All language subtitles for Attenborough.First.Life.(2010).Conquest.2

I'm on a fantastic journey
to look for the origins of life.

I shall be travelling, not only
around the world, but back in time,

to try and build a picture

of what life was like
in that very early period.

Last time I saw how,
600 million years ago,

simple cells evolved into
the first multi-cellular animals.

In this programme,
I investigate what happened next.

I will look for evidence in both

fossils and living creatures
of what happened in that

far, distant past,

when the fundamental features
of modern animals

were being established
for the first time.

One group, the arthropods,
were the great pioneers.

They were the first big predators.

They had eyes.

Legs.

And hard external skeletons,

They were the first
to crawl out of water

to conquer the land and the air.

600 million years ago,
the world was very different

from the planet we know today.

The land was entirely
without animals or plants.

But the oceans
were teeming with life.

The first proto-animals
were immobile organisms

that lived on the sea floor
and extracted their nourishment

from the water flowing around them.

But once animals developed mouths

and the ability move,
evolution took off.

Canada's Rocky Mountains.

Here we can find evidence
of a sudden explosion of life

when animals started to evolve
with astonishing rapidity.

It happened during a period
called the Cambrian.

And it began 542 million years ago.

During the next
10-20 million years,

animals increased in numbers,
diversity and size as never before.

And as they got bigger,
so they became more complex.

And they're preserved to an
extraordinary degree of perfection

in the rocks right below me.

The Burgess Shales,
where a rich seam of fossils

documents this Cambrian explosion
in astonishing detail.

All this area was once the floor
of a shallow sea, teeming with life.

As sediment settled down onto
the floor, so it became compressed

and turned into mudstones and shales
that you can see around me here.

About a century ago,

an American geologist from
the Smithsonian Institution

was making a survey
of this part of the Rockies.

And he came walking
along this particular path.

And when he got
to precisely this spot,

he noticed a tiny fossil
of a kind he had never seen before.

He bent down and picked it up
and it looked like this.

What sort of a creature
could this be?

It was only the first
of the enigmatic creatures

to come from the Burgess Shales.

Since then over 65,000 different
specimens of now extinct

Cambrian animals have been
from this one small quarry.

Many species have never been
found elsewhere.

It seems that the Burgess Shales
were deposited in a place

where conditions for fossilisation
were uniquely perfect.

As a consequence, even bodies
of animals that were soft

and lacking any hard parts were,
nonetheless, preserved.

They survive as thin, almost
imperceptible layers,

that you only see
if you get the light just right.

It's these fossils that have
transformed our understanding

of how animals we know today
have come to be the way they are.

In some of these specimens
we can glimpse shapes and forms

that look faintly familiar.

But many of these bizarre creatures
seem like nothing we know of today.

This is one of the more mysterious
animals from the Shales.

There are two clues as to how
this creature might have lived.

It has flaps
along the side of its body,

but no legs,
and also a broad, flat tail.

So it's reasonable to assume
that they helped it swim

and that it lived not
crawling along the floor,

but up higher in the water.

But the really, truly mysterious
thing about it is that here

on its head it had five eyes,

each of them like
a kind of little mushroom.

And beneath that it had a long
proboscis

with which it grabbed things.

It's a truly primitive animal

and one that, still,
we don't fully understand.

It's been named opabinia.

And it seems to have been
a kind of evolutionary experiment.

It's almost as if an assortment
of different body parts

had been put together
in something of a hurry.

What other animal has five eyes?

And opabinia
wasn't the only oddball.

Wiwaxia was once thought to be an
ancestor of earthworms,

but now is considered
to be an early snail.

Most of the Burgess Shale creatures

are unlike anything
ever discovered before.

There were countless
bizarre creatures

living in the Cambrian Seas,

This unprecedented surge
of diversity was something

that had never happened before
and would never happen again.

For many years, scientists
excavated and scrutinised the Shales

looking for the causes
of the Cambrian explosion.

Their first task
was to try and reconstruct

what these strange animals must have
looked like when they were alive

and that was not at all easy.

This is one of the oddest
of the fossils from Burgess Shales.

It seems to have five legs
along the bottom,

and curious kind of lobes
along the top,

which presumably were some devices,
which help it to feed.

But what kind of animal
is that with five walking legs

and feeding lobes along
the top of its back?

It was such an extraordinary
thought that the scientist

who described it thought
it was a kind of hallucination,

and he called it "hallucigenia".

But since then, more specimens
have shown that in fact,

this is probably the wrong way up
and that it was really like that.

The projections at the bottom
are, in fact, legs.

And those along the top
are tipped with sharp spines

that were presumably, defensive.

Perhaps these animals evolved these
strange shapes

because they needed
to protect themselves?

But if so, from what?

Where were the predators?

No-one could find
a likely candidate.

And then the answer came
from a couple of fossil species

that they had known almost
from the very beginning.

One of the strangest
fossils found here is this.

It's also one of the commonest.

But what is it?

Well, it has what looks like legs,
so you might think

it was some kind of caterpillar,
or shrimp maybe.

But the most mysterious thing
about it was that

they never found one with a head.

Then there was another mystery,

not as common as the headless
shrimp,

but one that looked
like a sort of jellyfish,

with radiating lines out,
and this strange hole in the middle.

And about twenty years ago,

it was discovered that actually,
there is a link between

this and this.

This bit is not a separate shrimp,
it's actually a claw.

And this bit is not a jellyfish,
it's a mouth.

And in the mouth
you can see something

that looks very significant.

Could these be teeth?

And were these not legs but spikes,
used to stab and grab prey?

The two were, in fact, connected.

But now we have
a most perfect fossil,

which really demonstrates
that that is indeed the case.

This, you might say, is
the Mona Lisa of the Burgess Shales.

This specimen, at last,
gave scientists a picture

of the complete animal.

It had plates along its back,
and a tail at the rear end.

It was a swimmer.
And between those two spiked claws

at the front there was a mouth...

with teeth.

This was the hunter
they had been looking for.

The scientist who discovered
the claws called them anomalocaris,

meaning strange shrimp.

That name is now used
for the whole animal.

With its large tail and flexible
plates along its flanks,

anomalocaris could propel itself
through the water at speed.

Other specimens show that it could
grow to a length of nearly a metre,

two feet or so.

It was, as far as we know,
the first big predator on Earth.

We can get clues
as to what it was like

from an animal that is alive today.

It's much smaller than anomalocaris,
though remarkably similar.

And it lives in Australia,
here on the Great Barrier Reef.

Professor Justin Marshall
has been studying these ferocious

and powerful hunters
for over 20 years.

You have to very cautious
about the way you handle them.

If you pick them up they can
knock the ends off your fingers.

Fishermen call them
thumb splitters because

as they handle them they get
thumbs and fingers split open.

The other, slightly more technical
name for them is mantis shrimp.

They have a very ancient ancestry.

Fossils of almost identical
creatures have been found

that date back 400 million years.

This animal is almost as ancient
as anomalocaris itself.

It lurks in burrows,
waiting for its victims

to swim within range of its claws.

Looking at the fossils
of anomalocaris

and comparing them to mantis shrimps,

one could imagine that these
animals are similar.

They both have big raptorial
appendages

that are shot out
at the front to grasp prey.

You could imagine
them lurking behind a rock

waiting for unwitting prey
to come past.

And bang! Suddenly that's dinner.

The mantis shrimp illustrates
the essential characteristics

of this brand new predator class
of animals.

Superb vision,
great speed and superior size.

Like anomalocaris, it's considerably
larger than its victims.

It also has extremely acute vision,

with 12 different types
of colour receptors in its eyes.

We have just three.

And it's one of
the fastest animals alive,

some species striking with
the speed of a pellet from a gun.

It's unlikely anomalocaris was as
fast, or that it saw its prey

so clearly, but nonetheless,
it was a formidable predator,

just as the mantis shrimp is today.

Even a glimpse of a finger
through glass is enough

to make this animal strike,

and with alarming force.

So why did the mantis shrimp
evolve in this way?

Well, obviously...

in order that it could

outfox and outmanoeuvre,
and eventually catch its prey.

It's become very fast,
very powerful,

and capable of great patience.

And those are characteristics
of predators everywhere.

So the fossilised remains
of anomalocaris

are evidence that hunting
had begun in the Cambrian.

And as predators became bigger,
faster and stronger,

so their prey had to develop
increasingly elaborate defences.

Opabinia's five eyes
helped it spot trouble.

And Hallucigenia protected itself
with those spines along its back.

One of the world's leading
experts on the Burgess Shales,

Dr Jean-Bernard Caron,
believes that it was the arrival

of predators like anomalocaris
that stimulated the great

Cambrian explosion of diversity.

It is during the Cambrian

that we can start seeing animals with
legs, eyes, swimming.

This didn't exist before
and this evolved very, very quickly

at the beginning of the Cambrian.

But once you have a big predator,
presumably the rest of life,

which it was feeding on,

had to evolve quite fast
to develop some sort of defences.

Would that be true?

Well, we think that this evolution
occurred relatively quickly because,

in a place like the Burgess Shale
you find organisms

that may have had
some kind of defensive mechanism,

which is thought to be a response
to higher predatory levels.

Arms race, if you want,
between predators and prey.

One result of this duel
between predators and prey

was the development of armour.

Animals everywhere
were absorbing calcium carbonate

and other inorganic substances
from the seawater

and mineralising their bodies.

Many of them, like wiwaxia,
that early mollusc,

and ancestors of the squid,
ammonites,

developed protective shells.

But one group, the arthropods,
which had jointed legs,

encased their entire bodies
with hard armour plating.

And what began as defensive armour,
necessary for survival,

brought with it another great
advantage.

Hard parts can be used not only
to give protection,

but to provide support for a body.

Ha-ha!

This spider crab is a crustacean.

And it secretes chitin from
its body,

which it then strengthens
with calcium carbonate.

And a whole range of creatures

have skeletons like this,
based on chitin.

Arthropods today include shrimps,
lobsters and crabs,

as well as land-living creatures,

such as millipedes,
scorpions and insects.

But the ancestors of all of them
first appeared in the Cambrian Seas.

Over 50% of fossils
in the Burgess Shales

are arthropods
of one kind or another.

But one family was
particularly abundant and varied.

Just across the valley
from the quarry,

near the summit of Mount Stephen,

almost every rock you turn over
contains their remains.

Here, they are found
all over the place.

They're called trilobites.

Trilobites because their bodies
were in three sections.

Here on this slab
there are several of them.

That's the head.

There's the middle bit.
And there's the tail.

One, two, three trilobites.

Trilobites, at this particular time,

right at the beginning
of the Cambrian,

began to proliferate
into all sorts of forms.

These creatures,
for the next 250 million years,

were probably the most advanced
forms of life on this planet.

To see how advanced the trilobites
eventually became,

I'm going to North Africa.

In Morocco, on the southern flanks
of the Atlas Mountains,

the hills contain
an amazing variety of them.

They were only discovered
a few years ago,

but now the demand for them
is so great

that digging them out
has become a major industry.

These rocks, which were laid down
about 150 million years after

the Burgess Shale,
also contain trilobites.

The trouble is,
the rock is very hard

and the trilobites are quite rare.

But when these people find them,

their specimens are absolutely
extraordinary.

Some species have features
that are so delicate

that it can take days,
sometimes weeks,

to fully prepare a specimen.

Skilled technicians
use dentists' drills

to get down to the finest detail.

Every particle of rock
must be carefully removed,

with enormous patience
and absolute precision.

The end results reveal
that trilobites

moulded their external skeletons

into an almost unbelievable
variety of shapes.

And that enabled them to colonise
a great variety of habitats,

just as modern arthropods
still do today.

There were about 50,000 different
trilobite species that we know of,

and doubtless there are still
many more to be discovered.

Their hard exoskeletons

not only ensured their abundance
in the fossil record,

they also tell us a lot
about their owners' lives.

Many of the trilobites
that are found in these cliffs

are curled up like this one.

Sometimes even more tightly
than this is,

with their tail tucked
underneath their heads.

And it's clear that this was some
kind of protective posture,

just as it is for some
kinds of woodlice

that you find in the garden today.

That protected them
against their enemies.

But there are so many that
are curled in these deposits,

together with others that have
their backs arched upwards

and others
in other strange postures,

that it seems that they are the
victim of some kind of catastrophe.

The sea floor, it seems,
was quite steep.

And every now and again,

the mud that accumulated on
the bottom slipped down

in a submarine avalanche,

carrying the animals
that lived in it and on it,

higgledy-piggeldy,
and burying them alive.

Moroccan trilobites
are big business these days.

Particularly rare species
sell for thousands of pounds.

The world's leading trilobite
experts,

such as Professor Richard Fortey,

come here to study
these extraordinary animals.

He believes that
their external skeleton

was the key to their success.

The trilobites
did almost everything

you possibly can do
with an exoskeleton.

I think that skeleton
was what gave them an advantage.

They were protected. They could
do all kinds of interesting things.

They could grow spines.

They could get flat, like pancakes.

They could protect themselves
by getting thick exoskeleton

with pobbles all over it.

It was a great advantage to them,
just as it is to crabs and lobsters

living today, which of course
weren't around

at the time of the trilobites.

So they utilised the virtues
of having a tough exoskeleton,

to radiate into all kinds of
ecological niches.

You can see one of the most
comprehensive collections

of trilobite fossils

just a few miles from where
they're quarried, at Erfoud Museum.

The collection here reveals
just how varied

the trilobite skeleton could be.

There is no question
that an exoskeleton

gave the trilobites protection.

But it also gave them something else
of great value.

There must have been many reasons
why trilobites were so successful.

But one of them, unquestionably,
was their power of sight.

They had eyes.

not just eyespots that could tell
the difference

between light and dark,

but complex eyes
that could form detailed pictures

of their surroundings, for the first
time in the history of life.

Eyes like these.

Most animals on Earth today
have eyes of one kind of another.

Most are made of soft tissue,
as ours our.

But trilobite eyes are unique.

Their lenses are derived from their
mineralised external skeleton.

They're made of rock.

Each one of these
little dots is a lens.

And each is made from calcite,

a crystalline form of chalk.

Trilobites were the only organisms

ever really to use this stuff
as their lens material.

And in doing so they evolved
very sophisticated vision indeed.

For example, these sorts of
trilobites had very large lenses.

And each lens is readily visible
with the naked eye

and each one is biconvex.

And it's been proven that individual
lenses have little bowls inside them

to help them focus more precisely.

These creatures were among
the first,

certainly, to actually focus
a picture, weren't they?

It wasn't just a question of telling
light from dark,

they could do better than that?

On no, these, these had really
sophisticated vision.

The kind of trilobites that have
these eyes were probably hunters.

Some people have claimed that they
could form stereoscopic images,

using both eyes, so they could
really home in on the prey.

May predators today,
including ourselves,

have 3D, or stereoscopic vision.

It makes it possible for a hunter
to accurately judge the distance

between itself and its prey.

But not all trilobites
were predators.

Some were inoffensive creatures
that lived by munching mud.

But sight must have been valuable

for them too, enabling them to
spot enemies in time to escape.

There are trilobite eyes
with more than 5,000 lenses.

5,000? More than 5,000 lenses.

Now each of those,
does it have an image?

Each doesn't have an image, but
if they go for lots of tiny lenses,

they're particularly
sensitive to movement,

i.e. something changing
between one lens and the next.

This trilobite's eyes are so big
they extend right round its head

and meet in the middle.

And that suggests that the animal
swam high above the sea floor

and had a 360-degree view
of the scene below.

With each lens capable
of detecting movement,

its owner must have been able to see
an enemy coming from any direction.

But the shape of a trilobite's
eyes can reveal more than the

kind of image they produced.

Eyes can tell us a surprising amount
about how and where an animal lived.

This one with its eyes on turrets
probably lived in the sea where it

was gloomy, but nonetheless there
was enough light for the animal to

be able to see on either side of it.

This one, on the other hand, has
eyes also on turrets, but at the top

it has flanges, like sun shades.

So it's, er, likely that it
lived in the shallow, sunlit sea

and valued shades above its
eyes so it didn't get dazzled.

This one, however, has very
reduced eyes, and it may well be

that it skated along the mud along
the bottom,

where it was gloomy anyway
and there wasn't much to see,

so like an animal living in a cave,
it slowly lost the use of its eyes.

And finally there's this creature,

and this is the one I
think is particularly delightful.

This one has its eyes on stalks.

And probably lived under the mud,

gobbling up food there
with its, just its eyes

peeking out of the top, to see
whether there was danger around.

So trilobites were the first animals
to see clearly.

But they had other senses as well,
perhaps some

we don't even know about.

Take this species with this bizarre
trident structure on its nose.

What was it for?
Some kind of motion sensor?

Prehistoric radar, perhaps?

Trilobites were, without question,

the most successful
animals of their time.

They flourished in
all parts of the ocean.

Indeed, they could be counted
as one

of the most successful kinds
of animals
in the entire history of life.

Most trilobites are quite small,
rather like beetles are today.

But the biggest living beetle is
about that big, the goliath beetle.

Trilobites, on the other hand,
grew very big indeed. Like this one.

And this is by no means the biggest.

The biggest known is nearly
a metre, nearly three feet long.

And it's thought that these
really big ones grew to this size

because they lived in cold waters,
and that's a tendency of animals

in cold, to grow large.

And at the time that these rocks
were laid down, Africa,

where we are now,
and where these are found,

was down by the South Pole.

Spectacular though these are,

they were by no means the largest
arthropods in the ocean at the time.

The trilobites had remote cousins,
also arthropods, that had grown

into monsters.

Their remains are much rarer,
and often fragmentary,

but some of the most complete
have been found in Scotland.

ALARM SOUNDS

One of the best
is held in the vaults

of Edinburgh's National Museum.

Gosh!

Well, this is a magnificent example
of just how big an animal can grow

if it has an external skeleton.

This is a creature called
the Eurypterid, or a sea scorpion.

And it was a hunter.

It had a pair of powerful pincers
at the top, just behind its head.

It was obviously a monster,
a terror of the seas.

And this is by no means the
biggest of the eurypterids.

Sea scorpions were the
top predators of their day.

As far as we know,
they were the biggest arthropod

that has ever existed.

The discovery of a large
fossilised claw suggests

that they could grow up to two and
a half metres, eight feet in length.

So arthropods of one kind or another

were certainly dominant
420 million years ago.

The seas were full of life.

From huge complex animals
like this sea scorpion

creeping along the bottom,

to simple creatures, like jellyfish,
floating on the surface waters.

But the land was barren
and without animals of any kind.

But there was food up there,
simple plants,

and that tempted some animals
to venture out of the water.

Surviving on land, however,
was a problem for them.

Coming from the sea,
they had to evolve ways

of preventing their bodies
from drying out.

And even more difficult, they had to
develop a method of breathing air.

The very first animals
had simply absorbed

dissolved oxygen from the water

through the skins
of their soft bodies.

As they began to move and grow
bigger, they needed more energy,

more quickly.

And that meant

they had to improve their method
of collecting dissolved oxygen.

Bigger, more complex animals,

like for example, this lobster,

have to have specialised devices,
which are called gills.

Here in the lobster they are
these flaps underneath its abdomen,

which is flaps forwards

and backwards to increase the flow
of oxygenated water over them.

But the trouble with gills is that
they only work when they're wet.

In the dry,
they do not absorb oxygen.

So if animals are to live on land,

they had have to have a new way
of breathing.

The Burgess Shales,

that astonishingly rich treasury
of Cambrian fossils,

contain the remains of just one

particularly rare species that may
well have been the very first animal

to make that move onto land.

It was not, as you might think,
an amphibian, it was not even

a true arthropod, but
one of their far distant cousins.

This little creature,

from the Burgess Shale seas,
is thought to be the ancestor

of the very first creature that went
on to land. It's called Aysheaia.

And we don't have to imagine what it
was like in life,

because there's a creature,
that seems to be almost identical,

that is alive today.

It lives in many parts of the
tropics, including the rainforest,

here in Queensland, Australia.

It's nocturnal and seldom seen.

It spends most of its time
hidden away inside rotten logs.

Ah, it's nice and wet!

Certainly, er, perfect
for what we're looking for.

You need local expertise
to find one.

I generally find
that it's just from the outside

of the, er, core of the tree.

All nice and... Oh! What is that?
Ooh, look at that.

And this enchanting
little creature

is what we were looking for.

Sometimes called a velvet worm,

or to give it its scientific name,
Peripatus.

If there is such a thing
as a living fossil,

this surely must be one of them.

Because it seems to be
almost identical

with that fossil, Aysheaia,
which we saw in the Burgess Shales.

It looks at first sight like a worm.

But of course no worm has legs.
In fact,

it seems to be halfway

between a worm

and an insect.

Aysheaia, of course,
lived in the sea.

But this little creature
lives on land.

And it has one further attribute,

which Aysheaia could not have had.

It has tiny little holes
all along its flanks,

which enable it to breathe air.

So this is one
of the first creatures

that moved on to land,

540 million years ago.

Velvet worms may have been the
first animals to set foot on land,

but they have hardly changed during
the following half-billion years.

Why?

Well, unlike true arthropods,
their bodies are covered,

not by an exoskeleton,
but by soft, permeable skin.

That lack of an external skeleton
means that their bodies,

unsupported by water,
can't grow any bigger.

It also means that in order to
prevent themselves from drying out,

they have to stay
in damp environments.

True arthropods, like this scorpion,

a descendent of those giant sea
scorpions, were not so restricted.

They had external skeletons.

That meant that not only were their
bodies protected from drying out,

but they were strong and rigid
enough to allow them to grow bigger

and get around without
the support of water.

So how and when did true arthropods
with exoskeletons

draw their first breath of air?

The answer can be found in this.

It is perhaps the smallest and most
fragmentary fossil I've seen so far,

but don't be fooled by appearances.

It's almost certainly
one of the most significant.

This specimen was collected in Cowie
Harbour, here in Scotland, in 2004.

Even though it's so small,
under the microscope you can see

extraordinary detail.

This is the main body of the animal
with its segments.

And here are its legs.

But above each there is a tiny hole.

That is a spiracle, through which
the animal was able to breathe air

just as insects do today.

And since it breathed air,
if it had gone into the water

it would have drowned.

So this is a truly land-living
animal and what is more,

it's the first and oldest
that we know.

It's 428 million years old.

But what kind of creatures were
these early land-dwelling arthropods

Animals very like them
are still quite common

in many parts of the world.

There are certainly plenty of them
in those Australian rainforests.

One sort are millipedes,

which today grow as long as that
and live on vegetation

and rotting wood,
harmless vegetarians.

But there's also another multi-leg
creature, which is a much more

difficult customer.

This is one of them.

A centipede. A very formidable
hunter, with a powerful bite,

and some centipedes have bites
that are lethal to human beings.

What kind of a bite this one has,

I don't know.

But when I let him out I shall do so

very carefully, because
I don't propose to find out.

Come on.

So multi-legged arthropods
invaded the land and became

more successful than ever.

Back in Scotland,

there is impressive evidence
of just how successful they became.

This is a small fishing village

on the East Coast of Scotland
called Crail.

Nothing particularly strange
about it, you might think...

until, that is,
you go down to the shore.

And then you can see something
that is really extraordinary.

Standing here and there
on the beach are fossils,

not of animals, but of plants.

This huge circular stump
looks just like the base of a tree.

And indeed
that is what it is, or rather,

what it was, 335 million years ago.

But it wasn't a tree
like trees we know today.

It was related

to the small plants that are
alive today called horsetails.

But this tree grew to 90 feet.

It was immense.

When they were alive, during a
period called the Carboniferous,

long after the Cambrian,

this whole area was very different

from the windswept coastline
of today.

This was a time when the continents
of the world were grouped together

and forests were widespread.

So much plant life
was pumping out oxygen

that the composition
of the atmosphere began to change.

This had a profound effect
on animal life.

In the forest that was growing
near Crail, the ancient trees

were rooted in a sandy swamp.

And on the expanses of sand that
stretched between those huge trees,

sand that's now turned
to this sandstone,

there are tracks.

Tracks that come in pairs,
there's one pair that goes up there.

There's another pair that
goes up here.

And when you look at them
in detail, you can see,

particularly on this pair, that each
track has a number of dimples in it.

And those
are the imprints of individual feet.

So this animal had a lot of feet.

It's thought to have been
a giant millipede.

It was about...

four and a half feet long,
one and a half metres.

And it had 26 or 28 segments.

A magnificent beast.

Arthropleura.

A giant millipede,

probably the biggest terrestrial
arthropod that has ever existed.

The largest specimen discovered so
far was nearly as long as a car...

two and a half metres.

The Carboniferous was the golden
age for the arthropods,

for the air was now particularly
rich in oxygen.

Today the atmosphere
contains around 21% oxygen.

Back in the Carboniferous,

it was around 35% and that enabled
animals to grow very big indeed.

But growing large
was not their only success.

Some other arthropods in these
carboniferous rainforests

were evolving in a different way.

Instead of becoming
huge and ponderous,

they became agile and speedy.

To do that it's better to be
short rather than long, and some

reduced their segments and ran
around on just three pairs of legs,

as silverfish and
bristletails do today.

These early insects then
made another dramatic move...

they developed wings and became the
first animals of any kind to fly.

Truly the invertebrates
had colonised

not only the land, but the air.

And in an atmosphere
so rich in oxygen,

they did so in a truly dramatic way.

This giant dragonfly,

the biggest flying insect that has
ever existed, is called Meganeura.

Its wings were nearly
three feet across.

But the golden age of the
giant arthropods was not to last.

The rainforest died back, and
oxygen in the atmosphere dropped.

Giant insects are no longer
alive today and that may be

because the proportion of oxygen in
the atmosphere is very much lower.

But nonetheless,
insects have managed to find a way

of overcoming the problems of size.

They've become colonial.

Just as in the far distant,
remote past,

individual cells clubbed together
to form a larger organism,

such as a sponge,

so hundreds of thousands
of individual insects, termites,

have cooperated to build this nest.

And a colony like this
can crop as much vegetation

from the surroundings
as a bigger animal like an antelope.

So by living in vast colonies
like this,

arthropods can still dominate
their surroundings.

They've become super-organisms...

hundreds of thousands of individuals
all descended from the same female,

working and behaving as one.

So arthropods remain

one of the most successful
groups of animals on the planet.

They've spread to all its corners.

Insects alone make up at least 80%
of all animal species.

But arthropods weren't the only
ones to make this move on to land.

The Burgess Shales -

the place where the beginnings
of all this proliferation of life

in the Cambrian period
are recorded in unparalleled detail.

Among the ancestors
of all the insects,

spiders, the scorpions,
the shellfish, the crustaceans,

the shrimps, the sponges,

there's just one tiny little
creature, very insignificant,

which we human beings might think is
perhaps the most important of all.

Because this...

is the first creature to
have the sign of a backbone,

and thus, therefore, is probably
the ancestor of us all.

It's a tiny, worm-like
creature called Pikaia.

It was not a fearsome hunter.

It had no teeth for attack and
no external skeleton for defence.

But Pikaia did have something new.

Instead of an external skeleton,

it had an internal one,
a thin gristly rod...

the beginnings of a backbone.

It, or something very like it,
was the ancestor of all vertebrates.

From such a creature as this,
the first fish evolved.

Some of them, living in swamps,
started to gulp air and wriggled up

onto the land. They gave rise
to moist-skinned amphibians.

Some of them developed scaly,
impermeable skins that enabled them

to colonise the driest places...

they were the reptiles.

And from them came the birds.

And the mammals.

Today mammals, like this rhinoceros,

are the biggest of all
living animals.

Hello, old boy. How are you?

How are you?

'All mammals, including ourselves,
extract oxygen from the air with

'the end of internal lungs,
and distribute it through our bodies

'in our blood.'

There we are. There's a good lad.

'But we also owe
our success, and our size,

'to the nature of our skeletons.'

Animals with an internal skeleton,
like this rhinoceros,

have a huge advantage over animals
whose skeleton is external.

A white rhinoceros, like this,

is one of the biggest land animals
alive today.

Compare him

with him... a rhinoceros beetle.

Its skeleton is external.

It's very powerful.

It can carry 850 times
its own weight.

But it can't grow much bigger.
Because the only way it can grow is

by shedding its skeleton
and growing a new one.

And while its skeleton is not there,
its body is unsupported.

And after a certain size, the body
will collapse under its own weight.

Here.

Here we are, come on boy.
Come on boy.

Despite these differences,
it's no coincidence that

backboned animals evolved many of
the same features as the arthropods.

Teeth.

Legs.

Shells. Eyes.

And wings.

Any animal group needs such
things if they are to colonise

all the Earth's varied habitats.

A journey that began for me near
my boyhood home in Charnwood Forest

has taken me around the world
and through 600 million years

of evolutionary history.

I've seen evidence
of how single-celled life

dominated the planet
for billions of years,

until a global ice age triggered
the emergence of the first animals.

Many animal groups
lasted millions of years.

But eventually their time ran out
and they disappeared.

But others endured.

And between them they evolved

into the wondrous variety of life
that inhabits this planet today.

Life originated in the oceans.

After an immense period of time,
some creatures managed to crawl up

onto the land.

Those animals may seem to us
to be very remote,

strange, even fantastic.

But all of us alive today
owe our very existence to them.