"The southwest states of North America ... a region of extremes   from the Colorado river and desert canyons to artificial landscapes   that teem with life   including one of the world's most vibrant cities." "This is Las Vegas a man-made oasis deep in the Nevada desert." "Only a century ago, this wonderland was sand and scrub... today it's one of the Continent's fastest-growing cities." "All this depends on water pumped from the Colorado river 50 miles away." "Without this imported water, there would be no Vegas." "But during the last lce Age, the Las Vegas Valley had a plentiful supply of water, and it was a magnet for all kinds of wildlife." "Just 13,000 years ago - not long in the vast time-scale of a continent this valley overflowed with lakes and ponds, fringed with reed beds and swamps ..." "All kinds of creatures would have been drawn to this natural refuge..." "One group of new arrivals in this land of opportunity were people." "As the ice Age ended and new pathways opened up across the continent, these hunters caught their first glimpse of the Canyonlands." "Imagine if we could travel back in time to see this wild new world and the strange and terrifying animals that lived here 13,000 years ago." "Using evidence left behind by these creatures, we will recreate life in the ice Age Canyonlands." "It's taken millions of years to carve the red rock sculptures of the Canyonlands... today they spread across several states including Colorado, Arizona, Utah and Nevada..." "These isolated, high plateaux are still home to some animals that were here at the end of the last ice age ..." "Today, the mountain lion is the largest predator that still patrols the canyons ... living much as it did 13,000 years ago." "It's a tough existence..." "Food is hard to come by, water too, and the desert climate swings from below zero overnight to nearly 40 degrees Centigrade by day." "At least there's no shortage of shade... a labyrinth of caves can offer shelter from the heat and cold and from the dangers of the night..." "There was a time when even mountain lions couldn't sleep in safety." "These caves are haunted by the ghost of another carnivore that dwarfed the mountain lion... probably the best known of all ice age hunters." "It killed with fangs like these, 20 centimetres long the sabre-toothed cat." "But how exactly were these chilling weapons used?" "With its 300-kilo frame and short legs, the sabre-tooth was not that fast." "It probably ambushed prey, using its huge weight to pin it down before delivering a slashing bite to the neck..." "Shock and loss of blood would quickly kill its victim." "And yet these lethal fangs must have caused problems for their owner too." "How do you eat with teeth this long?" "Even with a huge gape almost twice the span of any other cat the sabre-tooth could barely open its mouth wide enough to lift these massive canines clear of its lower jaw." "That would have made it very difficult to take a bite." "But it also had these special cheek teeth they suggest it ate through the sides of its mouth, slicing off manageable strips of flesh." "Even so, the sabre-tooth must have been forced to leave much of its meal for scavengers." "The mountain lion with its more modest canines can eat almost anything from mountain sheep to birds and even plants." "But today, like every other desert dweller, its main problem isn't food, it's water." "Away from the main rivers, waterholes are rare and soon evaporate in the heat ... and it may be months before they get refilled." "A real downpour may happen only once a year, but it can have a massive impact." "Storms don't just sustain life in the desert, they have helped to sculpt this spectacular landscape." "Rain runs off bare rock and gathers in the canyons, quickly escalating into flash floods that can carry away huge chunks of rock..." "Constantly shaping and reshaping..." "over millions of years." "Creating a dreamscape of spires and gullies." "Over these millions of years, the larger rivers" "The Colorado, Green and San Juan have carved out canyons up to one mile deep..." "Water has sculpted the cliffs and gouged out innumerable caves ... caves that store a wealth of clues from the ice age past." "One of the most remarkable cave sites was discovered on the Arizona-Utah border." "Here, the dry air preserved piles of evidence ... not bones or teeth but... dung." "Football-sized dung balls, which dated right back to the ice Age... carpeting the cave floor 10 metres deep." "But what colossal beast could have deposited them here?" "It was the largest of all ice age animals ... a 10 tonne relative of modern elephants, more than 4 metres tall." "The Columbian mammoth." "So, was this cave just a latrine, or were the mammoths here for other reasons... to escape bad weather, or the midday heat?" "Perhaps they used it as a night shelter, or came to visit salt licks, like some elephants do in Africa today." "No one really knows, but this prehistoric dung-pile offers plenty of other information about how Columbia mammoths lived." "It's mostly composed of grass, like elephant dung balls today." "To get enough food to sustain their huge bodies, mammoths had to graze for up to 20 hours a day consuming up to a quarter ton of grass." "When not eating, they were on the move, in search of fresh supplies." "They probably migrated through the river valleys and the bigger canyons, careful not to stray too far from water." "But the continent these mammoths travelled through looked very different from the one we know today." "During the ice age, much of north America was blanketed with massive ice sheets up to two miles thick." "And when the great thaw began, the changes in the north brought a new era to the desert." "... for the first time, people were able to make the arduous journey south." "Today we can still map their route from stone tools left behind... ln just a few hundred years they spread down from the Great Plains, through the Canyonlands and all the way to Mexico." "They even took the mighty Colorado river and its apparently impenetrable canyons in their stride." "lncluding the Grand Canyon carved out over millions of years this is erosion on an epic scale" "280 miles long, up to 18 wide and more than one mile deep." "For people, crossing this forbidding landscape must have been a superhuman feat." "But for other animals, it seems to be no barrier to travel." "Up here on the roof of Canyonlands are big horn sheep that seem to live almost off thin air... eking out a living from the meagre vegetation." "Specialist desert plants like cactus offer little nutrition... and their defensive spines make what goodness they do contain extremely difficult to reach." "But the hardy bighorn have evolved to get all they need from these plants, including moisture they need only visit standing water every few days." "And the females can still produce enough milk for their young." "But 13,000 years ago, another climber scaled these dizzy heights... and left a clue to its identity high in a cave on the Grand Canyon walls ..." "A skull... with vegetarians' teeth..." "and short horns." "It belonged to a mountain goat... a common sight here in the ice Age... with a shaggy coat to beat the biting winds." "Scenes like this would have been common back then.." "herds tip-toeing miraculously across suicidal slopes..." "Now found only in the Rockies further north, they spend most of their time high up on the mountain slopes, but each spring they make their way down to the canyon bottom, where the river has exposed fresh earth and rock." "It's a crucial time of year the goats are shedding winter coats and losing vital minerals with the fur." "By nibbling these salt licks they can top up their supplies." "Even newborn kids must make the perilous descent to collect these crucial salts." "...other ice age creatures also roamed these precipitous cliffs." "ln this Grand Canyon cave, scientists made a remarkable discovery recreated here." "Over 200 bones that, when put together, reveal a creature that's been dead for 13,000 years..." "From measuring these bones we know it was about as large as a black bear." "lts teeth have telltale grooves that are similar to the tree sloths still alive today in South America." "So, what strange beast died here?" "A Shasta ground sloth, once as common in the southwest as the bighorn are today." "Like the mammoths, it left more than bones and teeth for us to analyse..." "But the ground sloth's desiccated dung balls tell a different story to the mammoth dung." "They contain not just grass but many different plants... more than 100 species, representing almost every plant that once grew near the cave." "The Shasta ground sloth had a varied menu... prickly pear, saltbush and yucca..." "Even the tough leaves of the Joshua tree..." "The dung also reveals how Shasta ground sloths dined on different foods at different times of year... globe mallow and other desert flowers only bloom in spring but they were obviously gorged on when available..." "What did the sloths use caves for?" "It's been suggested they were birthing dens, but they may simply have been sleeping quarters, a shelter from the cold desert night." "One recent study of the sloths' bone chemistry suggests that they were very sensitive to temperature they may have come inside for warmth." "But a roof over their head was no guarantee of a good night's sleep..." "Among the Shasta ground sloth bones was this strange skull... resembling a mini sabre-tooth and from a creature just as bloodthirsty a vampire bat." "Vampires like this one are no longer found in North America, but once they lived in these caves sleeping by day, feeding at night on any warm blood that they could find." "The vampire bat uses tiny sabre teeth to nick its victim's flesh, then laps the blood by curling up its tongue into a kind of straw..." "Anti-clotting agents in the bat's saliva keep the blood flowing until it's full..." "Not all reminders of the history of Canyonlands are tucked away in caves... the open strata of the cliffs reveal millions of years of geology..." "Each layer represents a chapter in the story of the past all the way back to the age of the dinosaurs." "This dark band is slightly different it's not rock, but debris from more recent times... lt's a rubbish dump - or midden made of leftovers from thousands of small meals, all stuffed into the crevice and" "glued together with urine and droppings." "Who recycled all this debris - and why?" "It's the desert packrat, common all over the Canyonlands." "Generations of packrats contribute to the same middens over thousands of years, helping to form a tough protective shield around their rambling nests..." "And they help scientists to look into the past." "Ingredients like prickly pear spines and juniper berries reveal just what vegetation grew across the Canyonlands - and when." "Thanks to the packrats, we know that the bare rock of the high plateau was once green parkland with conifer trees and lush grassy meadows." "There were forests of juniper..." "And the bare canyon walls were covered in a rich mosaic of trees and scrub." "Down on the drier plains Joshua trees flourished..." "But the most symbolic desert plant today the nine-metre-tall saguaro cactus was rare 13,000 years ago." "Now there are spectacular saguaro forests but back then these broad valleys were carpeted with oaks, sagebrush and juniper." "Such dramatic changes tell us it was once much wetter and milder here than it is today." "Proof of this damper climate can be found and in perhaps the last place on earth you'd expect..." "Death Valley..." "100 metres below sea level, this is the lowest point in the Western hemisphere." "It's also one of the hottest, driest places on earth, with daytime temperatures that soar to 50 degrees centigrade." "And it may not rain for years at a time." "Yet even in this furnace, there is life... it exists in the many spring-fed pools that dot the valley floor." "These are desert pupfish and they manage to survive in water several times more salty than the sea, sometimes at temperatures of nearly 40 degrees." "Most pools support their own individual species and each pool is their entire world this is where they hatch, feed, breed and die..." "But how did tiny fish end up living in the middle of the desert?" "The answer's all around in the vast salt flats that separate the pupfish pools." "This is the dry bed of a huge lake that existed here during the ice age." "When the climate warmed, the lake began to dry out, and the pupfish only managed to survive where springs continued to supply water." "Cut off from each other, pupfish then evolved into the many different species found today." "The existence of this prehistoric lake proves that the Canyonlands were once a wetter, greener place." "And that explains the different vegetation changes that we see recorded in the packrat middens." "The lake that filled Death Valley was huge." "lts waterways, marshes and reed beds would have been a magnet for all kinds of wildlife, and a pit-stop for migrating birds..." "Vast flocks of cranes and geese flew in to winter here." "For several months, they'd gather strength before embarking on the long trip north to breed." "ln this rich hunting ground, the cranes could eat their fill of fish, amphibians and water plants." "There were larger animals here as well." "The mild wet climate and abundant vegetation made the Canyonlands an ideal habitat for grazers... including some that would seem strangely out of place today." "Camels were very common and like Columbia mammoths and" "Shasta ground sloths they left plenty of dung pellet clues." "Dissecting their dung shows they had a varied diet from fine desert grasses to the toughest shrubs and trees." "We may think of bison as belonging to the open prairies further north, but back then they were equally at home grazing the valleys of the southwest..." "They spent their whole lives following the rains in search of fresh grass." "This pattern of continuous migration ruled the lives of many creatures here including horses similar to modern zebra." "But 13,000 years ago, a new threat arrived in the canyonlands." "These first hunters had one big advantage... their prey had little or no experience of humans and was therefore easier to approach." "They were armed with flint spear points and tried and tested hunting strategies... working as a team, they were a match for any desert prey ..." "The hunters' success wasn't bad news for all desert creatures." "Their kills must have provided leftovers for scavengers like ravens ..." "Ravens still scan the Canyonlands for food... and build their nests amid the pinnacles and towers." "Some of the ravens' ledges have been found to hold unique clues to the desert's past  bone fragments from large animals like mountain goats  wild asses  and camels." "But how did they get all the way up here?" "Alongside is the answer, it's a huge beak ... from a giant bird." "... An ice age condor." "Condors soared across the canyons on their huge three-metre wingspan, seeking carrion below." "Condors weren't the only scavengers 13,000 years ago, but they were big enough to overshadow many rivals including foxes." "With their immensely strong beaks, condors could rip through almost any carcass, tearing through the hide to reach the meat inside." "Smaller birds like cara caras waited for discarded scraps." "Fossils show that many other scavenging birds cruised the ice age canyons vultures, storks and eagles." "But if they survived by eating carrion, who was doing the killing?" "The fossils also show there was a front line of top predators..." "Cheetah - the sprinter..." "Wolf - the pack hunter..." "And lions - bigger and more powerful than any seen today." "All these hunters generated leftovers for scavengers to squabble over." "But there was one more killer working these canyons... the most notorious of all ice age assassins..." "Most of what we know about this hunter comes not from caves, but from a very different source..." "natural tar pits." "A single tar pit has been found with over 2,000 skeletons... of sabre-toothed cats." "By studying the skeletons pulled from these pits, we can piece together how the flesh-and-blood cats lived and died." "These cats were hugely powerful... similar in size to African lions today, but heavier and densely muscled weighing 300 kilos or more." "All this and then the terrifying canine teeth, which gave the cats their name." "A tiny bone found in the throat suggests the sabre-tooth could roar... and so perhaps communicate with its neighbours..." "Other bones tell other stories..." "Many show some kind of injury..." "including broken teeth  smashed legs  and dislocated hips... nothing unusual in animals that wrestled heavy prey." "But what is amazing is that these bones often show signs of healing meaning the cats lived on for months or years, even when permanently crippled." "But if they couldn't hunt, how did they stay alive?" "Some scientists believe that sabre-tooths were social animals and healthy members of the group supported weaker relatives." "But on the other hand, they may have simply used their terrifying looks to scare smaller hunters wolves for example away from their kills." "At the end of the last ice age, more sophisticated hunters started to arrive." "They were about to change the hierarchy of the Canyonlands forever." "Following the rivers, feeding on whatever big game crossed their path, their small bands quickly spread across the entire region." "From the moment these hunters set foot here, many ice age creatures started to decline and became destined for extinction." "But they left a trail of hidden clues throughout the caves and canyons of the desert, ... and each one helps us build a clearer picture of the past." "And if we can fit these fragments back together, we can bring a lost world back to life." "Combining all this evidence, we can now go back 13,000 years and recreate a day in the life of North America's ice age Canyonlands ..." "The sun breaks over the rim of the canyons and begins to warm the cool night air..." "An early riser lumbers through the valley, and in the marshes along the river, roosting cranes begin to stir..." "The winter's almost over, they will soon be leaving for the long flight north to breed." "Others have already stumbled upon breakfast it's a bison carcass but no meal comes easy... lt takes all the wolves' teamwork to extract it from the mud... and even then it's unlikely to feed the whole pack." "High above, a solitary hunter leaves her cliff-top den..." "From here she can survey her vast range she hasn't eaten for a few days and she may have many miles to go to find a meal." "Signs of life, but out of even her league..." "Columbia mammoths graze the high plateau." "Other members of the herd are still emerging from their night-time shelter in a large cave." "For these ten-tonne giants, it's a struggle to survive." "This canyon with its sparse vegetation won't support their massive appetites for long." "They'll have to move on in a few days' time." "The sabre-tooth starts to move down through the gullies to the flats around the river, where she knows there will be far more prey..." "Another big cat has the same thing on its mind she too sets off towards the river but her path is blocked." "Even a mountain lion doesn't have the power or the weapons to compete with sabre-tooths..." "Better to take the long way round." "With the sabre-tooth on her way down, the cliff-tops are a safer place." "By managing to scrape a living up here, bighorn sheep avoid the dangers of the open valley floor." "But even they need water every now and then, and have to scramble down to reach the river." "Some members of the mammoth herd come down to drink before they start the daily grazing marathon..." "Once in the meadows, they mingle with horses and wild asses... camels and bison ... all drawn by the spring flush of new grasses, flowering plants and sprouting bushes." "The Shasta ground sloth waits until the morning chill has gone before he ventures out." "He comes back to his cave each evening, but by day he wanders miles around the Canyonlands, dining on anything that takes his fancy." "The ground sloth's lucky he can tackle tougher plants than mammoths in fact, he can eat almost anything." "The sabre-tooth's already hot on his trail... but so far the sloth is preoccupied with breakfast." "Camels browse the trees and bushes... like the sloth, they're tempting game for any hunter..." "After taking shelter in the canyon overnight, the camels too converge on the river... and must run the risk of crossing open ground." "Their expedition quickly draws the sabre-tooth's attention... they're softer targets than the faster, more elusive prey..." "Once at the river's edge, the camels are at their most vulnerable... hemmed in between the cliff-sides and the Colorado river." "It will take the camels only minutes to refill their 100 litre tanks... but they've been side-tracked by lush browsing on the riverbank just long enough to let the cat catch up..." "The sabre-tooth's not built for long pursuits... but if she can creep close enough she'll use a burst of speed to launch an ambush..." "One hit... and one bite..." "is all it takes." "The camel is as good as dead..." "The cat withdraws out of harm's way... leaving blood loss and shock to do the rest." "But as the sabre-tooth moves in to claim her kill, she's not alone... a second cat emerges from the bushes..." "This one has a badly damaged leg, the legacy of ambushing a bison, and she couldn't possibly compete for food." "But will the hunter tolerate another cat at her kill?" "These two are not rivals..." "they're blood relatives." "The hunter shares her food to help the injured cat survive." "But even for the fittest sabre-tooths, new competition means life is about to get a lot tougher." "While human hunters quickly find their feet here in the southwest and increase their numbers, sabre-tooths - like many other giants of the ice age are now living on borrowed time..." "Soon only the ghosts of these great cats will haunt the valleys and plateaux of the Canyonlands."