{841}{891}Dawn over a silent forest
{894}{978}a few hundred miles|from the South Pole.
{980}{1057}It is the end of months|of total darkness
{1059}{1138}and as the sun's rays|filter down through the trees,
{1141}{1222}they reveal a cold, harsh world.
{1225}{1318}Polar dinosaurs are adapted|to cope with extreme conditions,
{1321}{1412}but even they|struggle to stay alive.
{1805}{1872}This far south,|the first day of spring
{1874}{1925}lasts only a few minutes,
{1925}{2016}but it triggers the start|of an astonishing story
{2016}{2064}of survival through the polar year.
{2560}{2611}It is the mid-Cretaceous period
{2613}{2680}and dinosaurs|are more widespread than ever,
{2682}{2730}reaching every part of the globe.
{2733}{2826}But one place is a special|challenge - the South Pole.
{2829}{2922}Here, a giant continent|made up of South America,
{2927}{2973}Australia and Antarctica
{2975}{3030}is kept warm by ocean currents
{3030}{3131}that are forced down|from the equator to encircle it.
{3131}{3220}Instead of ice caps,|there are lush forests.
{3222}{3299}But unlike the unchanging|tropical climate elsewhere,
{3301}{3399}Antarctica has seasons -|from hot summers under midnight sun
{3402}{3478}to cold winters of total darkness.
{3613}{3682}(Cheeping cry )
{3685}{3745}Leaellynasaura is a dinosaur
{3747}{3848}that has adapted|to this extreme climate.
{3850}{3948}Throughout winter, they survive|in the heart of the forest,
{3951}{3996}but now, in spring,
{3999}{4080}they emerge to feed|on the fresh plant growth.
{4083}{4147}They are just two metres long
{4150}{4238}and their most distinctive feature|is their large eyes,
{4238}{4332}which help them|find food in the dark winter.
{4363}{4378}They are sociable little animals|that live in small clans,
{4378}{4457}They are sociable little animals|that live in small clans,
{4457}{4545}enabling them to make|the most of scarce resources.
{4548}{4622}The clan is dominated|by one breeding pair,
{4625}{4670}and the hierarchy ensures
{4672}{4744}that one of them|is always on lookout duty.
{4744}{4843}He issues reassuring clicks|as long as the coast is clear.
{4845}{4917}(Whirring clicks )
{5226}{5241}(Squeaking)
{5241}{5296}(Squeaking)
{5579}{5675}The sentry has spotted|a giant amphibian, Koolasuchus.
{5677}{5727}He has massively powerful jaws,
{5730}{5831}weighs about half a tonne...|and is a carnivore.
{5965}{6022}In the water, Koolasuchus is lethal,
{6022}{6133}but on land, his legs have trouble|dragging his bulk around
{6135}{6243}and he is no threat|to the lithe little dinosaurs.
{6245}{6327}He has been hibernating|over winter in the forest,
{6329}{6428}and now faces what for|him is an arduous journey of 200m
{6430}{6516}to get back|to the river for the summer.
{6622}{6670}This bizarre-looking creature
{6672}{6766}is a relic from a time|before dinosaurs.
{6768}{6828}In most parts of the world,
{6828}{6919}competition from crocodiles|drove them to extinction.
{6921}{7005}Here, the waters|get too cold for crocodiles,
{7010}{7082}and the last Koolasuchus survive,
{7084}{7130}still patrolling the waterways,
{7132}{7192}just as their ancestors did
{7195}{7267}150 million years before them.
{7852}{7940}As spring takes hold|and the days grow longer,
{7943}{8015}a forest bursts into life.
{8307}{8401}Many of the plants in these|unique conifer and fern forests
{8403}{8499}have specially adapted to lie|dormant during the dark of winter.
{8501}{8554}0nly with the spring light
{8557}{8641}do they start|to photosynthesize again.
{8792}{8887}For the clan, it is also|a time of feverish activity.
{8887}{8974}Having mated with the spring|sunrise, they now build nests.
{9051}{9134}The dominant pair|builds in the centre
{9137}{9221}and other subordinate|animals work around them.
{9223}{9314}Many of these piles of leaves|act as decoys
{9317}{9369}to help protect the main nest.
{9425}{9484}But no matter how busy they are,
{9487}{9566}they always have|to remain alert to danger.
{9729}{9741}A polar allosaur -
{9741}{9763}A polar allosaur -
{9765}{9859}a summer visitor|from warmer lands to the north.
{9969}{10058}He is a one-tonne ambush predator.
{10182}{10247}(Rumbling growl)
{10249}{10312}(Squawking)
{10494}{10571}(Ferocious roar)
{10640}{10738}The allosaur is the largest and|fiercest killer in the forest,
{10741}{10801}but he was spotted by the sentry.
{10803}{10882}As the clan|melt into the undergrowth,
{10882}{10971}he is no match|for their speed and agility.
{11187}{11295}Spring across the polar forests|brings the movement of many animals.
{11297}{11388}In the sky,|lines of pterosaurs head south
{11391}{11446}for their summer roosts.
{11448}{11549}And among the trees, there is|the echo of unfamiliar sounds.
{11551}{11602}(Booming call)
{11604}{11681}The largest|of all the summer migrants
{11683}{11738}is coming to the forest.
{12266}{12335}These unusual calls|herald the arrival
{12338}{12429}of huge herds of Muttaburrasaurus|from the north.
{12431}{12479}For the last two months,
{12482}{12580}they have been migrating 800 km|down the coast of Australia,
{12582}{12640}following the sun to the south.
{12642}{12731}They do this every year|to strip the lush vegetation
{12733}{12805}and find secure sites|to lay their eggs.
{12935}{12947}The herds have a major impact|on the forest.
{12947}{13016}The herds have a major impact|on the forest.
{13016}{13071}Each adult weighs about 3 tonnes
{13076}{13174}and can pluck food from branches|several metres off the ground.
{13177}{13242}While feeding, they keep in touch
{13244}{13325}using their specially adapted noses|to produce trumpeting calls.
{13436}{13491}(Horn-like call)
{13498}{13560}As the forest gets more crowded,
{13563}{13635}the clan's nests|need constant attention.
{13637}{13723}The lead female treats her pile|of leaves like an incubator
{13726}{13795}and uses her sensitive beak|to monitor the temperature.
{13841}{13896}Then she adds and removes vegetation
{13896}{13968}to keep the eggs|at about 30 degrees centigrade.
{13968}{14071}Already, the baby Leaellynasaura|can be heard inside,
{14074}{14121}responding to their mother's clicks.
{14157}{14165}(Faint cheeps )
{14165}{14196}(Faint cheeps )
{14225}{14318}The nests also have to be protected|round the clock.
{14320}{14445}Fur-coated mammals thrive|in these Antarctic forests,
{14445}{14531}and some are easily large enough|to steal an egg.
{14591}{14651}But the Leaellynasaura|has an unusual defence.
{14918}{15001}It is enough to see off|this egg thief,
{15004}{15100}but the little dinosaur|knows there will be others.
{15287}{15383}The Muttaburrasaurus continue|to arrive on the flood plains
{15383}{15455}and are watched from|the forest edges by hungry eyes.
{15579}{15632}The allosaur is testing the herd,
{15634}{15694}probing for sick or old animals.
{15694}{15742}These herbivores are slow,|but find safety in size and numbers.
{15829}{15901}(Booming roars )
{16433}{16447}The allosaur is no match|for a healthy bull Muttaburrasaurus,
{16447}{16533}The allosaur is no match|for a healthy bull Muttaburrasaurus,
{16533}{16596}and he is forced to back down.
{16692}{16797}By late spring, the tree ferns|and conifers are in full flush
{16797}{16845}and have formed a thick canopy,
{16848}{16905}soaking up every bit of sunlight.
{16970}{17063}Many of the nests|have now fallen victim to predators,
{17066}{17171}but the clan has ensured that|the dominant pair's has survived.
{17198}{17262}Secure within are three hatchlings.
{17310}{17406}For the first two weeks of their|lives, they will stay in the nest
{17409}{17481}while the adults|take turns collecting food
{17483}{17529}and bringing it back to them.
{17651}{17723}(Squeaking)
{17759}{17852}The lead female takes great care|to maintain the nest.
{17888}{17958}To stop predators|sniffing out her brood,
{17960}{18054}she removes the old eggshells|and eats the unhatched eggs.
{18104}{18173}This also recycles the nutrients.
{18502}{18574}At this stage,|the hatchlings are vulnerable
{18576}{18679}and can easily become lost|on the forest floor if they stray.
{18682}{18758}All the adults|watch out for wanderers,
{18761}{18830}in case a predator moves in.
{18833}{18934}Within weeks, this little hatchling|will be strong enough to keep up,
{18936}{19039}but for now, he is returned|to the safety of the nest.
{19303}{19370}It is now summer|and permanently light.
{19372}{19459}The sun will not set|for another five months.
{19459}{19545}At this time,|the forest floor comes alive
{19547}{19614}with polar insects, like this weta,
{19617}{19708}out hunting for food|among the leaf litter.
{19768}{19873}They themselves are food for|larger animals, like the tuatara.
{19876}{19924}It is a reptile,
{19924}{19998}but one surviving from a time|long before the dinosaurs.
{20000}{20053}It will remain long after them, too,
{20056}{20159}clinging on in the land|that will become New Zealand.
{20233}{20281}The Muttaburrasaurus herd
{20283}{20355}is being tormented by bloodsuckers.
{20358}{20439}Summer brings out|swarms of biting flies,
{20442}{20526}and although dinosaurs|are covered in tough, scaly skin,
{20528}{20576}they do have softer parts.
{20578}{20677}The insects concentrate on areas|like the inside of the ear,
{20679}{20741}where they can pierce the skin|and suck out a meal.
{21000}{21103}These swarms can drive|their gigantic hosts wild,
{21103}{21187}and soon the herd|has to move away from the river.
{21269}{21367}In the forest, the Leaellynasaura|enjoy the summer bounty
{21370}{21456}and, despite the dangers|around them, sleep.
{21458}{21530}During these long months of sun,
{21533}{21609}they rely heavily|on their patterned skin
{21612}{21686}to camouflage them among the ferns.
{21712}{21789}Sleep is the last thing on the minds
{21791}{21851}of the hatchlings playing nearby.
{21854}{21959}They have grown and are now|practising the sort of agile moves
{21962}{22031}which may one day save their lives.
{22194}{22288}Wherever the young are,|their mother is not far away,
{22290}{22367}acting as lookout|for her increasingly active brood.
{22540}{22592}0n the banks of the river,
{22592}{22676}an old Muttaburrasaurus|has been brought down,
{22679}{22772}and a male allosaur|feeds off the rotting flesh.
{22842}{22890}The polar allosaur is a descendant
{22892}{22976}of the carnivores of the Jurassic,|50 million years before.
{22978}{23033}His type are rare in the Cretaceous,
{23036}{23098}but they survive at the South Pole.
{23101}{23173}(Rumbling growls)
{23247}{23336}Although there is enough meat|for 20 allosaurs,
{23338}{23439}it is unlikely|this rival female will be tolerated.
{23465}{23511}(Roaring)
{23568}{23638}(Roaring)
{23868}{23966}She is driven away|by the hungry male.
{24105}{24156}A fully-grown polar allosaur
{24158}{24237}needs about|100 kilos of meat a week.
{24239}{24297}She will need to come back
{24297}{24359}once the male has eaten his fill.
{24491}{24580}Later,|under the light of the midnight sun,
{24580}{24630}one of the young Leaellynasaura
{24633}{24700}ventures down to the river alone.
{24997}{25045}(Squeaks )
{25258}{25328}Saved by his lightning reactions.
{25402}{25481}But the young Leaellynasaura|has much to learn
{25484}{25558}about the dangers|of his forest home.
{25618}{25666}(Thunderclap )
{25781}{25846}In the time of dinosaurs,
{25848}{25966}Antarctica suffers summer storms|that cause widespread flooding.
{26119}{26206}These floods drive|forest creatures together,
{26208}{26261}and this can lead to confrontation.
{26263}{26297}(Squealing cry )
{26359}{26450}The Leaellynasaura|have spotted a rival clan
{26452}{26515}and it triggers|an aggressive response.
{26517}{26599}Each clan must defend|its area of forest,
{26601}{26685}so it does not face|competition for food.
{26685}{26738}The interlopers must be put off
{26738}{26810}by a convincing show of strength.
{27251}{27299}It has worked.
{27301}{27392}The rivals retreat|and, for the moment,
{27395}{27462}the clan's territory is safe.
{27539}{27618}After the rains,|the floodwaters quickly subside
{27620}{27738}and dinosaurs can return|to the riverbanks to feed.
{27740}{27786}When there is plenty of food,
{27788}{27884}herbivores can be|very tolerant of each other.
{27886}{27980}As the Muttaburrasaurus|tear at the podocarp trees,
{27982}{28054}the Leaellynasaura|gather up the fruit
{28054}{28121}that gets scattered on the ground.
{28349}{28428}Although a risky harvest,
{28428}{28502}the clan must take|every opportunity the forest offers,
{28505}{28562}because time is running out.
{28637}{28689}The seasons draw on,
{28692}{28771}and for the first time|in four months, the sun sets.
{28773}{28821}Autumn has arrived
{28824}{28912}and the forest prepares|for a polar winter.
{29231}{29279}Up and down the river valleys,
{29282}{29349}the Muttaburrasaurus|sense the change,
{29354}{29414}and begin their long trek north.
{29584}{29656}(Booming grunts )
{29728}{29800}0ccasionally,|some of these giant migrants
{29802}{29850}get lost in the forest.
{29852}{29924}But what for them|is a minor problem
{29927}{30025}can mean life or death|for the Leaellynasaura clan.
{30133}{30200}The noise these huge herbivores make
{30202}{30257}prevents the Leaellynasaura sentry
{30260}{30325}from hearing|more threatening sounds.
{30922}{31006}(Squealing and roaring)
{31315}{31413}The giant carnivore|has killed the dominant female.
{31475}{31535}It is a bitter blow.
{31787}{31876}Winter is coming,|and without a lead female,
{31878}{31953}there will be tension in the clan.
{32248}{32293}In the gathering gloom,
{32295}{32389}the Koolasuchus|senses the drop in temperature
{32391}{32473}and reluctantly leaves|his summer home.
{32550}{32626}0nce again,|he lumbers into the forest
{32626}{32693}in search of a suitable shelter
{32696}{32799}to hibernate through the cold,|dark months that lie ahead.
{32945}{33039}The low light also triggers|a change in the forest plants.
{33041}{33099}They stop growing
{33101}{33156}and photosynthesis halts.
{33159}{33207}Some will shed their leaves,
{33209}{33286}others will just lie dormant.
{33353}{33422}(Chirruping cry )
{33427}{33521}The Leaellynasaura have to work|extra hard to find food,
{33521}{33569}searching for fungus
{33571}{33684}and nutritious roots|beneath the forest floor.
{33686}{33753}At this time of year,|their survival strategy
{33756}{33849}is to move to the heart of|the forest, where it rarely freezes
{33852}{33969}and to keep active|to maintain their body temperature.
{33971}{34077}But it is clear that the summer|predators have taken their toll.
{34079}{34130}0nly one hatchling has survived
{34132}{34197}and they still have no lead female.
{34513}{34561}Towards the end of autumn,
{34564}{34640}the last day passes in a few minutes
{34643}{34691}and the long twilight begins.
{34882}{34976}Life in the polar forest|faces its biggest killer -
{34978}{35026}freezing temperatures.
{35134}{35189}Some polar creatures, like the weta,
{35189}{35237}have learned to cope with cold
{35240}{35309}by allowing themselves|to become frozen.
{35499}{35551}In the winter sky,
{35551}{35659}the Southern Lights whip and flicker|over the silent forest.
{35954}{36067}Under the sleeping trees,|it is almost pitch-black,
{36069}{36115}but with image-enhancement,
{36117}{36175}we get a Leaellynasaura's-eye view|of the clan.
{36206}{36220}The dinosaurs are still active,|but the ground has frozen
{36220}{36302}The dinosaurs are still active,|but the ground has frozen
{36304}{36355}and it has become almost impossible
{36357}{36424}to scrape a living out of the soil.
{36544}{36599}Even pond water is frozen,
{36602}{36712}and the Leaellynasaura resort|to using their hard beaks.
{36964}{37064}Temperatures this low don't usually|last long in the forest,
{37067}{37148}but with their|strict social order in tatters,
{37151}{37242}the fate of this clan|hangs in the balance.
{37244}{37304}They push deeper into the forest.
{37491}{37563}There has been no light|for two months
{37565}{37669}and another cold snap forces|the clan to take drastic action.
{37700}{37786}They have evolved|one further adaptation to the cold.
{37788}{37865}They huddle together|and drift into torpor.
{37868}{37923}In suspended animation,
{37925}{37990}they can resist|the effects of the cold,
{37992}{38098}but they cannot stay like this|for more than a couple of days.
{38136}{38210}The first hints of salvation|are small.
{38213}{38294}Under his rock, the weta|is revived from his deep freeze
{38297}{38366}by a slight rise in temperature.
{38719}{38815}0n the horizon,|the sun's rays grow stronger
{38817}{38887}and there is the promise of spring.
{38915}{38973}(Squeaking cries )
{38975}{39069}The forest silence is shattered|by an agitated clan.
{39071}{39117}Two males are fighting.
{39119}{39203}This is the mating season|for the Leaellynasaura,
{39205}{39292}and the males|are competing for dominance.
{39335}{39431}These fights are short|but can sometimes be vicious.
{39879}{39934}Having asserted his authority,
{39937}{40011}the victorious male|chooses a mate and, at last,
{40013}{40100}the clan can start to re-establish|round a dominant pair.
{40102}{40198}Their annual struggle to survive|can begin again.
{40383}{40428}Life at the poles
{40431}{40524}is a remarkable evolutionary|achievement for the dinosaurs.
{40526}{40618}But eventually, a slight cooling|in the world's climate
{40620}{40690}will spell doom|for these lush Antarctic forests.
{40692}{40740}And, without them,
{40742}{40862}all these unique dinosaurs|will also disappear.
{41200}{41287}Away from the poles,|the dinosaurs continue to thrive
{41289}{41373}for another 40 million years|before extinction.
{41375}{41421}In the final programme,
{41423}{41493}we see how,|just before the end of their reign,
{41498}{41593}they evolved|the most terrifying predator of all.
{41593}{41670}(Ferocious roar)