All language subtitles for History.Of.Life.Series.2013.S01E01.1080p.AMZN-WEB.DL.DDP20.H.264-iND_track3_[eng]

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The environments of the
sea and land are so starkly

different that a transition
from one to the other

seems virtually impossible.

Nevertheless, they are the
dual stage of a grand drama

which took place over the
course of 4 billion years.

Some creatures birthed in the
sea climbed up onto the land,

while others returned to the
oceans from whence they came.

This odyssey from sea to land,
and then back to the sea,

is an integral part of
the history of life.

It is thanks to the pioneering
creatures that first set foot

on land that human
beings exist today.

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This is a desert located
150 kilometers southwest

of Cairo, the capital of Egypt.

It is a vast sea of
sand which seems to

be utterly bereft of life.

Yet, it is this barren land
that harbors vestiges of the

greatest mystery in
the history of life.

To paleontologists who
trace the history of life,

this is a treasure
trove of information.

Buried within the hot
desert sand are ancient bones.

Thirty years ago, Philip
Gingerich of the University of

Michigan made a
startling discovery here.

He discovered the
fossil of an ancient whale.

And this means it's an
experiment in whale evolution

that didn't happen before
and was very sucessful

but didn't happen after.

You can see it looks
like recent bone.

It looks like it died
yesterday but here it is in

the sandstone for
37 million years.

So that's why Wadi
El-Hitan is important.

He unearthed over a thousand
fossils in this place called

Wadi El-Hitan or
Valley of the Whales.

Thirty-seven
million years ago,

these parched lands were
covered by the Tethys Ocean.

Before Professor Gingerich
discovered this fossil,

not much was known about the
origins of the modern whale.

Whales are a rare instance
where a terrestrial animal

returned to the
sea, but until then,

the exact reasons for
this remained a mystery.

The key to unraveling this
mystery is Basilosaurus,

the ancient forerunner
of the modern whale.

Thirty-seven
million years ago,

Basilosaurus ruled
the Tethys ocean.

It was 16 meters
long, with a gaping

mouth and serrated teeth.

And unlike most
other aquatic creatures,

it had a pair of hind legs.

Today, vertebrates
dominate the world.

And the hind legs of
the Basilosaurus are a

characteristic that is unique
to land-dwelling animals.

Man is one of them.

In order find the link
between Basilosaurus and

land-dwelling animals,
we must travel back eons

to the origins of life itself.

4.5 billion years ago,
Earth in its infancy was an

environment hostile to life.

The atmosphere was
over 80 degrees Celsius

and devoid of any oxygen.

But after millions of
years, a miracle occurred.

The first living organisms
appeared on the Earth,

birthed by the ocean.

3.5 billion years ago, the
ocean was rich with oxygen,

and the horizon glowed with
the sapphire hue of the water.

It was at this time
that Stromatolite,

the first form of
life, appeared.

This primitive organism was
in fact colonies of blue-green

algae which survived through
photosynthesis and produced

abundant amounts of oxygen.

Thanks to this organism,
Earth's atmosphere became

oxygen-rich,
creating an environment

that was conducive to life.

500 million years ago, the
seas began to teem with an

endless variety of
strange-looking creatures.

They possessed long
tentacles and fearsome spines,

and were protected
by stone-hard armor.

This sudden proliferation
of life is called the

Cambrian explosion of life.

Scientists believe that
the ancestors of most of the

animals in existence
today appeared at this time.

This creature swimming through
the water using its wing-like

appendages is Anomalocaris.

Over a meter long, this animal
was the largest and most

fearsome predator of
the Cambrian oceans.

Thanks to its powerful jaws,
it could pierce through the

hard armor of a
trilobite with a single bite.

In the seas, competition for
survival grew increasingly

fierce, and creatures
were forced to modify

themselves in order to survive.

During this time, a
transformation occurred which

would alter the course
of evolutionary history.

This change occurred
in the tiny Pikaia,

a creature no larger
than the size of a thumb,

which was the constant
target of larger predators.

When we look at Pikaia, we
are really stepping into the

door of vertebrate evolution.

We are there, as we say in
English, on the ground floor.

These are the opening moments
of this extraordinary story

which is going to take
another half a billion years.

The Pikaia developed a stiff rod
on its back called a notochord.

It was the
precursor of the spine.

When we look closely, we
actually see that there are

quite a lot of details.

We can see the front end
and we can see the tail.

And then most interesting,
roughly along here,

there is a
distinctly different zone.

The notochord proved to be a
revolutionary improvement.

The notochord and the V-shaped
muscles around it called

myomeres, worked in concert to
propel this creature forward,

giving it
unprecedented speed and power.

This is how Pikaia
probably looked as it swam.

Its propulsion method is
similar to that of modern fish.

Despite being an
apex predator,

Anomalocaris soon
became extinct.

But Pikaia managed to survive.

While it was armed with
neither eyes nor a protective

shell, it could elude even
the fiercest of predators

using its superior speed.

Pikaia's legacy is significant
in the history of evolution.

Once you got a notochord,
once you got the myomeres,

then you're on the
way to becoming a fish.

Once you're on the
way to becoming a fish,

you're on the way to
becoming a vertebrate.

And once you are on the way
to becoming a vertebrate,

then you're on the
way to becoming us.

Had the Pikaia become extinct,
the history of life on earth

would have ended 5 hundred
million years ago in the sea.

Instead, these tiny
proto-vertebrates were slowly

preparing to become fish.

470 million years ago, the
primitive notochords become

fully developed
vertebral columns.

This is the
fossilized ancestor of all

vertebrates including man.

And the black pieces you can
see on the surface here are

pieces of an Arandaspis
fish called Sacabambaspis.

Now these are some of the
very earliest fishes where the

scales and armor was on
the surface of fishes.

While the fossil
is incomplete,

it shows the
distinct traces of scales,

a feature that is
unique to fish.

This is
Arandaspis, the first fish.

It was covered in scales like
the countless fish species

that came after it, but
because it did not have fins,

it was an awkward and
painstakingly slow creature.

Also, it was a jawless fish
which sucked water through an

opening in its belly, and
subsisted on the various

microorganisms which
it was able to strain.

After another
hundred million years,

a new fish appeared.

This is a fishing
village in Indonesia.

Here, fishermen
caught a strange fish which

they had never
before seen in their lives.

The fish that had become
tangled in their nets was none

other than a living fossil.

So, what does
this fish look like?

They open the lid
and clear the ice away

to reveal the coelacanth.

Scientists had previously
thought that the species had

already gone extinct during
the Cretaceous period when

dinosaurs still
roamed the earth.

It takes the
strength of three men to

lift the fish onto a table.

These animals can grow
up to 2 meters long and

reach 90 kilograms in weight.

Like most other
ancient fish species,

they are armed with sharp
teeth and thick scales.

Also, they carry their
eggs with them and give

birth to fully developed young.

But the feature that makes this
fish truly unique is its fins.

The fish is equipped
with large, powerful fins.

This foreshadowed an important
new evolutionary development.

This is Miguasha National
Park located in Quebec, Canada.

The sedimentary layers here are
up to 380 million years old.

Although this is a
northern coastal area,

it was a tropical region
located near the equator

hundreds of
millions years ago.

At the time, a river
flowed through this area.

And it was populated by a
diverse array of fauna that

comprised a
complicated food chain.

It is here, in the geological
strata of the cliff,

that traces of a significant
evolutionary leap can be found.

On exhibit in the museum
is a fossil of a fish that is

strikingly similar
to the coelacanth.

The species first appeared
in the Devonian period.

It was a large fish that
breathed through its lungs and

possessed a set
of powerful fins.

Called Eusthenopteron,
its name literally

means "Powerful Fins."

The fins of the fish have a
feature that had not been

found in previous species.

The fins contain bones.

We have one major element
that is articulating with the

shoulder girdle and this
element is the humerus,

exactly the same element that
we're finding in our arm or in

the arms of the
earliest tetrapods.

The boned fins of
Eusthenopteron are proof that

the limbs of terrestrial
animals originated in fish.

But why did this fish
develop bones in its fins?

These most likely will be
used to move in a very swampy

environment, just to
move among the plants.

So that is giving not just a
very thin fin but that will

give a very strong paddle that
the animal will be able to

push the plant to get into an
environment to find its food.

Eusthenopteron was
a skilled swimmer.

It used its powerful
fins to propel itself

freely through the water.

Also, it was an
excellent hunter with

well-developed jaws and teeth.

But the Devonian
seas were the stage for a

fierce battle for survival.

And Dunkleosteus
ruled supreme.

At 6 meters in
length, Dunkleosteus

was a true behemoth.

It was a placoderm which
possessed powerful jaws

and a thick plate of armor.

Equipped with
razor sharp teeth,

it often preyed
on Eusthenopteron.

In order to avoid
this vicious predator,

Eusthenopteron
undertook a risky journey.

It left the ocean in
search of a new habitat.

It used its powerful fins in
order to swim into a river,

and then to other
bodies of freshwater.

In the water,
there are huge fish,

some of them
about 16 feet long,

of all different
kinds, armored fish,

all kinds of predatory fish.

It was a remarkable period.

During the Devonian
period 370 million years ago,

the land was a place
full of opportunity.

Trees appeared,
foresting the barren terrain,

and rivers began to flow.

The fish which populated these
rivers heralded a new era in

evolutionary history.

Paleontologist Neil Shubin
discovered a fossil which would

shock the scientific world and
be called the "Missing Link."

He discovered this heretofore
unknown species on Ellesmere

Island in Northern Canada.

It was named Tiktaalik, or
"Large Freshwater Fish" in

Inuktitut, the language of the
local Native American tribe.

Although it had a
flat, lizard-like head,

its scales showed that
it was clearly a fish.

And for the first time, we're
seeing the kinds of fish that

can actually leave the water,
that can make the transition

from life in
water to life on land.

So all kinds of new
things are happening.

Tiktaalik harbors clues to
the gradual evolution of

land-dwelling
animals from the sea.

Unlike most other fish, the
Tiktaalik had a flat head with

eyes on the top of its skull.

Another
distinctive feature is this.

Tiktaalik possessed a neck.

This was a new
feature that wasn't

present in previous fish.

Tiktaalik use this neck to
rotate its head freely and

scour its surroundings.

But the real reason that
Tiktaalik is called the

"Missing Link" is its fins.

Its fins are more powerful
and intricately designed

than that of Eusthenopteron.

Tiktaalik had shoulders,
elbows and even wrists.

Now what's very special about
this is not only that these

are bones that
compare to our own arms,

but if you look at
the surfaces of this,

there's surfaces for
all kinds of muscles.

And not just any
kinds of muscles,

muscles that would've
helped the animals do a kind of

a push-up to support
itself against the ground.

Tiktaalik was a
revolutionary fish.

It could move its neck freely,
and scour its surroundings

with its eyes located
on top of its skull.

Its fins were equipped
with elbows and wrists,

and were strong enough to
support its gigantic body.

The appearance of
this fish signaled a new

movement towards the land.

Thus began the long and
arduous process of adjusting

to the new
terrestrial environment.

So, how did Tiktaalik
use its versatile fins?

Mudskippers which live in
the tidelands of Korea,

give us an idea of how
Tiktaalik must have moved.

The mudskipper uses its
pectoral fins to support

itself while crawling
around on its belly.

Tiktaalik must have climbed
onto the land using its fins

in much the same manner.

Water was loaded
with competitors.

Large fish, small fish,
everything competing for food.

Some of those
fish would eat you.

If you look at land,
there are plants there,

there's food there and these
early insect-like creatures.

So there are advantages for
creatures leaving the water to

go to land, to remove
themselves from the

competition for
food resources,

but also to escape some
of the predation that was

going on in the water as well.

After Tiktaalik, the
evolution of the fish

became even more accelerated.

Paleontologist Jennifer
Clack shows us a sketch of

a small lizard-like creature.

This is Acanthostega, a
species which marked another

turning point in the
history of evolution.

Acanthostega is a freshwater
fish which lived 360 million

years ago during
the Devonian period,

It had four almost
fully formed legs and

breathed air using its lungs.

Also, it had
something very unique

which Tiktaalik did not have.

One of the first things
that we found was that on each

limb, there were
eight fingers or toes,

which was a big surprise.

It was the first creature in
the history of evolution to

have fingers and toes.

Previously people had thought
that the primitive number for

fingers and toes was five
because that's what we have.

But it turns out that when
tetrapods with limbs first

evolved, they had
more than five.

Acanthostega had eight but we
also have other animals from

the same time
with seven or six.

This is a shallow lake in
the late Devonian period.

Acanthostega uses its webbed
feet to dart through the

water, weaving through various
obstacles along the way.

It hides among aquatic plants
and snatches a passing fish.

Acanthostega which possessed
both lungs and gills...

...finally took the
first steps onto land.

The adjustment to land
did not happen overnight.

The appearance
of the first spine,

fin equipped with
muscle and bone,

and the first legs and
toes was the result of billions

of years of trial and error.

Millions of years passed
by after the appearance of

Acanthostega and the
competition for survival in

the water grew
increasingly fierce.

But it was a different
story altogether on land.

The terrestrial ecology was
still full of opportunities.

Then, 280 million years
ago, the first complete

tetrapod appeared on land.

Descended from Acanthostega,
it could only breathe air

through its lungs, and it
didn't have to return to the

water in order to spawn.

The adaptation to
land was complete.

It was a moment of
monumental significance on par

with Man's landing on the moon.

The transition from life in
water to life on land is one

of the great events in
the history of life.

And it's an event that
changed the world forever.

For the first time, we have
creatures walking on land,

feeding on land.

But it's not just an event
that's captured in the past,

it's actually an event that's
inside our own bodies because

many of the features that
occurred for the first time in

the fish that walk on
land is part of us.

In many cases, the fish that
climbed onto land were the

weakest members
of the food chain.

They left behind the fiercely
competitive underwater

environment in
order to survive.

But through
change and adaptation,

they achieved the herculean
feat of adapting to a

completely new and
alien environment.

Once tetrapods had
reached the land,

they began to proliferate
at a breakneck pace.

They diverged into millions of
species including amphibians,

reptiles, birds
and even mammals.

Among their ancestors, mammals
reared and breastfed their

young, and became the
masters of the earth.

Once the weakest
creatures of the sea,

they achieved a
brilliant success through

their mastery of the land.

But there is a mystery
in the history of life

that still remains unsolved.

It is the existence of
mammals in the ocean.

This is a marine
mammal called the dugong.

It uses its fins like arms
and feeds on aquatic plants.

It breathes air
through its lungs,

so it must surface regularly.

It also births its
young and breastfeeds them.

So, why does the dugong
possess characteristics that

are common to
land-dwelling mammals?

The dugong swims away without
revealing any of its secrets.

We returned to the
Egyptian desert in order

to unravel this mystery.

Called Wadi Al-Hitan or
Valley of the Whales,

this desert has
been designated as a

World Heritage by UNESCO.

There is a line of
vertebrae in the sand.

Although this fossil was
called the "Lizard King" when

it was first
discovered, that was later on

proven to be a misnomer.

Basilosaurus was
far from a lizard.

Basilosaurus represents an
early stage of whale evolution.

It's one of the
first aquatic whales,

fully aquatic whales.

Once the dominant
species of the Tethys Ocean,

this primitive whale
lived from 42 million

to 34 million years ago.

The largest whale at the time,
this creature swam by weaving

its long body
through the water.

It had a pair of
underdeveloped hind legs which

seem puny in comparison
to its gargantuan size.

This is the clue which will
help us unravel this mystery.

This is a Basilosaurus fossil
unearthed in Wadi Al-Hitan.

This animal was also
called the "Walking Whale"

because of its hind legs.

Although they
were small, the legs

were fully formed appendages.

They are proof that Basilosaurus
once roamed the land.

The general trend,
life started in the sea.

This means that
the general trend,

from our point
of view at least,

is to come out on to the land
and the whale has gone back.

And so in that sense, it's a
reversal, it's backwards.

There is another mammal
that returned to the ocean.

It's Dorudon, a smaller
primitive whale that was

around 5 meters long.

The raging desert winds
revealed whales that had been

buried for
countless millennia.

Professor Philip Gingerich
has recently discovered a new

fossil embedded in a
cliff in Wadi Al-Hitan.

It's a fossil of Dorudon.

This is the first time that we
know how complete is dorudon,

how many
backbones, how long it is,

it's the first time we know
that these whales have legs and

feet and toes and it's because
of excellent preservation.

This whale with large jaws,
serrated teeth and tiny hind

legs is directly linked
to land-dwelling mammals.

It was a skilled
swimmer that lived in the

oceans 37 million years ago.

But its method of
swimming was completely

unlike that of any fish.

This is another clue which hints
at the origins of the whale.

The mechanics of dorudon are
reminiscent of the manner in

which land mammals use
their spines in order to run.

What is going on?

65 million years ago, at the
end of the Cretaceous period,

a giant asteroid collided
with the Earth, killing off

the dinosaurs which had
reigned supreme for many eons.

This was the
incident which spurred the

whale to return to the sea.

After the Cretaceous-Paleogene
extinction event and dinosaurs

are gone, the marine
reptiles are gone,

then there is no top
predator in the sea.

And so I see it more
as an opportunity,

not something pushing
from behind but something

pulling from in front.

So, which species was it exactly
that returned to the sea?

This fossil of
Pakicetus is the key to

unraveling this mystery.

This creature had 4 powerful
legs and seems to have nothing

in common with the whale.

Also, its vertebrae were
still attached to each other,

making its spine suitable
for terrestrial inhabitation.

Yet, it had a specialized
ear bone inside its skull.

Only whales possess
this bone which is used to

detect sounds underwater.

This is a sea near modern-day
Pakistan 50 million years ago.

Pakicetus was an amphibious,
wolf-like creature.

It took to the seas because
they were abundant with food

and less populated than land.

It also possessed long
webbed toes which allowed

it to swim freely in the water.

And it possessed a specialized
ear bone which allowed it to

hear the sounds of
its underwater prey.

The animal used this hearing
to catch fish with its long

snout and razor sharp teeth.

To hear in water is completely
different than to hear in air.

And so the hearing
apparatus has to be modified.

This ancestor of the whale
transformed its body to adapt

to its new,
underwater lifestyle.

Although it could only detect
underwater sounds at first,

later developments allowed it
to locate the direction from

which the sounds came.

This creature
changed everything in

order to adapt to the water.

Its forelegs became its
pectoral fins and its

superfluous hind
legs devolved.

Also, its tail became
wide and flat in order to

propel it through the water.

Lastly, its nostrils moved
towards the top of its skull

to facilitate
underwater breathing.

In this way, the
ancestor of the whale adapted

completely to the ocean.

Pakicetus, which had
maintained an amphibious

lifestyle for
countless millennia,

finally left the
land for good.

It had completed its
transformation and become

primitive whales such as
Dorudon and Basilosaurus.

This return to the ocean
is one of the most amazing

incidents to occur in the
history of life on the Earth.

The fish coming out on
land very early in vertebrate

history and the whale
going back to the sea late in

vertebrate history
have this similarity.

I think both are taking
advantage of some opportunity.

It's a nice comparison because
it shows that evolution is not

determined and directional.

Instead it is opportunist and
if the opportunity is behind,

we will go back.

But this is not the
end of the story.

34 million years ago, around
the end of the Eocene Epoch,

the Tethys Ocean which was
heavily populated by primitive

whales, began to dry up,
and the temperature

of the earth plummeted.

It was at this time
that Basilosaurus,

the largest whale species of
the era, and its lesser cousin,

Dorudon, met
with different fates.

It was the smaller species,
Dorudon that managed to

survive in the frigid waters
where food had become scarce.

And it became the forefather
of the modern whale.

On the other hand, the large
and inefficient Basilosaurus

could not avoid extinction.

In this way, these rare
primitive whales have become

buried in the sands of time.

Nevertheless, these
prehistoric behemoths leave us

with an unmistakable message.

Some people are interested
in stars and outer space

and how far we can see.

I'm interested in time and how
far back we can see because

all our understanding and
expectation for the future is

conditioned on what we
understand about the

present and the past.

The study of deep time, the
study of life through time,

understanding
where we came from,

how we are a
part of the earth,

how we are a part of
the history of the earth.

To some, fossils are merely
the petrified remains of

creatures from ages past.

But it is these creatures that
risked their lives to forge a

pathway into the unknown
terrestrial environment.

And their legacy has
withstood the test of time,

not only surviving in
the new environment,

but thriving in it.

We are their legacy.