Original subtitles

♪

MAN: I was taken out to this site

in the middle of the desert.

I had no idea what awaited me.

And then I saw them, and I just started crying.

NARRATOR: These trackways in the Arabian Desert

are footprints in time.

They were made seven million years ago

by prehistoric elephants.

They take us back to a bygone world

and its vanished creatures.

How did elephants from so long ago

give rise to the magnificent animals we know today?

How did any of the animals in this African landscape

become what they are?

For generations, it was a mystery.

Now scientists are revealing the answers...

WOMAN: You can see the exceptional preservation

of soft tissues.

NARRATOR: ...piecing together an epic story.

Fossils are the key.

MAN: Fossils are the messengers of the past.

I believe that.

MAN: Imagine I'm taking you on a safari,

but a safari back in time.

You'll be confronted with these magical creatures,

a slice of Africa that is now gone.

NARRATOR: This film unlocks the evolution

of four of the world's most spectacular creatures--

crocodiles,

birds,

whales...

[whale singing]

[roars]

and elephants.

Like every animal alive today, they have a deep time history,

a lineage full of twists and turns,

shaped by strange ancestors from long ago--

bizarre ancient crocs...

MAN: This thing was built like a greyhound.

NARRATOR: ...feathered dinosaurs...

WOMAN: Dinosaurs never went extinct.

In fact, birds are dinosaurs.

NARRATOR: ...a whale ancestor that lived on land.

MAN: It more looks like a dog with a long snout.

NARRATOR: With new tools at their fingertips,

researchers are filling in the gaps in the story of life,

charting the rise and fall of ancient animals,

revealing why some died out while others survived.

MAN: How did these ancient worlds flourish,

and why did they disappear?

So, this is to me, really sort of the ultimate story.

NARRATOR: It's not just a story about the past.

It tells us about the world today, its creatures,

and what they may be facing in the future.

WOMAN: There used to be dozens of species of elephants,

and now there are just three.

And if we're not careful, we will lose them as well,

and that will be the end of the lineage of elephants.

NARRATOR: It's a story millions of years in the making,

of lost creatures rediscovered

and the surprising lessons of deep time.

♪

♪

♪

Madagascar,

250 miles off the coast of Africa.

This island is a perfect laboratory

for the study of evolutionary change.

Isolated here for millions of years,

species have transformed in unique ways.

Scientists have long studied

the evolution of the island's chameleons, bats, and lemurs.

Now the search is on for the ancient history

of one of Earth's strangest animals--

the crocodile.

♪

In flooded underground caves,

researchers are looking for the remains

of an extinct croc species.

It may have disappeared just 2,000 years ago,

a recent twist in the story of crocs.

EVON HEKKALA: Some people see crocodiles as this animal

that's unchanging through time.

And, actually, we know now that that's not true,

but they look like it.

I'm Dr. Evon Hekkala, and I use DNA

to look at how crocodiles have changed in the recent past

and how they are related to each other in deeper time.

Most of the living species of crocodile

are really, really hard to tell apart,

unless you're somebody who spends all your time

thinking about crocodiles, like me.

NARRATOR: Cold-blooded,

ferocious,

but strangely beautiful,

the 14 living crocodile species are all very similar.

They all have the same reptilian body plan...

low to the ground

and armored from head to toe in thick scales.

♪

They seem like living fossils,

some hangover from the age of dinosaurs.

But are they?

Is this really an animal frozen in time?

Perhaps the mysterious species in the cave

will provide some answers about recent crocodile evolution.

HEKKALA: So, there's this crocodile that existed

on the island of Madagascar until relatively recently,

and it disappears about the same time that humans got here,

and that crocodile was called

the horned crocodile of Madagascar.

And so, one of the big questions is, what was that crocodile?

Who were its relatives?

And what happened to it?

It's one of the biggest mysteries.

♪

NARRATOR: Today there is only one species on Madagascar...

the famous Nile crocodile...

one of the fiercest of Africa's predators.

♪

[wildebeest bellowing]

♪

Scientists think it squeezed out the smaller horned croc,

but there's a lot they don't know.

There may be answers in the flooded caves.

A dive team sets out

to search for the bones of the horned croc.

The caves are a time capsule,

where the remains of ancient animals

have been preserved for thousands of years.

HEKKALA: I knew from speaking with some other people

that there were supposedly crocodile skulls in this cave

of this species that no one has seen for at least 200 years,

but more likely 1,000 years.

NARRATOR: Evon waits, hoping the skulls are there.

HEKKALA: And I'm sitting there and I'm thinking,

just the anticipation is like, "Any minute,

I'm going to get to see this thing."

It must be so exciting when they bring things in.

You have no idea what they're going to bring.

WOMAN: Yeah, yeah, it's like Christmas every time.

NARRATOR: Deep in the caves,

divers have to squeeze through tight spaces.

If they brush the bottom,

they can stir up clouds of silt and lose their way.

♪

A half hour in, they see it--

a skull.

♪

♪

♪

WOMAN: What do you think?

HEKKALA: It looks like a crocodile!

WOMAN: Does it?

HEKKALA: So excited.

WOMAN: A skull? HEKKALA: Yeah.

WOMAN: Look at that, it looks perfect.

HEKKALA: Oh, it's beautiful. Wow!

WOMAN: Oh, my God! It is a crocodile.

HEKKALA: You know, half the collections

are just pieces, so...

WOMAN: That is so gorgeous.

You got it?

HEKKALA: Yeah, I've got it.

This is a skull of the extinct horned crocodile of Madagascar,

and when researchers first started coming

to Madagascar from Europe, they saw these crocodile skulls,

and they weren't sure exactly what they were.

They didn't look exactly like Nile crocodiles.

They realized it was a separate species.

This individual is the first individual I've seen

that came out of a cave, a water-filled cave,

so that is pretty exciting.

NARRATOR: If Evon's lucky,

she'll be able to extract its DNA

and learn where the horned croc fits

into the story of crocodile evolution.

The results will take time, but one thing is clear--

apart from its small but distinctive horns,

this animal was very similar to the crocs alive today--

armored, low to the ground,

with short legs and large, powerful jaws.

To us, this body plan is what defines a crocodile,

but millions of years in the past,

there was more than one way to be a croc.

HEKKALA: One of the cool things that's happening these days

is that we're finding out that the ancient crocodilians

were incredibly diverse,

and there are all different forms of them.

NARRATOR: Scientists are now discovering

the earliest ancient crocs.

They were nothing like the animals alive today.

To meet the very first crocs,

we must trace one branch of the vast tree of life

far back in deep time, 230 million years

into the geologic period called the Triassic.

It's hard to imagine such a vast expanse of time.

HANS SUES: We throw around numbers as scientists,

but at the same time, do we really understand what it means

that 100 million years have passed?

I'm Hans Sues. I'm a paleontologist

at the Smithsonian Institution in Washington, D.C.,

and I study fossils.

If you look, for instance, at your historical time,

you can think back to your grandparents

and that time frame that people are still comfortable with.

But you go further back, go, say, back thousands of years

when much of North America was covered by ice,

a very different world.

But go further back yet.

Go back to 100 million years,

and this world would have been entirely unrecognizable,

would have been like going to another planet

and seeing life forms that were, for the most part,

utterly alien to our experience,

and this is really difficult to grasp.

NARRATOR: There is little about the planet of the Triassic

we would recognize.

The continents we know today had not yet formed.

They were all contained in one huge land mass

surrounded by water--Pangaea.

Most of Pangaea was dry,

with blazing hot summers and cold winters.

From Triassic period rocks,

scientists know much of the interior was desert.

Fossilized plant remains tell them that closer to the sea,

there were open, fern-filled woodlands.

It was here, along with the dinosaurs,

that the first crocs evolved.

In the beginning,

they were even more successful than the dinosaurs,

and to our eyes, they look totally bizarre.

ANJAN BHULLAR: Well, the Triassic was, in many ways,

actually the age of crocodiles,

and in any Triassic landscape,

you would have seen this vast diversity

of crocodile relatives with many body forms.

My name is Bhart-Anjan Bhullar. I go by Anjan.

I'm a paleontologist,

and I would say that I am a historian of life.

NARRATOR: Anjan Bhullar has been unearthing the bones

of the very first crocodile relatives.

Two of them were found together

near some sandstone cliffs in southern Utah.

BHULLAR: Well, these are two of the most extraordinary

skeletons from the crocodile line that have ever been found.

This large animal here is something called a Poposaur.

It is the only complete skeleton

of one of these animals that's ever been found.

All of the subtle features on it, I mean, it's just,

it's the find of a lifetime.

These animals show us what crocodiles were like

at the beginning of their evolution,

and they're very, very different.

The extraordinary thing about this animal

is that it was really trying to be a dinosaur

before dinosaurs were dominant,

in that it was actually walking around on two legs.

You see how large and how heavily built

the legs of this animal are

compared to these tiny little arms.

And so, this animal couldn't rest any of its weight

on its arms.

NARRATOR: Poposaurus was a fierce,

fast-moving land predator,

acting for all the world like a dinosaur.

And it wasn't the only strange Triassic croc

to be found in Utah.

BHULLAR: In fact, the Poposaur, this large skeleton,

was the first thing we found,

and we dug out this big skeleton.

Then right underneath it was a tiny foot.

And underneath that foot was this animal here,

which is the only complete specimen

of what we call a sphenosuchian-grade

stem crocodile that's ever been found.

NARRATOR: They called the sphenosuchian "Little Foot."

It was even stranger than Poposaurus.

BHULLAR: And so, the Poposaur is something like a mountain lion,

whereas the sphenosuchian, you look at this animal,

and it's got a slender little body,

it's got extraordinarily long legs,

extraordinarily long arms,

and these arms were taking its weight,

unlike those of the Poposaur.

And so this thing was built almost like a greyhound

with a heavy head and a long tail.

It was an animal that was utterly built for speed.

♪

NARRATOR: It's hard to imagine an animal

less like the lumbering, heavy-set modern crocodiles.

How did Anjan even know they were related?

BHULLAR: There are many features,

subtle features of the skeleton

that tell us it's actually from the crocodile line.

NARRATOR: One tell-tale clue

is the structure of the feet and ankles.

Another is in the skull.

BHULLAR: Among the crocodile relatives,

there are a few iconic features.

One of those is the heavy reinforcement

of the skull bones, especially the jaws.

These animals had strong skulls and a very powerful bite.

NARRATOR: By comparing details like these,

scientists can figure out

if fossils are related to each other

and arrange them on a family tree.

BHULLAR: As our ways of thinking about evolution have improved,

we've realized that instead of

a sort of general overall similarity,

we should really be focusing on unique shared characters.

NARRATOR: If two fossils share unique characteristics,

the odds are that they once shared a common ancestor, too.

BHULLAR: This spread on the table in front of me

encompasses more than 220 million years of evolution.

And in fact, if I look at this group,

I can actually start to see that a couple of these animals

share that reinforced skull form.

NARRATOR: That tells Anjan they belong

in the crocodile line,

whereas other fossils, superficially similar, don't.

BHULLAR: These fossils actually

have a much more lightly built skull,

almost a bird-like lightly built skull,

so these two don't pertain to the ancestry of crocodiles.

NARRATOR: By focusing on details like ankles and skulls,

scientists can build a family tree of crocs

and reveal the twists and turns of their deep time history.

The strange creatures of the Triassic were part

of the first great flowering of the crocodile family tree,

but 200 million years ago,

much of that tree was cut back...

[rumbling]

...when a mass extinction

wiped out the vast majority of the animals of land and sea.

As the supercontinent Pangaea began to break up,

volcanoes pumped vast amounts of carbon dioxide into the air,

acidifying the oceans.

The planet warmed, and habitats were transformed.

Most of the Triassic crocodile relatives,

including Poposaurus and Little Foot, died out.

SUES: Extinctions are of great interest

to evolutionary biologists

because they basically reset the evolutionary game.

We know that organisms, over time,

try to adapt to particular ecological circumstances,

however, every once in a while during the history of life,

there have been catastrophic events of such magnitude

that thousands or millions of species were wiped out

in what basically in deep time is a single moment.

NARRATOR: There have been five major extinctions

in Earth's history.

Through the lens of deep time,

we can see they caused profound destruction

and changed the history of life on Earth.

The mass extinction that ended the Triassic period

ushered in a new chapter in the story of crocs.

In the Jurassic and Cretaceous periods, crocs flourished again,

but in new and even stranger ways.

A record of those wondrous creatures is preserved

in one of the most spectacular landscapes on Earth--Patagonia.

♪

DIEGO POL: After the Triassic- Jurassic extinction event,

many groups diversified in the Jurassic.

Dinosaurs were certainly the most conspicuous

because they were big and they were very abundant,

but other groups began to diversify

in a very, very impressive way, and crocs were one of them.

I'm Diego Pol. I'm a paleontologist.

I work here in Patagonia in the eastern coast,

in the southern tip of South America,

and I study crocs.

I really love to drive, you know, in places like this

because it's really like you are driving through time.

NARRATOR: For the duration

of the Jurassic and Cretaceous periods,

almost 150 million years,

crocs vied with dinosaurs for dominance.

They stopped being only the land animals

they were in the Triassic

and experimented with radically new ways of being.

POL: So, the Triassic is over.

We're moving into the Jurassic,

and dinosaurs were evolving and diversifying,

but also crocs were diversifying at the same time.

You start seeing animals like Dakosaurus,

is the swimming marine croc that adapted their forelimbs

into paddle-like flippers.

And then you have freshwater gigantic crocs

like Sarcosuchus that's about 12 meters long.

It was eating dinosaurs.

And then you have herbivorous crocs like Notosuchians.

Look at this animal.

It, it really looks nothing like a croc.

It has a short snout, very high,

the eye sockets are pointing to the sides,

and the, the crazy, crazy thing

is that it moved the lower jaw back and forth.

And this was a way

of the upper teeth and the lower teeth

to slide against, against each other,

and in that way, this animal was processing the plant matter.

NARRATOR: So, here was an ancient croc

that chewed like a goat.

Diego has spent much of the last 20 years

excavating ancient crocs

from the barren outcrops of Patagonia.

But back when those creatures lived,

the world was a very different place.

The continents were forming, and it was hot.

POL: It was much warmer planet.

There were no ice caps on the poles.

There was, uh, a time

when conifers dominated the ecosystem.

NARRATOR: In the warming greenhouse world

of the Jurassic and Cretaceous, crocs prospered.

This was their golden age.

POL: They became so diverse

that in some places you go, and you basically only find crocs.

So, we can see a really, really crazy diversity

in the Cretaceous.

And then about 66 million years ago,

it all went away.

NARRATOR: What happened to the many Cretaceous crocs?

It seems most of them perished the same way as the dinosaurs.

SUES: It was long realized that around 66 million years ago,

there was a major extinction of animals and plants

on land and in the oceans.

On land, the most famous casualty were the dinosaurs.

[crash]

NARRATOR: Scientists agree that an asteroid strike

brought on the global devastation,

but many now argue it was not the only cause

of the mass extinction.

From the fossil record, they can see that climate changes

were already pushing many species to extinction

before the asteroid impact.

SUES: So basically, this impact is sort of thought,

if not the sole cause of the extinction,

certainly the coup de grâce for a great many lineages.

[growls]

NARRATOR: Ancient crocs were reduced

to a fraction of what they once had been.

POL: So, out of this wonderful diversity,

only a few species made it through.

And the ones that actually made it through

were very particular in many ways.

They were certainly adapted

to living in the freshwater environment.

They were adapted to, uh, feeding in water.

They were predators.

They were not herbivores. They were not land crocodiles.

They were not marine crocodiles.

So only a tiny fraction of that diversity made it through.

NARRATOR: The crocodiles that made it through

were the shoreline predators

that lived half in water and half on land.

Their low, tank-like body plan

may have been one secret of their survival.

It allows them to lie semi-submerged in the shallows

and ambush their prey with ferocious speed.

[splash]

The success of that lethal design

is why crocodiles today all seem so similar.

HEKKALA: So, crocodiles have this form

that's very, very successful.

They have sort of an armored body plan that allows them

to be a successful predator in aquatic environments.

Aquatic environments can be more stable

than other kinds of environments,

like terrestrial environments, and so it makes sense

that they've retained this body plan from deep time,

from the ancestral crocodilians

that were around the globe millions of years ago.

It works really well. Why change it?

NARRATOR: Of course, that classic body plan

is no guarantee of survival.

The horned croc of Madagascar died out just centuries ago,

likely pushed out by the giant Nile croc.

Results from Evon's work

suggest the species are more closely related

than anybody realized.

♪

It's a great example of how DNA analysis

has become a vital tool for paleontologists.

♪

HEKKALA: One of the exciting things

about the new tool kit we have today,

the ability to use DNA to look at evolutionary history,

is we can use it as sort of a metric

for change over time and lineages.

So, with living species, we can take their DNA

and we can calculate back how long it takes

to accumulate the number of changes we see in the genome.

And we can say this corresponds to a split

three million years ago or six million years ago

or 20 million years ago.

NARRATOR: DNA has shown that both crocodiles and alligators

are descended from a common ancestor

that lived 80 million years ago.

HEKKALA: The ancestral lineage

that the true crocodiles came from

diverged from the group that includes all the alligators

about 60 to 80 million years ago.

And then, even more recently,

this thing that we've always thought

as the sort of primordial crocodile, the Nile crocodile,

we recently have found, using molecular clock dating,

that the Nile crocodile is just a baby.

It just arose probably

within the last four to six million years.

It's a young'un on the landscape

of, uh, crocodilians in the modern world.

NARRATOR: So, despite their prehistoric appearance,

it turns out that over their 230-million-year history,

crocodiles have been in constant evolution.

They have proved themselves to be one

of the most resilient lineages on the face of the planet.

HEKKALA: For me, these crocodiles sort of represent

an organism that, through the history of life on Earth,

it's found a way to persist.

NARRATOR: The story of the crocodile lineage

is of deep time transformations

that produced a wild diversity of croc species,

followed by a steep decline.

Today there are just a handful of crocs,

and the strange animals that gave rise to them are all gone.

The surviving crocs are all very similar,

all shoreline predators of the tropics.

But while the crocodile lineage has bottlenecked,

another lineage is experiencing a wild explosion of diversity.

[squawking]

♪

♪

[cawing]

[honks]

[quacking]

[honking]

Birds have colonized every environment on Earth.

And they come in an astonishing variety

of shapes, colors, and sizes.

[whistling]

JULIA CLARKE: There are more species of birds

than any other group of vertebrates that lives on land.

♪

They can cross the Himalayas on wing.

They can dive into a part of the ocean

where sunlight does not reach.

They can migrate between continents.

So, they are truly remarkable.

I'm Julia Clarke,

and I'm a professor of vertebrate paleontology

at the University of Texas at Austin.

[ducks quacking]

Well, I think the captivation of birds

is that they have this intelligence

that we don't really understand.

It's sort of like this foreign or alien intelligence

that is in our everyday spaces,

which is the premise of, like, a lot of sci-fi movies,

if you think about it, you know, they're among us.

And, if you look closely,

I think there's a lot to be fascinated with,

even in everyday birds.

NARRATOR: Birds have colonized

not only the natural environments of the planet,

but also the urban spaces created by humans.

CLARKE: There are more than 10,000 species of birds,

but even more striking than that,

there are more than half that number

is just within one lineage, songbirds,

so that means that the birds that are in your backyard

are part of what is truly an extraordinary evolution.

NARRATOR: So, what's the story behind the spread of birds

across the planet?

How did they come to be everywhere and so diverse?

CLARKE: Things that can seem so commonplace,

crows or pigeons in a park,

are the leavings of an amazing history

that stretches back hundreds of millions of years.

NARRATOR: Our understanding of that evolutionary history

began with one extraordinary fossil

discovered in the 1860s in Germany--Archaeopteryx.

CLARKE: This fossil, to many people,

might just look like roadkill

or something that hit your window.

But in fact, to me, these bones, they come to life.

And the wings are moving,

covered in feathers, but with mobile claws at their tips.

Most striking is a long, bony tail with feathers.

NARRATOR: 150 million years old, archaeopteryx was a bird.

It had feathers, and it could fly.

But with its claws, tail, and toothed beak,

there was something almost dinosaur-like about it.

It led proponents of the new theory of evolution

to make a sensational claim:

Birds must have evolved from dinosaurs.

CLARKE: When I look at this, I see an icon of evolution.

It was one of the first key and totally unavoidable

pieces of evidence consistent with evolution.

NARRATOR: But the theory that birds evolved from dinosaurs

met intense opposition.

How could something so huge and heavy

evolve into something so small and light?

One of the biggest objections

was that no dinosaur had ever been found with a wishbone,

in birds, the crucial brace for the chest

that makes flight possible.

The search was on.

If scientists could find a dinosaur with a wishbone,

they would clinch the case.

But for a century, they failed.

♪

Then, in the 1960s,

paleontologist John Ostrom hit pay dirt...

a dinosaur fossil with a wishbone.

He called it Deinonychus, terrible claw.

JACQUES GAUTHIER: Here we have Deinonychus antirrhopus,

the fossil that changed everything that we know

about the origin of birds

and fundamentally altered

our understanding

of how flight evolved.

NARRATOR: Deinonychus was a ferocious predator

with wing-like arms and all the bones and muscles

necessary for flight,

but it couldn't fly.

GAUTHIER: Here's an animal with forelimbs

much too short and much too heavy in the body

to be able to fly,

yet it has all the bells and whistles

that we associate with the flight stroke.

[squawking]

NARRATOR: Not only that-- it had feathers, too.

But all this had nothing to do with flight.

Its feathers were for warmth,

and its clawed wings were for killing.

[squawks]

GAUTHIER: The arms up against the body

and shoot it down and forward,

grab your prey, drag it up and back.

Down and forward, up and back, down and forward, up and back.

That's the flight stroke.

So, all the details, the basic architecture, at least,

of the flight stroke is evolved in an animal

that is not using it to fly.

NARRATOR: Amazingly, these tools built for killing

would eventually power flight.

[squawks]

GAUTHIER: So, you have feathers

and you have the flight stroke colliding in one animal,

so the skies were no longer a barrier

to the evolution of dinosaurs.

And that's why we think that birds are living dinosaurs.

NARRATOR: Deinonychus was powerful evidence

that dinosaurs gave rise to birds.

But the many stages of that evolution were still unknown.

To complete the story, scientists needed more fossils.

Another long wait began.

♪

Then, in the 1990s,

farmers in a remote province of northeastern China

blew the story of bird evolution wide-open.

[clucking]

They had been turning up rocks

with the outlines of birds in them

for as long as they could remember.

They had no idea these were the bird/dinosaur fossils

scientists had been waiting for.

By the late 1990s,

fossil fever had broken out in Liaoning Province.

[man speaking Chinese]

[rooster crows]

NARRATOR: A single fossil could bring a year's income.

As farmers scoured the landscape,

the fossils started to pour in,

hundreds of ancient birds from the time of the dinosaurs.

JINGMAI O'CONNOR: Bird fossils are extremely rare,

typically, in the fossil record.

And up until the eighties,

all we really had was Archaeopteryx.

So, without anything in between

this bird that looks very much like a dinosaur

and birds that look very much like living birds,

without any fossils to fill in this gap,

we had no idea how the modern bird evolved.

But the fossils from Western Liaoning

started to show us the transitional forms.

They showed us the earliest birds with beaks,

the earliest birds with short tails, like living birds.

My name is Jingmai O'Connor,

and I am a vertebrate paleontologist.

You know, I have a very strong personality, a bit unusual,

well, at least for a scientist.

To be honest, my bird obsession grew with my studies.

I've developed this deep fascination and love

for these, this incredible group of animals.

NARRATOR: Jingmai's obsession with birds was cemented

by the fossils of Liaoning.

They are priceless.

Bird fossils are extremely rare

because bird bones are so delicate.

But here in northeastern China, 130 million years ago,

a unique combination of circumstances

created the perfect conditions for their preservation.

O'CONNOR: If you were able to come back here

131 to 120 million years ago and looked out,

you would have seen lakes as far as the eye could see,

with active volcanoes going off around them

and a forested environment

growing by the shores of these lakes,

and this forest would have been teeming

with small feathered dinosaurs.

[rumbling]

NARRATOR: As those small feathered dinosaurs died

and fell or were washed into lakes,

they were quickly buried in layers of volcanic ash.

♪

The result?

An extraordinary record of Cretaceous bird/dinosaurs

perfectly preserved in stone.

O'CONNOR: The amazing thing about these fossils

is the exceptional preservation of soft tissues

which reveal these extinct animals

in a level of detail that we paleontologists

never previously thought possible.

NARRATOR: Fossilized along with the birds were plants and seeds,

allowing scientists to reconstruct

the forested environment of the time.

Together, the wealth of Liaoning fossils reveal a world

where creatures representing every stage

of dinosaur-to-bird evolution lived side by side.

They show how nature experimented

with every aspect of what would finally make a bird--

beaks, wings, feathers, and flight.

Here was a sort of evolutionary laboratory

in which many different combinations

of dinosaur and bird characteristics were tried out.

There was Caudipteryx, a small feathered dinosaur

that had wings but couldn't fly.

O'CONNOR: You can see, with its very robust hind limbs

and its very small forelimbs,

this was definitely not a flying dinosaur.

NARRATOR: Living alongside it were creatures that flew

but still had many dinosaur characteristics--

teeth, long tails, and claws on their wings.

O'CONNOR: Here we have a primitive bird named Jeholornis.

It has lost almost all its teeth.

It has a shoulder girdle

that looks almost like that of living birds,

but then it has this tail

that is actually longer than that of Archaeopteryx.

♪

NARRATOR: And there were creatures like Confuciusornis,

almost identical to modern birds.

O'CONNOR: If you were in northeastern China

during the early Cretaceous,

you would see flocks of Confuciusornis flying overhead.

NARRATOR: The feathered dinosaurs of Liaoning

are a reminder that evolution

does not move in a straight line.

SUES: There's a common perception

that evolution proceeds in a very linear fashion.

So, you have a little dinosaur

that somehow decides, quote, unquote, to become a bird.

But actually, the many bird features

were gradually acquired.

There were a lot of dead ends in this evolutionary process.

[squawking]

NARRATOR: Just like Deinonychus, the Liaoning fossils show

that wings and feathers evolved separately

and for reasons that have nothing to do with flight.

[squawks]

It was only after millions of years

that these things came together

to make the creature we call a bird.

O'CONNOR: In fact, what we've learned

from this huge diversity of fossils

is that these features that we associate with modern birds

actually evolved multiple times.

And I'm not only talking about flight,

I'm talking about beaks,

I'm talking about the abbreviated tail.

NARRATOR: The Liaoning fossils opened a window

on the profusion of feathered dinosaurs

that populated the whole world many millions of years ago.

What happened to them all?

Most died out in the same extinction event

that killed the big terrestrial dinosaurs and most crocs.

[crash]

But like the crocs, a few birds squeaked through.

Those few survivors gave rise to all the birds on Earth today.

[honking]

But how did that amazing story of survival play out?

Remarkably, scientists are solving that mystery

not from bones, but from DNA.

ERICH JARVIS: So, what happened is

that this mass extinction occurs,

maybe as a result

of a big, giant meteorite,

then climate change and so forth.

A few groups of birds survive,

only five percent of the species survive.

My name is Erich Jarvis.

I'm a professor at the Rockefeller University

in New York.

I study how the brain produces learned behaviors,

specifically like language.

[chirping]

JARVIS: See, that's a call.

NARRATOR: Erich is especially interested

in how bird songs evolved.

But songs don't fossilize.

So, along with other scientists,

Erich hoped the answer might come from genetics.

JARVIS: And we all wanted to know,

is the bird family tree correct?

Because there are many papers that were coming out,

changing the tree from one year to another,

and it keeps screwing up our experiments, basically.

NARRATOR: It was an international consortium

of scientists working to pin down the avian tree of life.

And in the process, they would answer the big question--

how did the birds that survived the asteroid

go on to take over the planet?

Erich and his colleagues compared the genomes

of different bird species

to calculate their degrees of similarity.

They could then figure out

when they last shared common ancestors.

JARVIS: Fossils is anatomical structures

with shapes, of course,

and that anatomical structure you can measure,

you can quantify the volume, the size,

the shape, and so forth

and use that information to infer relatedness,

whereas the genome is pieces of DNA, the genetic code,

that you can also use to infer relatedness.

The genome has millions, hundreds of millions

of pieces of information in the sequence.

Which one is more accurate?

Most people trust the DNA to be more accurate.

NARRATOR: DNA sleuthing can't replace the work

of paleontologists with fossils,

but it made for a big break

in the case of recent bird evolution.

It showed that just a handful of birds

survived the mass extinction to give rise

to the amazing diversity of birds today.

JARVIS: First thing we figured out

is that those ones that survived,

with the deepest branches in the tree that we generated,

were the ones that were shorebirds,

that can survive in water, that can survive in land,

that can survive in different habitats.

NARRATOR: Along with shorebirds like ducks and geese,

the ancestors of ostriches and emus also survived.

JARVIS: Then those few four or five lineages that survive,

in a 15-million-year window,

gave rise to every species that we are looking at now today.

NARRATOR: How exactly did that small group of survivors

give rise to modern birds?

Scientists are still working that out.

CLARKE: I think that why birds are so species-rich

is a big question,

and it's not one that's going to be easily answered.

There's so many innovations that have been proposed

to explain this incredible number of species we have today.

And some of them are, of course, flight.

And some of them are rapid growth to adult-size,

so baby birds grow to full-size superfast.

Other strategies are things like bright colors

or complex color patterns,

complex modes of communication that can be deployed

in attracting a mate or defending a territory.

These kinds of behaviors are thought to be linked

to rapid speciation rates.

So, these are all big, open questions,

and there is, as yet, no simple answer.

NARRATOR: Whatever the reason

for the amazing diversity of birds,

scientists are finally in a position

to see the whole vast avian tree of life.

Arising with the dinosaurs, the bird lineage experimented

for millions of years with feathers, beaks, and wings.

It barely survived a major extinction event

before finally flowering

in the 10,000 species alive today.

[honking]

But while the bird lineage exploded

and birds colonized every habitat on Earth,

another lineage concentrated on colonizing just the seas.

♪

No animal embodies the beauty and awe of the seas

more than whales.

[whale singing]

What science now knows

about these leviathans of the deep is amazing.

[singing]

Bowhead whales can live for up to 200 years,

longer than any other mammal on Earth.

Sperm whales can dive to depths of over 3,000 feet

and stay underwater

for an hour and a half without breathing.

Blue whales are the biggest creatures

to ever have lived on Earth,

bigger than even the largest dinosaurs.

♪

Up to 100 feet long and 200 tons in weight,

they have a heart the size of a small car.

And these giants of the deep sing to each other,

communicating over vast distances in a language of song

that researchers still don't fully understand.

It's just one of the many mysteries

still surrounding whales.

JACKIE HILDERING: What I've learned more than anything else

as a scientist is how little we know.

There's this presumption that we know so much.

We don't.

I'm Jackie Hildering.

[camera shutter clicks]

I'm a whale researcher and educator.

♪

[whale blows]

[laughs]

Mom and calf, Obsidian and Ripple.

Yes, yes.

[clicking]

It's mind-blowing to see the number of humpbacks here,

considering what a rarity it was to used to see them.

[whale blows]

And I'm trying to figure out who they all are.

And this is... [click]

Claw.

It's a female. She's had a baby.

NARRATOR: Jackie has been working

with the humpback whale population

off northern Vancouver Island for almost 20 years.

She knows each of them individually

by the distinctive marks on their tail flukes.

HILDERING: What I can't express properly

is what it feels like to know who they are.

That the one that just went by I've known since he was a calf

and was here with his mother in 2007.

NARRATOR: With others, Jackie is working to understand

humpback family groups and their epic migrations.

Every year, they swim up to 6,000 miles,

mating in the warm waters of the equator,

feeding in the cold food-rich waters nearer the poles.

How did these gargantuan animals

and their remarkable behavior evolve?

For so long, it was a mystery.

MARK UHEN: We've known that whales are mammals

since the 18th and 19th centuries

because they're warm blooded and they suckle their young,

but we didn't know where they came from.

I'm Mark Uhen, and I work at George Mason University,

and I study the evolution of whales and other marine mammals.

[click]

[click]

[click]

Darwin talked about the origin of whales

in his classic book "The Origin of Species,"

where he said someone he knew

had observed a bear swimming around,

skimming insects off the surface of the water,

and he suggested that perhaps something like a bear

could have evolved into a whale,

the kind of whale that filter-feeds

by doing something similar

and getting better and better at it over time.

Now, Darwin was not correct about that,

but at least he could conceptualize of a way

that whales had evolved.

But basically, we didn't know where whales came from

until extremely recently.

NARRATOR: The fascination with whale evolution

began in the 19th century.

Stories of sea monsters filled the popular imagination.

When the first fossil whale was unearthed,

its discoverers thought they'd found a gigantic sea serpent.

It was called Basilosaurus.

UHEN: It was discovered in North America

along the Gulf Coast in the 1830s,

and it was actually the first fossil whale

ever to be scientifically named and studied.

The gentleman who named it, a man named Harlan,

had read about large sea serpents

being discovered elsewhere in the world,

and so he thought that this was something similar,

and thus he named this animal Basilosaurus,

which means king lizard.

NARRATOR: Up to 50 feet long with ferocious teeth,

Basilosaurus was a formidable marine predator.

Finally, in 1841, it was identified as a whale

and dated to about 35 million years ago.

For almost a century after its discovery,

Basilosaurus remained the oldest known whale.

It was assumed to be the ancestor of all living whales.

UHEN: So, after the discovery of Basilosaurus,

there were other whales found

that were just a little bit earlier and more primitive,

but not by very much,

maybe five million years older than Basilosaurus.

And it didn't push the origin back in time,

and we really didn't discover a whole lot more

about the origin of whales.

NARRATOR: One of those other early whales was Dorudon,

a little bit smaller than Basilosaurus.

It would turn out to play a bigger role in whale evolution

than its discoverers imagined.

But where did those early whales come from?

They must have evolved from something, but what?

The deep origins of the whale lineage were a mystery

until 1975, when a paleontologist went

on a fossil hunting expedition to Pakistan.

He wasn't looking for early whales at all.

PHILIP GINGERICH: I was interested

in how archaic mammals changed into modern mammals.

Things like the first horses, that's what I was interested in.

My name is Philip Gingerich.

I'm a professor emeritus of paleontology

at the University of Michigan.

I took several students with me and colleagues from Paris,

and we looked first in Punjab Province,

then south in Sindh.

We still hadn't found anything very interesting.

And we went to the Northwest Frontier Province.

And there, high on a hill,

we found a little jaw of a land mammal.

NARRATOR: Later they found a piece of skull,

and its strange ear bones finally unlocked the secrets

of early whale evolution.

GINGERICH: This is what was left, the back of a skull,

and if you look at the underside,

it has the covering of the ear on the right side,

and that covering is missing on the left side.

NARRATOR: Those ear bones turned out to be the key.

Philip thought he was looking at the skull of something

like a primitive deer,

but it unmistakably had the ear bones of a whale.

GINGERICH: Whales have a special structure of the ear

to be able to hear in water.

It turns out that they effectively see in water

by using sound, and so to do this,

the ears have become modified.

[whale singing]

UHEN: The ear bones of whales are very dense,

and that density helps them to hear sound in the water.

Mammal ears originally evolved in terrestrial animals,

and so their structure is optimal for hearing in air.

And in water, sound behaves really differently.

So, for example, if you go into a pool or under a lake,

you can hear sound, but it's a little muffled,

but the one thing you can't do is you can't figure out

where the sound is coming from around you.

And that's because the way mammals do this

is they use the difference in time

between when a sound hits your right ear and your left ear

to figure out what direction the sound is coming from,

so if the sound is off to my right,

it hits my right ear first, then my left ear,

and so my brain says, "The sound is over to my right."

But in water, the tissue of your face and skull

is about the same density as water,

so the sound, rather than going around my skull to my left ear,

goes right through it, so it gets to my left ear

at almost the same time as my right ear.

And I can't tell where the sound is coming from.

So, the added density to whale ears,

that's reestablishing their ability

to hear directionally underwater.

NARRATOR: Philip's fossil had that same distinctive ear,

and it was 49 million years old.

That could only mean one thing--

here at last was one of the very first whales.

Philip named it Pakicetus.

GINGERICH: Once we knew it was a whale,

we knew it was the oldest whale anyone had ever found.

NARRATOR: Pakicetus pushed the origins of whales

back 15 million years

to the time when the Indian subcontinent

was slowly crashing into Asia.

Where Pakicetus was found was once an ocean shoreline.

Its ears made it clear Pakicetus spent time underwater,

but other fragments of skeleton

also clearly showed it walked on four legs.

How did this strange beast

give rise to the giants we know today?

♪

At the Museum of Natural History in Paris,

one of the birthplaces of paleontology,

they have been assembling the skeletons of prehistoric animals

for over 200 years.

They now have one of the few complete reconstructions

of the extraordinary whale ancestor, Pakicetus.

CHRISTIAN DE MUIZON: You see it's a quadrupedal animal

with the higher forelimbs and hind limbs.

It means that this animal was,

uh, definitely partly terrestrial.

I am Christian de Muizon.

I'm a paleontologist working

at the Natural History Museum in Paris.

And obviously it's quite a strange animal,

very small, doesn't whale-looking at all.

It more looks like a dog with a long snout.

NARRATOR: Pakicetus is one of the strangest surprises

of evolution, a whale ancestor

that looks like a small wolf with webbed feet for swimming.

GINGERICH: The key thing about it

is it has elongated finger and toe bones,

so, clearly, it's already semiaquatic.

[sniffing]

NARRATOR: Pakicetus was a creature of the shoreline,

hunting for fish and perhaps other small animals

in the shallows.

UHEN: And we think that it was using its longer snout

to probe for aquatic prey in the water,

and so it was feeding in the water

while almost certainly going out on land

to breed and have their young.

NARRATOR: Once they adapted to life in the shallows,

it took ten million years

for the descendants of Pakicetus to become fully aquatic.

Why did it take so long?

Because to live underwater, they had to change.

It is one of the most remarkable stories

of total physical transformation in the annals of evolution.

[whale singing]

UHEN: After Pakicetus,

whales take about 10 to 12 million years

to evolve into fully aquatic forms.

And during that time, their hind limbs tend to get smaller

and their skulls tend to get longer,

and the naris, which is the hole in the skull where the nose is,

moves up the skull.

In addition, their forelimbs tend to turn into flippers,

and they get more vertebrae in their back,

which makes their bodies longer.

NARRATOR: When Basilosaurus arrived on the scene

35 million years ago,

along with its evolutionary cousin, Dorudon,

there'd be no mistaking that these were whales

that lived their whole lives in water.

But there was still one great transformation

to take place in whales--

baleen feeding.

CARLOS PEREDO: So, near the base of the whale family tree,

there's this major split

into the two groups that we have today.

We have toothed whales, and then we have baleen whales

that actually lose their teeth entirely,

and they grow what are called baleen plates

that are made of keratin,

so they're actually more like hair or fingernails.

And these whales use it to filter their food,

so they'll take big gulps of water,

and they'll actually filter their prey,

little tiny microscopic organisms out of that water

using the baleen plates.

♪

NARRATOR: The split into toothed whales, like orcas and dolphins,

and baleen whales, like blue whales and humpbacks,

happened about 30 million years ago.

It turns out it occurred in the descendants

not of Basilosaurus but of Dorudon.

UHEN: Basilosaurus is sort of a sideline.

We don't think it gave rise to anything alive today.

NARRATOR: The toothed whales remained,

like their ancient ancestors,

predators living mostly in coastal waters.

There they could feed on fish

or, like some of the orcas, seals and baby sea lions.

♪

The baleen feeders underwent a much greater transformation.

With a radically new way of filter-feeding,

they moved into the deep oceans and became huge.

Why?

For a long time,

the massive size of some baleen whales was a puzzle.

[blowing]

But it turns out that in the ocean,

great size is an advantage.

UHEN: If you look at the energy budget of these animals,

they use fewer calories per unit body mass when you get bigger,

and so they're more efficient when they're huge.

They're also more efficient when they move,

when they swim at large body size,

so there's advantages to being large in the ocean.

[blowing]

NARRATOR: The huge size of baleen whales is also linked

to one of the last great planetary transformations.

PEREDO: Argentina and South America

become completely separate from Antarctica,

and that changes the currents in the ocean system,

and it seems to really have a profound impact

on what whales are doing.

NARRATOR: The cold current that began to circle Antarctica

led to a vast upsurge in the krill population

that baleen whales feed on.

With large amounts of food

and the efficient baleen filter-feeding system,

there was simply nothing to stop baleen whales

from becoming huge.

[blowing]

UHEN: It was suggested early on

that the reason that terrestrial mammals can't be that big

is because of gravity.

Anything much bigger than the largest mammals

we see in the fossil record

would be crushed due to the force of gravity,

like their limbs couldn't hold their bodies up.

But whales are approximately neutrally buoyant,

and so gravity doesn't affect them.

And so freed from that constraint,

the baleen whales keep getting

bigger and bigger and bigger over time

because the largest ones are the most efficient.

[whale grunting]

NARRATOR: Along with baleen, whales have developed

sophisticated fishing behaviors to trap their prey.

Humpbacks rely on the help of gulls.

[squawking]

HILDERING: And what's happening is the diving birds

are forcing the herring together, that form a huge ball,

that gives the gulls at the surface

a chance to propel themselves down

and try to grab a herring,

and then somehow the humpbacks know

that there's a concentration of feed there.

And they come with their huge mouths, gulp it down,

get rid of the salt water through their baleen,

and swallow.

[camera shutter clicking]

NARRATOR: Jackie's work has led her to marvel

at the delicate web of relationships

linking humpbacks to every aspect of the marine ecosystem.

HILDERING: It's perfection.

It's been going on longer than we can understand.

Knowing whales keeps me in a state of humility and mystery...

which I think is how a human life is well lived.

It makes me feel connected.

It makes me feel appropriately small in the presence of giants.

[whale singing]

NARRATOR: Over millions of years,

whales grew huge as they explored the seas,

but another mammal grew huge as it explored the earth,

evolving its own remarkable tools for life on land.

[roars]

♪

[trumpets]

♪

For millennia, these stately creatures

have patrolled the African savannas,

transforming the land as they go.

♪

♪

♪

PAULA KAHUMBU: We're driving along tracks

that the elephants have made.

Uh, they've been walking on these trails

probably for hundreds of years.

They create paths that they then use for generations.

♪

My name is Paula Kahumbu.

I'm an ecologist, and I run WildlifeDirect.

It's a Kenyan-based conservation organization

to really change hearts and minds and the laws

to protect our incredible wildlife.

♪

Elephants are such extraordinary animals.

The more we learn about them, the more we realize

that we actually are only just scratching the surface.

Every new discoveries emerge

that elephants can understand things

that we couldn't have dreamed possible.

And I think we'll never uncover their secrets.

NARRATOR: The intelligence and memory of these enigmatic giants

is legendary.

[grumbling]

Their complex elephant mind has allowed them

to evolve a social life with many parallels to our own.

KAHUMBU: Elephants are incredibly social animals.

They live in family groups.

And the family groups will have everybody

from the grandmothers, the daughters, the mothers,

the aunts, the cousins, the nieces, the nephews,

everybody all together,

so huge range of different-sized elephants

all walking together and feeding together.

NARRATOR: Scientists have shown that elephants communicate

through calls, touch, and even low frequency vibrations,

which can travel underground for miles.

But there's still a lot that they don't fully understand.

KAHUMBU: It would be amazing

if we could actually uncover what it is that they know.

I really think that we are blundering about right now

because we don't even have the tools

to measure how they communicate.

NARRATOR: And Paula is certain

that along with their ability to talk to each other,

they experience many of the same emotions we feel--

grief, anger, and empathy.

She senses a mysterious inner life.

KAHUMBU: When you sit with them for hours,

this, like, wealth of sensations

just keep coming and coming and coming,

and it just seems to be endless.

I feel like I can really sense

what is going on with those elephants.

And the longer I spend with elephants,

the more I feel in tune with them.

NARRATOR: As much as she admires them,

Paula is keenly aware that elephants today are in trouble.

[roaring]

KAHUMBU: There used to be dozens of species of elephants,

and now there are just three.

And if we're not careful, we will lose them as well,

and that will be the end of the lineage of elephants.

NARRATOR: Could the ancient lineage of elephants

really be coming to an end?

How did these magnificent animals go from myriad species

to just three today?

And how did the ancient histories

of humans and elephants become so intertwined?

[trumpets]

As with every lineage,

it's a story that begins in deep time,

a story told by fossils,

most of them found in the birthplace of elephants--

Africa.

♪

The deep origins of elephants

lie in the Turkana Basin in Northern Kenya.

In a place called Buluk, scientists are finding fossils

that point to a magnificent age of elephants.

They reveal the ancient history

of the mammals with trunks called proboscideans.

BILL SANDERS: This is from the right side of the jaw.

Fossils are the messengers of the past.

I believe that.

I think that we, as paleontologists,

are trying to be the interpreters

of the messengers from the past.

They give you the opportunity to see

the kind of incredible journey that elephants had to make

to become elephants.

It took 60 million years to make an elephant.

I'm Bill Sanders.

I'm a paleontologist at the University of Michigan.

I specialize on studying the evolution

of proboscideans, including elephants.

NARRATOR: Today, Buluk is one

of the hottest, driest places on Earth,

but 17 million years ago,

it was a lush forest with rivers and wetlands.

SANDERS: It's a very wet climate.

It's a very equable climate, very warm climate.

It's a great place to be a browser.

It's a great place to go out and look for vegetation,

a great place to go get a salad, Africa in the early Miocene.

NARRATOR: How can scientists reconstruct

those vanished environments?

It turns out ancient landscapes

leave traces just like ancient animals do.

ELLEN MILLER: We often find fossil wood and fossil seeds,

so that's telling us something about the environment,

and, uh, the red sediments around us are ancient soils,

they're actually ancient floodplain deposits,

so the animals would have been living out on these floodplains

in these forested areas.

I'm Ellen Miller.

I'm a paleontologist

associated with the Turkana Basin Institute.

We're trying to reconstruct the whole environment

that these animals were living in.

If you go in and just pick up the bones,

it's like, it's like taking the chocolate chips

out of the cookies.

So, we work with geologists and climate scientists

and isotope specialists and all kinds of people, geochemists.

NARRATOR: The painstaking work of Ellen and her colleagues

is allowing them to reconstruct

the whole vanished world of ancient Buluk.

MILLER: So, if you were to be transported back

to the early Miocene of Buluk, 17 million years ago,

it would have been a mature meandering river system

and a woodland,

and there would have been a whole host

of different kinds of elephants.

So, you would have had the Deinotheres.

They're very, very primitive.

They're about a third or a half the size of a modern elephant,

and they would have been kind of snuffling along the riverbanks

because they seemed to really like a closed canopy forest

and a wet environment.

But at the same time,

you have the Amebelodons, the shovel-tuskers.

The lower incisors are these big, long shovel-like tusks,

so they would have used them to scoop up their dinner.

NARRATOR: As scientists excavate, they are astonished

by the diversity of strange beasts they are discovering.

♪

Ancient Buluk was a sort of Jurassic Park of elephants.

ISAIAH NENGO: Imagine I'm taking you on a safari,

but a safari back in time.

You'll be confronted with these magical creatures,

a slice of Africa that is now gone.

You'd be confronted here with amazing herds of elephants.

♪

You have a herd of, of Deinotheres.

You, you have a herd of these elephant ancestors

called the Gomphotheres.

It would be mind-blowing to, to, to confront this scene.

I think the Miocene 16 million years ago at Buluk,

that would have been the center of the empire

of the age of the elephants.

[blows]

My name is Isaiah Nengo, and I am the Associate Director

for the Turkana Basin Institute.

When you're out there and you pick up a piece of bone,

you pick up a fragment of a skull or you pick up a tooth,

and it, it strikes you that

"Man, I'm the first person to ever look at this thing.

I am the first person to know that this exists."

There's an immense joy.

There's, uh, there's no way to describe it.

NARRATOR: The ancient elephants here bear witness

to a glorious flowering of the elephant lineage

about 17 million years ago.

But what were their origins,

and how did they come by their magnificent tusks and trunks?

30 million years ago, there was a species called Palaeomastodon.

It was probably the first elephant ancestor

to actually look like an elephant.

SANDERS: If you saw them on the landscape,

you would say, "Yeah, that thing is like an elephant."

They walk around like a walking card table,

like elephants do today,

probably very carefully with three legs on the ground

at any one time.

We believe from the shape of where their nose is

and the anatomy around it, they must have had a trunk,

which is very cool.

So, it's at 30 million years of Palaeomastodons

that we begin to get that framework for elephants,

the beginning of recognizability for elephants.

NARRATOR: But where did Palaeomastodon come from?

Beyond 30 million years ago,

the elephant fossil record seemed to disappear.

For decades, the earliest origins of the elephant lineage

were a mystery.

But then, in the 1990s, a French paleontologist and his team

were excavating in an abandoned phosphate mine in Morocco.

In layers dating to 56 million years ago,

he came across fossil remains of a mysterious animal

about the size of a small dog.

He called it Phosphatherium.

Later he came across fragments of the jaws and teeth

of an older, even smaller creature.

This one was no bigger than a rabbit.

As he puzzled over both fossils,

he noticed something very strange.

Their teeth seemed to be miniature replicas

of an elephant's teeth.

The more he looked, the more certain he became.

They must be ancestral elephants,

the oldest ever discovered.

It was an astonishing conclusion.

The oldest elephant ancestor was the size of a rabbit.

[man speaking French]

NARRATOR: Emmanuel brought his fossils

back to the Paris Museum of Natural History.

Today he keeps them in a filing cabinet in his office.

SANDERS: I give a lot of credit

to my colleague Emmanuel Gheerbrant

because it's like a detective story.

It's a real puzzler to figure out what they are,

and he found these things,

and he started looking at their teeth,

and he realized they had some subtle features on their molars,

the arrangement of the cusps on their molars

that said, "I am a proboscidean."

NARRATOR: Finally, scientists could see the very beginnings

of the elephant evolutionary tree.

NARRATOR: It starts with the tiny 60-million-year-old

creature with the miniature elephant teeth.

Emmanuel called it Eritherium.

NARRATOR: So much of the story of elephant evolution

can be told by teeth.

[grumbling]

NARRATOR: As elephants evolved, incisors slowly became tusks.

[roars]

They helped those early elephant relatives

browse in the ancient African forests.

SANDERS: We see that they have large front teeth,

and their jaw has grown forward in their mouth

so that their front teeth are a bit separated

from their back teeth,

so their front teeth are specializing.

They're specializing for grabbing food,

for acquiring food, for nipping food,

for chopping food.

NARRATOR: As incisors became tusks,

they took on the functions they have in elephants today.

SANDERS: They're used for acquiring food,

for knocking down plants so you can reach food.

They're used for social display.

Tusks are the defining features of elephants,

and it's like their behavior is tied up in having these tusks.

NARRATOR: And as tusks grew,

they propelled the evolution of the trunks

that would become the hallmark of all later elephants.

SANDERS: So, I think once you start to get tusks,

then trunks follow that.

It is important because they have to have something

to get past the tusks

in order to reach the food in their environment.

NARRATOR: As trunks grew, they slowly became

the amazingly sensitive organ of touch and smell they are

in modern elephants.

SANDERS: Trunks are made up

of something like 72,000 tiny muscle fibers,

so they're highly complex, and they can move them around

the way that you can move your hand around playing the piano.

Elephants have tremendous control over their trunk.

It's not just flopping around and sucking up water.

They can really be very gentle.

They can pick a penny up off the ground with their trunk.

Those trunks get a big workout.

NARRATOR: Tusks, trunks, and great size

were obviously successful elephant adaptations

to their forest environment,

but they didn't just help elephants

respond to their environment,

they gave them the capacity to change it, too.

NENGO: So, I think of all the species that we know of,

apart from humans, the only other mammals

that we know have the capacity

to be able to alter the natural ecosystems they live in

in a short time in a very big way

would be the elephants.

SANDERS: Proboscideans are big animals,

and you can imagine any big animal going through a landscape

is knocking down trees,

moving vegetation out of the way, creating paths.

NARRATOR: For that, Bill believes we humans owe them

a debt of gratitude.

He thinks elephants helped create the perfect conditions

for a certain group of apes millions of years later

to come down out of the trees

and begin to explore the savannas.

Those were our ancestors, the australopithecines.

The famous early human Lucy was discovered not far from Buluk.

Bill is convinced that she and our other early human ancestors

flourished in a landscape

that had been unintentionally prepared for them by elephants.

SANDERS: This idea of elephants opening things up

and creating the conditions of success for early hominids

might not be an exaggeration to say

that we might not be here without elephants.

NARRATOR: And just like our ancestors,

elephants did not stay put.

After millions of years in Africa,

they started to leave.

SANDERS: Proboscideans leave Africa multiple times.

Different groups leave at different times.

The first major foray out of Africa

is around 18 million years.

One suspects that you follow the vegetation

and you follow the available land paths,

so if Africa is docking with Eurasia

as continents move around a bit,

and you find familiar plants,

you don't really know you've left Africa,

and you just keep moving.

"Oh, and there's, over--

there's another pasture over there that seems pretty good.

Oh, well, wait.

Over that hill, that looks pretty green, too."

They get out at about 18 million years

in a serious way, out to Eurasia,

and they make it all the way to Japan in rapid time,

within a period of about a million years

after getting out of Africa.

♪

NARRATOR: Until recently, all we knew

of those ancient elephant species that left Africa

was from a few fossil bones.

But then, a dramatically different kind of discovery

brought them to life.

In the deserts of Abu Dhabi,

scientists discovered not bones, but footprints.

They were made by ancient elephants,

a vivid record of their great migration out of Africa.

FAYSAL BIBI: It's phenomenal because when you're actually

on the landscape,

it seems like the elephants just passed there yesterday,

but we know, geologically speaking, that's impossible.

These are very, very old sediments.

My name's Faysal Bibi.

I'm a paleontologist

at the Natural History Museum in Berlin.

So, it was, it was almost an afterthought

to image the tracks from the air.

And then we went back to the hotel that night,

and we started to put the imagery together.

As we realized what we had, we basically, our jaws dropped.

NARRATOR: What they saw was the footprints of an entire herd

of ancient elephants on the move,

a snapshot in time

of elephant behavior seven million years ago.

Back then, this desert was a lush savanna.

The muddy ground after a rainfall

captured their footprints perfectly,

all made by one of the strangest of elephant relatives.

♪

BIBI: It's probably ten minutes

in the lives of these individuals,

this herd that walked across the landscape,

and those ten minutes are forever preserved in these rocks

for us to see.

NARRATOR: And in that ten-minute snapshot,

Faysal can see all the dynamics of the herd--

the adults and calves,

a single bull male and a number of females.

BIBI: Yeah, so we have, it's a minimum

of 13 individuals actually.

You're walking along, and here was a large individual.

There was probably the matriarch.

They slow down. They speed up a little.

There was a smaller guy.

He's on the edge, so we're clearly not too worried

about any predators coming along on this landscape.

And then, perhaps, just the day before or the day after,

we've had the large bull who also crossed this landscape.

NARRATOR: Not long after Faysal and his team

made their discovery,

they took Bill Sanders to see it.

SANDERS: I had no idea what awaited me.

And then I saw them.

All the footprints of an entire herd

going on for about 260 meters,

and you can see baby footprints,

juvenile footprints, female footprints,

and then one great track of a big bull male

that must have come along later and crossed that track

and sort of checking out the herd.

We rarely get that opportunity.

I work on elephants, I love elephants,

and I'm seeing their behavior crystalized in time,

all the way back to the very beginnings of elephants.

And I just started crying.

And my colleagues all sort of applauded,

and they realized I was not crying out of sadness.

I was crying because I was ecstatic.

NARRATOR: Like skilled trackers,

the scientists could read the ancient footprints

and reconstruct a remarkably detailed picture

of that day seven million years ago.

BIBI: We could estimate the actual size

of these individuals

based on stride lengths of modern elephants,

where their weights are known,

and their stride lengths are known.

And their estimated weights

go from a few hundred kilos for the small one,

up to 5,000 kilos or so for the largest in the group,

and possibly 6,000 or so for the solitary individual

that was walking at that site.

NARRATOR: That makes them as big as any bull elephant today.

From fossils found nearby,

we know that they were magnificent animals,

four-tusked beasts called Stegotetrabelodons.

[trumpets]

BIBI: And here you are, you're on this landscape,

and you can imagine them having just been here,

like it was yesterday.

NARRATOR: Over generations,

their ancestors made the journey from Africa,

thousands of miles away.

[grumbling]

BIBI: They're extinct, they're long gone,

and they haven't just left us their bones and teeth,

this is an imprint of their society.

♪

NARRATOR: The discoveries in Abu Dhabi show

that by seven million years ago,

the social behavior of elephants had already evolved.

[elephant trumpets]

KAHUMBU: The fact that, uh, these ancient elephants

behaved very similarly to modern elephants

in a way confirms that it is a very successful strategy

to have these families working together.

They are incredibly cooperative as families.

You'll see females looking after each other's calves.

The young will actually have a very high death rate

if there aren't aunts around to look after the babies.

NARRATOR: Their close family bonds have been a key

to the success of elephants for generations.

[grunting]

Even though Stegotetrabelodons disappeared

a few million years ago,

their descendants and other elephant species

soon populated much of the globe.

Some, like the mammoths,

adapted to the cold of Siberia and North America.

Others, like the Gomphotheres, headed for the warmer climes

of southern Asia and Central America.

It had taken 60 million years, but the elephant lineage

had become one of the most successful on the planet.

Just 50,000 years ago,

elephant species were on all continents

except Australia, Antarctica, and South America.

So, what happened to them all?

SANDERS: A long debate among my colleagues

in my field has been,

what are the agencies for the extinction

of the elephants that we see,

for example, mammoths and mastodons?

NARRATOR: One hypothesis is climate change.

At the end of the last ice age, 10,000 years ago,

the world warmed.

The cold-adapted elephants of Siberia and North America

just couldn't deal with it.

SANDERS: In the Northern Hemisphere,

in northern latitudes, you have all this glaciation,

and these changes are happening very, very rapidly.

NARRATOR: But for millions of years,

the mammoths and mastodons managed to weather

similar climate changes.

What was different about the warming

at the end of the last ice age?

Bill believes it was our own ancestors

who tipped the balance.

SANDERS: So, we see the great sites in Eurasia

where indigenous peoples like 10,000 years ago

and 50,000 years ago and 60,000 years ago

were slaughtering these elephants in great numbers.

There is a tremendous predation pressure,

and imagine if you've got predation pressure

hitting you on one side,

and now you've got this climate change

and what it does to the landscape,

what it does to the plants and the available resources.

♪

NARRATOR: By 4,000 years ago, the world was left

with just the African, Asian,

and forest elephants we know today,

and now these are under threat as well.

This time, it has nothing to do with the end of an ice age,

just us.

♪

In 1800, there were an estimated 25 million elephants.

Today there are less than a million,

and the number is falling fast, thanks to habitat loss

and the relentless slaughter of elephants for ivory.

♪

KAHUMBU: Poaching now is very mechanized.

It's industrial.

In some places, we're losing 1,000 elephants in a month.

It's being done with not just weapons,

but with aircraft, trains and trucks and ships

to move the ivory out of Africa very quickly.

NARRATOR: The tusks that helped elephants survive

for millions of years have become a liability.

It's a new kind of evolutionary pressure,

human generated,

and in Africa,

it's causing elephants to change almost overnight.

KAHUMBU: Over the millennia,

elephants have evolved to have these huge tusks

because the most successful elephants are the ones

that had the biggest tusks.

But over the last few hundred years,

us human beings have been killing elephants

for those tusks.

There are some populations of elephants

who have very small tusks because poachers

are selectively removing elephants with big tusks,

and so the only females that get to breed

are the ones which have very small tusks,

and so you increasingly see tusklessness

in some of these elephant populations.

It would be such a tragedy if these magnificent animals

lost the one thing that makes them, you know,

so unique--their tusks.

NARRATOR: Even as they adapt, elephants are at risk.

Like so many other creatures,

they now face a new era of extinction.

SANDERS: If we lose elephants,

we put a big hole in the fabric of our coexistence

with other animals on Earth.

We've damaged in a way that we can't fix our ecological web,

our interdependent ecological web.

And we like to think of ourselves

as being separate from that,

but we really are inextricably linked.

NARRATOR: Everywhere the natural world is being transformed.

♪

Our own lineage has become

the planet's dominant evolutionary force,

shaping the web of life that exists all around us.

This one recently arrived species

is now the worldwide presence to which all others must adapt.

Our impact is so huge that our era

has been given its own name--

the Anthropocene, the age of humans.

It has seen the extinction rate among natural species

soar to hundreds of times what it was before our arrival.

As scientists race to chart the planetary changes,

they can look back at lessons from deep time.

They're observing many of the things that happened

in earlier extinctions--

rising CO2 levels leading to acidification of the oceans

and rapid climate change.

Habitat destruction.

Many believe we are witnessing

our planet's sixth mass extinction,

but the first one caused by a single species.

Like others, it will reset the evolutionary clock.

We just don't know how.

SUES: Today when we live in a world

where human populations are gradually changing

the face of the globe

by turning natural environments into artificial environments,

by pollution and many other ways

of interfering with natural systems,

we are very much confronted with the question

of evolution and extinction.

You can't have evolution without extinction,

but extinction really complicates our efforts

to get the big picture.

NARRATOR: We now know that mass extinctions

are an engine of evolution, clearing out environments,

making room for new species to evolve.

But in the past, they have usually taken millions of years.

This one is happening fast, in a matter of generations.

Viewed through the lens of deep time, that is a nanosecond,

too fast for many living things to adapt...

but maybe not too fast for us to make a difference.

Crocs have lived on Earth for almost 230 million years.

They've survived cataclysmic extinction events,

but today, 5 of the 14 crocodile species

are critically endangered.

HEKKALA: Most of the living crocodilians

were on the verge of extinction by the 1970s.

We were on the verge of losing all of them

when we put in place protection.

NARRATOR: Protections have helped.

In Australia, both fresh and salt water crocs have rebounded

thanks to strong steps like restrictions on hunting.

But what about the other great survivors of deep history?

10,000 species of birds still cover the globe.

Some have adapted to cities,

where they live beside us in seeming harmony.

But that's not the whole story.

CLARKE: We are hugely impacting bird evolution.

This is in habitat loss, consumption or killing,

poisons, the use of toxins in our environment.

[chirping]

NARRATOR: With 40 percent of bird species in decline,

there's reason to worry, but also reason to hope.

We managed to turn things around for iconic species

like the bald eagle and California condor.

And innovative programs show that more is possible.

In 1974,

only four Mauritius kestrels were left in the wild.

Today, there are 100 times as many,

thanks to predator control and captive breeding.

Ocean creatures need protection, too.

It took 50 million years for whales to become

the wondrous giants of the deep we know today.

[gunshot]

But in just two centuries, industrial whaling

brought many of them to the brink of extinction.

In the 20th century alone,

almost three million whales were slaughtered.

HILDERING: It's unthinkable now that we exploited whales

to the extent of, in the case of humpbacks,

driving down their population

to 10 percent of what they were globally.

They were almost pushed over the edge.

We only stopped whaling on northern Vancouver Island

in 1967.

Humpbacks we stopped in 1965.

So, we thought of them so very differently.

We saw them as a, as a resource.

But with humpbacks, we have a second chance.

NARRATOR: While some whales are critically endangered,

whaling bans have made a difference.

Humpbacks have rebounded,

and blue whale populations, which fell to just 1,500,

seem to be slowly increasing.

HILDERING: One of the many things that the whales do

is they remind us how connected we are

and of our capacity for change.

[grumbling]

NARRATOR: Around the planet,

others are heeding that reminder,

committing themselves to protect endangered animals and places.

[roaring]

In Kenya, Paula Kahumbu admires

one of the last true giants left on Earth,

a tusker named Tolstoy.

[grumbling]

KAHUMBU: I feel very humbled to be able to meet Tolstoy.

He is a giant of giants.

He's not just a big tusker, he's a super tusker.

There are very, very few elephants of that size

with tusks of that length left in the world.

You know, when, when you're with Tolstoy,

it's, one of the biggest rushes you get

is that "I'm alive." Right?

You just feel this sense of life.

It gives you goosebumps just to know that this elephant

is aware of your presence, and you're tiny and he's huge.

It's, he's beautiful.

It's just the most incredible experience.

NARRATOR: To know that Tolstoy is the product

of an evolutionary journey

that has been going on for eons

only makes him more precious.

And Tolstoy is not alone.

Crocodiles and birds, whales and elephants

are just four life forms among millions.

The tree of life is vast,

encompassing everything that has ever lived.

What will its branches look like after the age of humans?

The answer is up to us.

♪

♪