Somewhere on the edge
of a Jurassic forest, a mother dinosaur
is laying her eggs.
She is a 25-ton Diplodocus.
Each football-sized object is carefully placed
in a deep trench.
Tenderly she buries her clutch, and then
abandons them to their fate.
Out on the fern plains, the rest of her
gigantic herd grazes.
She is one of a great 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 used to stretch
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 on the edge of the forest.
It is time for them to hatch, but there are signs
they have been discovered by an egg thief.
The culprit is an Ornitholestes, a two-meter
long carnivore that is closely related to the dinosaurs
that will evolve into birds.
Normally he hunts small lizards and mammals
in the forest.
The hatchling is an extra treat.
Only 10 meters away from the carnivore,
the forest floor moves.
Right under the predator's gaze,
a baby Diplodocus, or sauropodlet, has hatched.
All around her, her brothers and sisters
are also struggling free from their
buried eggs beneath the surface.
And there is safety in numbers.
The Ornitholestes is too busy eating
to start chasing 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 her legs can carry her.
Their mother laid them at the edge of the forest
because she was too big to go in deeper,
but the little sauropodlets have to.
They 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 immediately
start their lifelong obsession with eating.
Newly hatched, they only weigh a few kilograms,
but they will have to grow by one ton a year
until they are adults.
That's an astonishing two to three kilograms a day.
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 all too 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.
Dinosaurs like Stegosaurus, with its
distinctive row of spinal plates.
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, and some of the older ones
are over 40 meters in length.
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 elegant, whiplike ends
that are used for communication between
members of the herd.
Such a huge herd on the move attracts
an array of smaller animals.
As they eat and trample 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 specializes in life amongst these giants.
These pterosaurs feed on insects
and spend their entire lives hanging on
to the Diplodocus.
They fight, feed and breed on creatures
that are 150,000 times heavier than they are.
Each Diplodocus drops over a ton of dung
on the prairie every day.
This attracts yet more insects.
Especially the dung beetles.
Millions of years from now, the 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 a night of rain, the redwoods steam
in the tropical morning temperatures,
and a dinosaur's dawn chorus fills the air.
A year has passed since the sauropodlets
fled into the denser part of the forest,
and deep in a canyon, the little female grazes.
She is already over three meters long.
She feeds with other yearlings that stick together
in a creche for safety.
They are here because the walls of the canyon
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-ton male Stegosaurus.
He, too, is a herbivore, but very dangerous.
The large plates on his back are primarily there
for display.
It is the meter-long spikes on his tail
that make him so lethal.
These he can wield with devastating effect,
despite having a very small brain for his body size.
The creche moves further down the canyon,
away from the Stegosaurus.
But two Allosaurus have also been drawn here
by the smell of prey.
The Stegosaurus flushes blood into his plates,
creating a frightening display of color.
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 ton now,
they are not as well hidden as they used to be.
As they grow, their teeth become more like the adults'.
These are simple pegs that are not designed
to nip or chew.
Instead they are perfect for stripping ferns
of their leaves.
Nearby, the vast skeleton of an adult 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 10 years, she will be almost as large as this.
But the creche realize 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 so many trees in the search for food.
The Diplodocus are actually after the ferns
that grow between the trees, because
their teeth are more suited to these soft,
green leaves, rather than woody branches.
One 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.
While the gut digests, the body is free
to continue its remorseless search for food.
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 meters long and weighs
over five tons.
She has also started to develop the spines
and long whip tail of adulthood.
Old predators in the forest are no longer a threat.
Ornitholestes displays his long quills
in a futile gesture of aggression.
The Diplodocus have remained in a creche
but they are starting to get too large
for the forest.
There is not enough food, and the trees increasingly
restrict their movement.
Soon they will have to leave, and join an adult herd
on the plains.
There is more room down 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 start to flee, but to support
their weight they always need three legs
on the ground.
So, despite the danger, they can
only manage to amble.
The blaze, however, moves much faster
and that night a huge firestorm hits the area.
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.
Only three members of the creche have survived
and they have been driven out onto the open prairies.
This is exposed territory for the youngsters.
They are still 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-meter high sauropod
that specializes in grazing on the treetops.
His kind can effortlessly harvest cones and fresh leaves
no other dinosaur can reach, and they have
grown enormous on it.
These adults weigh over 70 tons, 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.
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.
A herd of gigantic adults responds to their calls.
One elderly female sizes up the two newcomers.
She accepts them.
They fall into line behind an adult, safe at last.
The herd of Diplodocus is at full strength.
It contains a range of members, from 12 meter long
adolescents to gigantic old adults
three times their size.
It is the mating season, and for the first time,
the female that hatched 10 years ago
in the forest is old enough, and large enough,
to reproduce.
The males have started to display.
During this, they rock back on their tails
to impress potential mates.
Occasionally, fights break out.
With creatures this size, the forces at work
during these confrontations are colossal,
enough to shatter ribs and shake the ground.
The victor wins the right to mate.
Our female is approached by a young male.
She responds to his calls first by stamping,
and then generating very low frequency
mating calls.
This so-called infrasound is too low for most
animals to hear.
However, 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 is going to have to carry at least an extra
10 tons 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 she is still 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.
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
and it will 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
and their lowland prairies became flooded
because the sea levels began to rise.
This created vast inland seas, and in the next program
we will meet the giant carnivorous reptiles
that patrolled them.