Dawn over a silent forest
a few hundred miles from the South Pole.
It is the end of months of total darkness,
and as the sun's rays filter down through
the trees, they reveal a cold, harsh world.
Here there are polar dinosaurs, adapted to cope
with extreme conditions.
But even they struggle to stay alive.
This far south, the first day of spring
lasts only a few minutes, but it triggers
the start of an astonishing story of survival
through the polar year.
It is the mid-Cretaceous period,
and dinosaurs are now more widespread than ever,
reaching every part of the globe.
But one place is a special challenge.
The South Pole.
Here, a giant continent made up
of South America, Australia, and Antarctica
is kept warm by ocean currents that are forced down
from the equator to encircle it.
Instead of ice caps there are lush forests.
But unlike the unchanging tropical climate elsewhere,
Antarctica has seasons, from hot summers
under midnight sun, to cold winters
of total darkness.
Leaellynasaura is a dinosaur that has adapted
to this extreme climate.
Throughout the winter, they survive
in the warm, sheltered heart of the thick forest,
but now in spring, they emerge to feed
on the fresh plant growth.
They are just two meters long, and their
most distinctive feature is their large eyes
which help them find food in the dark winter.
These dinosaurs are sociable little animals
that live in small clans, enabling them to
make the most of scarce resources.
The clan is dominated by one breeding pair
and the hierarchy ensures that a Leaellynasaura
is always on lookout duty.
He regularly issues reassuring clicks
as long as the coast is clear.
The sentry has spotted a giant amphibian,
Koolasuchus.
He has massively powerful jaws, weighs about
half a ton, and is a carnivore.
In the water, Koolasuchus is lethal.
But on land, his legs have trouble
dragging his bulk around, and he is
no threat to the lithe little dinosaurs.
He has been hibernating over winter
in the forest, and now faces what, for him,
is an arduous journey of 200 meters
to get back to the river, where he will spend
his summer.
This bizarre-looking creature is a relic
from a time before dinosaurs.
In most parts of the world, competition
from crocodiles has driven these magnificent amphibians
to extinction.
But here, the waters get too cold for crocodiles
and the world's last Koolasuchus survive,
still patrolling the waterways, just as their
ancestors did, 150 million years before them.
As spring takes hold, and the days grow longer,
the forest bursts into life.
Many of the plants in these unique
conifer and fern forests have specially adapted
to lie dormant during the dark of winter
and only with the spring light do they
start to photosynthesize again.
For the clan, it is also a time of
feverish activity.
Having mated with the first spring sunrise,
they are now building nests.
It is a team effort, with the dominant pair
building in the center, and other subordinate animals
working around them.
Many of these piles of leaves will never
hold eggs, but act as decoys to help
protect the main nest.
But no matter how busy these little
dinosaurs are, they always have to remain
alert to danger.
A polar Allosaur, a summer visitor
from warmer lands to the north.
He is a one-ton ambush predator.
The Allosaur is the largest and fiercest
killer in the forest, but he was spotted
early enough by the sentry, and as the clan
melt into the undergrowth, he is no match
for their speed and agility.
Spring across the polar forests brings
the movement of many animals.
In the sky, lines of pterosaurs head south
for their summer roosts.
And among the trees there is the echo
of unfamiliar sounds.
The largest of all the summer migrants
is coming to the forest.
These unusual calls herald the arrival
of huge herds of Muttaburrasaurus from the north.
For the last two months, they have been
migrating 800 kilometers down the coast
of Australia, following the sun to the south.
These dinosaurs move towards the pole
every year, to strip the lush vegetation
and find secure sites to lay their eggs.
The herds have a major impact on the forest.
Each massive adult weighs about three tons
and can pluck food from branches several meters
off the ground.
While feeding, the dinosaurs keep in touch
using their specially-adapted noses
to produce a range of trumpeting calls.
As the forest becomes more crowded,
the clan's nests need constant attention.
The lead female treats her pile of rotting leaves
like an incubator, and uses her sensitive beak
to monitor the temperature.
Then she adds and removes vegetation to keep the eggs
at about 30 degrees Centigrade.
Already the baby Leaellynasaura
can be heard inside, responding to their
mother's clicks.
The nests also have to be protected
round the clock.
Fur-coated mammals thrive in these
antarctic forests, and some are easily large enough
to steal a dinosaur egg.
But the Leaellynasaura has an unusual defense.
It is enough to see off this egg thief.
But the little dinosaur knows there will be others.
The Muttaburrasaurus continue to arrive on the floodplains
and are watched from the forest edges
by hungry eyes.
The Allosaur is testing the herd,
probing for sick or old animals.
These herbivores are slow, but find safety
in size and numbers.
The Allosaur is no match for a healthy
bull Muttaburrasaurus, and he is forced
to back down.
By late spring, the tree ferns and conifers
are in full flush, and have formed a thick canopy
soaking up every bit of sunlight.
Many of the nests have now fallen victim
to predators, but the clan has ensured that at least
the dominant pair's has survived.
Secure within are three hatchlings.
For the first two weeks of their lives,
they will stay in the nest while the adults take turns
collecting food and bringing it back to them.
The lead female takes great care
to maintain the nest.
To stop predators sniffing out her brood,
she removes the old eggshells
and eats the unhatched eggs.
This also recycles the nutrients.
At this stage, the hatchlings are vulnerable
and can easily become lost on the forest floor
if they stray.
All the adults watch out for wanderers
in case a predator moves in.
Within weeks, this little hatchling will be strong enough
to keep up with the adults.
But for now, he is promptly returned
to the safety of the nest.
It is now full summer, and permanently light.
The sun will not set for another five months.
At this time of year, the forest floor
around the nests comes alive with polar insects
like this weta, out hunting for food
among the leaf litter.
They themselves are food for larger animals
like the tuatara.
It is a reptile, but one surviving from a time
long before the dinosaurs.
It will remain long after them, too,
clinging on in the land that will become
the islands of New Zealand.
Out in the open, the Muttaburrasaurus herd
is being tormented by bloodsuckers.
Summer brings out swarms of biting flies
and although dinosaurs are covered in
tough, scaly skin, they do have softer parts.
The insects concentrate on areas
like the inside of the ear, where their mouths
can pierce the skin and suck out a meal.
These swarms can drive their gigantic hosts wild,
and soon the herd has to move away from the river.
Inside the forest, the Leaellynasaura enjoy
the summer bounty and, despite the dangers
around them, sleep.
During these long months of sun they rely heavily
on their patterned skin to camouflage them
among the ferns.
Sleep is the last thing on the minds
of the hatchlings that are playing nearby.
They have grown, and are now practicing
the sort of agile moves which may
one day save their lives.
Wherever the young are, their mother
is not far away, acting as lookout for
her increasingly active brood.
On the banks of the river, an old Muttaburrasaurus
has been brought down, and a male Allosaur
feeds off the rotting flesh.
The polar Allosaur is a smaller descendant
of the great carnivores of the Jurassic,
50 million years before.
His type are rare in the Cretaceous, but they
survive here at the South Pole.
Although there is enough meat at this kill
for 20 Allosaurs, it is unlikely the approach
of a rival female will be tolerated.
She is driven away by the hungry male.
A fully-grown polar Allosaur needs about
100 kilos of meat a week.
She will need to come back once the male
has eaten his fill.
Later, under the light of the midnight sun,
one of the young Leaellynasaura
ventures down to the river alone.
Saved, by his lightning reactions.
But the young Leaellynasaura has much
to learn about the dangers of his forest home.
In the time of dinosaurs, Antarctica suffers
regular summer thunderstorms, that sweep
across the polar forest, causing widespread flooding.
These floods drive forest creatures together,
and this can lead to confrontation.
The Leaellynasaura have spotted a rival clan,
and it is enough to trigger an aggressive response.
Each clan must defend its area of forest
so it does not face competition for food.
It is crucial that the interlopers are
put off by a convincing show of strength.
It has worked.
The rivals retreat, and for the moment
the clan's territory is safe.
After the rains, the floodwaters quickly subside
and dinosaurs can return to the river banks
to feed.
When there is plenty of food, herbivores
can be very tolerant of each other.
As the Muttaburrasaurus pluck and tear
at the podocarp trees, the Leaellynasaura
scamper among them, gathering up the
red fruit that gets scattered on the ground.
Although a risky harvest, the clan must take
every opportunity the forest offers,
because time is running out.
The seasons draw on, and for the first time
in four months, the sun sets.
Autumn has arrived, and the forest
prepares for a polar winter.
Up and down the river valleys, the Muttaburrasaurus
sense the change, and begin their long trek north.
Occasionally, some of these giant migrants
get lost in the forest.
But what for them is a minor problem
can mean life or death for the Leaellynasaura clan.
The noise these huge herbivores make
prevents the Leaellynasaura sentry
from hearing other, more threatening sounds.
The giant carnivore has killed the dominant female.
It is a bitter blow.
Winter is coming, and without a lead female
there will be tension in the clan.
In the gathering gloom, the Koolasuchus
senses the drop in temperature and reluctantly
leaves his summer home.
Once again he lumbers into the forest,
in search of a suitable shelter to hibernate
through the cold, dark months that lie ahead.
The low light also triggers a change
in the forest plants.
They stop growing, and photosynthesis
grinds to a halt.
Some will shed their leaves, others will
just lie dormant.
The Leaellynasaura now have to work extra hard
to find food, searching for fungus
and nutritious roots beneath the forest floor.
At this time of year their survival strategy
is to move to the heart of the forest,
where it rarely freezes, and to keep active
to maintain their body temperature.
But as the clan gathers round a waterfall,
it is clear that the summer predators
have taken their toll.
Only one hatchling has survived,
and they still have no lead female.
Towards the end of autumn, the last day
passes in a few minutes, and the long twilight begins.
Life in the polar forest faces its biggest killer,
freezing temperatures.
Some polar creatures, like the weta,
have learned to cope with the cold
by allowing themselves to become frozen.
In the winter sky, the Southern Lights
whip and flicker over the silent forest.
Under the sleeping trees it is almost pitch-black.
But with image enhancement, it is possible
to get a Leaellynasaura's eye view of the clan.
The dinosaurs are still active, but this year
the ground has frozen, and it has become
almost impossible to scrape a living
out of the soil.
Even pond water has frozen, and the Leaellynasaura
resort to using their hard beaks.
Temperatures this low don't usually last
long in the forest, but facing this harsh time
with their strict social order in tatters
means the fate of this clan hangs in the balance.
They push deeper into the forest.
There has been no light for two months
and another cold snap forces the clan
to take drastic action.
They have evolved one further adaptation
to the cold.
As a group they huddle together and drift
into a state of torpor.
In this suspended animation, their bodies
can resist the effects of the cold, but they
cannot stay like this for more than a
couple of days.
The first hints of salvation are small.
Under his rock, the weta is revived from his
deep freeze by a slight, but sustained, rise
in temperature.
On the horizon the sun's rays grow stronger
and there is the promise of spring.
The forest silence is shattered by an
agitated clan.
Two males are fighting.
This is the mating season for the Leaellynasaura
and the males are competing for dominance.
These fights are short, but can
sometimes be vicious.
Having asserted his authority, the victorious male
chooses a mate, and at last, the clan can start
to reestablish round a dominant pair.
Their annual struggle to survive can begin again.
Life at the poles is a remarkable evolutionary
achievement for the dinosaurs, but eventually,
a slight cooling in the world's climate
will spell doom for these lush Antarctic forests.
And without them, all these unique dinosaurs
will also disappear.
Away from the poles, the dinosaurs continue
to thrive for another 40 million years before extinction.
In the final program, we will see how
just before the end of their reign,
they evolved the most terrifying predator
that has ever walked the earth.