"Daybreak on North America's great plains." "Denver International Airport is coming to life and about to receive the first arrivals of the day." "By midnight, more than fifteen hundred aircraft will have touched down here, delivering tens of thousands of people to this modern metropolis." "But when did people first come to the plains?" "It's not so long ago in the life story of a continent ... just 13,000 years since this was virgin territory." "And back then different giants cruised the landscape." "Imagine if we could travel back in time and see these plains as they were then, emerging from the grip of the last great ice age an area of pristine wilderness, stretching for one and a half million square miles," "untouched by man and brimming with extraordinary animals..." "But 13,000 years ago, an even more extraordinary animal arrived..." "What if we could follow in the footsteps of these first hunters, as they entered the unknown and staked their claim to these vast spaces?" "What would this wild new world have looked like through their eyes?" "And what strange creatures would they have encountered here on the American Serengeti?" "As North America emerged from the grip of the last lce Age, the door was opened to outsiders for the very first time." "As these early immigrants pushed their way south, they found themselves in a land of unimaginable opportunity, overflowing with game animals  animals with no experience of humans or their weapons..." "The arrival of these hunters coincided with a time of great change on the plains." "Within the next few hundred years, many ice age animals vanished forever." "So 13,000 years on, how do we know anything about this lost world?" "There are still clues to be found... if you know where to look." "ln the Bighorn Mountains of Wyoming is a hidden cave, recreated here, where over the millennia, thousands of animals have fallen to their deaths." "Preserved below the surface are bones dating all the way back to the ice age." "Remains of bison lie alongside antelope and rabbit but they're mixed with those of camels, extinct horses, giant wolves..." "Even the mastodon is buried here a long-dead relative of modern elephants..." "And this was once a bear, but not like any bear in North America today." "Claw marks gouged into the cave wall show the bear was not killed outright by the fall it made a desperate attempt to climb back out." "It was a short-faced bear, an ice age heavyweight." "What else can we tell about it from its bones?" "lts weight was more than 700 kilos twice that of a grizzly bear today." "Upright, it would have stood four metres tall." "It was the largest flesh-eating mammal that ever walked the earth." "The Wyoming cave - appropriately christened 'Natural Trap' provides a unique window on the ice age." "During its coldest era, much of North America was covered by huge ice sheets up to two miles thick." "But as the continent began to warm, the ice sheets started shrinking." "Corridors began to open up along the coast and through the mountains letting people migrate south from Alaska for the first time." "Before them lay the almost limitless great plains stretching all the way from the Rocky Mountains to the Mississippi River and beyond to Mexico." "Across this area, the shifting ice left deep scars on the land... lt carved out thousands of lakes and ponds, and left the tapestry of streams and rivers that drain the plains..." "The death throes of the last great ice age left a signature that we can read today." "These giant 'potholes' were left behind by blocks of buried ice that melted, leaving hollows that later filled with water." "For thousands of years since then, they've been vital pit stops for migrating birds... the millions of cranes, geese and ducks that follow ancient routes across the plains." "These rolling hills are made of debris dumped by the retreating ice." "It also left rich grasslands, able to support hundreds of millions of bison... vast herds drifting with the seasons, always searching for fresh grazing." "Pronghorn antelopes are unique to North America and among the toughest creatures on the plains." "Surviving year round in the open they must cope with freezing winter temperatures and scorching summer heat." "Every spring these open spaces echo to the sounds of courting sage grouse, as males compete to win a mate." "Migrating Sandhill cranes strut and dance for their partners before heading further north towards their nesting grounds." "Small birds breed here, after an epic journey from their winter home." "These cliff swallows have flown thousands of miles from South America." "Mud from the ancient riverbanks is good for building nests... lt also holds more evidence that will help us to reconstruct the ice age past." "Every now and then,new clues resurface... hinting at what else might lie beneath." "ln this dried up pond in South Dakota, known as Hot Springs, scientists unearthed great piles of bones." "What kind of creature died here?" "The bones reveal it stood four metres tall and weighed more than 10 tonnes... there's nothing fitting that description living here today." "Here's the give-away a pair of tusks two metres long... the trademark of a Columbian mammoth, the biggest animal to roam the ice age plains." "By comparing it to elephants in Africa today, can we shed light on how those ice age elephants lived and what they lived on?" "These are mammoth teeth huge molars the size of bricks." "They have deep ridges very similar to those of modern elephants, suggesting mammoths, too, survived by grinding vast amounts of grass." "Plant fragments trapped between the ridges can still be identified today." "Thousands of years after this mammoth died, we know exactly what it ate for its last meal." "Grass is a tough, abrasive food." "Even with protective enamel ridges, these teeth would gradually have worn down." "But just like modern elephants, the mammoths had evolved a way to deal with this." "As one set of teeth was eroded, another grew up to take its place." "The evidence suggests they had six sets in all, to last a lifetime - up to 60 years." "The South Dakota mammoth didn't make it to old age and it was not alone." "The site turned out to be a mammoth graveyard, hiding more than 50 skeletons all from animals in their prime." "There's no sign they were killed by hunters, so how did so many healthy mammoths die?" "The site was once a spring-fed pond, full of water." "Mammoths were tempted in to drink... but when they tried to climb back out the banks were steep and slippery..." "Just like the short-faced bear imprisoned underground, some became trapped..." "Scavengers would have been attracted by the mammoths' plight... the bones of wolf, coyote and the short-faced bear have also been recovered from the dried up sediment." "The search for food was probably their downfall too." "These prairie ponds are like time capsules, and they store another kind of data showing how the plains have changed across millennia." "Each spring, pollen from nearby plants is blown into the water." "It sinks and settles layer upon layer on the bottom, building into a databank of local plant life that we can still read today." "And grass pollens aren't the only clues still sandwiched in the sediment." "There are a wide variety of tree pollens too from aspens, spruce and other trees, both conifers and deciduous." "This store of pollen paints a picture of the plains of 13,000 years ago... a picture that looks very different from the open prairie grassland of today." "But why did this region look so different back then?" "The ice sheets to the north, although retreating 13,000 years ago, still dominated the climate here." "It was much milder and wetter than today ideal conditions for woodland to flourish." "This is how much of the northern plains must have looked when the first people arrived  not open prairie as it is now, but a parkland of trees and grassy meadows." "This is a relic of those times the Osage orange." "Every autumn it produces these enormous fruits huge numbers of them more the size of grapefruits than mere oranges." "But there's no animal alive today that's big enough to pick and eat them, so this bumper crop just rots." "The Osage orange glory days are long gone... but its harvest was once an annual feast for many ice age animals... including browsing mammoths." "Fruit must have been a real treat for these grass eaters." "The Osage orange seeds were carried far across the plains, before being deposited pre-packed in their fertiliser 'grow-bags' ready to take root." "As the ice age waned, the milder climate and the mix of vegetation meant the plains were able to support a range of wildlife as diverse as Africa's Serengeti today." "There were at least five kinds of horse including a wild ass and another that resembled modern zebra." "And North America's very own antelope the pronghorn... 13,000 years ago several different species roamed the plains." "The pronghorn lived alongside other grazers still around today, including bison." "This animal was common too but now it would seem very out of place." "Bigger than its modern relatives, the ice age camel was extremely hardy, able to eat almost any kind of food." "Elk, like many ice-age animals, survive almost unchanged." "The rich parkland was ideal for these large deer." "But one creature more than any other has remained a constant symbol of the plains since people first set foot here..." "the bison." "Adult bison are formidable... two metres tall and weighing more than a tonne." "They too sheltered near the trees in winter, taking to the plains again in spring when new grass started sprouting." "Bison calves are born in summer and can run within a few hours of their birth." "They have no choice the herd won't wait in its eternal quest to find new grazing." "Smaller grazers are still found here too but they stay put instead of wandering the plains." "Prairie dogs inhabit rambling subterranean 'towns' that stretch tens of square miles." "These highly social creatures stay within a short dash of their door ready to retreat from predators or bad weather." "There's always maintenance work to do, but major renovations have to wait until after rain, when the soil is soft." "All this working and re-working helps the land recover from the impact of so many bigger feet and appetites." "At summer's end, male bison help to move the sun-baked soil, as the rutting season starts." "They roll in dust and paw the ground to try to dominate their rivals." "The dust bath also helps to dislodge irritating insects." "A prairie dog colony is usually surrounded by short, nutritious grass thanks to the many teeth in town." "This constant grazing stimulates fresh growth and also keeps the field of vision clear for spotting predators." "Larger neighbours are attracted to these verdant meadows, just as they were 13,000 years ago." "Columbian mammoths had to feed almost round the clock, to fuel their bulky bodies." "But as the ice age ended, food was not the mammoth's biggest problem..." "A new and deadly predator began to infiltrate the plains, a match for any prey, even the mighty mammoth." "These people knew how to make lethal weapons... they left spear points, knife blades and other tools scattered all across the plains." "And they spread fast." "The evidence suggests it took them only a thousand years to spread across the entire northern continent." "What can we learn today about the lifestyle of these butchers of the plains?" "They left a string of clues to how they lived, including strange pyramids of rocks." "Inside are bones of animals that show how they were slaughtered and cut up for meat." "These cairns are thought to be cold-weather larders, marking prehistoric hunting camps." "When hunting parties had more meat than they could eat or carry, they would stash the surplus under these rocks to be collected later." "They seem to have used bones as markers." "ln a Colorado gully, hunters carried out a mammoth massacre, leaving behind the remains of at least 16 animals." "The site recreated here contains a treasure trove of evidence relating to the mammoths' daily life." "Again by comparing mammoth bones to elephants, we can calculate the sex and age of all the animals that died here... and deduce the make-up of a Columbian mammoth herd." "These are the bones of juveniles, up to around 14 years old both males and females." "Several adults lie here too all females." "...including one huge specimen, at least 40 years old." "This range of age and sex exactly matches that of a modern-day African elephant herd." "An older matriarch, the leader of the herd, is accompanied by her daughters and other female relatives... and they in turn are with their young, both male and female." "But where were the adult males when this herd was destroyed?" "A unique clue to their lives was uncovered in Nebraska." "Recreated here are the skulls of two gigantic males that died with their tusks interlocked." "But how could this have happened?" "Again, our best bet is to look at elephant society." "During the breeding season, sexually mature bull elephants fight for access to the female herds." "The tangled tusks are direct evidence that mammoths were aggressive too." "Because these two bull mammoths both had broken tusks, they could have fought at closer quarters than they would do normally... twisting and turning they became locked in a deadly embrace..." "Even more bizarre, this twist of fate then caused a third fatality... beneath one mammoth's shoulder blade was the skull of a coyote, pressed into the ground!" "While we can only speculate on just how the coyote died, it's likely it was scavenging around the decomposing carcasses when one caved in and crushed it." "Coyotes are still on the plains today." "They hunt their food as well as scavenge carcasses but small live prey can be more trouble than large dead ones!" "Prairie dogs are always on alert... and once a trespasser is spotted, the entire town vanishes into thin air." "Prairie dogs aren't really dogs at all they're rodents but coyotes are full-blooded members of the canine clan and like all dogs, they sometimes hunt in groups to tackle bigger prey." "Some prey, however, are just too big, even for a pack of coyotes." "But 13,000 years ago, there was another kind of canine hunter here one that gave even the bison a run for their money." "The wolf... the ultimate pack hunter." "A lone wolf weighs as much as four coyotes, but one on one it's still no match for a bison." "Wolves, though, live and hunt in packs of up to 15, and when they launch a co-operative attack, they're devastating." "First they get the bison on the run, then filter out the weak and vulnerable... and select the perfect target." "Striking together wolves can bring down prey many times their own size." "A million such chases must have taken place across these plains... and we can still find echoes of these distant life or death encounters." "Not all evidence lies locked in bone and rock." "These pronghorn antelopes among the great survivors of the ice age reveal a lot about the distant past." "As well as being tough enough to stand extremes of temperature, they're famous for their speed." "A sprinting pronghorn can top 60 miles an hour and cruise at 30 for several hours." "This kind of speed requires a very finely tuned physique." "Pronghorn have a massive heart and run with their mouths gaping open, forcing extra air into their huge lungs." "But what's the point?" "No predator can run this fast even the wolves can only manage 40 miles an hour... so why do pronghorn feel this need for speed?" "This is why once there was a predator here that could outrun the pronghorn a cheetah." "13,000 years ago, the ice age cheetah was the pronghorn's greatest enemy... and pronghorn would have needed all their amazing speed." "The American cheetah was larger than its African cousin, but it had the same Achilles heel." "A cheetah's high-performance muscles overheat in minutes and unlike pronghorn, it can't switch to cruising speed." "So if the pronghorn managed to outrun the cheetah for the crucial first few hundred metres, it would probably survive." "The cheetah hasn't roamed the plains of North America for thousands of years but pronghorn are still primed for the chase." "Other extinct links to Africa have been found in caves deep in the Ozark mountains of Missouri." "Preserved in mud were huge prints recreated here, more than 18 centimetres wide." "What could have made them?" "They belong to another ice age cat the top cat of the plains... a lion." "Larger than any lion alive today, this would have been an awesome predator." "These caves were probably its winter den." "With such abundant game down on the plains, this hunter's life must have been pretty good." "Sheer size and power and the benefit of life within a pride made it the unmatched ruler of the plains." "By looking at the lions of Africa today, we can imagine how these ice age cats once lived... in small prides based around a group of hunting females." "Like wolves, lions work together to win larger prey." "After a leading hunter launches the attack, the others move in, helping to dispatch the victim with a suffocating bite." "But even for these rulers of the plains, the good life had to end... they would be toppled by another predator with even sharper skills." "The ice age lions joined the list of victims... animals that had lived here for hundreds of millennia but were soon lost forever." "Today few signs remain that any of them were ever here   odd traces scattered far and wide across the plains." "But if we piece together bones and teeth, plant fragments and the clues from animals alive today, we can begin to bring a lost world back to life." "So let's go back in time, back 13,000 years, to relive one day in the life of North America's great ice age plains." "It's early morning at the end of a long, hot summer... even major rivers are beginning to run low." "A Columbian mammoth herd follows the river valley... they can't risk straying far from water." "Once they've quenched their thirst the next priority is food." "They head out to the nearby meadows, where they'll graze most of the day, processing mountains of dry grass." "Autumn is mating season and a couple of nomadic males have started shadowing the herd." "By sparring, they decide who will have access to the females coming into heat  who will father the next generation." "Most power struggles are resolved through ritual intimidation." "But if two evenly matched males cross paths, this posturing can escalate into a full-blown fight." "Both these opponents have a broken tusk letting them get closer to each other during combat." "Suddenly a freak clash leaves them in a deadlock, inextricably entwined." "If they can't free themselves, they'll both end up the losers." "As a constant source of food and water even when there's been no rain for months, this valley draws thousands of other grazers." "And all this meat in one small area attracts a scavenger ... the short-faced bear." "Led by his super sensitive nose, his long limbs carry him many miles a day in search of carrion." "He's picked up a scent, but where's the carcass?" "Sometimes the smaller, speedier scavenger gets there first... on this occasion a coyote." "Right now the short-faced bear will take whatever he can get he hasn't had a decent meal in days, and needs at least one good-sized carcass every week to stay alive." "This time the coyote's left him nothing but the skeleton." "But with his huge, bone-crunching jaws the bear can crack them open for the marrow locked inside." "With water so scarce elsewhere, animals from miles around converge here in the valley." "Which is good news for the local lions... their pride territory is now overflowing with food." "Once the midday heat subsides, the females rouse themselves to hunt." "The scene is set for a daily ice age drama." "Only the very largest are safe now." "Patience is the key..." "the lionesses close in, waiting for their opportunity." "The first charge causes chaos but this is just what the lions want." "ln the melee, they've already pinpointed their prey." "The leader pounces, and a horse is down... meanwhile, the spooked herds stampede up the valley." "But they're running straight into another trap... a hidden cave, already full of ice age victims." "... and now it claims another." "Above ground, the members of the valley pride - mothers, sisters and cubs feast." "But their success hasn't gone unnoticed." "From many miles away, the short-faced bear can smell blood on the breeze." "He sniffs his way towards the source." "Meanwhile, satisfied and sleepy, the pride settles down for a snooze." "More than twice the weight of the pride's most powerful lion, the short-faced bear is a daunting sight." "lts trump card is to use its massive size to frighten hunters from their kill." "But the lions won't give up their hard-won meal without a fight." "This time, the bear's scare tactics just don't work... the lions' numbers are against him and, despite his gnawing hunger, he backs down." "The autumn winds are rising, carrying another scent across the plains... and once again the bear's nose sets his course." "This trail leads to the cave and the freshly dead bison..." "just out of reach." "Hunger makes the bear risk everything." "He falls and joins the bison in its tomb." "Now he can eat his fill... but after that there's no way out." "ln time he'll be just one more ice age specimen." "Outside, another group of predators head for their cave at dusk ... pack hunters even more effective than the lion or the wolf." "Still relatively new here, they'll eventually transform the ice age plains, and build their own future by exploiting the herds of the American Serengeti." "Even the giants that now dominate this ice age world will soon be gone." "But they'll leave clues behind, and one day distant generations will pick up their trail and tell their story." "Next week on Wild New World we discover why mammoths didn't make it through to modern times." "And we explore how North America's wildlife has adapted to living in a very human world." "Find out how we recreated these prehistoric landscapes at bbc.co.uk/nature."