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

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

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to try and build a picture

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of what life was like
in that very early period.

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Last time I saw how,
600 million years ago,

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simple cells evolved into
the first multi-cellular animals.

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In this programme,
I investigate what happened next.

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I will look for evidence in both

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fossils and living creatures
of what happened in that

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far, distant past,

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when the fundamental features
of modern animals

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were being established
for the first time.

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One group, the arthropods,
were the great pioneers.

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They were the first big predators.

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They had eyes.

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Legs.

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And hard external skeletons,

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They were the first
to crawl out of water

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to conquer the land and the air.

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600 million years ago,
the world was very different

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from the planet we know today.

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The land was entirely
without animals or plants.

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But the oceans
were teeming with life.

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The first proto-animals
were immobile organisms

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that lived on the sea floor
and extracted their nourishment

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from the water flowing around them.

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But once animals developed mouths

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and the ability move,
evolution took off.

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Canada's Rocky Mountains.

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Here we can find evidence
of a sudden explosion of life

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when animals started to evolve
with astonishing rapidity.

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It happened during a period
called the Cambrian.

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And it began 542 million years ago.

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During the next
10-20 million years,

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

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

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And they're preserved to an
extraordinary degree of perfection

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in the rocks right below me.

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The Burgess Shales,
where a rich seam of fossils

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documents this Cambrian explosion
in astonishing detail.

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

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

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

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About a century ago,

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an American geologist from
the Smithsonian Institution

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was making a survey
of this part of the Rockies.

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And he came walking
along this particular path.

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And when he got
to precisely this spot,

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

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

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What sort of a creature
could this be?

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It was only the first
of the enigmatic creatures

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to come from the Burgess Shales.

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Since then over 65,000 different
specimens of now extinct

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Cambrian animals have been
from this one small quarry.

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Many species have never been
found elsewhere.

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It seems that the Burgess Shales
were deposited in a place

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where conditions for fossilisation
were uniquely perfect.

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As a consequence, even bodies
of animals that were soft

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and lacking any hard parts were,
nonetheless, preserved.

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They survive as thin, almost
imperceptible layers,

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

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It's these fossils that have
transformed our understanding

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

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In some of these specimens
we can glimpse shapes and forms

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that look faintly familiar.

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

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

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

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It has flaps
along the side of its body,

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

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

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and that it lived not
crawling along the floor,

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but up higher in the water.

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

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on its head it had five eyes,

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each of them like
a kind of little mushroom.

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And beneath that it had a long
proboscis

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with which it grabbed things.

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It's a truly primitive animal

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

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It's been named opabinia.

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

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

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had been put together
in something of a hurry.

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What other animal has five eyes?

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And opabinia
wasn't the only oddball.

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Wiwaxia was once thought to be an
ancestor of earthworms,

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but now is considered
to be an early snail.

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Most of the Burgess Shale creatures

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are unlike anything
ever discovered before.

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There were countless
bizarre creatures

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living in the Cambrian Seas,

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This unprecedented surge
of diversity was something

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that had never happened before
and would never happen again.

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For many years, scientists
excavated and scrutinised the Shales

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looking for the causes
of the Cambrian explosion.

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Their first task
was to try and reconstruct

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

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and that was not at all easy.

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

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It seems to have five legs
along the bottom,

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and curious kind of lobes
along the top,

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

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But what kind of animal
is that with five walking legs

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and feeding lobes along
the top of its back?

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It was such an extraordinary
thought that the scientist

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who described it thought
it was a kind of hallucination,

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and he called it "hallucigenia".

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

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

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

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And those along the top
are tipped with sharp spines

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that were presumably, defensive.

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Perhaps these animals evolved these
strange shapes

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because they needed
to protect themselves?

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But if so, from what?

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Where were the predators?

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No-one could find
a likely candidate.

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And then the answer came
from a couple of fossil species

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that they had known almost
from the very beginning.

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One of the strangest
fossils found here is this.

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It's also one of the commonest.

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But what is it?

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

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it was some kind of caterpillar,
or shrimp maybe.

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But the most mysterious thing
about it was that

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they never found one with a head.

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Then there was another mystery,

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not as common as the headless
shrimp,

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but one that looked
like a sort of jellyfish,

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

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And about twenty years ago,

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it was discovered that actually,
there is a link between

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this and this.

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

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

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And in the mouth
you can see something

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that looks very significant.

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Could these be teeth?

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

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The two were, in fact, connected.

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But now we have
a most perfect fossil,

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which really demonstrates
that that is indeed the case.

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

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This specimen, at last,
gave scientists a picture

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of the complete animal.

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

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It was a swimmer.
And between those two spiked claws

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at the front there was a mouth...

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with teeth.

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This was the hunter
they had been looking for.

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The scientist who discovered
the claws called them anomalocaris,

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meaning strange shrimp.

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That name is now used
for the whole animal.

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With its large tail and flexible
plates along its flanks,

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anomalocaris could propel itself
through the water at speed.

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

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two feet or so.

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

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We can get clues
as to what it was like

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from an animal that is alive today.

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

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

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Professor Justin Marshall
has been studying these ferocious

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and powerful hunters
for over 20 years.

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

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

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Fishermen call them
thumb splitters because

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

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

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They have a very ancient ancestry.

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Fossils of almost identical
creatures have been found

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that date back 400 million years.

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This animal is almost as ancient
as anomalocaris itself.

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It lurks in burrows,
waiting for its victims

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to swim within range of its claws.

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Looking at the fossils
of anomalocaris

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and comparing them to mantis shrimps,

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one could imagine that these
animals are similar.

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They both have big raptorial
appendages

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that are shot out
at the front to grasp prey.

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You could imagine
them lurking behind a rock

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waiting for unwitting prey
to come past.

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And bang! Suddenly that's dinner.

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The mantis shrimp illustrates
the essential characteristics

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of this brand new predator class
of animals.

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Superb vision,
great speed and superior size.

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

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It also has extremely acute vision,

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with 12 different types
of colour receptors in its eyes.

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We have just three.

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And it's one of
the fastest animals alive,

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

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

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

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just as the mantis shrimp is today.

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Even a glimpse of a finger
through glass is enough

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to make this animal strike,

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and with alarming force.

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So why did the mantis shrimp
evolve in this way?

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Well, obviously...

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in order that it could

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outfox and outmanoeuvre,
and eventually catch its prey.

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It's become very fast,
very powerful,

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and capable of great patience.

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And those are characteristics
of predators everywhere.

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So the fossilised remains
of anomalocaris

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are evidence that hunting
had begun in the Cambrian.

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And as predators became bigger,
faster and stronger,

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so their prey had to develop
increasingly elaborate defences.

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Opabinia's five eyes
helped it spot trouble.

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And Hallucigenia protected itself
with those spines along its back.

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

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

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of predators like anomalocaris
that stimulated the great

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Cambrian explosion of diversity.

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It is during the Cambrian

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

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

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at the beginning of the Cambrian.

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

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which it was feeding on,

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

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Would that be true?

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

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in a place like the Burgess Shale
you find organisms

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that may have had
some kind of defensive mechanism,

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

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

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One result of this duel
between predators and prey

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was the development of armour.

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Animals everywhere
were absorbing calcium carbonate

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and other inorganic substances
from the seawater

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and mineralising their bodies.

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Many of them, like wiwaxia,
that early mollusc,

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and ancestors of the squid,
ammonites,

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developed protective shells.

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

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encased their entire bodies
with hard armour plating.

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And what began as defensive armour,
necessary for survival,

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brought with it another great
advantage.

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Hard parts can be used not only
to give protection,

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but to provide support for a body.

245
00:19:37,000 --> 00:19:38,600
Ha-ha!

246
00:19:38,600 --> 00:19:43,040
This spider crab is a crustacean.

247
00:19:43,040 --> 00:19:46,240
And it secretes chitin from
its body,

248
00:19:46,240 --> 00:19:50,640
which it then strengthens
with calcium carbonate.

249
00:19:50,640 --> 00:19:52,920
And a whole range of creatures

250
00:19:52,920 --> 00:19:55,920
have skeletons like this,
based on chitin.

251
00:19:58,720 --> 00:20:02,520
Arthropods today include shrimps,
lobsters and crabs,

252
00:20:02,520 --> 00:20:04,680
as well as land-living creatures,

253
00:20:04,680 --> 00:20:07,520
such as millipedes,
scorpions and insects.

254
00:20:07,520 --> 00:20:12,600
But the ancestors of all of them
first appeared in the Cambrian Seas.

255
00:20:16,880 --> 00:20:19,640
Over 50% of fossils
in the Burgess Shales

256
00:20:19,640 --> 00:20:23,160
are arthropods
of one kind or another.

257
00:20:23,160 --> 00:20:27,800
But one family was
particularly abundant and varied.

258
00:20:29,880 --> 00:20:32,200
Just across the valley
from the quarry,

259
00:20:32,200 --> 00:20:34,560
near the summit of Mount Stephen,

260
00:20:34,560 --> 00:20:38,440
almost every rock you turn over
contains their remains.

261
00:20:40,240 --> 00:20:43,520
Here, they are found
all over the place.

262
00:20:43,520 --> 00:20:45,520
They're called trilobites.

263
00:20:45,520 --> 00:20:49,800
Trilobites because their bodies
were in three sections.

264
00:20:49,800 --> 00:20:53,000
Here on this slab
there are several of them.

265
00:20:53,000 --> 00:20:55,160
That's the head.

266
00:20:55,160 --> 00:20:58,680
There's the middle bit.
And there's the tail.

267
00:20:58,680 --> 00:21:02,560
One, two, three trilobites.

268
00:21:02,560 --> 00:21:04,920
Trilobites, at this particular time,

269
00:21:04,920 --> 00:21:07,440
right at the beginning
of the Cambrian,

270
00:21:07,440 --> 00:21:11,720
began to proliferate
into all sorts of forms.

271
00:21:11,720 --> 00:21:16,400
These creatures,
for the next 250 million years,

272
00:21:16,400 --> 00:21:21,240
were probably the most advanced
forms of life on this planet.

273
00:21:23,720 --> 00:21:27,920
To see how advanced the trilobites
eventually became,

274
00:21:27,920 --> 00:21:29,720
I'm going to North Africa.

275
00:21:29,720 --> 00:21:34,960
In Morocco, on the southern flanks
of the Atlas Mountains,

276
00:21:34,960 --> 00:21:37,920
the hills contain
an amazing variety of them.

277
00:21:42,400 --> 00:21:44,840
They were only discovered
a few years ago,

278
00:21:44,840 --> 00:21:47,360
but now the demand for them
is so great

279
00:21:47,360 --> 00:21:50,800
that digging them out
has become a major industry.

280
00:21:57,360 --> 00:22:02,280
These rocks, which were laid down
about 150 million years after

281
00:22:02,280 --> 00:22:06,400
the Burgess Shale,
also contain trilobites.

282
00:22:06,400 --> 00:22:08,960
The trouble is,
the rock is very hard

283
00:22:08,960 --> 00:22:11,600
and the trilobites are quite rare.

284
00:22:11,600 --> 00:22:13,760
But when these people find them,

285
00:22:13,760 --> 00:22:17,600
their specimens are absolutely
extraordinary.

286
00:22:25,480 --> 00:22:29,520
Some species have features
that are so delicate

287
00:22:29,520 --> 00:22:33,040
that it can take days,
sometimes weeks,

288
00:22:33,040 --> 00:22:35,600
to fully prepare a specimen.

289
00:22:35,600 --> 00:22:38,600
Skilled technicians
use dentists' drills

290
00:22:38,600 --> 00:22:40,560
to get down to the finest detail.

291
00:22:44,560 --> 00:22:47,720
Every particle of rock
must be carefully removed,

292
00:22:47,720 --> 00:22:51,960
with enormous patience
and absolute precision.

293
00:22:56,920 --> 00:22:59,360
The end results reveal
that trilobites

294
00:22:59,360 --> 00:23:02,000
moulded their external skeletons

295
00:23:02,000 --> 00:23:05,440
into an almost unbelievable
variety of shapes.

296
00:23:22,280 --> 00:23:27,600
And that enabled them to colonise
a great variety of habitats,

297
00:23:27,600 --> 00:23:30,760
just as modern arthropods
still do today.

298
00:23:36,560 --> 00:23:41,680
There were about 50,000 different
trilobite species that we know of,

299
00:23:41,680 --> 00:23:45,040
and doubtless there are still
many more to be discovered.

300
00:23:51,840 --> 00:23:53,400
Their hard exoskeletons

301
00:23:53,400 --> 00:23:56,880
not only ensured their abundance
in the fossil record,

302
00:23:56,880 --> 00:24:00,960
they also tell us a lot
about their owners' lives.

303
00:24:03,560 --> 00:24:07,680
Many of the trilobites
that are found in these cliffs

304
00:24:07,680 --> 00:24:10,680
are curled up like this one.

305
00:24:10,680 --> 00:24:12,960
Sometimes even more tightly
than this is,

306
00:24:12,960 --> 00:24:16,400
with their tail tucked
underneath their heads.

307
00:24:16,400 --> 00:24:19,600
And it's clear that this was some
kind of protective posture,

308
00:24:19,600 --> 00:24:22,440
just as it is for some
kinds of woodlice

309
00:24:22,440 --> 00:24:25,240
that you find in the garden today.

310
00:24:25,240 --> 00:24:28,560
That protected them
against their enemies.

311
00:24:28,560 --> 00:24:32,200
But there are so many that
are curled in these deposits,

312
00:24:32,200 --> 00:24:35,480
together with others that have
their backs arched upwards

313
00:24:35,480 --> 00:24:37,680
and others
in other strange postures,

314
00:24:37,680 --> 00:24:43,160
that it seems that they are the
victim of some kind of catastrophe.

315
00:24:43,160 --> 00:24:46,680
The sea floor, it seems,
was quite steep.

316
00:24:46,680 --> 00:24:48,640
And every now and again,

317
00:24:48,640 --> 00:24:51,720
the mud that accumulated on
the bottom slipped down

318
00:24:51,720 --> 00:24:53,600
in a submarine avalanche,

319
00:24:53,600 --> 00:24:56,880
carrying the animals
that lived in it and on it,

320
00:24:56,880 --> 00:25:00,600
higgledy-piggeldy,
and burying them alive.

321
00:25:09,960 --> 00:25:14,000
Moroccan trilobites
are big business these days.

322
00:25:14,000 --> 00:25:19,080
Particularly rare species
sell for thousands of pounds.

323
00:25:21,960 --> 00:25:25,000
The world's leading trilobite
experts,

324
00:25:25,000 --> 00:25:27,240
such as Professor Richard Fortey,

325
00:25:27,240 --> 00:25:30,400
come here to study
these extraordinary animals.

326
00:25:34,480 --> 00:25:37,120
He believes that
their external skeleton

327
00:25:37,120 --> 00:25:40,160
was the key to their success.

328
00:25:40,160 --> 00:25:42,480
The trilobites
did almost everything

329
00:25:42,480 --> 00:25:46,520
you possibly can do
with an exoskeleton.

330
00:25:46,520 --> 00:25:50,920
I think that skeleton
was what gave them an advantage.

331
00:25:50,920 --> 00:25:55,240
They were protected. They could
do all kinds of interesting things.

332
00:25:55,240 --> 00:25:57,280
They could grow spines.

333
00:25:57,280 --> 00:26:00,360
They could get flat, like pancakes.

334
00:26:00,360 --> 00:26:03,200
They could protect themselves
by getting thick exoskeleton

335
00:26:03,200 --> 00:26:04,440
with pobbles all over it.

336
00:26:04,440 --> 00:26:08,280
It was a great advantage to them,
just as it is to crabs and lobsters

337
00:26:08,280 --> 00:26:10,920
living today, which of course
weren't around

338
00:26:10,920 --> 00:26:12,760
at the time of the trilobites.

339
00:26:12,760 --> 00:26:17,400
So they utilised the virtues
of having a tough exoskeleton,

340
00:26:17,400 --> 00:26:20,640
to radiate into all kinds of
ecological niches.

341
00:26:25,440 --> 00:26:29,000
You can see one of the most
comprehensive collections

342
00:26:29,000 --> 00:26:30,640
of trilobite fossils

343
00:26:30,640 --> 00:26:35,080
just a few miles from where
they're quarried, at Erfoud Museum.

344
00:26:39,160 --> 00:26:42,120
The collection here reveals
just how varied

345
00:26:42,120 --> 00:26:44,600
the trilobite skeleton could be.

346
00:26:48,080 --> 00:26:50,880
There is no question
that an exoskeleton

347
00:26:50,880 --> 00:26:53,280
gave the trilobites protection.

348
00:26:53,280 --> 00:26:57,400
But it also gave them something else
of great value.

349
00:26:59,480 --> 00:27:03,080
There must have been many reasons
why trilobites were so successful.

350
00:27:03,080 --> 00:27:07,760
But one of them, unquestionably,
was their power of sight.

351
00:27:07,760 --> 00:27:09,000
They had eyes.

352
00:27:09,000 --> 00:27:11,640
not just eyespots that could tell
the difference

353
00:27:11,640 --> 00:27:13,280
between light and dark,

354
00:27:13,280 --> 00:27:16,840
but complex eyes
that could form detailed pictures

355
00:27:16,840 --> 00:27:20,760
of their surroundings, for the first
time in the history of life.

356
00:27:20,760 --> 00:27:24,240
Eyes like these.

357
00:27:24,240 --> 00:27:29,920
Most animals on Earth today
have eyes of one kind of another.

358
00:27:29,920 --> 00:27:33,760
Most are made of soft tissue,
as ours our.

359
00:27:33,760 --> 00:27:36,640
But trilobite eyes are unique.

360
00:27:36,640 --> 00:27:41,680
Their lenses are derived from their
mineralised external skeleton.

361
00:27:41,680 --> 00:27:43,120
They're made of rock.

362
00:27:45,360 --> 00:27:48,600
Each one of these
little dots is a lens.

363
00:27:48,600 --> 00:27:50,800
And each is made from calcite,

364
00:27:50,800 --> 00:27:53,880
a crystalline form of chalk.

365
00:27:53,880 --> 00:27:56,400
Trilobites were the only organisms

366
00:27:56,400 --> 00:28:02,440
ever really to use this stuff
as their lens material.

367
00:28:02,440 --> 00:28:06,960
And in doing so they evolved
very sophisticated vision indeed.

368
00:28:06,960 --> 00:28:13,000
For example, these sorts of
trilobites had very large lenses.

369
00:28:13,000 --> 00:28:16,800
And each lens is readily visible
with the naked eye

370
00:28:16,800 --> 00:28:19,080
and each one is biconvex.

371
00:28:19,080 --> 00:28:23,920
And it's been proven that individual
lenses have little bowls inside them

372
00:28:23,920 --> 00:28:26,400
to help them focus more precisely.

373
00:28:26,400 --> 00:28:29,000
These creatures were among
the first,

374
00:28:29,000 --> 00:28:31,960
certainly, to actually focus
a picture, weren't they?

375
00:28:31,960 --> 00:28:35,040
It wasn't just a question of telling
light from dark,

376
00:28:35,040 --> 00:28:36,720
they could do better than that?

377
00:28:36,720 --> 00:28:39,520
On no, these, these had really
sophisticated vision.

378
00:28:41,040 --> 00:28:44,760
The kind of trilobites that have
these eyes were probably hunters.

379
00:28:44,760 --> 00:28:49,280
Some people have claimed that they
could form stereoscopic images,

380
00:28:49,280 --> 00:28:52,720
using both eyes, so they could
really home in on the prey.

381
00:28:55,440 --> 00:28:59,080
May predators today,
including ourselves,

382
00:28:59,080 --> 00:29:02,480
have 3D, or stereoscopic vision.

383
00:29:02,480 --> 00:29:06,360
It makes it possible for a hunter
to accurately judge the distance

384
00:29:06,360 --> 00:29:08,960
between itself and its prey.

385
00:29:18,040 --> 00:29:21,640
But not all trilobites
were predators.

386
00:29:21,640 --> 00:29:25,080
Some were inoffensive creatures
that lived by munching mud.

387
00:29:25,080 --> 00:29:27,760
But sight must have been valuable

388
00:29:27,760 --> 00:29:31,600
for them too, enabling them to
spot enemies in time to escape.

389
00:29:31,600 --> 00:29:34,240
There are trilobite eyes
with more than 5,000 lenses.

390
00:29:34,240 --> 00:29:37,280
5,000? More than 5,000 lenses.

391
00:29:37,280 --> 00:29:39,720
Now each of those,
does it have an image?

392
00:29:39,720 --> 00:29:43,000
Each doesn't have an image, but
if they go for lots of tiny lenses,

393
00:29:43,000 --> 00:29:45,200
they're particularly
sensitive to movement,

394
00:29:45,200 --> 00:29:49,240
i.e. something changing
between one lens and the next.

395
00:29:50,960 --> 00:29:55,120
This trilobite's eyes are so big
they extend right round its head

396
00:29:55,120 --> 00:29:57,240
and meet in the middle.

397
00:29:57,240 --> 00:30:01,480
And that suggests that the animal
swam high above the sea floor

398
00:30:01,480 --> 00:30:05,640
and had a 360-degree view
of the scene below.

399
00:30:07,160 --> 00:30:10,400
With each lens capable
of detecting movement,

400
00:30:10,400 --> 00:30:14,640
its owner must have been able to see
an enemy coming from any direction.

401
00:30:17,120 --> 00:30:20,760
But the shape of a trilobite's
eyes can reveal more than the

402
00:30:20,760 --> 00:30:22,760
kind of image they produced.

403
00:30:24,920 --> 00:30:31,120
Eyes can tell us a surprising amount
about how and where an animal lived.

404
00:30:31,120 --> 00:30:37,240
This one with its eyes on turrets
probably lived in the sea where it

405
00:30:37,240 --> 00:30:41,440
was gloomy, but nonetheless there
was enough light for the animal to

406
00:30:41,440 --> 00:30:44,760
be able to see on either side of it.

407
00:30:44,760 --> 00:30:50,000
This one, on the other hand, has
eyes also on turrets, but at the top

408
00:30:50,000 --> 00:30:53,040
it has flanges, like sun shades.

409
00:30:53,040 --> 00:30:57,120
So it's, er, likely that it
lived in the shallow, sunlit sea

410
00:30:57,120 --> 00:31:01,800
and valued shades above its
eyes so it didn't get dazzled.

411
00:31:01,800 --> 00:31:06,720
This one, however, has very
reduced eyes, and it may well be

412
00:31:06,720 --> 00:31:09,480
that it skated along the mud along
the bottom,

413
00:31:09,480 --> 00:31:12,760
where it was gloomy anyway
and there wasn't much to see,

414
00:31:12,760 --> 00:31:17,200
so like an animal living in a cave,
it slowly lost the use of its eyes.

415
00:31:17,200 --> 00:31:20,480
And finally there's this creature,

416
00:31:20,480 --> 00:31:24,080
and this is the one I
think is particularly delightful.

417
00:31:24,080 --> 00:31:27,960
This one has its eyes on stalks.

418
00:31:27,960 --> 00:31:30,840
And probably lived under the mud,

419
00:31:30,840 --> 00:31:34,080
gobbling up food there
with its, just its eyes

420
00:31:34,080 --> 00:31:38,120
peeking out of the top, to see
whether there was danger around.

421
00:31:40,080 --> 00:31:44,960
So trilobites were the first animals
to see clearly.

422
00:31:44,960 --> 00:31:48,080
But they had other senses as well,
perhaps some

423
00:31:48,080 --> 00:31:50,400
we don't even know about.

424
00:31:50,400 --> 00:31:55,840
Take this species with this bizarre
trident structure on its nose.

425
00:31:55,840 --> 00:31:59,200
What was it for?
Some kind of motion sensor?

426
00:31:59,200 --> 00:32:02,280
Prehistoric radar, perhaps?

427
00:32:03,880 --> 00:32:06,240
Trilobites were, without question,

428
00:32:06,240 --> 00:32:09,440
the most successful
animals of their time.

429
00:32:09,440 --> 00:32:12,640
They flourished in
all parts of the ocean.

430
00:32:12,640 --> 00:32:15,160
Indeed, they could be counted
as one

431
00:32:15,160 --> 00:32:19,160
of the most successful kinds
of animals
in the entire history of life.

432
00:32:21,160 --> 00:32:25,880
Most trilobites are quite small,
rather like beetles are today.

433
00:32:25,880 --> 00:32:31,160
But the biggest living beetle is
about that big, the goliath beetle.

434
00:32:31,160 --> 00:32:36,280
Trilobites, on the other hand,
grew very big indeed. Like this one.

435
00:32:36,280 --> 00:32:38,160
And this is by no means the biggest.

436
00:32:38,160 --> 00:32:42,160
The biggest known is nearly
a metre, nearly three feet long.

437
00:32:42,160 --> 00:32:46,000
And it's thought that these
really big ones grew to this size

438
00:32:46,000 --> 00:32:50,840
because they lived in cold waters,
and that's a tendency of animals

439
00:32:50,840 --> 00:32:52,640
in cold, to grow large.

440
00:32:52,640 --> 00:32:56,800
And at the time that these rocks
were laid down, Africa,

441
00:32:56,800 --> 00:32:59,560
where we are now,
and where these are found,

442
00:32:59,560 --> 00:33:01,240
was down by the South Pole.

443
00:33:04,640 --> 00:33:07,120
Spectacular though these are,

444
00:33:07,120 --> 00:33:11,800
they were by no means the largest
arthropods in the ocean at the time.

445
00:33:11,800 --> 00:33:17,080
The trilobites had remote cousins,
also arthropods, that had grown

446
00:33:17,080 --> 00:33:19,720
into monsters.

447
00:33:19,720 --> 00:33:22,760
Their remains are much rarer,
and often fragmentary,

448
00:33:22,760 --> 00:33:26,800
but some of the most complete
have been found in Scotland.

449
00:33:33,600 --> 00:33:35,720
ALARM SOUNDS

450
00:33:39,840 --> 00:33:42,040
One of the best
is held in the vaults

451
00:33:42,040 --> 00:33:44,200
of Edinburgh's National Museum.

452
00:34:03,680 --> 00:34:06,040
Gosh!

453
00:34:06,040 --> 00:34:13,280
Well, this is a magnificent example
of just how big an animal can grow

454
00:34:13,280 --> 00:34:16,200
if it has an external skeleton.

455
00:34:16,200 --> 00:34:20,400
This is a creature called
the Eurypterid, or a sea scorpion.

456
00:34:20,400 --> 00:34:22,680
And it was a hunter.

457
00:34:22,680 --> 00:34:27,520
It had a pair of powerful pincers
at the top, just behind its head.

458
00:34:27,520 --> 00:34:31,920
It was obviously a monster,
a terror of the seas.

459
00:34:31,920 --> 00:34:36,880
And this is by no means the
biggest of the eurypterids.

460
00:34:39,760 --> 00:34:44,200
Sea scorpions were the
top predators of their day.

461
00:34:44,200 --> 00:34:47,240
As far as we know,
they were the biggest arthropod

462
00:34:47,240 --> 00:34:49,040
that has ever existed.

463
00:34:50,760 --> 00:34:54,880
The discovery of a large
fossilised claw suggests

464
00:34:54,880 --> 00:34:58,800
that they could grow up to two and
a half metres, eight feet in length.

465
00:35:07,520 --> 00:35:10,200
So arthropods of one kind or another

466
00:35:10,200 --> 00:35:15,440
were certainly dominant
420 million years ago.

467
00:35:15,440 --> 00:35:18,320
The seas were full of life.

468
00:35:18,320 --> 00:35:21,840
From huge complex animals
like this sea scorpion

469
00:35:21,840 --> 00:35:23,320
creeping along the bottom,

470
00:35:23,320 --> 00:35:27,520
to simple creatures, like jellyfish,
floating on the surface waters.

471
00:35:27,520 --> 00:35:33,360
But the land was barren
and without animals of any kind.

472
00:35:35,000 --> 00:35:40,160
But there was food up there,
simple plants,

473
00:35:40,160 --> 00:35:46,040
and that tempted some animals
to venture out of the water.

474
00:35:46,040 --> 00:35:50,040
Surviving on land, however,
was a problem for them.

475
00:35:50,040 --> 00:35:52,240
Coming from the sea,
they had to evolve ways

476
00:35:52,240 --> 00:35:55,200
of preventing their bodies
from drying out.

477
00:35:55,200 --> 00:36:01,400
And even more difficult, they had to
develop a method of breathing air.

478
00:36:01,400 --> 00:36:04,000
The very first animals
had simply absorbed

479
00:36:04,000 --> 00:36:06,120
dissolved oxygen from the water

480
00:36:06,120 --> 00:36:09,320
through the skins
of their soft bodies.

481
00:36:09,320 --> 00:36:12,480
As they began to move and grow
bigger, they needed more energy,

482
00:36:12,480 --> 00:36:15,480
more quickly.

483
00:36:15,480 --> 00:36:17,240
And that meant

484
00:36:17,240 --> 00:36:21,200
they had to improve their method
of collecting dissolved oxygen.

485
00:36:25,600 --> 00:36:29,600
Bigger, more complex animals,

486
00:36:29,600 --> 00:36:32,360
like for example, this lobster,

487
00:36:32,360 --> 00:36:35,920
have to have specialised devices,
which are called gills.

488
00:36:35,920 --> 00:36:40,680
Here in the lobster they are
these flaps underneath its abdomen,

489
00:36:40,680 --> 00:36:42,440
which is flaps forwards

490
00:36:42,440 --> 00:36:47,480
and backwards to increase the flow
of oxygenated water over them.

491
00:36:47,480 --> 00:36:52,200
But the trouble with gills is that
they only work when they're wet.

492
00:36:52,200 --> 00:36:56,000
In the dry,
they do not absorb oxygen.

493
00:36:56,000 --> 00:36:58,800
So if animals are to live on land,

494
00:36:58,800 --> 00:37:03,560
they had have to have a new way
of breathing.

495
00:37:08,800 --> 00:37:10,320
The Burgess Shales,

496
00:37:10,320 --> 00:37:14,480
that astonishingly rich treasury
of Cambrian fossils,

497
00:37:14,480 --> 00:37:16,760
contain the remains of just one

498
00:37:16,760 --> 00:37:21,400
particularly rare species that may
well have been the very first animal

499
00:37:21,400 --> 00:37:24,240
to make that move onto land.

500
00:37:24,240 --> 00:37:27,920
It was not, as you might think,
an amphibian, it was not even

501
00:37:27,920 --> 00:37:31,440
a true arthropod, but
one of their far distant cousins.

502
00:37:36,840 --> 00:37:39,200
This little creature,

503
00:37:39,200 --> 00:37:44,920
from the Burgess Shale seas,
is thought to be the ancestor

504
00:37:44,920 --> 00:37:50,800
of the very first creature that went
on to land. It's called Aysheaia.

505
00:37:50,800 --> 00:37:54,400
And we don't have to imagine what it
was like in life,

506
00:37:54,400 --> 00:37:59,360
because there's a creature,
that seems to be almost identical,

507
00:37:59,360 --> 00:38:01,040
that is alive today.

508
00:38:03,520 --> 00:38:08,320
It lives in many parts of the
tropics, including the rainforest,

509
00:38:08,320 --> 00:38:11,200
here in Queensland, Australia.

510
00:38:17,800 --> 00:38:21,040
It's nocturnal and seldom seen.

511
00:38:25,400 --> 00:38:31,040
It spends most of its time
hidden away inside rotten logs.

512
00:38:32,720 --> 00:38:35,400
Ah, it's nice and wet!

513
00:38:35,400 --> 00:38:38,480
Certainly, er, perfect
for what we're looking for.

514
00:38:38,480 --> 00:38:42,240
You need local expertise
to find one.

515
00:38:44,320 --> 00:38:47,120
I generally find
that it's just from the outside

516
00:38:47,120 --> 00:38:48,720
of the, er, core of the tree.

517
00:38:51,000 --> 00:38:54,760
All nice and... Oh! What is that?
Ooh, look at that.

518
00:38:55,080 --> 00:38:59,520
And this enchanting
little creature

519
00:38:59,520 --> 00:39:01,320
is what we were looking for.

520
00:39:06,280 --> 00:39:10,320
Sometimes called a velvet worm,

521
00:39:10,320 --> 00:39:13,920
or to give it its scientific name,
Peripatus.

522
00:39:15,800 --> 00:39:20,120
If there is such a thing
as a living fossil,

523
00:39:20,120 --> 00:39:22,920
this surely must be one of them.

524
00:39:22,920 --> 00:39:26,720
Because it seems to be
almost identical

525
00:39:26,720 --> 00:39:33,240
with that fossil, Aysheaia,
which we saw in the Burgess Shales.

526
00:39:33,240 --> 00:39:38,560
It looks at first sight like a worm.

527
00:39:38,560 --> 00:39:43,560
But of course no worm has legs.
In fact,

528
00:39:43,560 --> 00:39:46,880
it seems to be halfway

529
00:39:46,880 --> 00:39:49,600
between a worm

530
00:39:49,600 --> 00:39:51,520
and an insect.

531
00:39:53,040 --> 00:39:57,360
Aysheaia, of course,
lived in the sea.

532
00:39:57,360 --> 00:40:01,200
But this little creature
lives on land.

533
00:40:01,200 --> 00:40:03,920
And it has one further attribute,

534
00:40:03,920 --> 00:40:09,000
which Aysheaia could not have had.

535
00:40:09,000 --> 00:40:12,640
It has tiny little holes
all along its flanks,

536
00:40:12,640 --> 00:40:15,520
which enable it to breathe air.

537
00:40:15,520 --> 00:40:20,560
So this is one
of the first creatures

538
00:40:20,560 --> 00:40:22,800
that moved on to land,

539
00:40:22,800 --> 00:40:26,520
540 million years ago.

540
00:40:44,720 --> 00:40:48,600
Velvet worms may have been the
first animals to set foot on land,

541
00:40:48,600 --> 00:40:53,480
but they have hardly changed during
the following half-billion years.

542
00:40:55,080 --> 00:40:57,560
Why?

543
00:40:57,560 --> 00:41:00,160
Well, unlike true arthropods,
their bodies are covered,

544
00:41:00,160 --> 00:41:06,480
not by an exoskeleton,
but by soft, permeable skin.

545
00:41:06,480 --> 00:41:11,280
That lack of an external skeleton
means that their bodies,

546
00:41:11,280 --> 00:41:13,400
unsupported by water,
can't grow any bigger.

547
00:41:13,400 --> 00:41:19,080
It also means that in order to
prevent themselves from drying out,

548
00:41:19,080 --> 00:41:23,520
they have to stay
in damp environments.

549
00:41:23,520 --> 00:41:25,360
True arthropods, like this scorpion,

550
00:41:25,360 --> 00:41:30,440
a descendent of those giant sea
scorpions, were not so restricted.

551
00:41:30,440 --> 00:41:32,760
They had external skeletons.

552
00:41:34,320 --> 00:41:39,000
That meant that not only were their
bodies protected from drying out,

553
00:41:39,000 --> 00:41:42,440
but they were strong and rigid
enough to allow them to grow bigger

554
00:41:42,440 --> 00:41:45,560
and get around without
the support of water.

555
00:41:54,040 --> 00:41:57,640
So how and when did true arthropods
with exoskeletons

556
00:41:57,640 --> 00:41:59,680
draw their first breath of air?

557
00:42:05,360 --> 00:42:08,160
The answer can be found in this.

558
00:42:08,160 --> 00:42:13,080
It is perhaps the smallest and most
fragmentary fossil I've seen so far,

559
00:42:13,080 --> 00:42:16,360
but don't be fooled by appearances.

560
00:42:16,360 --> 00:42:19,960
It's almost certainly
one of the most significant.

561
00:42:26,120 --> 00:42:33,720
This specimen was collected in Cowie
Harbour, here in Scotland, in 2004.

562
00:42:33,720 --> 00:42:38,720
Even though it's so small,
under the microscope you can see

563
00:42:38,720 --> 00:42:41,120
extraordinary detail.

564
00:42:41,120 --> 00:42:47,160
This is the main body of the animal
with its segments.

565
00:42:47,160 --> 00:42:51,000
And here are its legs.

566
00:42:51,000 --> 00:42:55,760
But above each there is a tiny hole.

567
00:42:57,720 --> 00:43:03,040
That is a spiracle, through which
the animal was able to breathe air

568
00:43:03,040 --> 00:43:06,120
just as insects do today.

569
00:43:06,120 --> 00:43:10,160
And since it breathed air,
if it had gone into the water

570
00:43:10,160 --> 00:43:11,680
it would have drowned.

571
00:43:11,680 --> 00:43:17,160
So this is a truly land-living
animal and what is more,

572
00:43:17,160 --> 00:43:19,920
it's the first and oldest
that we know.

573
00:43:19,920 --> 00:43:24,280
It's 428 million years old.

574
00:43:28,000 --> 00:43:32,920
But what kind of creatures were
these early land-dwelling arthropods

575
00:43:39,000 --> 00:43:42,960
Animals very like them
are still quite common

576
00:43:42,960 --> 00:43:44,520
in many parts of the world.

577
00:43:44,520 --> 00:43:48,360
There are certainly plenty of them
in those Australian rainforests.

578
00:43:51,360 --> 00:43:54,000
One sort are millipedes,

579
00:43:54,000 --> 00:43:59,400
which today grow as long as that
and live on vegetation

580
00:43:59,400 --> 00:44:02,080
and rotting wood,
harmless vegetarians.

581
00:44:02,080 --> 00:44:07,440
But there's also another multi-leg
creature, which is a much more

582
00:44:07,440 --> 00:44:09,080
difficult customer.

583
00:44:11,320 --> 00:44:13,360
This is one of them.

584
00:44:13,360 --> 00:44:19,120
A centipede. A very formidable
hunter, with a powerful bite,

585
00:44:19,120 --> 00:44:23,640
and some centipedes have bites
that are lethal to human beings.

586
00:44:23,640 --> 00:44:26,920
What kind of a bite this one has,

587
00:44:26,920 --> 00:44:29,160
I don't know.

588
00:44:29,160 --> 00:44:31,120
But when I let him out I shall do so

589
00:44:31,120 --> 00:44:36,480
very carefully, because
I don't propose to find out.

590
00:44:36,480 --> 00:44:38,440
Come on.

591
00:44:45,840 --> 00:44:50,720
So multi-legged arthropods
invaded the land and became

592
00:44:50,720 --> 00:44:52,520
more successful than ever.

593
00:44:59,640 --> 00:45:01,200
Back in Scotland,

594
00:45:01,200 --> 00:45:06,320
there is impressive evidence
of just how successful they became.

595
00:45:08,520 --> 00:45:11,600
This is a small fishing village

596
00:45:11,600 --> 00:45:15,200
on the East Coast of Scotland
called Crail.

597
00:45:15,200 --> 00:45:18,760
Nothing particularly strange
about it, you might think...

598
00:45:18,760 --> 00:45:22,640
until, that is,
you go down to the shore.

599
00:45:22,640 --> 00:45:26,880
And then you can see something
that is really extraordinary.

600
00:45:31,760 --> 00:45:34,800
Standing here and there
on the beach are fossils,

601
00:45:34,800 --> 00:45:38,160
not of animals, but of plants.

602
00:45:40,520 --> 00:45:46,600
This huge circular stump
looks just like the base of a tree.

603
00:45:46,600 --> 00:45:49,800
And indeed
that is what it is, or rather,

604
00:45:49,800 --> 00:45:54,320
what it was, 335 million years ago.

605
00:45:54,320 --> 00:45:57,360
But it wasn't a tree
like trees we know today.

606
00:45:57,360 --> 00:45:59,200
It was related

607
00:45:59,200 --> 00:46:02,600
to the small plants that are
alive today called horsetails.

608
00:46:02,600 --> 00:46:07,080
But this tree grew to 90 feet.

609
00:46:07,080 --> 00:46:08,800
It was immense.

610
00:46:12,000 --> 00:46:15,680
When they were alive, during a
period called the Carboniferous,

611
00:46:15,680 --> 00:46:17,640
long after the Cambrian,

612
00:46:17,640 --> 00:46:19,640
this whole area was very different

613
00:46:19,640 --> 00:46:22,200
from the windswept coastline
of today.

614
00:46:24,800 --> 00:46:28,960
This was a time when the continents
of the world were grouped together

615
00:46:28,960 --> 00:46:31,240
and forests were widespread.

616
00:46:34,520 --> 00:46:37,560
So much plant life
was pumping out oxygen

617
00:46:37,560 --> 00:46:41,440
that the composition
of the atmosphere began to change.

618
00:46:45,720 --> 00:46:49,720
This had a profound effect
on animal life.

619
00:46:54,800 --> 00:46:58,480
In the forest that was growing
near Crail, the ancient trees

620
00:46:58,480 --> 00:47:01,360
were rooted in a sandy swamp.

621
00:47:01,360 --> 00:47:06,160
And on the expanses of sand that
stretched between those huge trees,

622
00:47:06,160 --> 00:47:09,480
sand that's now turned
to this sandstone,

623
00:47:09,480 --> 00:47:11,320
there are tracks.

624
00:47:11,320 --> 00:47:15,560
Tracks that come in pairs,
there's one pair that goes up there.

625
00:47:15,560 --> 00:47:19,240
There's another pair that
goes up here.

626
00:47:19,240 --> 00:47:22,000
And when you look at them
in detail, you can see,

627
00:47:22,000 --> 00:47:26,920
particularly on this pair, that each
track has a number of dimples in it.

628
00:47:29,400 --> 00:47:34,320
And those
are the imprints of individual feet.

629
00:47:34,320 --> 00:47:37,160
So this animal had a lot of feet.

630
00:47:37,160 --> 00:47:41,320
It's thought to have been
a giant millipede.

631
00:47:41,320 --> 00:47:43,600
It was about...

632
00:47:43,600 --> 00:47:46,600
four and a half feet long,
one and a half metres.

633
00:47:46,600 --> 00:47:50,280
And it had 26 or 28 segments.

634
00:47:50,280 --> 00:47:53,120
A magnificent beast.

635
00:48:10,160 --> 00:48:11,720
Arthropleura.

636
00:48:14,160 --> 00:48:16,240
A giant millipede,

637
00:48:16,240 --> 00:48:21,600
probably the biggest terrestrial
arthropod that has ever existed.

638
00:48:21,600 --> 00:48:26,440
The largest specimen discovered so
far was nearly as long as a car...

639
00:48:26,440 --> 00:48:28,040
two and a half metres.

640
00:48:30,280 --> 00:48:34,760
The Carboniferous was the golden
age for the arthropods,

641
00:48:34,760 --> 00:48:38,520
for the air was now particularly
rich in oxygen.

642
00:48:38,520 --> 00:48:43,280
Today the atmosphere
contains around 21% oxygen.

643
00:48:43,280 --> 00:48:45,160
Back in the Carboniferous,

644
00:48:45,160 --> 00:48:50,800
it was around 35% and that enabled
animals to grow very big indeed.

645
00:48:53,480 --> 00:48:57,840
But growing large
was not their only success.

646
00:48:57,840 --> 00:49:01,840
Some other arthropods in these
carboniferous rainforests

647
00:49:01,840 --> 00:49:04,040
were evolving in a different way.

648
00:49:04,040 --> 00:49:07,320
Instead of becoming
huge and ponderous,

649
00:49:07,320 --> 00:49:09,520
they became agile and speedy.

650
00:49:09,520 --> 00:49:13,960
To do that it's better to be
short rather than long, and some

651
00:49:13,960 --> 00:49:17,840
reduced their segments and ran
around on just three pairs of legs,

652
00:49:17,840 --> 00:49:20,680
as silverfish and
bristletails do today.

653
00:49:25,560 --> 00:49:29,720
These early insects then
made another dramatic move...

654
00:49:29,720 --> 00:49:35,600
they developed wings and became the
first animals of any kind to fly.

655
00:49:41,000 --> 00:49:44,640
Truly the invertebrates
had colonised

656
00:49:44,640 --> 00:49:46,320
not only the land, but the air.

657
00:49:48,200 --> 00:49:51,360
And in an atmosphere
so rich in oxygen,

658
00:49:51,360 --> 00:49:54,440
they did so in a truly dramatic way.

659
00:49:56,200 --> 00:49:58,480
This giant dragonfly,

660
00:49:58,480 --> 00:50:03,920
the biggest flying insect that has
ever existed, is called Meganeura.

661
00:50:12,520 --> 00:50:15,760
Its wings were nearly
three feet across.

662
00:50:21,440 --> 00:50:28,120
But the golden age of the
giant arthropods was not to last.

663
00:50:28,120 --> 00:50:33,120
The rainforest died back, and
oxygen in the atmosphere dropped.

664
00:50:35,280 --> 00:50:40,280
Giant insects are no longer
alive today and that may be

665
00:50:40,280 --> 00:50:44,600
because the proportion of oxygen in
the atmosphere is very much lower.

666
00:50:44,600 --> 00:50:48,160
But nonetheless,
insects have managed to find a way

667
00:50:48,160 --> 00:50:51,040
of overcoming the problems of size.

668
00:50:51,040 --> 00:50:53,200
They've become colonial.

669
00:50:54,720 --> 00:50:58,200
Just as in the far distant,
remote past,

670
00:50:58,200 --> 00:51:02,840
individual cells clubbed together
to form a larger organism,

671
00:51:02,840 --> 00:51:04,160
such as a sponge,

672
00:51:04,160 --> 00:51:08,720
so hundreds of thousands
of individual insects, termites,

673
00:51:08,720 --> 00:51:11,800
have cooperated to build this nest.

674
00:51:11,800 --> 00:51:15,080
And a colony like this
can crop as much vegetation

675
00:51:15,080 --> 00:51:20,080
from the surroundings
as a bigger animal like an antelope.

676
00:51:33,760 --> 00:51:36,360
So by living in vast colonies
like this,

677
00:51:36,360 --> 00:51:39,800
arthropods can still dominate
their surroundings.

678
00:51:41,520 --> 00:51:44,120
They've become super-organisms...

679
00:51:44,120 --> 00:51:48,680
hundreds of thousands of individuals
all descended from the same female,

680
00:51:48,680 --> 00:51:51,160
working and behaving as one.

681
00:51:58,280 --> 00:52:00,560
So arthropods remain

682
00:52:00,560 --> 00:52:03,600
one of the most successful
groups of animals on the planet.

683
00:52:08,040 --> 00:52:11,680
They've spread to all its corners.

684
00:52:15,800 --> 00:52:21,960
Insects alone make up at least 80%
of all animal species.

685
00:52:25,040 --> 00:52:29,360
But arthropods weren't the only
ones to make this move on to land.

686
00:52:33,920 --> 00:52:35,880
The Burgess Shales -

687
00:52:35,880 --> 00:52:40,080
the place where the beginnings
of all this proliferation of life

688
00:52:40,080 --> 00:52:43,760
in the Cambrian period
are recorded in unparalleled detail.

689
00:52:47,520 --> 00:52:51,520
Among the ancestors
of all the insects,

690
00:52:51,520 --> 00:52:56,920
spiders, the scorpions,
the shellfish, the crustaceans,

691
00:52:56,920 --> 00:52:59,440
the shrimps, the sponges,

692
00:52:59,440 --> 00:53:04,520
there's just one tiny little
creature, very insignificant,

693
00:53:04,520 --> 00:53:10,600
which we human beings might think is
perhaps the most important of all.

694
00:53:10,600 --> 00:53:11,840
Because this...

695
00:53:11,840 --> 00:53:16,720
is the first creature to
have the sign of a backbone,

696
00:53:16,720 --> 00:53:22,040
and thus, therefore, is probably
the ancestor of us all.

697
00:53:25,480 --> 00:53:29,600
It's a tiny, worm-like
creature called Pikaia.

698
00:53:32,360 --> 00:53:34,800
It was not a fearsome hunter.

699
00:53:34,800 --> 00:53:41,480
It had no teeth for attack and
no external skeleton for defence.

700
00:53:41,480 --> 00:53:44,400
But Pikaia did have something new.

701
00:53:46,960 --> 00:53:49,800
Instead of an external skeleton,

702
00:53:49,800 --> 00:53:53,240
it had an internal one,
a thin gristly rod...

703
00:53:53,240 --> 00:53:55,600
the beginnings of a backbone.

704
00:53:55,600 --> 00:53:59,760
It, or something very like it,
was the ancestor of all vertebrates.

705
00:54:01,800 --> 00:54:06,160
From such a creature as this,
the first fish evolved.

706
00:54:06,160 --> 00:54:10,360
Some of them, living in swamps,
started to gulp air and wriggled up

707
00:54:10,360 --> 00:54:17,240
onto the land. They gave rise
to moist-skinned amphibians.

708
00:54:17,240 --> 00:54:21,440
Some of them developed scaly,
impermeable skins that enabled them

709
00:54:21,440 --> 00:54:23,200
to colonise the driest places...

710
00:54:23,200 --> 00:54:24,960
they were the reptiles.

711
00:54:24,960 --> 00:54:28,000
And from them came the birds.

712
00:54:31,040 --> 00:54:32,640
And the mammals.

713
00:54:35,680 --> 00:54:38,800
Today mammals, like this rhinoceros,

714
00:54:38,800 --> 00:54:41,600
are the biggest of all
living animals.

715
00:54:43,840 --> 00:54:47,080
Hello, old boy. How are you?

716
00:54:47,080 --> 00:54:49,160
How are you?

717
00:54:49,160 --> 00:54:53,440
'All mammals, including ourselves,
extract oxygen from the air with

718
00:54:53,440 --> 00:54:57,000
'the end of internal lungs,
and distribute it through our bodies

719
00:54:57,000 --> 00:54:58,120
'in our blood.'

720
00:54:58,120 --> 00:55:00,960
There we are. There's a good lad.

721
00:55:00,960 --> 00:55:05,280
'But we also owe
our success, and our size,

722
00:55:05,280 --> 00:55:07,600
'to the nature of our skeletons.'

723
00:55:09,200 --> 00:55:14,320
Animals with an internal skeleton,
like this rhinoceros,

724
00:55:14,320 --> 00:55:21,080
have a huge advantage over animals
whose skeleton is external.

725
00:55:21,080 --> 00:55:24,480
A white rhinoceros, like this,

726
00:55:24,480 --> 00:55:28,600
is one of the biggest land animals
alive today.

727
00:55:28,600 --> 00:55:31,240
Compare him

728
00:55:31,240 --> 00:55:34,120
with him... a rhinoceros beetle.

729
00:55:35,640 --> 00:55:38,920
Its skeleton is external.

730
00:55:38,920 --> 00:55:41,640
It's very powerful.

731
00:55:41,640 --> 00:55:44,800
It can carry 850 times
its own weight.

732
00:55:44,800 --> 00:55:49,480
But it can't grow much bigger.
Because the only way it can grow is

733
00:55:49,480 --> 00:55:52,120
by shedding its skeleton
and growing a new one.

734
00:55:52,120 --> 00:55:58,000
And while its skeleton is not there,
its body is unsupported.

735
00:55:58,000 --> 00:56:05,080
And after a certain size, the body
will collapse under its own weight.

736
00:56:05,080 --> 00:56:06,000
Here.

737
00:56:08,680 --> 00:56:11,880
Here we are, come on boy.
Come on boy.

738
00:56:11,880 --> 00:56:15,960
Despite these differences,
it's no coincidence that

739
00:56:15,960 --> 00:56:21,520
backboned animals evolved many of
the same features as the arthropods.

740
00:56:21,520 --> 00:56:23,640
Teeth.

741
00:56:23,640 --> 00:56:26,200
Legs.

742
00:56:26,200 --> 00:56:30,280
Shells. Eyes.

743
00:56:30,280 --> 00:56:31,520
And wings.

744
00:56:31,520 --> 00:56:34,560
Any animal group needs such
things if they are to colonise

745
00:56:34,560 --> 00:56:38,080
all the Earth's varied habitats.

746
00:56:45,120 --> 00:56:49,880
A journey that began for me near
my boyhood home in Charnwood Forest

747
00:56:49,880 --> 00:56:54,520
has taken me around the world
and through 600 million years

748
00:56:54,520 --> 00:56:55,640
of evolutionary history.

749
00:56:57,200 --> 00:57:00,280
I've seen evidence
of how single-celled life

750
00:57:00,280 --> 00:57:03,000
dominated the planet
for billions of years,

751
00:57:03,000 --> 00:57:08,240
until a global ice age triggered
the emergence of the first animals.

752
00:57:11,520 --> 00:57:14,560
Many animal groups
lasted millions of years.

753
00:57:14,560 --> 00:57:18,400
But eventually their time ran out
and they disappeared.

754
00:57:29,280 --> 00:57:31,600
But others endured.

755
00:57:35,280 --> 00:57:37,720
And between them they evolved

756
00:57:37,720 --> 00:57:42,560
into the wondrous variety of life
that inhabits this planet today.

757
00:57:44,760 --> 00:57:48,080
Life originated in the oceans.

758
00:57:48,080 --> 00:57:53,800
After an immense period of time,
some creatures managed to crawl up

759
00:57:53,800 --> 00:57:55,600
onto the land.

760
00:57:55,600 --> 00:57:59,080
Those animals may seem to us
to be very remote,

761
00:57:59,080 --> 00:58:01,720
strange, even fantastic.

762
00:58:01,720 --> 00:58:07,480
But all of us alive today
owe our very existence to them.

763
00:58:30,080 --> 00:58:32,120
Subtitles by Red Bee Media Ltd

764
00:58:32,120 --> 00:58:34,160
E-mail subtitling@bbc.co.uk