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
Polar dinosaurs are 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 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
(Cheeping cry)
Leaellynasaura is a dinosaur
that has adapted to this extreme climate
Throughout winter, they survive in the heart of the forest,
but now, in spring,
they emerge to feed on the fresh plant growth
They are just two metres long
and their most distinctive feature is their large eyes,
which help them find food in the dark winter
They 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 one of them is always on lookout duty
He issues reassuring clicks as long as the coast is clear
(Whirring clicks)
(Squeaking)
The sentry has spotted a giant amphibian, Koolasuchus
He has massively powerful jaws,
weighs about half a tonne 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 200m
to get back to the river for the summer
This bizarre-looking creature
is a relic from a time before dinosaurs
In most parts of the world,
competition from crocodiles drove them to extinction
Here, the waters get too cold for crocodiles,
and the 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,
a 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
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 spring sunrise, they now build nests
The dominant pair builds in the centre
and other subordinate animals work around them
Many of these piles of leaves act as decoys
to help protect the main nest
But no matter how busy they 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-tonne ambush predator
(Rumbling growl)
(Squawking)
(Ferocious roar)
The allosaur is the largest and fiercest killer in the forest,
but he was spotted by the sentry
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
(Booming call)
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 km down the coast of Australia,
following the sun to the south
They do this 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 adult weighs about 3 tonnes
and can pluck food from branches several metres off the ground
While feeding, they keep in touch
using their specially adapted noses to produce trumpeting calls
(Horn-like call)
As the forest gets more crowded,
the clan's nests need constant attention
The lead female treats her pile of 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
(Faint cheeps)
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 an egg
But the Leaellynasaura has an unusual defence
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 flood plains
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
(Booming roars)
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 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
(Squeaking)
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,
but for now, he is returned to the safety of the nest
It is now summer and permanently light
The sun will not set for another five months
At this time, the forest floor 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 New Zealand
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 they 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
In 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 playing nearby
They have grown and are now practising 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 descendant
of the carnivores of the Jurassic, 50 million years before
His type are rare in the Cretaceous,
but they survive at the South Pole
(Rumbling growls)
Although there is enough meat for 20 allosaurs,
it is unlikely this rival female will be tolerated
(Roaring)
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
(Squeaks)
Saved by his lightning reactions
But the young Leaellynasaura has much to learn
about the dangers of his forest home
(Thunderclap)
In the time of dinosaurs,
Antarctica suffers summer storms that cause widespread flooding
These floods drive forest creatures together,
and this can lead to confrontation
(Squealing cry)
The Leaellynasaura have spotted a rival clan
and it triggers an aggressive response
Each clan must defend its area of forest,
so it does not face competition for food
The interlopers must be 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 riverbanks to feed
When there is plenty of food,
herbivores can be very tolerant of each other
As the Muttaburrasaurus tear at the podocarp trees,
the Leaellynasaura gather up the 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
(Booming grunts)
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 more threatening sounds
(Squealing and roaring)
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 halts
Some will shed their leaves,
others will just lie dormant
(Chirruping cry)
The Leaellynasaura 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 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 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,
we get a Leaellynasaura's-eye view of the clan
The dinosaurs are still active, but the ground has frozen
and it has become almost impossible
to scrape a living out of the soil
Even pond water is frozen,
and the Leaellynasaura resort to using their hard beaks
Temperatures this low don't usually last long in the forest,
but with their strict social order in tatters,
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
They huddle together and drift into torpor
In suspended animation,
they 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 rise in temperature
On the horizon, the sun's rays grow stronger
and there is the promise of spring
(Squeaking cries)
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 re-establish 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 programme,
we see how, just before the end of their reign,
they evolved the most terrifying predator of all
(Ferocious roar)