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This is Earth.
Four point four billion years ago.

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A toxic world with no hope of life.

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Then everything changed.

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Another planet, Thea, smashed into Earth

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and the two planets fused,

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creating a brand new world.

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Our world.

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Even today,
Thea lies right beneath our feet.

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A smaller chunk of Thea became our moon.

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And slowly our oceans formed.

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Until life on Earth was ready to begin.

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But who would inherit this blue planet?

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This series tells the extraordinary story
of life before the dinosaurs.

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A time when strange and savage

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creatures fought a ruthless
battle to rule the Earth.

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Amongst them were
our own earliest ancestors,

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whose survival would decide
whether we humans would exist at all.

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As they evolved,

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these bizarre creatures
created the blueprint

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not only for our bodies,

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but for everything living today.

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This is life's forgotten story.

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An epic war for our world.

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A war between monsters.

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This is our planet,

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five hundred and thirty million years ago.

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Nothing yet lives on land,

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but in the ocean it's a different story.

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Life has already been evolving
for millions of years

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at a slow and steady pace.

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The seas are full of simple,

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soft bodied creatures,

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blindly drifting in the currents.

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Now, however, in the coastal shallows below,

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evolution has stepped on the accelerator.

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Predators have taken their first bite.

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This is Anomalocaris,
Earth's first super predator.

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This two metre long monster owes his success

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to a monumental evolutionary landmark.

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Eyes.

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They may look bizarre but they're not unique.

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Many predators in the Cambrian seas

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have also evolved eyes.

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And so have their prey.

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The consequences have been explosive.

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Being able to see and react to enemies

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has triggered an arms race
between hunter and hunted.

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This battle continues today

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and is a major force behind the variety of life.

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To combat being visible and vulnerable,

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eighty percent of creates in these shallow seas

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have sturdy skeletons
on the outside of their bodies.

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These armoured animals are called Arthropods.

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In the future,

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they'll give rise to insects and spiders.

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But in these crowded waters

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there's competition everywhere,

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and even the mighty Anomalocaris's defences
are constantly put to the test.

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Rigid armour splits if bent too far,

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leaving the loser vulnerable.

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To a completely different threat.

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This is Haikouichthys.

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He's the size of your thumbnail,

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but he's an evolutionary giant.

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He's the first ever fish.

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Our earliest known ancestor.

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He's unique,

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because instead of having
armour on the outside,

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he's tough inside.

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He's evolved a primitive backbone.

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He's the very first vertebrate.

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Forerunner of all future backboned animals,

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from the dinosaur, to the elephant, to us.

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His flexible backbone makes him

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more manoeuvrable than
spineless Anomalocaris.

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He can scavenge flesh,
then dart away unharmed.

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Our tiny backboned ancestors
have survived a sea of monsters,

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but there are still many more battles ahead.

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They must adapt or die.

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Evolution takes over.

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As millions of years pass,

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fish build on their basic design.

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The muscles around their backbone

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evolve into a powerful tail
and fins appear.

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They evolve a distinct head.

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He may not look like you or I,

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but this odd fish is becoming
the blueprint for our own bodies.

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This is Cephalaspis.

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She's a peaceful grazer who sucks up algae
through her jawless mouth.

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But she's also developed
a tough protective head and thick scales.

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Our ancestor's arthropod enemies
have also been evolving

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and they're ready for round two.

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A hundred million years have passed

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and the fight for survival has filled
the Silurian seas with variety.

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Some creatures here
would be recognisable today.

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Sponges filter food alongside sea urchins.

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The orthocone is a distant relative
of squid and cuttlefish,

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but he's as long as a truck.

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This world is terrorised by

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a new improved generation
of armoured arthropods.

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Meet Brontoscorpio.

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He's a metre long
monster scorpion with gills

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and a stinger the size of a light bulb.

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He zeros in on his next meal.

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But Cephalaspis has evolved
an early warning system.

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Special sensors on her skin
detect the tiniest vibrations in the water.

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We've inherited similar senses.

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They make us sensitive to touch.

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With her defensive headgear,
Cephalaspis can't swim fast for long.

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She must rest frequently.

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Soon she'll tire completely.

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Cephalaspis suddenly changes her path.

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She's picking up bad vibrations.

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Something Brontoscorpio can't detect.

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Pterygotus is the Titan of sea scorpions.

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The biggest arthropod of all time.

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More than three metres long,

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she's the size of a crocodile.

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She has turned the tables on Brontoscorpio.

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He'll make a good meal for her young.

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In such dangerous seas
there's nowhere to hide.

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When breeding seasons comes,

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the Cephalaspis congregate to
head for the one place

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they might escape a scorpion's grasp.

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Fresh water, inland.

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Land at this time is like an alien planet.

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It's a barren expanse of roasting rock
hotter than the Sahara.

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The air would be toxic to us.

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It has much less oxygen

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and three hundred times more
carbon dioxide than today.

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But some forms of life
have gained a foothold in this furnace.

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The first pioneering plants.

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Cooksonia has a unique survival strategy.

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It's the first plant to send shoots upwards,
trapping extra light to help it grow.

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This basic design will eventually
lead to our tallest forests.

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The Cephalaspis convoy ploughs upriver,
away from the sea.

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They're making the marathon journey

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back to the spawning grounds
where they hatched.

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Incredibly our fish ancestors
already use memory.

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They use familiar landmarks to navigate.

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Their toughened heads
protect a vital weapon.

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One of the first complex brains.

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It's much more developed
than their scorpion rivals

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who have no memory at all.

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It's thanks to these primitive fish

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that we can think and solve problems today.

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But the fish have
underestimated their enemy.

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It is the arthropods and not our ancestors

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who have taken the first momentous steps
out of the sea into dry land.

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Brontoscorpio has a huge advantage.

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As well as gills

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he has simple lungs made up of
hundreds of thin layers of tissue.

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He can't breath in and out like we do.

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He just absorbs the oxygen into his blood.

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Equipped to maximise
the little oxygen available

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and with their armour
to protect them from the sun,

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the scorpions patrol the shoreline,

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scavenging on whatever
the sea washes up next.

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Finally the fish approach their destination.

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They've navigated their way
back to the spawning pool,

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where their lives began.

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Weak from their long journey,

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now they have to cross a ridge of rock

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to make it from the river, to the pool.

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The first fish make it through
and start to lay their eggs.

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But the exhausted Cephalaspis have company.

167
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Passing scorpions have stumbled
on this bounty.

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But the fish have numbers on their side.

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The clever Cephalaspis
have navigated their way,

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while Brontoscorpio are only here by luck.

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They're soon stuffed to the gills
while the fish keep jumping.

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One scorpion is still hungry,
but he can't feed.

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He's become a prisoner in his own skin.

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His rigid skeleton is now a handicap.

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It can't grow with his body.

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He needs to shed his hard skin
and then grow another,

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expanding while the new one is still soft.

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For such a large creature,
this is a long process.

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Next morning,
there's no sign of life in the spawning pool.

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The scorpion has missed his chance.

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Our ancestors have survived.

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They've laid their eggs
and are returning to the sea.

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Brain has triumphed over brawn,

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and soon they won't be such soft targets.

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Evolution starts to give
them weapons to fight back.

186
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Over millions of years,

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the fish's gills adapt to form
the first jaw with the very first teeth.

188
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Now they're equipped to go on the attack.

189
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Some develop tougher bones and muscles
in their fins and shoulders,

190
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which become the first limbs.

191
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This is where our arms and legs began.

192
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With this four-limbed design,

193
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our ancestors finally haul themselves
out of water on to land.

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This is the giant amphibian, Hynerpeton.

195
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The prototype land dweller
for the next three hundred million years.

196
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Hynerpeton are over a metre
and a half in length,

197
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much larger than most amphibians today.

198
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They've carved out a home
along the water's edge.

199
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Arthropod enemies still exist,

200
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but they've shrunk
since their Brontoscorpio glory days.

201
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Still, life for this pioneer
is far from easy.

202
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It's a whole new world.

203
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In the last fifty million years,
plants have developed into trees.

204
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And with nothing around to eat them,

205
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they've grown into vast forests
pumping oxygen into the air.

206
00:21:08,567 --> 00:21:13,504
Hynerpeton has evolved complex lungs
to exploit this new oxygen.

207
00:21:16,775 --> 00:21:21,405
His lungs are sacks, just like ours,
and he breaths like we do.

208
00:21:21,613 --> 00:21:26,050
Forcing air in and out
so his blood can absorb more oxygen.

209
00:21:28,787 --> 00:21:32,518
We still rely on the design
developed in this strange amphibian.

210
00:21:34,926 --> 00:21:38,623
Hynerpeton can breath on land,
but he's still water bound.

211
00:21:41,199 --> 00:21:44,896
His skin is much thinner than ours
and it dries out in minutes,

212
00:21:45,103 --> 00:21:46,968
so he has to keep it wet.

213
00:21:51,877 --> 00:21:54,710
And water is a danger zone.

214
00:22:06,391 --> 00:22:09,690
The fish are now our ancestor's enemies.

215
00:22:14,933 --> 00:22:17,959
Primitive sharks
are constantly on the hunt.

216
00:22:37,589 --> 00:22:42,925
But even sharks are small fry
in comparison to some flesh eating fish.

217
00:22:46,298 --> 00:22:52,259
Hyneria weighs two tons.
And is five metres long.

218
00:22:55,273 --> 00:22:57,867
She's an insatiable carnivore.

219
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The amphibian limbs are his saving grace.

220
00:23:24,436 --> 00:23:25,926
For now.

221
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As the burning sun dips,
Hynerpeton can spend more time on land.

222
00:23:35,814 --> 00:23:37,941
This stretch of shoreline is his territory

223
00:23:38,150 --> 00:23:41,381
and his trump card with the opposite sex.

224
00:23:48,393 --> 00:23:51,089
Hynerpeton females are choosy

225
00:23:51,530 --> 00:23:55,125
and will only go for males
who can defend their turf.

226
00:23:56,535 --> 00:23:59,971
They also only mate during a short season.

227
00:24:07,112 --> 00:24:10,377
The male's future
depends on passing on his genes

228
00:24:10,582 --> 00:24:13,415
and tonight could be his last chance.

229
00:24:21,293 --> 00:24:24,626
As night arrives,
so does the competition.

230
00:24:27,032 --> 00:24:30,695
Another male with his eye
on this prime patch.

231
00:24:47,018 --> 00:24:48,315
To avoid injury,

232
00:24:48,520 --> 00:24:53,048
the males demonstrate their strength
in a strange push up contest.

233
00:25:15,914 --> 00:25:18,246
This rival is not up to the challenge,

234
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but now our male
may be too late for love.

235
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Dawn.

236
00:25:37,636 --> 00:25:41,367
And all the females in the area
have mated and moved on.

237
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Hynerpeton seems to
have missed his chance.

238
00:25:46,978 --> 00:25:51,472
The only attention he's attracting
comes from the dark waters of the lake.

239
00:26:01,326 --> 00:26:07,060
A female finally answers his call
and the male seizes the opportunity.

240
00:26:25,684 --> 00:26:28,915
Amphibian eggs are soft
and their young have gills,

241
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not lungs, so they must be laid in water.

242
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Where amphibians are most vulnerable.

243
00:26:51,476 --> 00:26:55,139
Hyneria can attack like
a killer whale after a seal.

244
00:26:57,015 --> 00:26:59,347
Only just missing her prey.

245
00:27:00,919 --> 00:27:04,218
But she has remarkably powerful fins.

246
00:27:11,129 --> 00:27:13,825
And she takes the male by surprise.

247
00:27:25,010 --> 00:27:27,570
The end for this Hynerpeton.

248
00:27:29,681 --> 00:27:31,911
But the amphibians are
about to find a way

249
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to leave the dangers
of the water behind for good.

250
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The key to their future success
lies in changing their eggs.

251
00:27:46,965 --> 00:27:49,798
They evolve a hard waterproof casing

252
00:27:50,001 --> 00:27:53,061
which protects the young inside
from the drying sun,

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so they can be laid on land.

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00:27:57,909 --> 00:28:00,309
The babies will hatch out,
fully developed,

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00:28:00,512 --> 00:28:03,174
air breathing and independent.

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They're the first ever
true vertebrate landlubbers.

257
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The very first reptiles.

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But as they move inland,
they'll face an ancient enemy.

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More deadly than ever before.

260
00:28:25,603 --> 00:28:28,231
The arthropods are back.

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00:28:30,675 --> 00:28:32,472
Next time on Walking with Monsters,

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we enter the world of killer bugs.

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From huge flesh eating spiders
to three metre millipede relatives.

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00:28:42,821 --> 00:28:45,051
And we meet the first giant reptiles,

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our strange sail-back ancestors

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who face their toughest enemy yet.

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Each other.