, would
they have had enough energy

for a high-intensity
activity like flight?

It's the most physically
demanding form

of vertebrate locomotion.

So you have to be warm-blooded.

NARRATOR:
But even if their metabolism
supported flight,

what about the equipment,
like wings and feathers?

For 20 years
this was the only snag

in the dinosaur-bird
evolution theory.

Where did feathers come from?

♪ ♪

In Liaoning, China,

the subsoil of the Chaoyang Bird
Fossil National Geopark

reveals a dinosaur world
that existed

between 112 and 132 million
years ago.

♪ ♪

Buried under volcanic ash,

the fossils are
spectacularly preserved.

The most famous are housed
in a vast building.

A long, winding walkway hangs
above the geological layers

and the fossils they contain.

(man speaking Mandarin)

MAN (translated):
We've discovered many
microraptors here,

as well as birds like
Confuciusornis.

NARRATOR:
But it's not just the sheer
number of fossils found here.

It's what they've
revealed to the world.

(speaking Mandarin)

(translated):
You can see that
the microraptor found here

has feathers.

NARRATOR:
Feathers--

a discovery that has
revolutionized

the world of paleontology.

Because a microraptor
is not a dino-bird,

but still a dinosaur--
a non-avian theropod.

In the '90s, with the discovery
of feathered dinosaurs,

I mean, it was one of the most
compelling arguments

for the "birds are dinosaurs"
hypothesis.

BRUSATTE:
The discoveries kept coming.

And now there are thousands

of feathered dinosaur fossils
that are known.

And it wasn't only small ones.

NARRATOR:
More than 100 years
after a link was first made,

birds were finally confirmed
as part of the dinosaur lineage.

And scientists
were one step closer

to understanding
the origins of flight.

But if anything,
this discovery raised

as many questions
as it answered.

Why did dinosaurs develop
feathers in the first place?

What advantage did they provide?

♪ ♪

Paleontologist Xu Xing,

from the Institute of
Vertebrates and Paleontology

in Beijing, discovered
the fossil of a dinosaur

with the answer-- Yutyrannus.

(Xu Xing speaking Mandarin)

XU (translated):
Its body is about the size

of the famous T. Rex.

It was almost nine meters long
and weighed almost 1.5 tons.

So we're talking about a giant.

♪ ♪

NARRATOR:
Approximately
125 million years old,

this is one of the oldest
fossils that shows

non-flying dinosaurs
with feathers.

(translated):
Here are
Yutyrannus's feathers,

You can see their length
on these blocks of sediment.

We can see that Yutyrannus' body
was covered in feathers,

from head to tail.

♪ ♪

NARRATOR:
But they don't look anything
like bird feathers we see today.

They appear
to be more like hair.

(Xu Xing speaking Mandarin)

(translated):
The most likely
hypothesis

is that there was
a cold spell

at the beginning of the
Cretaceous period.

Yutyrannus is, in a way,
the woolly mammoth of that time,

with long, fine feathers
that meant it could keep warm.

NARRATOR:
Acting almost like down,

it's been nicknamed by
scientists "dinofuzz."

A stark contrast to
the feathers of flying dinosaurs

like Archaeopteryx
and most modern-day birds.

But with a wealth of
feathered dinosaur fossils

found in just a few years,
scientists have pieced together

a timeline of feather evolution.

The earliest
feathered dinosaurs,

like Yutyrannus,
had straight feathers.

In the next generation
of dinosaurs,

these long hairs separated,
producing simple branches.

In many lineages,
this down then evolved

into more complex feathers
with a central spine,

barbs, and then barbules fitted
with small hooks

holding them together
to form a sail,

a more familiar
symmetrical feather.

But only asymmetric feathers

shaped more like
an airplane wing

are capable of creating pressure
differences, and therefore lift,

allowing for flapping flight
over long distances.

We know the changes
that took place,

but the question remains--
why did they happen and when?

Fossils from Liaoning
once again provide clues,

suggesting that the ancient
bird species Confuciusornis

had another use
for its feathers.

Confuciusornis
is a really special bird.

It's represented by
more than a thousand specimens.

And some of them are
exquisitely preserved.

♪ ♪

NARRATOR:
With so many fossils
of this kind of bird,

researchers around the world
have come together to work on

this project.

BAILLEUL (translated):
We realized
that there were two types

of specimen within
this species-- some with

very long tail feathers

and others with very short
tail feathers.

So we asked ourselves, "Why?"

CHINSAMY-TURAN:
So people postulated

that one of the morphs
was a male

and the other one was a female,

but it couldn't really
be very sure about it.

NARRATOR:
Paleontologist Anusuya Chinsamy-
Turan looked inside the bone,

taking a
less-than-millimeter-thick slice

to search for answers.

And one of the first specimens
I sectioned

actually happened to be one

that had the most
unusual bone tissue

inside its marrow cavity,
which we call medullary bone.

NARRATOR:
That's the brown area
on this slide.

And medullary bone
is so interesting

because you only find it
in female birds.

And they form it at the time
that they're ovulating

and they use that medullary bone
to calcify the egg shells.

So when I found this,
I said, "Oh, my goodness."

I didn't know which specimen
it had come from

because I only had
the little bits of bone.

And so I contacted
my colleague and I said,

"Can you double check
the specimen number

and see whether the specimen
has long tails or no tail?"

And he came
back to me and he said,

"Actually, the specimen
doesn't have any feathers."

So we could say for sure this
was a female Confuciusornis.

NARRATOR:
That meant the long tail
feathers

belonged to male Confuciusornis.

Not needed to aid their flight,

the feathers likely
served a different purpose.

In these marshy
landscapes of northeast China

120 million years ago,
it's mating season.

Confuciusornis females
have a lot of options.

And the males have to redouble
their efforts to attract them.

Competition is fierce

as they use their
spectacular tail feathers

to attract the best mate.

Ornamentation in dinosaurs
potentially led to feathers

that eventually
supported powered flight.

Then the hypothesis is
that you already have

these aerofoils,
these surface areas.

And so even though
their primary function

was ornamentation,

they must have had some
incipient locomotor function.

Even though they can't fly,

they still use their wings for
their terrestrial locomotion.

And then, eventually,
as these wings evolve

to be bigger and bigger
and have greater

and greater aerodynamic benefit,

they eventually reach a point
where they can be used

for powered flight.

NARRATOR:
Today, bird flight
is spectacularly complex.

They soar with ease.

But the transition

from a ground-based life to one
in the skies

would not have been an easy one.

It's something
that scientists are still

trying to understand.

Which of the newly-found
feathered,

and sometimes winged,
dinosaurs could fly?

(cawing)

How did they take
that glorious first leap?

Surprisingly, the oldest missing
puzzle piece,

collected over a century ago,
Archaeopteryx,

is still filling in gaps today.

In a synchrotron particle
accelerator

larger than two football fields,

scientists are
analyzing this precious fossil.

VINCENT FERNANDEZ (translated):
The synchrotron beam comes in
through that little window.

It will interact with
our object,

in this case a fossil,
and the images

are recorded by our detectors.

NARRATOR:
They fire a beam of X-rays

more than a million
times brighter

than the sun at the fossil.

FERNANDEZ (translated):
Because the synchrotron beam
is very intense,

we can get a signal
strong enough

to penetrate the entire width
of the plate

and virtually extract
the fossil from the rock.

NARRATOR:
This creates a 3D model
with resolution

down to one-thousandth

of the thickness of a hair.

VOETEN:
When we first saw the images,

we immediately realized that

the bone walls

of the humerus and the ulna

of Archaeopteryx look a lot
like those of flying birds.

NARRATOR:
The bone walls
are thin and hollow,

just like those of modern birds.

VOETEN:
That was our first indication

that Archaeopteryx
must indeed have flown.

NARRATOR:
As far back as
150 million years ago,

dinosaurs' ornamental "wings"

are already evolving
for gliding.

♪ ♪

To fly, Archaeopteryx
has to project itself

from a high point.

It uses its clawed fingers
to climb.

From its high vantage point,

it can spot its prey
very easily, and pounce on them

simply by spreading its wings.

But to truly conquer the skies,

gliding birds needed to learn
to flap.

There are several ideas
of how this happened.

The first, known as

the "tree-down" hypothesis,
suggests that

tree-dwelling birds flapped
their wings

to cushion their landing.

The second, known as

the "ground-up" hypothesis,
emphasizes the use

of wing flapping associated
with running

to escape danger
or catch up with prey.

(dinosaur calling)

But recently, another theory
has been suggested,

one that can be seen
in birds today.

♪ ♪

ASHELY HEERS:
So these are our
performers today.

This is Olympia in gray here,

this is Annie in brown,

and this is Twinkle Jemima,
or Twinky, for short.

NARRATOR:
To analyze the movement
of the wings in detail,

evolutionary biologist
Ashley Heers

needs to see them
in slow motion.

HEERS:
Here I've got my
high-speed video camera,

and I can visualize what the
camera is seeing on the laptop.

(birds squawking)

And so you can see that
she's really using her wings

to brake as
she gets ready to land there.

(voiceover):
I actually spend
a lot of my time

working with developing birds,
or baby birds,

because they can also
tell us a lot

about the evolution
of flight.

that we see that are documenting
this origin of flight.

And so,
in these developing birds,

we have this really
interesting system

where we can see in real time
how a living animal

goes from a flightless animal
to a flight-capable animal

and everything that happens
in between,

both anatomically
and behaviorally.

NARRATOR:
One of the behaviors seen

is wing-assisted running

on an inclined plane.

HEERS:
So on the left here,

we have a four-day
old chukar partridge.

It is flapping its wings

to really drive itself into
the substrate here

and increase traction with
its feet,

so that it can
ascend this steep incline.

NARRATOR:
This is not the only behavior

that hints that dinosaurs were
able to develop flapping flight.

HEERS:
They may use their wings
to leap into the air and fly,

either for a
very short distance,

or for thousands of miles.

They also use their wings
to come down out of trees

or off of elevated surfaces,

even to swim,
either across the water

or below the water.

And so living birds
show us that, you know,

they use lots
of different habitats

and they use their wings
for lots of different functions.

NARRATOR:
Bird flight developed

as an adaptation
to the environment,

as well as to allow
gliding down from trees

or to evade predators on land.

But what exactly was

this great environmental change?

And when did it allow birds
to take the final leap

to full flight?

♪ ♪

One site in particular
can transport us

back to a time when birds
were taking to the skies.

FIELD:
It's amazing to be driving
to Las Hoyas,

one of the world's
most important

early Cretaceous
fossil sites,

with some of the most important
early evidence

♪ ♪

NARRATOR:
After 30 years of excavations,

an entire prehistoric
landscape has been uncovered.

(translated): We're in what was
once a wetland,

where there is an enormous
diversity

And we know that this wetland
was freshwater

because it was completely
isolated from the sea.

NARRATOR:
Paleontologist Jesús Marugán
and his team

have uncovered a vast array
of plants, animals

and insects,

all part of a complex
and thriving ecosystem.

Digs here have revealed
thousands of fossils,

all between
125 and 129 million years old.

(dinosaur roaring)

MARUGÁN (in English):
You see all those crabs
and small crayfish?

FIELD:
Ah, each one of those blue marks
represent a crayfish!

MARUGÁN:
Yeah.

FIELD:
Amazing how many they are.

MARUGÁN:
It's more than 500.

We have the whole family,
from the larvae--

see how small they are?
Yeah.

To the juveniles,
to the adults.

Yeah, okay.
See, with all
the pincers and everything?

Yes, that's crazy!

You can really
tell they're crayfish!

NARRATOR:
To process this
huge amount of data,

Jesús is combining
traditional observation

with the very latest technology.

(Marugán speaking Spanish)

MARUGÁN (translated):
Smile for the camera!

NARRATOR:
They use a drone
to photograph the site

and geotags to help recreate

a 3D model of the environment.

Each colored sphere represents
a species or family of species.

The connections between these
spheres indicate interactions.

(speaking Spanish)

(translated):
The birds of Las Hoyas are found
here in this orange section;

the largest ecosystem.

It tells us that the birds were
not just passing through.

They were an integral part
of this ecosystem.

♪ ♪

NARRATOR:
Given the rarity
of bird fossils,

the sheer number found suggests
that birds were thriving here.

But that's not all.

These fossils paint
a picture of archaic birds

that are adapting
to geologic change.

Around 175 million years ago,

the super-continent
known as Pangea broke up.

New continents emerged

and oceans and seas rushed in
through the fault lines.

These new territories,
with their temperate climate,

gave rise to flowering plants,

which provided
a new food source.

BRUSATTE:
Those plants diversified,

all kinds of insects diversified
alongside them,

to pollinate the flowers.

And so birds were probably
part of this

general diversification of life
that started with plants

and bugs and reached all the way
to the dinosaurs.

NARRATOR:
Las Hoyas shows archaic birds
evolving right before our eyes,

and a class of ancient bird

called the Enantiornithes
is a perfect example.

Wow, so this is
Eoalulavis.

That's it, the original.

A beautifully preserved
skeleton.

You can see all the bones
of the forelimbs.

NARRATOR:
Eoalulavis is one
of these Enantiornithes,

and it's exceptional
in more ways than one.

In particular, it has developed
a highly sophisticated wing.

FIELD:
Eoalulavis.

This complicated name
has some important connotations.

FERNANDEZ:
Yeah, exactly.

These fossil bird, back in
the day when he was described,

was the first primitive bird

that preserved the alula.

NARRATOR:
The alula is a small mini-wing

on the leading edge
of the main wing.

It allows the bird
to increase lift at will.

This appendage gives the bird

great maneuverability in flight,
and for take-off and landing.

FIELD:
It's incredible that

this alula,
which of course

helps birds be more
maneuverable in flight,

was present in Eoalulavis,

because this fossil
is 129 million years old.
Yeah.

So that, of course,
tells us that

this structure has been around
in bird evolutionary history

for at least that long.

NARRATOR:
Thanks to this dexterity
in flight,

Eoalulavis is better able
to spot its prey

and swoop down upon them.

This is not the case

for all winged creatures
that populate the Eden

of Las Hoyas.

Europejara,
a gigantic pterosaur

with a wingspan of two meters,
needs plenty of space

on the ground to take off
and land.

And when danger strikes,
that can be the difference

between life and death.

(dinosaur roaring)

JARVIS:
We call this
convergent evolution.

Each time flying evolved
in animals--

whether it be birds, bats,

ancient flying dinosaurs--

the wings evolved in the
upper limb on either side,

not one on the head,

one on the tail
or the foot or whatever.

They evolved using
the upper limbs for flight.

NARRATOR:
In this world
130 million years ago,

dinosaurs, flying reptiles,
archaic birds

and ancestors
of early modern birds

all shared the skies together.

This was bird life at its peak.

A plethora of archaic species
living in trees,

perfectly adapted
to their environments.

Birds were
taking over the skies.

But it wasn't to last.

A cataclysmic event
shook the planet.

(whooshing)

A gigantic asteroid
six miles in diameter

collided violently with Earth.

(explosion)

Forests burned and volcanic
ash soon filled the skies,

blocking out the sun.

This was an extreme
survival situation,

one that 75% of Earth's species
weren't ready for.

(dinosaur calling)

Among the mammals,
the smallest,

some weighing less than
one pound,

managed to escape the
catastrophe,

as well as some reptiles
like turtles and crocodiles.

Birds were also hit hard.

Only the smallest,

such as Asterionis,
survived the chaos.

How is it that all but one
group of birds were wiped out?

What did they have
that no other archaic bird

and no other dinosaur had?

Janavis is a bird
that did not make it.

Its fossil dates back
67 million years,

to a time just before

the asteroid hit.

Close analysis is
helping us to better understand

the reasons
for its disappearance.

JUAN BENITO MORENO:
Here you can see this skeleton
of Janavis.

We have some of the bones,
particularly the arm bones

and part of
the vertebral column.

NARRATOR:
Equipped with teeth,
Janavis has an imposing stature.

Is this why it didn't
survive the asteroid strike?

The key difference between
Janavis and Asteriornis is size.

Asteriornis is much smaller,

a trait that was key
to its survival

post-asteroid strike.

So larger bodied animals,

through this
mass extinction event,

didn't do very well at all.

So a really
big bird like Janavis,

probably would have been
at a major disadvantage

compared to Asteriornis.

After the extinction event,

getting a meal for an
animal the size of Janavis

probably would not have
been a very easy thing to do.

MORENO:
They also had
very different ecologies.

That's true.
Janavis was basically
a sea bird.

Like one would have been fishing
and eating fish and squid.

Mm-hmm.
Asteriornis was more like
a generalist,

ground-dwelling bird eating
whatever he found at the beach.
Mm-hmm.

NARRATOR:
With the trees gone,

a large number of tree dwelling
birds could not survive.

Instead it was ground-dwellers
like Asteriornis

that held the advantage.

(fire crackling)

Archaic birds,
although more numerous,

were devastated by the asteroid.

Their ecosystems were destroyed.

In this hostile environment,
their imposing size,

life in the trees
and specialized diets

led to their extinction.

Only modern ground-nesting
birds,

with more flexible diets,

were resilient enough to survive
a decimated landscape.

The sun starts to shine again,
the dust has cleared,

and it illuminates
a world that's devastated,

a world that's almost empty.

There's no T. rexes anymore,
no Triceratopses anymore.

Most of the other birds
were gone as well.

And so, this would have been
a world of abundant opportunity,

open frontiers.

NARRATOR:
In the million years
that follow this apocalypse,

new ecosystems emerge.

Out of the ashes of the dinosaur
world, plant life re-appears.

And a whole system
of coevolution,

between flora and fauna erupts.

With little competition,

the surviving birds enjoy
unprecedented

evolutionary success.

JARVIS:
Those few survivors
then exploded

into new species
with the opening up

of new environments to become

most of the
10,000 species we see today.

♪ ♪

NARRATOR:
A site in Denmark bears witness

to this key moment in
bird evolution.

On an inland island to the north
of the Jutland peninsula

lies a geological formation

dating back 55 million years.

Made up of more

than 180 layers
of marine deposits

and volcanic ash,

these mineral strata form
the cliffs

of the small island of Fur.

Hundreds of bird fossils
have been unearthed

in this geological jumble.

Many of them are birds related
to today's cranes and rails.

They show that birds had begun
to thrive once more,

at least on the ground.

But were birds
back in the trees by this time?

To understand that,
we need to find birds

with more complex feet,

specialized for grasping
and perching in trees.

NARRATOR:
There is one that indicates

this change in behavior.

This one actually
looks very interesting,

and it seems like
it's got a more complex foot

that might be
specialized for grasping.

So it's not like
a modern perching birds foot

where you have
one, two, three forward

and one backwards.

It looks like
it's probably got two toes

pointing forwards,
and two pointing backwards.

And that is the condition

that you see in a few
modern groups of birds,

including woodpeckers,
parrots, and cuckoos.

The fact that this bird
seems to show pretty clear

specializations
for perching in trees,

tells us that
by 55 million years ago,

this lineage of birds was
probably already experimenting

with a tree-dwelling lifestyle.

NARRATOR:
Ten million years after

the asteroid hit,

the surviving modern birds
have diversified.

New species have appeared.

They have adapted
to colonize trees once more.

They diversified like crazy.

(birds cawing)

And most of
the birds we know today,

everything from ostriches

to emus to hawks to

hummingbirds to owls,
to songbirds

and everything in between

emerged during those
manic years,

decades, centuries, millennia,

after the asteroid
impact cleared the deck.

NARRATOR:
In certain regions
of this reborn world,

and because of
their geographical isolation,

some small surviving birds
grow impressively large.

Reaching gigantic proportions,

they evoke the ghosts
of carnivorous theropods.

One in particular appears
to be especially intimidating.

♪ ♪

The huge bird, named Gastornis,

was discovered in the
Paris basin

in 1855.

It was so big, people assumed
it was a fierce predator.

But was it?

If so, why doesn't
it rule the roost today?

(translated):
The reason we wanted
to do this research

was that in the '90s,

two American studies came

to two diametrically-opposed
conclusions,

one team said
it was herbivorous,

and the other team said
it was carnivorous.

With the advancements
of paleontological tools,

we thought we'd finally be able

to answer this
question definitively.

NARRATOR:
After crushing
the fossil Gastornis bones,

Paleornithologist Delphine Angst
extracted carbon-13

so that it could be measured
using a mass spectrometer.

We quite literally
are what we eat,

and levels of
carbon-13 correspond

to the amount, or lack of,
protein in our diets.

ANGST (translated):
That's it, everything's weighed,

we can start the manipulation.

ARNAUD (translated):
Great, the spectro is up
and running,

so we're ready to go.
ANGST (translated):
Perfect.

The carbon-13 analysis
of the Gastornis bones showed us

without any ambiguity
that it was clearly a herbivore.

Combined with other results
we already had,

it showed us that Gastornis

was 100% a herbivore,

and there's no possible doubt
about it.

NARRATOR:
Gastornis was
a peaceful herbivore.

It didn't run, but walked.

Despite being nearly
seven feet tall

and weighing
more than 400 pounds,

it was
not a terrifying predator.

ANGST (translated):
It disappointed a lot of people
that were sad

that the image of Gastornis
chasing little horses

through the forest was wrong.

My husband's still mad.

NARRATOR:
For several million years,

it walked its clumsy way
across Europe and North America.

But as with any great story,

the fate of birds
was to change again.

40 million years ago,
the continents collided,

allowing species
to move into new landscapes.

Previously isolated territories
were populated by new arrivals,

including newly evolved,
predatory mammals;

a terrible threat to
the peaceful giant Gastornis.

(leaves rustling)

Faced with
these faster creatures,

and despite their imposing size,

these large birds are not
sufficiently armed to compete.

They are doomed to extinction.

A recent discovery indicates

that other giant birds suffered
the same fate as Gastornis.

Found in New Zealand,

Kumimanu was a giant penguin,
as revealed by

its flipper bones.

You can see
here a Humboldt penguin.

That's your average-sized
penguin today.

An Emperor penguin,

which is the largest species
alive today.

And then this
behemoth here is Kumimanu.

So it's quite
an impressive bird.

By looking at the proportions,
the thickness, the length,

the width of this specimen,
we can estimate the body size.

And so we believe
Kumimanu probably weighed

about 150 kilograms.

NARRATOR:
That's 330 pounds.

In the first 15 million years
after the asteroid hit,

birds are triumphant.

They reclaim the reborn forests

and become rulers
of the skies and seas.

However, many of the giants,

like the colossal penguin
and the giant Gastornis,

eventually disappear.

Competition with mammals
is sounding the death knell

for these great birds.

Resistant to the
many climatic changes

that the Earth would
subsequently undergo,

today there are four groups
of birds.

JARVIS:
Land, higher-land birds,

waterbirds, the group that
includes the Columbiformes,

that's pigeons and so forth,

and flamingos and a group that
includes the hummingbirds.

NARRATOR:
And one subgroup in particular

has achieved astonishing
evolutionary success

in recent times.

This is the great family
of passerines.

Nesting in our towns,
parks and gardens,

passerines are
part of our daily lives.

Singing birds
that perch in trees,

they demonstrate
extraordinary adaptability.

Contrary to the saying,

sparrows' brains
are actually quite powerful.

FIELD:
Pretty good diversity
of birds around, Lizzie.

Yeah, I think most of them
are probably passerines.

Yeah, that makes sense,
I guess passerines

are the most diverse group
of birds in the world, right?

STEELL:
Mm-hm.

FIELD:
How many species are there?

STEELL:
There are more than 6,000,

which is more than half of
living bird diversity today.

FIELD:
That's a great view

of Eurasian magpie up there.

Yeah, that's a really nice
representative

of a big group of
passerine birds called Corvides.

FIELD:
And Corvids in general, I guess,
are probably most famous

for having some of
the very largest brains,

compared to body size,

of all birds.

So these are things like
crows, jays, ravens

and magpies just like this one,

which make them some of the most
intelligent birds in the world.

So it's easy to think about
magpies and their relatives

as the hominids
of the bird world.

They're the smart ones.
Exactly.

NARRATOR:
Passerine intelligence is
illustrated by their behavior:

the construction of their nests,
their exceptional memory,

and their ability
to communicate through song.

A skill
they share with us humans,

despite our evolutionary paths

diverging some
300 million years ago.

Something happened in nature
to get this convergence

to be similar between humans
and these modern birds.

So what we and others had found

is that in our forebrain area

evolved this new circuit,

and that circuit evolved
in a similar way

with a direct connection

to the voice circuit in
songbirds, humans,

parrots, and hummingbirds.

Why only these few species?

If you evolve vocal learning,

you're more likely to be eaten,

and you won't survive.

Only if you're at
the top of the food chain

or near the top of
the food chain, you can.

We found that songbirds
and parrots evolved

from apex predators.

(birds cawing)

NARRATOR:
Birds are beautiful examples

of evolution's power
to create variety.

Today, there
are more species of birds

than there are mammals or any
other terrestrial vertebrates.

They thrive around the world,

perfectly adapted

to the tremendous diversity
of environments and landscapes.

Birds are incredibly successful
today.

And I think it is
a really neat fact of life

that there are double the number
of bird species

than mammal species.

And by that measure, the age of
dinosaurs still continues today.

NARRATOR:
Long live the dinosaurs.

♪ ♪

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