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Dawn over a silent forest

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00:00:36,640 --> 00:00:40,156
a few hundred miles
from the South Pole

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00:00:40,240 --> 00:00:43,438
It is the end of months
of total darkness

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00:00:43,520 --> 00:00:46,831
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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00:00:50,440 --> 00:00:54,354
Polar dinosaurs are adapted
to cope with extreme conditions,

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00:00:54,440 --> 00:00:58,275
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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00:02:09,880 --> 00:02:13,556
Instead of ice caps,
there are lush forests

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00:02:13,640 --> 00:02:16,838
But unlike the unchanging
tropical climate elsewhere,

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Antarctica has seasons -
from hot summers under midnight sun

23
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to cold winters of total darkness

24
00:02:29,920 --> 00:02:32,879
(Cheeping cry)

25
00:02:32,960 --> 00:02:35,429
Leaellynasaura is a dinosaur

26
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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,

29
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they emerge to feed
on the fresh plant growth

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They are just two metres long

31
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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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00:03:01,151 --> 00:03:05,028
They are sociable little animals
that live in small clans,

34
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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,

36
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and the hierarchy ensures

37
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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)

40
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(Squeaking)

41
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The sentry has spotted
a giant amphibian, Koolasuchus

42
00:03:55,771 --> 00:03:57,888
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,

45
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but on land, his legs have trouble
dragging his bulk around

46
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and he is no threat
to the lithe little dinosaurs

47
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He has been hibernating
over winter in the forest,

48
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and now faces what for
him is an arduous journey of 200m

49
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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

52
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In most parts of the world,

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competition from crocodiles
drove them to extinction

54
00:04:47,651 --> 00:04:51,167
Here, the waters
get too cold for crocodiles,

55
00:04:51,251 --> 00:04:54,244
and the last Koolasuchus survive,

56
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still patrolling the waterways,

57
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just as their ancestors did

58
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150 million years before them

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00:05:26,307 --> 00:05:29,983
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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Only 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

71
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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 summer visitor
from warmer lands to the north

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00:06:54,492 --> 00:06:58,168
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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00:07:45,212 --> 00:07:49,650
Spring across the polar forests
brings the movement of many animals

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00:07:49,732 --> 00:07:53,567
In the sky,
lines of pterosaurs head south

85
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for their summer roosts

86
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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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00:08:30,132 --> 00:08:33,091
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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Each adult weighs about 3 tonnes

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and can pluck food from branches
several metres off the ground

100
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While feeding, they keep in touch

101
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using their specially adapted noses
to produce trumpeting calls

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(Horn-like call)

103
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As the forest gets more crowded,

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the clan's nests
need constant attention

105
00:09:27,118 --> 00:09:30,748
The lead female treats her pile
of leaves like an incubator

106
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and uses her sensitive beak
to monitor the temperature

107
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Then she adds and removes vegetation

108
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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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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,

117
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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,

121
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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,

125
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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

129
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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

135
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(Squeaking)

136
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The lead female takes great care
to maintain the nest

137
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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

139
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This also recycles the nutrients

140
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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

142
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All the adults
watch out for wanderers,

143
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in case a predator moves in

144
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Within weeks, this little hatchling
will be strong enough to keep up,

145
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but for now, he is returned
to the safety of the nest

146
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It is now summer
and permanently light

147
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The sun will not set
for another five months

148
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At this time,
the forest floor comes alive

149
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with polar insects, like this weta,

150
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out hunting for food
among the leaf litter

151
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They themselves are food for
larger animals, like the tuatara

152
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It is a reptile,

153
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but one surviving from a time
long before the dinosaurs

154
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It will remain long after them, too,

155
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clinging on in the land
that will become New Zealand

156
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The Muttaburrasaurus herd

157
00:14:03,728 --> 00:14:06,800
is being tormented by bloodsuckers

158
00:14:06,888 --> 00:14:10,279
Summer brings out
swarms of biting flies,

159
00:14:10,368 --> 00:14:13,918
and although dinosaurs
are covered in tough, scaly skin,

160
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they do have softer parts

161
00:14:16,048 --> 00:14:20,167
The insects concentrate on areas
like the inside of the ear,

162
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where they can pierce the skin
and suck out a meal

163
00:14:33,651 --> 00:14:37,930
These swarms can drive
their gigantic hosts wild,

164
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and soon the herd
has to move away from the river

165
00:14:44,725 --> 00:14:48,844
In the forest, the Leaellynasaura
enjoy the summer bounty

166
00:14:48,925 --> 00:14:52,475
and, despite the dangers
around them, sleep

167
00:14:52,565 --> 00:14:55,603
During these long months of sun,

168
00:14:55,685 --> 00:14:58,883
they rely heavily
on their patterned skin

169
00:14:58,965 --> 00:15:02,117
to camouflage them among the ferns

170
00:15:03,205 --> 00:15:06,403
Sleep is the last thing on the minds

171
00:15:06,485 --> 00:15:09,045
of the hatchlings playing nearby

172
00:15:09,125 --> 00:15:13,483
They have grown and are now
practising the sort of agile moves

173
00:15:13,565 --> 00:15:16,478
which may one day save their lives

174
00:15:23,285 --> 00:15:27,245
Wherever the young are,
their mother is not far away,

175
00:15:27,325 --> 00:15:30,523
acting as lookout
for her increasingly active brood

176
00:15:37,735 --> 00:15:39,852
On the banks of the river,

177
00:15:39,935 --> 00:15:43,372
an old Muttaburrasaurus
has been brought down,

178
00:15:43,455 --> 00:15:47,415
and a male allosaur
feeds off the rotting flesh

179
00:15:50,335 --> 00:15:52,292
The polar allosaur is a descendant

180
00:15:52,375 --> 00:15:55,925
of the carnivores of the Jurassic,
50 million years before

181
00:15:56,015 --> 00:15:58,291
His type are rare in the Cretaceous,

182
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but they survive at the South Pole

183
00:16:01,135 --> 00:16:04,094
(Rumbling growls)

184
00:16:07,095 --> 00:16:10,805
Although there is enough meat
for 20 allosaurs,

185
00:16:10,895 --> 00:16:15,094
it is unlikely
this rival female will be tolerated

186
00:16:16,175 --> 00:16:18,132
(Roaring)

187
00:16:20,455 --> 00:16:23,368
(Roaring)

188
00:16:33,015 --> 00:16:37,134
She is driven away
by the hungry male

189
00:16:42,895 --> 00:16:44,966
A fully-grown polar allosaur

190
00:16:45,055 --> 00:16:48,412
needs about
100 kilos of meat a week

191
00:16:48,495 --> 00:16:50,851
She will need to come back

192
00:16:50,935 --> 00:16:53,495
once the male has eaten his fill

193
00:16:58,975 --> 00:17:02,651
Later,
under the light of the midnight sun,

194
00:17:02,735 --> 00:17:04,772
one of the young Leaellynasaura

195
00:17:04,855 --> 00:17:07,654
ventures down to the river alone

196
00:17:20,135 --> 00:17:22,127
(Squeaks)

197
00:17:30,855 --> 00:17:33,814
Saved by his lightning reactions

198
00:17:36,935 --> 00:17:40,246
But the young Leaellynasaura
has much to learn

199
00:17:40,335 --> 00:17:43,407
about the dangers
of his forest home

200
00:17:45,935 --> 00:17:47,927
(Thunderclap)

201
00:17:52,735 --> 00:17:55,375
In the time of dinosaurs,

202
00:17:55,455 --> 00:18:00,405
Antarctica suffers summer storms
that cause widespread flooding

203
00:18:06,797 --> 00:18:10,427
These floods drive
forest creatures together,

204
00:18:10,517 --> 00:18:12,713
and this can lead to confrontation

205
00:18:12,837 --> 00:18:14,191
(Squealing cry)

206
00:18:16,757 --> 00:18:20,637
The Leaellynasaura
have spotted a rival clan

207
00:18:20,717 --> 00:18:23,277
and it triggers
an aggressive response

208
00:18:23,357 --> 00:18:26,828
Each clan must defend
its area of forest,

209
00:18:26,917 --> 00:18:30,354
so it does not face
competition for food

210
00:18:30,437 --> 00:18:32,554
The interlopers must be put off

211
00:18:32,637 --> 00:18:35,596
by a convincing show of strength

212
00:18:53,944 --> 00:18:55,936
It has worked

213
00:18:56,024 --> 00:18:59,813
The rivals retreat
and, for the moment,

214
00:18:59,904 --> 00:19:02,658
the clan's territory is safe

215
00:19:05,904 --> 00:19:09,181
After the rains,
the floodwaters quickly subside

216
00:19:09,264 --> 00:19:14,180
and dinosaurs can return
to the riverbanks to feed

217
00:19:14,264 --> 00:19:16,221
When there is plenty of food,

218
00:19:16,304 --> 00:19:20,264
herbivores can be
very tolerant of each other

219
00:19:20,344 --> 00:19:24,304
As the Muttaburrasaurus
tear at the podocarp trees,

220
00:19:24,384 --> 00:19:27,343
the Leaellynasaura
gather up the fruit

221
00:19:27,424 --> 00:19:30,223
that gets scattered on the ground

222
00:19:39,664 --> 00:19:42,941
Although a risky harvest,

223
00:19:43,024 --> 00:19:46,096
the clan must take
every opportunity the forest offers,

224
00:19:46,184 --> 00:19:48,574
because time is running out

225
00:19:51,578 --> 00:19:53,854
The seasons draw on,

226
00:19:53,938 --> 00:19:57,215
and for the first time
in four months, the sun sets

227
00:19:57,298 --> 00:19:59,290
Autumn has arrived

228
00:19:59,378 --> 00:20:03,133
and the forest prepares
for a polar winter

229
00:20:16,458 --> 00:20:18,415
Up and down the river valleys,

230
00:20:18,498 --> 00:20:21,297
the Muttaburrasaurus
sense the change,

231
00:20:21,378 --> 00:20:23,893
and begin their long trek north

232
00:20:31,018 --> 00:20:33,977
(Booming grunts)

233
00:20:37,058 --> 00:20:40,017
Occasionally,
some of these giant migrants

234
00:20:40,098 --> 00:20:42,169
get lost in the forest

235
00:20:42,258 --> 00:20:45,251
But what for them
is a minor problem

236
00:20:45,338 --> 00:20:49,378
can mean life or death
for the Leaellynasaura clan

237
00:20:53,938 --> 00:20:56,692
The noise these huge herbivores make

238
00:20:56,778 --> 00:20:59,088
prevents the Leaellynasaura sentry

239
00:20:59,178 --> 00:21:01,898
from hearing
more threatening sounds

240
00:21:26,778 --> 00:21:30,328
(Squealing and roaring)

241
00:21:43,258 --> 00:21:47,298
The giant carnivore
has killed the dominant female

242
00:21:49,858 --> 00:21:52,293
It is a bitter blow

243
00:22:02,778 --> 00:22:06,533
Winter is coming,
and without a lead female,

244
00:22:06,618 --> 00:22:09,736
there will be tension in the clan

245
00:22:21,978 --> 00:22:23,935
In the gathering gloom,

246
00:22:24,018 --> 00:22:27,932
the Koolasuchus
senses the drop in temperature

247
00:22:28,018 --> 00:22:31,455
and reluctantly leaves
his summer home

248
00:22:34,578 --> 00:22:37,776
Once again,
he lumbers into the forest

249
00:22:37,858 --> 00:22:40,612
in search of a suitable shelter

250
00:22:40,698 --> 00:22:45,056
to hibernate through the cold,
dark months that lie ahead

251
00:22:51,098 --> 00:22:55,058
The low light also triggers
a change in the forest plants

252
00:22:55,138 --> 00:22:57,494
They stop growing

253
00:22:57,578 --> 00:22:59,968
and photosynthesis halts

254
00:23:00,058 --> 00:23:02,015
Some will shed their leaves,

255
00:23:02,098 --> 00:23:05,296
others will just lie dormant

256
00:23:08,098 --> 00:23:11,057
(Chirruping cry)

257
00:23:11,138 --> 00:23:14,973
The Leaellynasaura have to work
extra hard to find food,

258
00:23:15,058 --> 00:23:17,015
searching for fungus

259
00:23:17,098 --> 00:23:21,809
and nutritious roots
beneath the forest floor

260
00:23:21,898 --> 00:23:24,697
At this time of year,
their survival strategy

261
00:23:24,778 --> 00:23:28,692
is to move to the heart of
the forest, where it rarely freezes

262
00:23:28,778 --> 00:23:33,694
and to keep active
to maintain their body temperature

263
00:23:33,778 --> 00:23:38,216
But it is clear that the summer
predators have taken their toll

264
00:23:38,298 --> 00:23:40,415
Only one hatchling has survived

265
00:23:40,498 --> 00:23:43,252
and they still have no lead female

266
00:23:56,467 --> 00:23:58,424
Towards the end of autumn,

267
00:23:58,507 --> 00:24:01,705
the last day passes in a few minutes

268
00:24:01,787 --> 00:24:03,779
and the long twilight begins

269
00:24:11,787 --> 00:24:15,747
Life in the polar forest
faces its biggest killer -

270
00:24:15,827 --> 00:24:17,784
freezing temperatures

271
00:24:22,307 --> 00:24:24,583
Some polar creatures, like the weta,

272
00:24:24,667 --> 00:24:26,624
have learned to cope with cold

273
00:24:26,707 --> 00:24:29,666
by allowing themselves
to become frozen

274
00:24:37,427 --> 00:24:39,578
In the winter sky,

275
00:24:39,667 --> 00:24:44,105
the Southern Lights whip and flicker
over the silent forest

276
00:24:56,387 --> 00:25:01,098
Under the sleeping trees,
it is almost pitch-black,

277
00:25:01,187 --> 00:25:03,144
but with image-enhancement,

278
00:25:03,227 --> 00:25:05,662
we get a Leaellynasaura's-eye view
of the clan

279
00:25:06,872 --> 00:25:10,943
The dinosaurs are still active,
but the ground has frozen

280
00:25:11,032 --> 00:25:13,103
and it has become almost impossible

281
00:25:13,192 --> 00:25:15,991
to scrape a living out of the soil

282
00:25:21,032 --> 00:25:23,308
Even pond water is frozen,

283
00:25:23,392 --> 00:25:27,989
and the Leaellynasaura resort
to using their hard beaks

284
00:25:38,441 --> 00:25:42,594
Temperatures this low don't usually
last long in the forest,

285
00:25:42,681 --> 00:25:46,118
but with their
strict social order in tatters,

286
00:25:46,201 --> 00:25:50,036
the fate of this clan
hangs in the balance

287
00:25:50,121 --> 00:25:52,636
They push deeper into the forest

288
00:26:00,281 --> 00:26:03,353
There has been no light
for two months

289
00:26:03,441 --> 00:26:07,674
and another cold snap forces
the clan to take drastic action

290
00:26:09,001 --> 00:26:12,597
They have evolved
one further adaptation to the cold

291
00:26:12,681 --> 00:26:15,879
They huddle together
and drift into torpor

292
00:26:15,961 --> 00:26:18,271
In suspended animation,

293
00:26:18,361 --> 00:26:21,115
they can resist
the effects of the cold,

294
00:26:21,201 --> 00:26:25,639
but they cannot stay like this
for more than a couple of days

295
00:26:27,201 --> 00:26:30,319
The first hints of salvation
are small

296
00:26:30,401 --> 00:26:33,792
Under his rock, the weta
is revived from his deep freeze

297
00:26:33,881 --> 00:26:36,840
by a slight rise in temperature

298
00:26:51,521 --> 00:26:55,515
On the horizon,
the sun's rays grow stronger

299
00:26:55,601 --> 00:26:58,480
and there is the promise of spring

300
00:26:59,681 --> 00:27:02,116
(Squeaking cries)

301
00:27:02,201 --> 00:27:06,115
The forest silence is shattered
by an agitated clan

302
00:27:06,201 --> 00:27:08,158
Two males are fighting

303
00:27:08,241 --> 00:27:11,757
This is the mating season
for the Leaellynasaura,

304
00:27:11,841 --> 00:27:15,391
and the males
are competing for dominance

305
00:27:17,241 --> 00:27:21,201
These fights are short
but can sometimes be vicious

306
00:27:39,841 --> 00:27:42,151
Having asserted his authority,

307
00:27:42,241 --> 00:27:45,313
the victorious male
chooses a mate and, at last,

308
00:27:45,401 --> 00:27:49,031
the clan can start to re-establish
round a dominant pair

309
00:27:49,121 --> 00:27:53,081
Their annual struggle to survive
can begin again

310
00:28:00,761 --> 00:28:02,718
Life at the poles

311
00:28:02,801 --> 00:28:06,715
is a remarkable evolutionary
achievement for the dinosaurs

312
00:28:06,801 --> 00:28:10,636
But eventually, a slight cooling
in the world's climate

313
00:28:10,721 --> 00:28:13,634
will spell doom
for these lush Antarctic forests

314
00:28:13,721 --> 00:28:15,713
And, without them,

315
00:28:15,801 --> 00:28:20,830
all these unique dinosaurs
will also disappear

316
00:28:34,921 --> 00:28:38,551
Away from the poles,
the dinosaurs continue to thrive

317
00:28:38,641 --> 00:28:42,078
for another 40 million years
before extinction

318
00:28:42,161 --> 00:28:44,118
In the final programme,

319
00:28:44,201 --> 00:28:47,114
we see how,
just before the end of their reign,

320
00:28:47,201 --> 00:28:51,161
they evolved
the most terrifying predator of all

321
00:28:51,241 --> 00:28:54,393
(Ferocious roar)