Somewhere on the edge of a Jurassic forest,
a mother dinosaur is laying her eggs.
(Deep grunting)
She is a 25-tonne Diplodocus.
Each football-sized object
is carefully placed in a deep trench.
Tenderly, she buries her clutch
and then abandons them.
0ut on the fern plains, the rest of her gigantic herd grazes.
She is one of a family of dinosaurs called the sauropods
that dominate this period in Earth's history.
They are the largest animals
that will ever walk the planet.
This is the Jurassic period,
and the giant continent of Pangaea
that stretched from pole to pole is now breaking up.
It is much wetter than the earlier Triassic period
and where there were once deserts,
there are now vast forests of conifer trees.
It is 70 million years since dinosaurs first appeared on Earth
and in this greener world,
they have evolved into a myriad of different forms.
Three months ago, a mother Diplodocus laid 100 eggs
in this clearing in the forest.
Now they are hatching,
but there are signs they have been discovered by an egg thief.
The culprit is an 0rnitholestes - a two-metre long carnivore,
closely related to dinosaurs that will evolve into birds.
Normally, he hunts small lizards and mammals in the forest.
This is an extra treat.
(Squawks )
0nly 10 metres away from the carnivore,
the forest floor moves.
(Squeaks )
(Squawks )
Right under the predator's gaze,
a baby Diplodocus, or sauropodlet, has hatched.
Her brothers and sisters are also struggling free
from their buried eggs beneath the surface.
And there is safety in numbers.
The 0rnitholestes is too busy eating to chase more sauropodlets.
He has had his fill.
A little female rests for an instant...
and then, along with the other survivors,
heads for the deep forest as fast as she can.
(Cheeping and squawking)
Their mother laid them at the edge of the forest
because she was too big to go deeper.
But the sauropodlets need the cover of the deep forest.
For the next few months, their only chance for survival
is to remain hidden from predators amongst the vegetation.
Between the trunks of huge redwood trees,
the forest floor is covered in a dense layer of ferns.
Beneath these,
the sauropodlets start their lifelong obsession with eating.
Newly hatched, they only weigh a few kilograms,
but they must grow by one tonne a year until adults -
an astonishing 2-3kg a day.
(Distant roaring)
However, the forest is not a perfect sanctuary.
When faced with danger, the sauropodlets lie very still
and depend on their camouflage for protection.
It may have worked this time,
but very often, the sharp-eyed predator gets his meal.
Not all of the landscape is covered in forest.
There are vast open fern prairies,
and this is where the titans of the Jurassic roam.
Dinsoaurs like Stegosaurus,
with its distinctive row of spinal plates.
(Rumbling growl)
These prairies are kept clear of trees
by the constant grazing of such giant herbivores,
and none have a larger impact on this environment
than the biggest dinosaurs of all - the sauropods.
There are many different types
of these gigantic, long-necked creatures.
These are Diplodocus - the longest of them all.
For protection, they move in herds of 30 or more.
Some older ones are over 40 metres long.
They use their very strong but stiff necks
to graze over large areas with little effort.
To balance their necks,
they have long tails with whip-like ends,
that are used for communication between members of the herd.
Such a huge herd moving attracts an array of smaller animals.
As they eat the vegetation, insects swarm around them,
and insect hunters, like these damselflies,
use the dinosaurs as gigantic feeding platforms.
There is even a tiny flying reptile, or pterosaur,
called Anurognathus
that specialises in life amongst these giants.
These pterosaurs feed on insects,
and spend their entire lives hanging onto the Diplodocus.
They fight, feed and breed
on creatures that are 150,000 times heavier than they are.
Each Diplodocus drops over a tonne of dung every day.
This attracts yet more insects...
especially the dung beetles.
Millions of years from now, descendants of these beetles
will clear elephant dung off the African grasslands,
but their peculiar lifestyle started here
in the Jurassic with the dinosaurs.
The herd of giants moves on,
carrying its own unique habitat with it.
After the rain, the redwoods steam in tropical temperatures
and a dinosaur's dawn chorus fills the air.
(Bellows and screeches )
A year has passed since the sauropodlets fled into the forest,
and deep in a canyon, the little female grazes.
She is already over 3m long.
She feeds with other yearlings,
sticking together in a creche for safety.
They are here because the canyon walls drip with moisture,
creating a thick layer of moss and fern.
But the canyon runs down to the prairie
and all this greenery attracts larger dinosaurs.
A seven-tonne male Stegosaurus.
He too is a herbivore, but very dangerous.
The large plates are primarily there for display.
It's the metre-long spikes on his tail that are lethal.
These he can wield with devastating effect,
despite having a very small brain for his size.
The creche moves down the canyon,
away from the Stegosaurus.
But two Allosaurus have been drawn here -
by the smell of prey.
(Low growling)
(Squeaks )
(Roaring)
(Snarling)
The Stegosaurus flushes blood into his plates,
creating a frightening display of colour.
(Roars )
Confused and intimidated by the herbivore's display,
the Allosaurus backs down.
Sauropodlets are small prey for the Allosaurus.
These are the lions of the Jurassic -
the top predators of their age.
The creche once again seek the sanctuary of the ferns,
even though, weighing half a tonne now,
they are not as well hidden as they used to be.
As they grow, their teeth become more like the adults'.
These are perfect for stripping ferns of their leaves.
Nearby, the vast skeleton of a Diplodocus lies where it fell.
Such huge, weight-bearing bones
are too large for any forest creature to remove.
The female sauropodlet can have little idea
that in ten years, she will be almost as large.
But the creche realise they are too near the edge of the forest,
and retreat into its green depths.
Elsewhere, an adult Diplodocus herd is clearing forest.
This is how they have shaped the landscape around them.
Vast areas of prairies and open forests are kept that way
because sauropods flatten trees in search of food.
The Diplodocus are after the ferns that grow between the trees.
Their teeth are more suited to soft green leaves
than woody branches.
0ne of the reasons these creatures are so massive
is because it allows them to have a hugely long gut
that can digest the toughest Jurassic vegetation.
Whole leaves pass into their guts
where stones the dinosaurs have swallowed
help grind their food down,
so that bacteria ferment it and release nutrients.
It is a process that produces a lot of excess gas.
(Phwrrrrrt!)
While the gut digests,
the body is free to continue its remorseless search for food.
(Squawking)
In the forest, an Anurognathus is hunting...
but not for insects.
He is looking for a host.
He finds it in an immature Diplodocus.
This is the female sauropodlet that hatched five years ago.
She is now 12 metres long and weighs over 5 tonnes.
She has started to develop
the spines and long whip tail of adulthood.
0ld predators in the forest are no longer a threat.
0rnithalestes displays his long quills
in a futile gesture of aggression.
(Grating squawks )
The Diplodocus have remained in a creche,
but they're getting too large for the forest.
Food is short and the trees restrict them.
Soon they must join the adults on the plains.
There is more room by the banks of a river
that runs through the forest,
but nature is about to take charge of these dinosaurs' future.
Drifting through the trees comes the scent of woodsmoke.
It is a smell that terrifies every forest dinosaur.
There is a huge forest fire to the south.
The Diplodocus flee,
but to support their weight,
they always need three legs on the ground.
So, despite the danger, they can only manage to amble.
(Low howling)
The blaze, however, moves faster
and that night, a huge firestorm hits the area.
(Distant howling)
Above the sound of the blaze
come the panicked cries of trapped dinosaurs.
These Jurassic fires are rare, but can be devastating.
Morning light reveals the bodies of forest-dwelling dinosaurs
that have perished in the flames.
Three members of the creche have survived.
They have been driven out onto the prairies.
This is exposed territory for them.
They are not large enough to repel an attack from an adult Allosaurus.
To the young Diplodocus, the other dinosaurs here are unfamiliar...
and huge.
This is Brachiosaurus - a 13-metre high sauropod
that specialises in grazing on the tree tops.
His kind can effortlessly harvest cones and fresh leaves
no other dinosaur can reach, and they have grown enormous.
These adults weigh over 70 tonnes,
making them the largest land animals that have ever existed.
The juvenile Diplodocus do not have the same size advantages
and urgently need the protection of an adult herd.
(Wailing)
Across a conifer heathland
come the plaintive calls of the young sauropods.
It is a cry adult animals are programmed to react to.
There are only two youngsters now...
and they need help.
(Growling)
A herd of gigantic adults responds to their calls.
0ne elderly female sizes up the two newcomers.
She accepts them.
They fall into line behind an adult, safe at last.
The herd is at full strength.
It contains a range of members - from 12-metre long adolescents
to adults three times their size.
It is the mating season, and for the first time,
the female that hatched ten years ago
is old enough and large enough to reproduce.
The males have started to display.
They rock back on their tails to impress potential mates.
0ccasionally, fights break out.
With creatures this size,
the forces at work during these confrontations are colossal -
enough to shatter ribs and shake the ground.
(Growling and bellowing)
The victor wins the right to mate.
0ur female is approached by a young male.
She responds to his calls first by stamping
and then generating very low frequency mating calls.
This infrasound is too low for most animals to hear.
He picks these signals up through the ground,
and responds by walking close to her, rubbing his body down hers.
She shows she is receptive.
Mating is a dangerous activity for the female.
She'll carry at least an extra 10 tonnes on her back.
As she has grown older,
the vertebrae over her hips have become fused and reinforced
to help her cope with this ordeal.
After a few days, the Diplodocus have calmed.
The female feeds on the edge of the herd,
but is not large enough to be immune from attack,
and she is unaware she is being watched.
An Allosaurus knows she is vulnerable.
The predators wait for her to become distanced from the herd.
(Roars )
Saved by the huge tail of a larger Diplodocus.
She rejoins the herd with deep wounds on her side,
but she will recover.
Diplodocus can live for 100 years,
and above a certain size,
they have no natural predators.
Sauropods dominate the late Jurassic.
It'll be millions of years before new dinosaur herbivores
evolve to replace them.
With their passing, life will never again be this large.
Eventually, the mighty sauropods went into decline.
Their lowland prairies became flooded
because the sea levels began to rise.
This created vast inland seas.
In the next programme,
we will meet the giant carnivores that patrolled them.