All language subtitles for Evolution.2026.S01E04.The.Dolphin.1080p.iP.WEB-DL.AAC2.0.H.264-playWEB_track3_[eng]

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.

BIRDS CHIRP
A bit of bird song...

INSECTS BUZZ
..whine of insects.

Crickets.

RUSTLING
A bit of rustling over there.

BUZZING
Incoming mosquito.

What about smell?
HE SNIFFS LOUDLY

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.

CHRIS CHUCKLES
Oh, yes!

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