All language subtitles for BBC.Evolution.4of5.The.Dolphin.1080p.x265.AAC.MVGroup.org

These waters are home to an animal
exquisitely adapted

to life below the waves.

I'm talking about the dolphin.

DOLPHIN CLICKS

In some ways, we couldn't be more
different,

and yet we share so much.

Oh, my goodness me!

Absolutely amazing.

DOLPHIN WHISTLES

Like us, these wild animals are highly
social...

..have sophisticated communication...

..work together to solve problems...

..and they're as interested in me as I
am in them.

CHRIS EXHALES LOUDLY

They're so curious. They just come up
and look at you.

I've never experienced anything like
this before.

Absolutely magical!

Driving this playful curiosity is a
giant, complex brain.

Some even larger than ours.

Dolphins are amongst the most
intelligent creatures

to have ever lived on Earth.

What is intelligence?

Well, there's a question that's easy
to ask

but a lot more difficult to answer.

You see, across the animal kingdom,

there are a range of species that
demonstrate intelligence.

Some bird species, pigs, bees,

even humans,

but some of those animals are
undeniably

more intelligent than others,

and, here in these waters, the
cleverest by far are those dolphins.

So the question is, how did the
dolphin get to become so smart?

Well, to answer that question, we must
turn back the clock

and follow a remarkable tale of
transformation.

Back to a time before mammals.

Before brains.

Before anything...

..could even think.

Countless lives have contributed to
this story,

but a few distant ancestors, each with
remarkable lifestyles,

have left legacies that have echoed
down the generations,

gifting the dolphin its brilliant
brain.

The story of intelligence begins a
very long time ago...

..on a planet devoid of thought,

ideas, curiosity.

No animals live on ancient Earth.

But it is a home.

Single cells live a simple
existence...

..with not a single brain cell between
them.

But, after Earth's billion-year-long
dark age...

..a revolutionary act is taking place.

You see, these cells have evolved the
ability...

..to sense light.

In that moment, where those first
cells

developed the ability to sense the
Sun,

the dark ages of life on Earth came to
an end.

It was truly a time of enlightenment,

and, if you bear with me, I'm going to
show you why it was so important.

Look at that!

There's a huge beetle over here,

lots of flies, of course,

and then moths.

Look at that beauty!

Stunning thing.

And of course they're turning up,

because moths are famously attracted
to light.

And the way moths detect the light is
similar to the way

that some bacteria detect light,

and not just contemporary bacteria,

but the bacteria that were living in
those ancient oceans.

Modern animals like moths use a
molecule called retinal.

It changes shape when it's struck by a
photon of light.

Like a switch, this allows cells to
sense light.

And genetic techniques have revealed
something extraordinary.

Three billion years ago,

those ancient bacteria sensed light

using the same molecule - retinal.

But they did something else that, in
time, would become

the foundation of intelligence.

They didn't just sense light,

they reacted to light.

We think that moths are drawn to the
flame, as it were,

because they use what light there is
at night,

typically the Moon and the stars,

to orientate themselves in their
environment,

but what this has allowed is the
development of a behaviour -

a basic instinct.

Now, we mustn't confuse that instinct
with intelligence.

I mean, let's face it, these moths
haven't been able

to out-think that innate behaviour and
not be drawn to this trap.

But that instinct,

fuelled by the ability to sense and
react to light,

was a crucial first step on the route
to becoming smarter.

And for the next step, we need to jump
forward through time...

..2.5 billion years.

Life continues to evolve...

..until we enter a new age of animals.

This tiny creature is an ancient
ancestor of the dolphin...

..and it's searching for a place to
hide.

But not from any predator.

From the punishing UV rays of the Sun.

To guide it, it has two
light-detecting spots

that only sense patches of light and
dark.

So, finding shelter is no easy task.

But among this population of
shade-seeking animals,

the dolphin's ancestor has a slight
edge.

It's inherited a series of mutations -
genetic changes...

..which mean instead of being flat,

its light-detecting spots

cave ever so slightly inwards,

becoming little dimples.

Now, it's a difference so small it
might seem insignificant,

but they give it an unexpected
advantage.

To understand all of this, we need to
think a bit about optics.

Here's a basic demonstration.

Imagine the flat surface of this plate
is that flat pigment spot,

covered with all of those
light-sensitive cells.

Now, when it's facing the Sun,

it's fully lit, it's fully saturated.

As it turns away, it's lit...

..and then it's not.

It's in shadow.

It's either or - light or dark.

Things are very different, though,
with a dimpled surface.

Look at this bowl.

Again, if it's facing the light full
on, then of course it's fully lit,

but look what happens as it turns
away.

Parts of its surface are in shadow

whilst, simultaneously, parts are lit.

Of course, if it turns completely
away, then it's in shadow,

but this is the critical part -

shadow and light at the same time.

And this is what gives these early
creatures

the chance to build up a rudimentary
map of their environment

using light and shade.

For the first time ever,

creatures are beginning to see the
world.

And in simple terms, these little
dimples,

these little buckets,

are the first proper eyes.

For the dolphin's ancestor,

these simple, dimpled eyes

allow it to sense more than just
shades of grey.

Instead,

it sees the first blurry images...

..giving it the ability to efficiently
find a place to hide

from the powerful Sun.

I know what you're thinking.

You're thinking, "How on earth can you
know that all of that is true,

"particularly when soft-bodied animals
with tiny worm-like eyes

"don't fossilise particularly well?"

Well, I can tell you that almost all
of the characteristics

of those earliest eyes can still be
found in living animals today.

Simple, light-detecting spots still
exist in some jellyfish

and limpets.

Dimpled, or "cup eyes",

are seen in modern-day flatworms.

And hiding in this forest is a curious
creature

with eyes like tiny buckets.

This is a fascinating animal.

It's a velvet worm.

I've always wanted to see one.

What can it see? Well, looking out
here,

a very crude picture of its
environment,

but very little detail,

so, if I were to take this animal to
the optician's,

it would be declared legally blind.

For the velvet worm that seeks damp
and dark places to shelter,

this basic vision is more than
sufficient.

But over half a billion years ago,

dimpled eyes were just the beginning.

Over generations, dimples grow deeper.

Protective cells grow over the
opening,

forming a lens...

..which focuses the Sun's rays onto a
layer of light-sensing cells -

a retina.

In a surprisingly short period of
evolutionary time,

those simple spots transform

into one of the most complex
biological instruments

evolution has ever produced.

By the Cambrian period, sophisticated
eyes are everywhere.

From those that come in pairs...

..to bizarre evolutionary experiments.

Now, you might be wondering

why I'm talking so much about eyes

in the story of intelligence.

That's because the senses, and vision
in particular,

played a critical role.

They changed the dynamics of life
entirely...

..because if animals can see the world
more clearly...

..then they can also...

..see each other.

To stay alive now,

you need your wits about you.

In the Cambrian period,

there was a sudden massive increase in
the diversity of new life,

so much so that we call it the
Cambrian Explosion.

There are a number of theories as to
why this might have happened.

It's likely that many of them come
into play, but, without ambiguity,

one thing is certain - the evolution
of the eye played a role -

because it opened up opportunities for
new predator-prey relationships,

and that alone would have driven an
increase in diversity.

But it's not just about the eye.

Take a look at this fossil.

This is an anomalocaridid animal.

It lived 500 million years ago, it's
related to lobsters,

and this was a ferocious predator in
the Cambrian period.

And these are its eyes.

Beautiful!

Look at the preservation here.

And these are compound eyes, like
contemporary insects

and crustaceans, and they appear to be
on stalks.

We think that this animal could move
its eyes

independently of one another,

looking in different directions at the
same time.

This was a massive increase in visual
complexity.

But how did the animal deal with it?

Well, look at this part here.

This represents an organ which is
very, very, very rarely fossilised.

This is the animal's brain.

It's thought that the first animals
had simple nervous systems,

but it's only when complex eyes come
on the scene

that fossilised brains are found.

We think these are the optic nerves,

passing all of that visual information
to the brain

to be analysed.

Now, brains have got their own
evolutionary history,

they didn't just appear overnight,

but in the wake of the Cambrian
Explosion,

they got bigger and they got more
complex,

potentially to deal with all of that
visual information.

It's a beautiful fossil.

Without the evolution of
light-sensitive cells,

we wouldn't have eyes, and without the
evolution of eyes,

we wouldn't have brains as we know
them today.

The modern animal kingdom is full of
eyes and brains

attuned to perceive the world in
whatever way is most useful.

Compound eyes give a wide field of
view to smaller brains.

Giant eyes that see like a camera
gather information in the depths.

And forward-facing eyes help large
brains navigate a 3D world.

But 500 million years ago,

animals and their newly-evolved brains

are just waking up to the world around
them.

As we leap forward again...

..the struggle for survival drives
brains to become more complex...

..and more strategic.

Welcome to the Silurian period...

..where the hunted have become the
hunters.

This fierce-looking animal is an early
female placoderm...

..and you don't want to mess with her.

You see, the predator-prey arms
race...

..has turned her into one formidable
fish.

Placoderms dominated the Earth's
aquatic ecosystems

for 60 million years,

and I've got a fossil of one here, and
what a fossil this is.

Just look at that!

It's very, very beautiful.

It came from Scotland and it lived 380
million years ago,

but look at the degree of preservation
here.

You can see all the bones in its
vertebrae, the dorsal fin here,

this is the head end, of course,
here's its eye.

Look at that.

Oh, wow.

And I've never got over the fact that
I can put my finger

on something which lived 380 million
years ago.

But getting back to placoderms, you're
going to say, you know,

"Why is this fossil so important?
There are loads of animals

"that lived and died out. Why is this
one such a big deal?"

Well, these were some of the first
animals

that had a jaw and a backbone,

so if we want to learn more about what
we call the jawed vertebrates,

and that's me, you, your children,
your gran,

your pets, dolphins,

then we've got to learn more about
placoderms.

Placoderm fossils of all shapes and
sizes

have been found on every continent on
the Earth.

Yet all share one intriguing feature.

Bony plates covering their heads.

Armour to protect the most precious
weapon

a predatory fish has in its arsenal.

Its brain.

The predator-prey arms race had turned
these creatures

into veritable little warships,

and I say "little" because this is a
small one.

Some of them grew up to four metres in
length.

But, sadly, as we know,

no amount of armour can protect us
from some things.

In these ancient waters,

a hidden threat is lurking.

Despite its armour, this early
placoderm

has fallen victim to a tiny invader.

A virus.

One whose impacts would ripple through
time.

Viruses have always been pulling the
strings of life.

They're master manipulators, silently
and ruthlessly

invading their hosts to take advantage
of them,

and we know how they work.

They break into their host's cells,
hijack those cells' machinery,

and then replicate themselves...

..over and over and over again,

until they burst out in a dangerous
explosion of infection,

giving us things like Covid, flu,
common cold.

But not all viruses act in this way.

Some break into the cell

and then insert their own genetic
material into the host's DNA,

potentially changing it forever.

These are called retroviruses...

..and we think that over 400 million
years ago,

a retrovirus was circulating in the
oceans,

infecting the bodies of many species
of ancient fish.

One of whom may have been this early
placoderm.

Luckily for her, however, her immune
system kicks into gear...

..and she recovers.

But, like a Trojan horse, some of the
virus

makes its way into her egg cells

and is passed on to her offspring.

Over generations, the hidden viral DNA
does something extraordinary.

It triggers one of the fish's genes to
go into overdrive...

..altering the way its nerve cells
develop...

..causing parts of the brain to turn
from grey

to eerily pale.

But instead of causing harm, the brain
is changed forever.

These infections likely happened
multiple times

in multiple species...

..and scientists think their effect
has been profound.

Oh, my God!

It's a Jesus Christ lizard.

I used to look at drawings and read
about these things

in my childhood animal encyclopaedias.

And it's named after the son of God

not because it so much walks on water

as runs very fast across the surface.

It's also got lightning-fast
reactions.

So how does it manifest all of this
speed, as it were?

Well, it comes down to its nerve
cells.

You see, each of its nerve cells have
long fibres called axons.

Those axons are wrapped in a fatty
sheath

of a substance called myelin and it
insulates them.

And what that means is that each nerve
cell

can communicate with the other far
more quickly,

and that happens in its brain

and it happens from the nerves that
run from its brain

to the muscles around its body.

It's as if it's got a super-fast
processor.

Nerve signals can travel up to 200
times faster

in axons insulated with myelin than
those without.

And therefore we can make the argument
that the origin of myelin

was the singularly most important
development

when it came to the evolution of the
vertebrate brain.

Now all we need this little lizard to
do is something biblical.

Today, myelin is found throughout the
jawed vertebrates.

All of these animals have myelin to
thank

for the fast signals inside their
brains.

And scientists have found that nerves
insulated with myelin

can't be produced without ancient
retroviral DNA...

..which has been transmitted down the
generations

from fishes that caught a virus

over 400 million years ago.

Evolution. You just can't beat it, can
you?

Well, you can, because it gets better.

You see, myelin didn't just speed
things up,

it allowed brains to develop more
computing power.

It allowed brains to evolve to become
more compact,

more complex, more powerful.

It was as if life had just got a
hardware upgrade

and this was therefore a significant
step up

in the evolution of intelligence

because, for the first time, the
vertebrate brain

was on the cusp of doing something it
had never been able to do before.

Thinking.

Across tens of millions of years...

..fast-thinking vertebrates dominate
the oceans.

But for the next chapter in the story
of the dolphin

and its amazing brain...

..we need to step out onto land.

This strange, hairless, burrowing
animal is a cynodont.

An ancestor of mammals, including the
dolphin.

Now, it lives underground for good
reason.

Predatory reptiles roam outside.

But, at some point, it's got to
venture out to eat.

As the day comes to an end, there's an
opportunity.

But there's just one problem.

It's getting dark.

Soon, its vision won't be much use.

Imagine what it was like for those
little cynodonts.

Now, I've got a cast of one of these
animals' skulls here.

You can see that "little" is the
appropriate word.

This skull is about the same size as a
rabbit.

So, they were small, opportunistic
hunters.

The problem was that when they
ventured out,

particularly in broad daylight,

there was a very good chance they'd be
hunted themselves.

There were loads of predators stalking
around the Triassic.

But when these little creatures
ventured out of their burrows

into the night, there were distinct
advantages for them.

At night there are fewer predators...

..and reduced competition for food.

But, of course, in the dark, food can
be harder to find.

What they would have experienced is
pretty much

what I'm experiencing now.

Human eyesight isn't brilliant in the
dark

but it's not that bad either.

So, if I close my eyes, now I'm
effectively blind, what happens?

Well, I immediately start to
concentrate

on my other senses, of course.
Firstly, hearing.

A bit of bird song...
BIRDS CHIRP

..whine of insects.
INSECTS BUZZ

Crickets.

RUSTLING A bit of rustling over there.

Incoming mosquito.
BUZZING

HE SNIFFS LOUDLY
What about smell?

Oh, yeah, that smells good.

I can smell all of that decomposing
leaf litter.

That's what I call "forest fruitcake".

A really rich, delicious mix of
odours.

And, I mean, I'm not bragging, but I
like to think

that my sense of smell is quite well
attuned in nature.

I've been sniffing it all of my life.

So, out here in the dark, I would be
fairly confident

using my sense of smell to help me
navigate.

Perhaps you wouldn't be quite so
confident,

and that would have been exactly the
same for those cynodonts.

Part of their population would have
had senses

which were more finely attuned, and
those would have been

the individuals that went out to
forage, found food,

and then made it safely back to their
burrows.

Super-sensing cynodonts would have
fared better navigating at night.

And it's thought this allowed some
groups to become nocturnal.

And as these cynodonts' senses
sharpened to the night...

..we think the flood of new
information being gathered

kick-started a monumental
transformation

in their descendants' brains.

Over tens of millions of years, the
brain changes shape.

Areas involved in smell and touch
expand...

..and the brain increases in size by
over 40%.

To process the new information, we see
a game-changing region

develop in the top layers of the
brain.

And with it, a new type of animal.

In under 50 million years, those
burrowing cynodonts

had evolved into something a little
bit like this.

The first mammals.

Now, I know that many of you probably
aren't that keen on rats.

I love them.

I love their little whiskers, whisking
away,

and those stiffened hairs are rooted
in skin

which is packed full of nerves,

sending masses of information to its
brain.

And then you've got its twitching
nose.

A nose far more sensitive than ours,

capable of smelling things like
explosives, even human cancers.

And its ears... Now, come on, those
are the prettiest little ears.

Radar dishes listening out for the
rustle of any potential predator.

But, of course, all of this extra
sensory information

needs to be processed,

so it was at about this time that an
area of the brain

called the neocortex began to develop
more fully.

And that was utterly, utterly
transformational

because it allowed these animals to
solve problems,

to learn, to develop memories,

and, with all of that extra sensory
processing,

to map their environment and plan
their next move.

The neocortex was an extraordinary
mammalian innovation.

And that neocortex is the outer layer
of the mammalian brain.

Sometimes smooth, sometimes wrinkly
and folded.

It receives and processes complex
sensory information...

..and it links it to other regions the
brain.

In today's mammals, it's essential for
learning...

..planning...

..prediction...

..decision-making.

The foundations of what we'd call
intelligence.

Now, of course, mammals aren't the
only intelligent animals.

Birds have a structure called the
"wulst"

that performs a similar function to
the neocortex.

And octopuses have one centralised
brain

and eight mini brains.

One for each arm.

But 200 million years ago, for the
mammals,

the neocortex helped unlock a more
intelligent way of life.

And to continue their story, we need
to take another leap through time...

..until...

..it's the mammals' turn to take
centre stage.

By now, those mammals have radiated
out

and diversified across the globe.

And it's here that we find one unique
group

on the verge of an extraordinary
transformation.

This is Indohyus.

The size of a cat, with deer-like legs
and the snout of a dog.

Quite frankly, it's a bit of a weirdo.

Tiptoeing on little hooves, it's on
the lookout for lunch.

LOUD SQUAWK

But it's not the only one.

This diminutive plant-eater is easy
pickings for predators

circling above.

But Indohyus has an escape plan.

A strategy adopted by another of
evolution's oddballs.

Indohyus was a lot smaller and more
dainty, but I give you...

..the tapir.

Oh, yes!
CHRIS CHUCKLES

What an animal!

I absolutely love tapirs.

I've liked them since I was a kid. I
don't know what it is about them.

I think it's because they're weird.

But what else have they got in common
with Indohyus?

Well, they're both herbivores, and, as
a consequence,

they need to be thinking about
avoiding carnivores.

This Baird's tapir can be predated by
jaguars.

So how do they avoid that?

Well, one of the things they've done
is developed an aquatic lifestyle.

Now, if you don't want to be buoyant
if you're in the water,

and, on that account, when they go
into the water,

they sink to the bottom.

They can walk across the bottom of
rivers, lakes and lagoons,

and that is the same as Indohyus.

Indohyus had heavy bones.

In fact, trying to evade predators on
a day-to-day basis

was at the core of driving

one of the most revolutionary
transformations in evolution.

For Indohyus and its heavy bones...

..water is a refuge.

And stepping away from land...

..turned out to be a masterstroke.

This new world offers up plentiful
food

and new opportunities.

Over generations, their relatives
become much more streamlined.

Limbs are replaced with paddle-like
flippers.

Nostrils migrate further away from
their long snouts.

Tails get flatter and more powerful.

And the once-hoofed mammals

are now completely aquatic.

This was one of the most astonishing
body transformations

in the course of evolutionary history.

In just over 10 million years,

these tiny, terrestrial, tiptoeing
animals

had transformed into sleek,
streamlined swimmers.

And I've got the cast of a skull of
one of them here.

This is Dorudon

and it lived 40 million years ago,

and the teeth do all of the talking.

Look here.

These massive canines for catching and
gripping the prey

and then these teeth here

for shearing it into tiny pieces.

This would have been an impressive
animal, but not the biggest.

One of its relatives, Basilosaurus,

grew to the length of a bus.

Those puny, cat-like animals

had transformed into monsters.

Superb.

But, of course,

things didn't stop there.

This is a cast of the skull of
Simocetus,

a distant relative of Dorudon,

and it lived 32 million years ago.

But look at the skull -

pretty radically different.

It's much shorter, it's far more
structurally complex on top here.

Simocetus was part of a new group of
marine mammals -

the odontocetes, or "toothed whales".

Look at this depression here.

We think an organ called the melon
might have sat here.

It's a fatty sphere. Sounds produced
from the nasal passages are focused

through it like a lens and projected
out into the animal's environment.

When they bounce back, they're
captured by the lower jaw,

part of which is hollow, transferred
to the inner ear,

which sends the information to the
brain.

You know what I'm saying here, don't
you?

Echolocation had evolved.

Echolocation!

What about that?

But we think something else radical

might have been happening at the same
time.

We think that animals like this might
have been

at the start of a journey from being
solitary hunters

to hunting together,

and this social behaviour would have a
profound effect

on the development of the brain.

As the toothed whales continued to
evolve...

..it's thought that many of them
became more and more social.

And the fossil record shows evidence
of their brains getting larger...

..until, around 11 million years
ago...

..an iconic family emerged.

Dolphins.

Today, over 40 species of dolphin can
be found worldwide...

..from the tiny...

..to the giant.

They live in groups...

..and have complex social
relationships.

And some species are amongst

the most intelligent animals on Earth.

This group of spotted dolphins

have spent their whole lives in the
Bahamas.

DOLPHINS CLICK AND WHISTLE

And their social lives govern their
behaviour.

Mothers, cousins,

friends, even rivals,

all roaming together in the waters
they call home.

I've just been to spotted dolphin
heaven!

I cannot tell you.

That was absolutely incredible.

At one point, I was just wrapped in a
vortex of spinning dolphins.

Oh, my goodness me.

CLICKS AND WHISTLES

And, of course, we know that they all
know one another,

not just now but throughout the course
of their lives.

They've got that phenomenal memory.

And to think they are down there
experiencing emotions

like joy.

I think they were feeling joy. I was
certainly feeling joy.

But then we know that they can even
experience grief as well.

DOLPHIN CLICKS

And the clicking!

The constant ticking.
"Tick-tick-tick-tick", all the time.

They're communicating to one another.

Now, there's a dispute amongst
scientists

as to whether they have a language,

but, from my point of view at the
moment,

I'm quite happy to fantasise, because
I would love,

absolutely love, to know what they
were all saying to one another!

Honestly...

Honestly, so, so good.

This is the soundtrack of a thriving
underwater society...

..underpinned by one of the most
complex brains on Earth.

Relative to their bodies, it's one of
the biggest of any animal,

with key regions thought to be
involved in self-awareness,

communication and understanding
emotions.

And that uniquely mammalian neocortex

has become one of the most intricately
folded brain surfaces

on the planet.

Brains are amongst the most
energy-expensive organs

to run in the body, but, boy, are they
worth that cost,

because if you've got a large, complex
brain, like those dolphins,

it gives you the capacity to develop
intelligence.

And the dolphins use that intelligence

to change their behaviour on a
day-to-day basis.

They can learn things.

They can then copy things from
dolphins that have learned things.

They've got cultural learning
capabilities.

And this social intelligence is the
most important tool in the box

when it comes to survival.

But get this,

they evolved that intelligence

in a world which is completely alien
to ours.

They evolved it...

..underwater!

We may never truly know what goes on
inside the mind of a dolphin,

but its brain tells a remarkable
story.

Three billion years of sensing...

..of struggle...

..and survival.

Of brains...

..and bodies...

..transformed.

Dolphins' minds, like ours for that
matter,

are remarkable pieces of biology.

It's for very good reason that we
think of our brains

as being the most complex objects in
the known Universe

and they're still surrounded by an
aura of mystery, of magic.

But here's one thing that we know for
certain.

Our brains, our minds,

simply wouldn't exist without the
power of evolution.

That blind journey of change,

of innovation, of exquisite beauty.

Next time...

..how the horse became one of nature's
greatest athletes.

Just look at her.

She's absolutely gorgeous.

Aren't you?

From life's first steps...

..to racing hearts and limbs built for
speed.

Let's see them in action.

DOG BARKS

This is a slithering, swimming,
sprinting odyssey,

with one final twist.

Us.

But first, how do we know that the
ancestors of dolphins

once walked on land?

- Dolphins are part of a larger group
called cetaceans,

which includes dolphins, whales and
porpoises.

- Cetaceans have the largest range in
body size

of any group of mammals on the planet.

- From really small, little harbour
porpoises

that are only a few feet long,

to the blue whale - the largest animal
on Earth,

and everything in between.

- And their origin can be traced back
to an ancient sea

that once stretched between India and
Asia.

Local and international scientists
have been searching for fossils

in India and Pakistan over many years,

where they found the remains of an
intriguing mammal.

- What I'm holding in my hand here is
a real fossil

of the skull of Indohyus.

There's four of these in the world.

I've got one right here.

- The name Indohyus actually means
India's pig.

- From the chemistry of the teeth, we
can tell that this animal ate

land plants, mostly leaves, and
flowers and fruits.

- From first appearances, Indohyus
looked like a regular land mammal...

..until a chance event revealed a
critical structure

hidden deep within its skull.

- I had a fossil preparator, his name
was Rick,

who was cleaning this off, he said,

"I'm very sorry, but I broke part of
this Indohyus skull",

and then I noticed that the ear bone
actually shows a feature

that's only present in whales and
dolphins, called the involucrum.

- The involucrum is a region of the
ear bone that has thickened.

In modern-day cetaceans, it amplifies
vibrations

transmitted in the skull, enhancing
their ability to hear under water.

- So that's really the smoking gun
that Indohyus is closely related

to whales and dolphins.

- Evidence that it was already
adapting to a life underwater,

completing the remarkable story

of how land mammals evolved into
marine cetaceans.

- It is one of the best fossil records
we have,

so we've got a lot of pieces of the
puzzle

to tell us what happened.

- Other transitional fossils have been
found across the region

that was once the ancient Tethys Sea.

- We have whales and dolphins that
look like crocodiles,

we have whales and dolphins that look
like seals

or otters or sea lions.

- It is probably one of the most
dramatic transformations

in all of the evolution of life.

Indohyus was not the kind of animal

that you would look at and say,

"You're going to get a blue whale out
of that",

"You're going to get a brain like a
dolphin brain out of that",

but that's what evolution does - it
makes big changes.

- Do you want to know how an elephant
is related to a clownfish?

Discover more in a poster from the
Open University on the tree of life.

To get your free copy, scan the QR
code on screen

or ring 0300 303 3460,

or visit connect.open.ac.uk/evolution