This is Earth. Four point four billion years ago.
A toxic world with no hope of life.
Then everything changed.
Another planet, Thea, smashed into Earth
and the two planets fused,
creating a brand new world.
Our world.
Even today, Thea lies right beneath our feet.
A smaller chunk of Thea became our moon.
And slowly our oceans formed.
Until life on Earth was ready to begin.
But who would inherit this blue planet?
This series tells the extraordinary story of life before the dinosaurs.
A time when strange and savage
creatures fought a ruthless battle to rule the Earth.
Amongst them were our own earliest ancestors,
whose survival would decide whether we humans would exist at all.
As they evolved,
these bizarre creatures created the blueprint
not only for our bodies,
but for everything living today.
This is life's forgotten story.
An epic war for our world.
A war between monsters.
This is our planet,
five hundred and thirty million years ago.
Nothing yet lives on land,
but in the ocean it's a different story.
Life has already been evolving for millions of years
at a slow and steady pace.
The seas are full of simple,
soft bodied creatures,
blindly drifting in the currents.
Now, however, in the coastal shallows below,
evolution has stepped on the accelerator.
Predators have taken their first bite.
This is Anomalocaris, Earth's first super predator.
This two metre long monster owes his success
to a monumental evolutionary landmark.
Eyes.
They may look bizarre but they're not unique.
Many predators in the Cambrian seas
have also evolved eyes.
And so have their prey.
The consequences have been explosive.
Being able to see and react to enemies
has triggered an arms race between hunter and hunted.
This battle continues today
and is a major force behind the variety of life.
To combat being visible and vulnerable,
eighty percent of creates in these shallow seas
have sturdy skeletons on the outside of their bodies.
These armoured animals are called Arthropods.
In the future,
they'll give rise to insects and spiders.
But in these crowded waters
there's competition everywhere,
and even the mighty Anomalocaris's defences are constantly put to the test.
Rigid armour splits if bent too far,
leaving the loser vulnerable.
To a completely different threat.
This is Haikouichthys.
He's the size of your thumbnail,
but he's an evolutionary giant.
He's the first ever fish.
Our earliest known ancestor.
He's unique,
because instead of having armour on the outside,
he's tough inside.
He's evolved a primitive backbone.
He's the very first vertebrate.
Forerunner of all future backboned animals,
from the dinosaur, to the elephant, to us.
His flexible backbone makes him
more manoeuvrable than spineless Anomalocaris.
He can scavenge flesh, then dart away unharmed.
Our tiny backboned ancestors have survived a sea of monsters,
but there are still many more battles ahead.
They must adapt or die.
Evolution takes over.
As millions of years pass,
fish build on their basic design.
The muscles around their backbone
evolve into a powerful tail and fins appear.
They evolve a distinct head.
He may not look like you or I,
but this odd fish is becoming the blueprint for our own bodies.
This is Cephalaspis.
She's a peaceful grazer who sucks up algae through her jawless mouth.
But she's also developed a tough protective head and thick scales.
Our ancestor's arthropod enemies have also been evolving
and they're ready for round two.
A hundred million years have passed
and the fight for survival has filled the Silurian seas with variety.
Some creatures here would be recognisable today.
Sponges filter food alongside sea urchins.
The orthocone is a distant relative of squid and cuttlefish,
but he's as long as a truck.
This world is terrorised by
a new improved generation of armoured arthropods.
Meet Brontoscorpio.
He's a metre long monster scorpion with gills
and a stinger the size of a light bulb.
He zeros in on his next meal.
But Cephalaspis has evolved an early warning system.
Special sensors on her skin detect the tiniest vibrations in the water.
We've inherited similar senses.
They make us sensitive to touch.
With her defensive headgear, Cephalaspis can't swim fast for long.
She must rest frequently.
Soon she'll tire completely.
Cephalaspis suddenly changes her path.
She's picking up bad vibrations.
Something Brontoscorpio can't detect.
Pterygotus is the Titan of sea scorpions.
The biggest arthropod of all time.
More than three metres long,
she's the size of a crocodile.
She has turned the tables on Brontoscorpio.
He'll make a good meal for her young.
In such dangerous seas there's nowhere to hide.
When breeding seasons comes,
the Cephalaspis congregate to head for the one place
they might escape a scorpion's grasp.
Fresh water, inland.
Land at this time is like an alien planet.
It's a barren expanse of roasting rock hotter than the Sahara.
The air would be toxic to us.
It has much less oxygen
and three hundred times more carbon dioxide than today.
But some forms of life have gained a foothold in this furnace.
The first pioneering plants.
Cooksonia has a unique survival strategy.
It's the first plant to send shoots upwards, trapping extra light to help it grow.
This basic design will eventually lead to our tallest forests.
The Cephalaspis convoy ploughs upriver, away from the sea.
They're making the marathon journey
back to the spawning grounds where they hatched.
Incredibly our fish ancestors already use memory.
They use familiar landmarks to navigate.
Their toughened heads protect a vital weapon.
One of the first complex brains.
It's much more developed than their scorpion rivals
who have no memory at all.
It's thanks to these primitive fish
that we can think and solve problems today.
But the fish have underestimated their enemy.
It is the arthropods and not our ancestors
who have taken the first momentous steps out of the sea into dry land.
Brontoscorpio has a huge advantage.
As well as gills
he has simple lungs made up of hundreds of thin layers of tissue.
He can't breath in and out like we do.
He just absorbs the oxygen into his blood.
Equipped to maximise the little oxygen available
and with their armour to protect them from the sun,
the scorpions patrol the shoreline,
scavenging on whatever the sea washes up next.
Finally the fish approach their destination.
They've navigated their way back to the spawning pool,
where their lives began.
Weak from their long journey,
now they have to cross a ridge of rock
to make it from the river, to the pool.
The first fish make it through and start to lay their eggs.
But the exhausted Cephalaspis have company.
Passing scorpions have stumbled on this bounty.
But the fish have numbers on their side.
The clever Cephalaspis have navigated their way,
while Brontoscorpio are only here by luck.
They're soon stuffed to the gills while the fish keep jumping.
One scorpion is still hungry, but he can't feed.
He's become a prisoner in his own skin.
His rigid skeleton is now a handicap.
It can't grow with his body.
He needs to shed his hard skin and then grow another,
expanding while the new one is still soft.
For such a large creature, this is a long process.
Next morning, there's no sign of life in the spawning pool.
The scorpion has missed his chance.
Our ancestors have survived.
They've laid their eggs and are returning to the sea.
Brain has triumphed over brawn,
and soon they won't be such soft targets.
Evolution starts to give them weapons to fight back.
Over millions of years,
the fish's gills adapt to form the first jaw with the very first teeth.
Now they're equipped to go on the attack.
Some develop tougher bones and muscles in their fins and shoulders,
which become the first limbs.
This is where our arms and legs began.
With this four-limbed design,
our ancestors finally haul themselves out of water on to land.
This is the giant amphibian, Hynerpeton.
The prototype land dweller for the next three hundred million years.
Hynerpeton are over a metre and a half in length,
much larger than most amphibians today.
They've carved out a home along the water's edge.
Arthropod enemies still exist,
but they've shrunk since their Brontoscorpio glory days.
Still, life for this pioneer is far from easy.
It's a whole new world.
In the last fifty million years, plants have developed into trees.
And with nothing around to eat them,
they've grown into vast forests pumping oxygen into the air.
Hynerpeton has evolved complex lungs to exploit this new oxygen.
His lungs are sacks, just like ours, and he breaths like we do.
Forcing air in and out so his blood can absorb more oxygen.
We still rely on the design developed in this strange amphibian.
Hynerpeton can breath on land, but he's still water bound.
His skin is much thinner than ours and it dries out in minutes,
so he has to keep it wet.
And water is a danger zone.
The fish are now our ancestor's enemies.
Primitive sharks are constantly on the hunt.
But even sharks are small fry in comparison to some flesh eating fish.
Hyneria weighs two tons. And is five metres long.
She's an insatiable carnivore.
The amphibian limbs are his saving grace.
For now.
As the burning sun dips, Hynerpeton can spend more time on land.
This stretch of shoreline is his territory
and his trump card with the opposite sex.
Hynerpeton females are choosy
and will only go for males who can defend their turf.
They also only mate during a short season.
The male's future depends on passing on his genes
and tonight could be his last chance.
As night arrives, so does the competition.
Another male with his eye on this prime patch.
To avoid injury,
the males demonstrate their strength in a strange push up contest.
This rival is not up to the challenge,
but now our male may be too late for love.
Dawn.
And all the females in the area have mated and moved on.
Hynerpeton seems to have missed his chance.
The only attention he's attracting comes from the dark waters of the lake.
A female finally answers his call and the male seizes the opportunity.
Amphibian eggs are soft and their young have gills,
not lungs, so they must be laid in water.
Where amphibians are most vulnerable.
Hyneria can attack like a killer whale after a seal.
Only just missing her prey.
But she has remarkably powerful fins.
And she takes the male by surprise.
The end for this Hynerpeton.
But the amphibians are about to find a way
to leave the dangers of the water behind for good.
The key to their future success lies in changing their eggs.
They evolve a hard waterproof casing
which protects the young inside from the drying sun,
so they can be laid on land.
The babies will hatch out, fully developed,
air breathing and independent.
They're the first ever true vertebrate landlubbers.
The very first reptiles.
But as they move inland, they'll face an ancient enemy.
More deadly than ever before.
The arthropods are back.
Three hundred million years ago
much of the Earth was covered in vast swamp forests.
Here, nothing is as it seems.
The fifty metre giants towering above this water world may look like trees,
but they're actually distant relatives of ferns.
Even the air is alien.
Over a third is oxygen.
Much higher than at any time in history.
This oxygen rich atmosphere has fuelled the growth of new,
super sized Arthropod predators.
This Mesothelae spider is the size of a human head.
She'd be hunting cats if she were alive today.
She's an ambush predator.
Operating from her underground headquarters.
Safe in her borrow,
she rests her feet on carefully constructed trip lines.
These allow her to pick up vibrations from the outside world.
Reptile,
Petrolacosaurus is hunting on the forest floor.
Unlike our amphibian ancestors,
he has tough scaly skin which traps moisture inside his body.
Vital for all land dwellers.
Because he doesn't dry out in the sun,
he can venture away from water.
But that means encountering new predators.
The reptile outruns the spider.
He's evolved a complex heart,
much more efficient than his enemy's.
In fact the template for our own.
It's a powerful pump that pushes blood and oxygen around his body to his muscles,
so he can run at high speed without stopping for a rest.
This time though he's trapped inside a log.
At first the spider's armour stops her squeezing in.
But she's not going to give up so easily.
Back in her lair,
Mesothelae will inject her victim with digestive juices
to dissolve him from inside.
There are other dangers in the swamp apart from predators.
The water levels can change rapidly.
They've risen.
The spider drags her dinner home, but something's wrong.
Her headquarters are flooding.
She'll have to evacuate.
She can't dig, so she'll have to find another hole she can adapt.
And once outside, she's vulnerable to larger predators.
Meganeurid is a monster dragon fly,
queen of the carboniferous skies.
With a wing span of almost a metre,
she's the size of an eagle with an appetite to match.
High above her carboniferous kingdom,
normally she's invincible.
But trouble's brewing.
The flood below is due to an approaching storm.
The super oxygenated atmosphere,
which has helped fuel the growth of the insects,
the Arthropods, is highly volatile.
A lightning strike could trigger an explosion.
The clock is ticking for the swamp.
The rising water levels suit one group of hunters.
Amphibians.
They've continued thriving over the last sixty million years.
Their thin skin still restrict them to the water's edge,
but they're now powerful predators with a devastating pair of jaws,
ready to ambush anything that wanders within reach.
The homeless spider tries her luck further inland.
But other Mesothelae fill the forest floor
and they don't like to share.
Neither does Arthropleura.
He's a distant relative of modern millipedes,
but as long as a car.
He can rear up, tall enough to look you right in the eye.
Although he's vegetarian,
his strong jaws could still deliver a nasty bite.
With rising waters,
Arthropleura's foraging leads him into dangerous territory.
In this clash of the titans,
the Arthropod's armour is his best defence.
Unless it gets split.
Impaled, his soft innards provide a feast.
The lightning storm is building, moving ever closer.
Just in time, the spider finds another hole.
A Petrolacosaurus is evicted,
but reptiles don't need burrows to avoid danger,
they have speed and stamina on their side.
Meanwhile, the spider starts to turn the hole into a hunter's lair.
Night falls.
And Mesothelae settles into her new silk-lined home
She tests the new trip lines.
They're already picking up vibrations from outside.
The storm is very close now.
Lightning strikes ignite the oxygen rich air.
The giant dragonflies are forced down from the canopy to seek shelter below.
An unexpected windfall for the water predators.
Amid the chaos,
Mesothelae seems safe in her bunker underground.
A huge fire, ignited by lightning,
has devastated Mesothelae's neighbourhood.
There are no signs of life above ground.
However, a Petrolacosaurus managed to outrun the flames.
But now he heads right into the spider's lair.
Mesothelae's hole was at the centre of the lightning strike.
The reptile gets a spider barbecue.
The era of the giant bugs is coming to an end.
The climate is drying and the atmosphere is losing oxygen.
The monster insects and spiders can't survive the change.
But with their efficient hearts and waterproof skin,
our versatile ancestors flourish in the new dry climate.
Evolution takes over.
Lacking restrictive armour
means the reptiles can start to make it big.
Their muscles and bones broaden and extend.
Their bodies mushroom into huge new shapes and forms.
Our distant ancestors have come a long way.
They've now conquered the land.
The world's first giant reptiles have arrived.
But they're not related to dinosaurs.
Their descendents will be of a very different kind.
Reptiles have now spread all across the globe.
Edaphosaurus bask in the early morning sun.
They're three metres long, as big as hippos,
and, like them, they're vegetarians.
Life in their new Permian home is a constant battle with the elements.
The climate swings between seasonal extremes.
From burning summers, to freezing winters.
A new species of plant has evolved,
able to withstand this cold, dry atmosphere.
Primitive conifers.
In this harsh world,
creatures need ways to regulate their body temperature.
Edaphosaurus are sluggish autumn morning chill,
but they'll soon warm up.
Thanks to the huge sail on their backs.
Their backbone has tall spines connected by a thin membrane of blood filled skin.
This large surface area can lose heat fast, if the Edaphosaurus need to cool down.
While to heat up,
they simply turn their sails towards the sun,
like a solar panel.
Amazingly, these strange sailbacks are related to us.
They're part of a very special group of creatures called mammal like reptiles.
It's down to them that we have control over our body temperature today.
But Edphosaurus aren't the only sailbacks,
and now their biggest enemy is one of their own kind.
This is Dimetrodon, a vicious carnivore.
The biggest reptile on Earth.
She'd normally attack adult Edaphosaurus,
but today she wants to avoid injury.
She's pregnant and almost ready to lay her eggs.
She finds a smaller, softer target.
This was only a mock charge,
a tactic to disperse the group and expose the vulnerable young.
The panicking Edaphosaurus flush their sails with blood,
flashing an eye spot to distract the predator's attention
from their vulnerable head.
But Dimetrodon can see through their disguise.
She locks on to her victim.
As well as her sheer size and power,
Dimetrodon has a killer edge.
As a mammal like reptile, she's evolved specialised teeth.
Incisors shear off chunks of flesh.
Serrated canines cut and slice.
We humans have inherited these same meat eating teeth.
We have a smaller version in our mouths today.
The young Edaphosaurus didn't stand a chance.
This is a crucial kill for the Dimetrodon.
Before she lays
she needs to eat enough to last her for the next seven months.
To boost her babies chances of survival,
she's evolved a basic form of parental care.
Guarding her eggs.
But the smell of blood has attracted more Dimetrodon.
Highly aggressive males.
The female knows better than to defend her kill.
By the time the group has finished
there'll be nothing left but bones.
While lions today consume seventy per cent of a carcass,
Dimetrodon eat ninety.
But they'll only eat intestines after shaking out the waste inside.
Dung is one thing a Dimetrodon can't stomach.
The female has built a nesting mound of earth and wood.
Inside, she digs a deep burrow.
And starts to lay her eggs.
She covers her brood carefully, ready to begin her guard duty.
Egg thieves lurk in the shadows.
Like this carnivorous amphibian.
But he's too small to make a full frontal attack.
He'll have to bide his time until the female turns her back.
The mother must also constantly monitor the nest's temperature.
Temperature control is vital for reptiles even before they hatch.
The mother piles on more earth if the babies are too cold.
And will remove a layer if they're too warm, otherwise the babies will die.
It's going to be a long seven months.
As autumn turns to bitterly cold winter,
the landscape is transformed.
Still the female keeps her vigil,
getting weaker all the time from lack of food.
Until finally winter melts into spring.
With the warmer weather,
the Edaphosaurus laze beneath the conifers,
shading their sails from the sun to avoid overheating.
But there's much activity at the nesting mound.
And it's not the mother who's digging.
Another female is desperate to lay her eggs.
If she takes over the mound,
she'll dig out and kill the incubating young already inside.
The resident mother may be weak,
but she won't give up her nest without a fight.
It's a battle neither can afford to lose.
Next morning, just one female remains at the nesting mound.
It's the resident mother. She's managed to wrestle off her rival.
But not without a sacrifice.
She won't be able to defend her eggs or herself for much longer.
And the thieving amphibian is poised to seize his chance.
As summer arrives, the Edaphosaurus are thriving in the heat.
The young have grown and test out their newfound strength.
But the mother Dimetrodon has reached the end of hers.
So weak, she's helpless as another intruder attacks her nest.
Luckily this large male has got his teeth
into something more substantial than her young. The amphibian.
The precious eggs are safe and ready to hatch.
The mother can hear them squeaking.
She's achieved her goal.
But at this moment her maternal bond is severed.
Unlike her mammal descendents, she won't nurture her young.
Her instinct now is to save herself, by finding food.
Without their mother's protection,
the babies will have to be ready to go it alone.
They take their first steps into a perilous world
and must make a mad dash for the safety of the trees.
A danger in a familiar form awaits them.
Adult Dimetrodon are cannibals.
Not all babies are helpless.
Some already instinctively know how to defend themselves.
They roll in dung. Something the adults can't stand.
Repelling their pursuers long enough to get a head start.
One adult is driven on by hunger and desperation.
The mother. She'll weed out weaker babies straight away,
which helps the strong ones and her species as a whole survive.
And now the reptiles evolve to tighten their grip on land.
Their legs straighten and lengthen,
holding them more upright and giving them speed.
Their backbones and muscles get stronger and they even start to look like mammals.
To house a larger brain their skull bones expand into an enormous head.
And out of their draw thrust huge, sharp teeth.
A new age of specialist reptiles had dawned.
After millions of years of evolution,
But now the war they've waged so long
is much more than a battle between predator and prey.
The whole planet is entering a different kind of crisis,
one that will destroy most of these monster reptiles
and wipe out 90 per cent of life on earth.
All the continents on earth have now drifted together
to create on giant land mass called Pangaea.
And at its centre lies the largest desert the world has ever seen.
It's a brutal world where animals have to be especially tough.
Perfect for reptiles.
This is a one-ton Siberian Scutosaurus,
a distant ancestor of turtles.
Although he has no shell, his back is covered in hard, bony plates.
And just as well: these sand dunes hide a fearsome predator.
Scutosaurus normally travel in herds.
But this old male's got left behind, and his keen nose senses danger.
Once he tires, he's vulnerable.
His attacker is a carnivorous Gorgonopsid.
She's fast, powerful, and equipped
with deadly weapons no hunter has had before.
Exhausted, trapped and weakened by his wound,
the old Scutosaurus has no fight left.
All he can do is wait for the killer blow.
The Gorgonopsid's huge jaws hold a pair of fangs 12 centimetres long.
She has evolved the world's first sabre teeth -
a lethal weapon some mammal predators will later use.
In this harsh landscape,
the reptile's biggest battle is now with the elements.
A massive surge in volcanic activity is beginning to superheat the atmosphere,
creating the highest temperature life on earth has ever known.
Each year the deserts spread.
Even here in Siberia, far north of the equator,
animals are forced to cluster around any lasting source of water,
no matter how small.
The huge female Gorgonopsid has come looking for a drink to wash down the Scutosaurus,
and even smaller Gorgonopsids will do well to keep out of her way.
Five metres long from nose to tail,
she's the top predator on earth.
There'll be nothing to rival her
until the dinosaurs evolve in 30 million years' time.
But unlike the dinosaurs,
these early reptiles are more closely linked to our ancestors,
mammals, than to lizards and crocodiles.
They don't have fur,
but they've already evolved scent glands in their skin.
This way, everyone can tell when the giant Gorgonopsid is around.
Despite the presence of these heavyweights,
smaller creatures also eke out a living around the waterhole.
Diictodon, a hardly little burrower, just half a metre long.
They live as pairs in spiral burrows which remain cool even in the desert heat.
Like the large predators outside,
Diictodon are distant reptile relatives of mammals,
and although it will be 30 million years before the first true mammals appear,
there are already family resemblances.
In particular, his hearing is linked to tiny bones in his lower jaw.
One day these will evolve into our middle ear bones,
something no reptile has.
Several pairs of Diictodon live around the waterhole,
but this is not a colony,
they compete furiously for the sparse vegetation that is their food.
This frequently leads to confrontation.
These clashes are one reason
why both males and females sport a pair of short tusks.
There is, however, one big advantage to living in a crowd:
if a neighbour spots danger, everyone soon knows about it.
A Gorgonopsid has come to investigate.
A single snap of those enormous jaws would crush Diictodon -
if they could get a grip.
But it's not always size that counts.
These tiny mouthfuls are more trouble than they're worth.
The Gorgonopsid knows that if she hangs around the waterhole for long enough,
eventually larger prey will come to her.
There is another, unseen, resident of this waterhole.
A monster much less suited than the reptiles to the changing climate.
A fugitive from when this desert world was lush and green.
It lies in ambush underwater, like a crocodile.
A giant amphibian Labyrinthodont.
But pound for pound, this female's picked the wrong target.
The amphibian's ambush attempt was probably driven by sheer desperation.
For generations this waterhole has supported a wide range of animals,
including several other Labyrinthodonts.
But this one is the last,
and as the water she depends on disappears, she's trapped.
The wet season arrives, but there's no rain.
With life under such pressure,
species are dying out at a rate
that won't be matched until humans evolve in 250 million years' time.
The waterhole is now no more than a large puddle.
Diictodon are more adaptable than most.
They can dig deeper to escape the heat,
carving out tunnels in the rock-hard mud.
But the giant amphibian is in big trouble,
and as she grows weaker, her enemy watches and waits.
It's a deadly game of cat and mouse.
But life here is about to change for everyone.
A migrating herd of Scutosaurus has sniffed out the waterhole.
It's possible the smelt the water several miles away,
and this could well be the first drink they've had in six months.
The desert plants are a poor source of nutrients,
but these large reptiles are designed to squeeze out every ounce,
although they cannot chew.
Their huge stomachs hold stones they've picked up from the desert.
These help grind the vegetation so their digestive juices can get to work.
The tough little Diictodons are used to dodging danger.
But the Gorgonopsid now keeps her distance.
Even she dare not attack such a large armoured herd.
It's a standoff.
It turns out the Scutosaurus are a bigger threat to life
around the waterhole than the predators.
Within a few days they have drunk it dry.
And moved on once again in their eternal search for food.
They represent the plight of all creatures on the continent of Pangaea.
The global drought is now obliterating millions of years of evolution.
Life everywhere is on the brink.
For animals that do not migrate,
the situation's reaching a crisis point.
Hunger drives the Gorgonopsid back to the Diictodon -
and this time she tries to dig them out.
But the Diictodon's hard work pays off.
Their tunnel in the sun-baked earth is deep enough to keep them safe.
Instead, the Gorgonopsid's nose leads her back to the dried-up waterhole.
She senses things are not as lifeless as they seem.
The giant amphibian.
Just before the waterhole dried up,
she must have burrowed into the damp mud,
forming a cocoon around herself,
in a last-ditch attempt to sit out the drought.
But in her torpid state,
she's helpless as the Gorgonopsid feasts.
Eventually storm clouds gather,
but instead of rainwater they bring sand.
The sandstorm sweeps in,
burying the waterhole completely.
The vast Pangaean deserts continue to spread,
snuffing out entire ecosystems.
Even the mighty Gorgonopsid has at last succumbed.
With no prey, even she could not survive.
Mummified in the sand,
this monster will soon be nothing but dust.
Over the next few million years,
the earth will suffocate under a stagnant blanket of heat,
sparking a mass extinction,
even greater than the one that will destroy the dinosaurs.
The future belongs to a tiny group of survivors,
small and adaptable enough to sit it out.
The Diictodon carry on digging throughout the drought.
This pair has unearthed plant tubers,
which hold enough water and nutrients to keep them going for several months.
As millions of years go by,
the climate shifts again,
and the reptiles are among the first to recover and repopulate the empty earth.
From creatures like little Diictodon, larger, stronger herbivores evolve.
These tough forerunners of mammals seem poised to seize control for good,
but they are in fact set to play out their final scene.
The dawn of the Triassic era,
and the earth has only just begun to show signs of recovery.
The deserts have stopped growing,
and huge forests of primitive conifer start to re-colonise the land.
In these new forests, plant eaters recover first.
One in particular. Like most of the large reptiles,
they may resemble dinosaurs,
but Lystrosaurus are more closely linked to mammals - and to us.
Astonishingly, their vast herds make up more than half of all life on earth.
Never again will a single species do so well.
Deep within the forests, though, a rival is evolving.
A new type of animal, destined to change the face of life on earth.
Meet Euparkeria, a tiny insect-eater.
He may not look much of a threat to the dominant reptiles,
but the key to his success is in his hip.
The way his thigh bone is attached
allows him to run on two legs, freeing his hands.
This kind of agility has never been seen before in reptiles,
and gives Euparkeria an edge.
Euparkeria will lay the foundations for a new group of reptiles - the dinosaurs.
Giants such as Tyrannosaurus and Diplodocus can all trace
their family tree back to this little insect hunter in the Triassic forests.
The monster herds of Lystrosaurus hoover up so much vegetation
that they constantly migrate to find fresh food.
They follow the seasonal rains,
and each year in Antarctica this brings them to the edge of a huge escarpment.
The only way down for these cumbersome animals is through a deep ravine.
The herd moves mostly at night, and come sunset,
they begin the dangerous descent.
It will take several hours for all of them to pass through the ravine,
and in some parts there's only space to move in single file,
which leaves them very vulnerable.
Lystrosaurus have sharp eyesight and a very good sense of smell.
But in these cramped conditions it's hard to spot trouble ahead.
They're being watched by a vicious nocturnal hunter - a therocephalian.
Lystrosaurus are strong opponents,
but this hunter doesn't rely on power to make a kill.
The attack is swift, and seems to have been unsuccessful.
But this predator's secret weapon is a poisonous bite.
Its venom is more lethal than a black mamba's,
and it quickly floods the Lystrosaurus's blood stream.
All the therocephalians have to do is wait for it to take effect.
The victim collapses, but the herd moves on without concern.
They have no social bonds.
The therocephalians close in for the kill.
Dawn at the foot of the escarpment,
and here the Lystrosaurus will face their biggest challenge yet.
They need to cross a river, but its banks are lined with open jaws.
Chasmatosaurs are the earliest ancestors of crocodiles and alligators.
Their strange overbite means once they get their teeth into a victim,
there is no chance of escape.
They don't normally gather in such numbers,
but they're here for a special event - the annual migration of the Lystrosaurus.
If you're a Euparkeria, the river's not a great place for hunting insects.
But he has speed on his side.
As the sun rises, the Chasmatosaurs are drawn towards the water.
Some of them haven't eaten
since the Lystrosaurus last passed this way a year ago.
Now they sense it's time to feed again.
The front of the vast Lystrosaurus herd finally reaches the river.
They're strong swimmers, but drowning is not the danger here.
They linger at the river's edge, reluctant to go in.
For reptiles, they have relatively large brains,
and they remember what happened last year.
But with more Lystrosaurus arriving all the time,
the backlog will soon force them in.
On the other side, lush grazing beckons,
and eventually the first one takes the plunge.
A strong swimmer, he quickly makes it to the other side.
But with the steep banks,
he's still got to find a place where he can get ashore,
and every extra moment in the water increases the risk.
More and more Lystrosaurus warily strike out for the other side.
But now the predators are homing in.
The first swimmer has made it, and clambers ashore.
But many of the herd now entering the water will not be so lucky.
Despite the carnage,
the herd is soon reforming on the other side.
The predators are quickly sated and exhausted.
Although many Lystrosaurus are dead,
it's still only a small proportion of the herd.
and the brief glory days of Lystrosaurus will soon be gone.
This is followed by a decline in all mammal-like reptiles,
consigning our ancestors to the shadows for millions of years.
Instead, it is creatures like Euparkeria that are about to usher in a new golden age.
These specialists on two legs will provide a cornerstone for
one of the greatest dynasties the world will ever see.
Their descendants will become the dominant life form on earth
for more than 170 million years,
and be known as the most notorious monsters of them all.
Welcome to the Age of Dinosaurs.