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Dawn over a silent forest

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a few hundred miles
from the South Pole.

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It is the end of months
of total darkness

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and as the sun's rays
filter down through the trees,

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they reveal a cold, harsh world.

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Polar dinosaurs are adapted
to cope with extreme conditions,

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but even they
struggle to stay alive.

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This far south,
the first day of spring

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lasts only a few minutes,

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but it triggers the start
of an astonishing story

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of survival through the polar year.

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It is the mid-Cretaceous period

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and dinosaurs
are more widespread than ever,

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reaching every part of the globe.

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But one place is a special
challenge - the South Pole.

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Here, a giant continent
made up of South America,

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Australia and Antarctica

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is kept warm by ocean currents

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that are forced down
from the equator to encircle it.

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Instead of ice caps,
there are lush forests.

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But unlike the unchanging
tropical climate elsewhere,

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Antarctica has seasons -
from hot summers under midnight sun

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to cold winters of total darkness.

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(Cheeping cry )

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Leaellynasaura is a dinosaur

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that has adapted
to this extreme climate.

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Throughout winter, they survive
in the heart of the forest,

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but now, in spring,

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they emerge to feed
on the fresh plant growth.

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They are just two metres long

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and their most distinctive feature
is their large eyes,

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which help them
find food in the dark winter.

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They are sociable little animals
that live in small clans,

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They are sociable little animals
that live in small clans,

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enabling them to make
the most of scarce resources.

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The clan is dominated
by one breeding pair,

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and the hierarchy ensures

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that one of them
is always on lookout duty.

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He issues reassuring clicks
as long as the coast is clear.

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(Whirring clicks )

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(Squeaking)

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(Squeaking)

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The sentry has spotted
a giant amphibian, Koolasuchus.

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He has massively powerful jaws,

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weighs about half a tonne...
and is a carnivore.

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In the water, Koolasuchus is lethal,

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but on land, his legs have trouble
dragging his bulk around

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and he is no threat
to the lithe little dinosaurs.

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He has been hibernating
over winter in the forest,

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and now faces what for
him is an arduous journey of 200m

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to get back
to the river for the summer.

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This bizarre-looking creature

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is a relic from a time
before dinosaurs.

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In most parts of the world,

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competition from crocodiles
drove them to extinction.

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Here, the waters
get too cold for crocodiles,

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and the last Koolasuchus survive,

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still patrolling the waterways,

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just as their ancestors did

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150 million years before them.

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As spring takes hold
and the days grow longer,

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a forest bursts into life.

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Many of the plants in these
unique conifer and fern forests

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have specially adapted to lie
dormant during the dark of winter.

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0nly with the spring light

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do they start
to photosynthesize again.

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For the clan, it is also
a time of feverish activity.

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Having mated with the spring
sunrise, they now build nests.

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The dominant pair
builds in the centre

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and other subordinate
animals work around them.

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Many of these piles of leaves
act as decoys

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to help protect the main nest.

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But no matter how busy they are,

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they always have
to remain alert to danger.

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A polar allosaur -

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A polar allosaur -

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a summer visitor
from warmer lands to the north.

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He is a one-tonne ambush predator.

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(Rumbling growl)

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(Squawking)

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(Ferocious roar)

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The allosaur is the largest and
fiercest killer in the forest,

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but he was spotted by the sentry.

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As the clan
melt into the undergrowth,

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he is no match
for their speed and agility.

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Spring across the polar forests
brings the movement of many animals.

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In the sky,
lines of pterosaurs head south

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for their summer roosts.

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And among the trees, there is
the echo of unfamiliar sounds.

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(Booming call)

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The largest
of all the summer migrants

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is coming to the forest.

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These unusual calls
herald the arrival

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of huge herds of Muttaburrasaurus
from the north.

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For the last two months,

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they have been migrating 800 km
down the coast of Australia,

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following the sun to the south.

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They do this every year
to strip the lush vegetation

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and find secure sites
to lay their eggs.

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The herds have a major impact
on the forest.

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The herds have a major impact
on the forest.

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Each adult weighs about 3 tonnes

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and can pluck food from branches
several metres off the ground.

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While feeding, they keep in touch

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using their specially adapted noses
to produce trumpeting calls.

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(Horn-like call)

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As the forest gets more crowded,

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the clan's nests
need constant attention.

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The lead female treats her pile
of leaves like an incubator

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and uses her sensitive beak
to monitor the temperature.

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Then she adds and removes vegetation

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to keep the eggs
at about 30 degrees centigrade.

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Already, the baby Leaellynasaura
can be heard inside,

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responding to their mother's clicks.

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(Faint cheeps )

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(Faint cheeps )

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The nests also have to be protected
round the clock.

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Fur-coated mammals thrive
in these Antarctic forests,

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and some are easily large enough
to steal an egg.

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But the Leaellynasaura
has an unusual defence.

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It is enough to see off
this egg thief,

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but the little dinosaur
knows there will be others.

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The Muttaburrasaurus continue
to arrive on the flood plains

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and are watched from
the forest edges by hungry eyes.

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The allosaur is testing the herd,

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probing for sick or old animals.

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These herbivores are slow,
but find safety in size and numbers.

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(Booming roars )

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The allosaur is no match
for a healthy bull Muttaburrasaurus,

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The allosaur is no match
for a healthy bull Muttaburrasaurus,

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and he is forced to back down.

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By late spring, the tree ferns
and conifers are in full flush

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and have formed a thick canopy,

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soaking up every bit of sunlight.

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Many of the nests
have now fallen victim to predators,

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but the clan has ensured that
the dominant pair's has survived.

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Secure within are three hatchlings.

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For the first two weeks of their
lives, they will stay in the nest

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while the adults
take turns collecting food

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and bringing it back to them.

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(Squeaking)

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The lead female takes great care
to maintain the nest.

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To stop predators
sniffing out her brood,

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she removes the old eggshells
and eats the unhatched eggs.

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This also recycles the nutrients.

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At this stage,
the hatchlings are vulnerable

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and can easily become lost
on the forest floor if they stray.

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All the adults
watch out for wanderers,

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in case a predator moves in.

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Within weeks, this little hatchling
will be strong enough to keep up,

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but for now, he is returned
to the safety of the nest.

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It is now summer
and permanently light.

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The sun will not set
for another five months.

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At this time,
the forest floor comes alive

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with polar insects, like this weta,

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out hunting for food
among the leaf litter.

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They themselves are food for
larger animals, like the tuatara.

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It is a reptile,

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but one surviving from a time
long before the dinosaurs.

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It will remain long after them, too,

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clinging on in the land
that will become New Zealand.

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The Muttaburrasaurus herd

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is being tormented by bloodsuckers.

164
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Summer brings out
swarms of biting flies,

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and although dinosaurs
are covered in tough, scaly skin,

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they do have softer parts.

167
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The insects concentrate on areas
like the inside of the ear,

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where they can pierce the skin
and suck out a meal.

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These swarms can drive
their gigantic hosts wild,

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and soon the herd
has to move away from the river.

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In the forest, the Leaellynasaura
enjoy the summer bounty

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and, despite the dangers
around them, sleep.

173
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During these long months of sun,

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they rely heavily
on their patterned skin

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to camouflage them among the ferns.

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00:15:05,746 --> 00:15:08,943
Sleep is the last thing on the minds

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of the hatchlings playing nearby.

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They have grown and are now
practising the sort of agile moves

179
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which may one day save their lives.

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Wherever the young are,
their mother is not far away,

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acting as lookout
for her increasingly active brood.

182
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0n the banks of the river,

183
00:15:42,585 --> 00:15:46,021
an old Muttaburrasaurus
has been brought down,

184
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and a male allosaur
feeds off the rotting flesh.

185
00:15:52,985 --> 00:15:54,941
The polar allosaur is a descendant

186
00:15:55,025 --> 00:15:58,574
of the carnivores of the Jurassic,
50 million years before.

187
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His type are rare in the Cretaceous,

188
00:16:01,025 --> 00:16:03,698
but they survive at the South Pole.

189
00:16:03,785 --> 00:16:06,743
(Rumbling growls)

190
00:16:10,045 --> 00:16:13,754
Although there is enough meat
for 20 allosaurs,

191
00:16:13,845 --> 00:16:18,043
it is unlikely
this rival female will be tolerated.

192
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(Roaring)

193
00:16:23,405 --> 00:16:26,317
(Roaring)

194
00:16:35,965 --> 00:16:40,083
She is driven away
by the hungry male.

195
00:16:45,845 --> 00:16:47,915
A fully-grown polar allosaur

196
00:16:48,005 --> 00:16:51,361
needs about
100 kilos of meat a week.

197
00:16:51,445 --> 00:16:53,800
She will need to come back

198
00:16:53,885 --> 00:16:56,445
once the male has eaten his fill.

199
00:17:01,925 --> 00:17:05,600
Later,
under the light of the midnight sun,

200
00:17:05,685 --> 00:17:07,721
one of the young Leaellynasaura

201
00:17:07,805 --> 00:17:10,603
ventures down to the river alone.

202
00:17:23,085 --> 00:17:25,076
(Squeaks )

203
00:17:33,805 --> 00:17:36,763
Saved by his lightning reactions.

204
00:17:39,885 --> 00:17:43,195
But the young Leaellynasaura
has much to learn

205
00:17:43,285 --> 00:17:46,357
about the dangers
of his forest home.

206
00:17:48,885 --> 00:17:50,876
(Thunderclap )

207
00:17:55,685 --> 00:17:58,324
In the time of dinosaurs,

208
00:17:58,405 --> 00:18:04,354
Antarctica suffers summer storms
that cause widespread flooding.

209
00:18:09,756 --> 00:18:13,385
These floods drive
forest creatures together,

210
00:18:13,476 --> 00:18:15,671
and this can lead to confrontation.

211
00:18:15,796 --> 00:18:17,149
(Squealing cry )

212
00:18:19,716 --> 00:18:23,595
The Leaellynasaura
have spotted a rival clan

213
00:18:23,676 --> 00:18:26,236
and it triggers
an aggressive response.

214
00:18:26,316 --> 00:18:29,786
Each clan must defend
its area of forest,

215
00:18:29,876 --> 00:18:33,312
so it does not face
competition for food.

216
00:18:33,396 --> 00:18:35,512
The interlopers must be put off

217
00:18:35,596 --> 00:18:38,554
by a convincing show of strength.

218
00:18:56,912 --> 00:18:58,903
It has worked.

219
00:18:58,992 --> 00:19:02,780
The rivals retreat
and, for the moment,

220
00:19:02,872 --> 00:19:05,625
the clan's territory is safe.

221
00:19:08,872 --> 00:19:12,148
After the rains,
the floodwaters quickly subside

222
00:19:12,232 --> 00:19:17,147
and dinosaurs can return
to the riverbanks to feed.

223
00:19:17,232 --> 00:19:19,188
When there is plenty of food,

224
00:19:19,272 --> 00:19:23,231
herbivores can be
very tolerant of each other.

225
00:19:23,312 --> 00:19:27,271
As the Muttaburrasaurus
tear at the podocarp trees,

226
00:19:27,352 --> 00:19:30,310
the Leaellynasaura
gather up the fruit

227
00:19:30,392 --> 00:19:33,190
that gets scattered on the ground.

228
00:19:42,632 --> 00:19:45,908
Although a risky harvest,

229
00:19:45,992 --> 00:19:49,064
the clan must take
every opportunity the forest offers,

230
00:19:49,152 --> 00:19:51,541
because time is running out.

231
00:19:54,608 --> 00:19:56,883
The seasons draw on,

232
00:19:56,968 --> 00:20:00,244
and for the first time
in four months, the sun sets.

233
00:20:00,328 --> 00:20:02,319
Autumn has arrived

234
00:20:02,408 --> 00:20:06,162
and the forest prepares
for a polar winter.

235
00:20:19,488 --> 00:20:21,444
Up and down the river valleys,

236
00:20:21,528 --> 00:20:24,326
the Muttaburrasaurus
sense the change,

237
00:20:24,408 --> 00:20:26,922
and begin their long trek north.

238
00:20:34,048 --> 00:20:37,006
(Booming grunts )

239
00:20:40,688 --> 00:20:43,646
0ccasionally,
some of these giant migrants

240
00:20:43,728 --> 00:20:45,798
get lost in the forest.

241
00:20:45,888 --> 00:20:48,880
But what for them
is a minor problem

242
00:20:48,968 --> 00:20:53,007
can mean life or death
for the Leaellynasaura clan.

243
00:20:57,568 --> 00:21:00,321
The noise these huge herbivores make

244
00:21:00,408 --> 00:21:02,717
prevents the Leaellynasaura sentry

245
00:21:02,808 --> 00:21:05,527
from hearing
more threatening sounds.

246
00:21:30,408 --> 00:21:33,957
(Squealing and roaring)

247
00:21:46,888 --> 00:21:50,927
The giant carnivore
has killed the dominant female.

248
00:21:53,488 --> 00:21:55,922
It is a bitter blow.

249
00:22:06,408 --> 00:22:10,162
Winter is coming,
and without a lead female,

250
00:22:10,248 --> 00:22:13,365
there will be tension in the clan.

251
00:22:25,608 --> 00:22:27,564
In the gathering gloom,

252
00:22:27,648 --> 00:22:31,561
the Koolasuchus
senses the drop in temperature

253
00:22:31,648 --> 00:22:35,084
and reluctantly leaves
his summer home.

254
00:22:38,208 --> 00:22:41,405
0nce again,
he lumbers into the forest

255
00:22:41,488 --> 00:22:44,241
in search of a suitable shelter

256
00:22:44,328 --> 00:22:48,685
to hibernate through the cold,
dark months that lie ahead.

257
00:22:54,728 --> 00:22:58,687
The low light also triggers
a change in the forest plants.

258
00:22:58,768 --> 00:23:01,123
They stop growing

259
00:23:01,208 --> 00:23:03,597
and photosynthesis halts.

260
00:23:03,688 --> 00:23:05,644
Some will shed their leaves,

261
00:23:05,728 --> 00:23:08,925
others will just lie dormant.

262
00:23:11,728 --> 00:23:14,686
(Chirruping cry )

263
00:23:14,768 --> 00:23:18,602
The Leaellynasaura have to work
extra hard to find food,

264
00:23:18,688 --> 00:23:20,644
searching for fungus

265
00:23:20,728 --> 00:23:25,438
and nutritious roots
beneath the forest floor.

266
00:23:25,528 --> 00:23:28,326
At this time of year,
their survival strategy

267
00:23:28,408 --> 00:23:32,321
is to move to the heart of
the forest, where it rarely freezes

268
00:23:32,408 --> 00:23:37,323
and to keep active
to maintain their body temperature.

269
00:23:37,408 --> 00:23:41,845
But it is clear that the summer
predators have taken their toll.

270
00:23:41,928 --> 00:23:44,044
0nly one hatchling has survived

271
00:23:44,128 --> 00:23:46,881
and they still have no lead female.

272
00:24:00,099 --> 00:24:02,055
Towards the end of autumn,

273
00:24:02,139 --> 00:24:05,336
the last day passes in a few minutes

274
00:24:05,419 --> 00:24:07,410
and the long twilight begins.

275
00:24:15,419 --> 00:24:19,378
Life in the polar forest
faces its biggest killer -

276
00:24:19,459 --> 00:24:21,415
freezing temperatures.

277
00:24:25,939 --> 00:24:28,214
Some polar creatures, like the weta,

278
00:24:28,299 --> 00:24:30,255
have learned to cope with cold

279
00:24:30,339 --> 00:24:33,297
by allowing themselves
to become frozen.

280
00:24:41,059 --> 00:24:43,209
In the winter sky,

281
00:24:43,299 --> 00:24:47,736
the Southern Lights whip and flicker
over the silent forest.

282
00:25:00,019 --> 00:25:04,729
Under the sleeping trees,
it is almost pitch-black,

283
00:25:04,819 --> 00:25:06,775
but with image-enhancement,

284
00:25:06,859 --> 00:25:09,293
we get a Leaellynasaura's-eye view
of the clan.

285
00:25:10,518 --> 00:25:11,318
The dinosaurs are still active,
but the ground has frozen

286
00:25:11,318 --> 00:25:14,788
The dinosaurs are still active,
but the ground has frozen

287
00:25:14,878 --> 00:25:16,948
and it has become almost impossible

288
00:25:17,038 --> 00:25:19,836
to scrape a living out of the soil.

289
00:25:24,878 --> 00:25:27,153
Even pond water is frozen,

290
00:25:27,238 --> 00:25:31,834
and the Leaellynasaura resort
to using their hard beaks.

291
00:25:42,382 --> 00:25:46,534
Temperatures this low don't usually
last long in the forest,

292
00:25:46,622 --> 00:25:50,058
but with their
strict social order in tatters,

293
00:25:50,142 --> 00:25:53,976
the fate of this clan
hangs in the balance.

294
00:25:54,062 --> 00:25:56,576
They push deeper into the forest.

295
00:26:04,222 --> 00:26:07,294
There has been no light
for two months

296
00:26:07,382 --> 00:26:11,614
and another cold snap forces
the clan to take drastic action.

297
00:26:12,942 --> 00:26:16,537
They have evolved
one further adaptation to the cold.

298
00:26:16,622 --> 00:26:19,819
They huddle together
and drift into torpor.

299
00:26:19,902 --> 00:26:22,211
In suspended animation,

300
00:26:22,302 --> 00:26:25,055
they can resist
the effects of the cold,

301
00:26:25,142 --> 00:26:29,579
but they cannot stay like this
for more than a couple of days.

302
00:26:31,142 --> 00:26:34,259
The first hints of salvation
are small.

303
00:26:34,342 --> 00:26:37,732
Under his rock, the weta
is revived from his deep freeze

304
00:26:37,822 --> 00:26:40,780
by a slight rise in temperature.

305
00:26:55,462 --> 00:26:59,455
0n the horizon,
the sun's rays grow stronger

306
00:26:59,542 --> 00:27:02,420
and there is the promise of spring.

307
00:27:03,622 --> 00:27:06,056
(Squeaking cries )

308
00:27:06,142 --> 00:27:10,055
The forest silence is shattered
by an agitated clan.

309
00:27:10,142 --> 00:27:12,098
Two males are fighting.

310
00:27:12,182 --> 00:27:15,697
This is the mating season
for the Leaellynasaura,

311
00:27:15,782 --> 00:27:19,331
and the males
are competing for dominance.

312
00:27:21,182 --> 00:27:25,141
These fights are short
but can sometimes be vicious.

313
00:27:43,782 --> 00:27:46,091
Having asserted his authority,

314
00:27:46,182 --> 00:27:49,254
the victorious male
chooses a mate and, at last,

315
00:27:49,342 --> 00:27:52,971
the clan can start to re-establish
round a dominant pair.

316
00:27:53,062 --> 00:27:57,021
Their annual struggle to survive
can begin again.

317
00:28:04,702 --> 00:28:06,658
Life at the poles

318
00:28:06,742 --> 00:28:10,655
is a remarkable evolutionary
achievement for the dinosaurs.

319
00:28:10,742 --> 00:28:14,576
But eventually, a slight cooling
in the world's climate

320
00:28:14,662 --> 00:28:17,574
will spell doom
for these lush Antarctic forests.

321
00:28:17,662 --> 00:28:19,653
And, without them,

322
00:28:19,742 --> 00:28:24,770
all these unique dinosaurs
will also disappear.

323
00:28:38,862 --> 00:28:42,491
Away from the poles,
the dinosaurs continue to thrive

324
00:28:42,582 --> 00:28:46,018
for another 40 million years
before extinction.

325
00:28:46,102 --> 00:28:48,058
In the final programme,

326
00:28:48,142 --> 00:28:51,054
we see how,
just before the end of their reign,

327
00:28:51,142 --> 00:28:55,101
they evolved
the most terrifying predator of all.

328
00:28:55,182 --> 00:28:58,333
(Ferocious roar)