{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 am...
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