"For 160 million years, the dinosaurs ruled this world... while living in their shadows was a group of animals which couldn't have been more different." "These were our ancestors - small furry creatures called mammals, clinging to safety wherever they could." "But the mammals' time would come." "65 million years ago, volcanic activity started to poison the atmosphere." "The last dinosaurs were already living on a sick planet when their nemesis arrived... from space." "A meteor 10 kilometres wide slammed into Earth to mark the end of the reign of dinosaurs." "This series is about what happened next." "The survivors of the extinction all had one thing in common - their size." "Nearly every animal over 10 kilograms had been wiped out, leaving a world of little creatures." "Among them were the mammals." "In Walking with Beasts, you will witness how mammals left behind these small beginnings and took over the world." "In the course of 20 million years, mammals got more and more successful, until they were the biggest, fiercest and most spectacular animals on the planet." "Whatever the climate, whatever the habitat, mammals made it their own." "Their great strength was their ability to adapt." "They grew to gigantic sizes." "They evolved into powerful killers - like the famous sabre tooth cats." "And they even laid claim to the oceans." "Then, around four million years ago, came mankind's own origins in a type of ape that came down from the trees and walked upright." "Our story of this epic time finishes just 30,000 years ago with the ice ages, when our planet turned cold and our ancestors hunted in the realm of the mammoth." "It is a time called the Eocene, and Earth has healed itself from the ravages of the massive meteor strike." "Much has changed since the time of the dinosaurs." "It is far hotter now and lush tropical rain forest has sprung up on every continent from the Arctic to Antarctica." "In this flowering new Eden, meteors no longer present as much of a threat." "Under the forest canopy thrives a menagerie of weird and wonderful creatures." "Here, the rule of scaly reptiles is a distant memory." "The animals that dominate now are covered in feathers or fur." "Mammals have adapted well to the new world and there is a staggering variety of them, but they are still small, and, as before, live under the shadow of bigger, deadlier animals." "(SCREECHING)" "The dinosaurs might be long gone, but they left the world a vicious legacy." "Their direct descendants are the birds." "For the first and only time in its history, birds rule the Earth." "This is the story of just 24 hours in one part of the Eocene's mysterious, global forest, in an area that will, one day, become Germany." "It is dawn, and, at the base of a fig tree, one animal has already had its first brush with death." "This is a female Leptictidium." "She is a metre long and a common sight in the forests of 50 million years ago." "Her kind have survived virtually unchanged since the time of the dinosaurs." "Life, though, is scarcely any easier now." "This is still a perilous world where she must live fast and will probably die young." "A typical mammal, she looks after her offspring until they are old enough to fend for themselves, but, with so many predators about, today is a bad day for her litter to leave the nest." "She, however, has to feed, whatever the risk." "She only has a short window of opportunity to do so, and that window is fading fast." "The cool early morning is an ideal time to catch the frogs, lizards and insects she feeds on." "Being cold-blooded, they have yet to warm up and are still sluggish." "She, however, is warm-blooded and fast-moving 24 hours a day." "This is one of the mammals' ancient advantages." "Also, to help track down her prey, she has an incredibly acute sense of hearing and a distinctive super-sensitive nose that can twitch to locate food among the leaf litter." "And she is agile enough to catch even flying insects." "The best morning hunting lasts only an hour or two, and time is ticking." "She must keep moving to find more." "At this time in Europe's history," "Germany is at the centre of much volcanic activity, and this whole patch of forest is riddled with geothermal springs." "In places, these form seething mud pools." "Boiling water, poisonous gas and earthquakes are ever-present threats that the animals have learnt to live with." "But not every hazard here is so easy to ignore." "As the sun gets higher, the daylight creatures are becoming active." "And that brings out the forest's more menacing side... ..the birds." "They are the top predators in this weird forest." "This is the largest, Gastornis, a half-tonne pile of muscle and feathers as tall as a grown man." "This is a female, and, for the last two months, her whole life has revolved around the one egg in her nest, now only hours from hatching." "She is fiercely territorial and, when another Gastornis gets too close..." "..she moves to protect her nest." "Since the great extinction, birds have been a success like mammals but, what is more, they have got big - big enough to take over the role of the predatory dinosaurs." "The two giants clash." "The small mammal escapes." "There are echoes here of a bygone age." "The Leptictidium needs a lot of food for her size." "Like all mammals, this is the price she pays for a warm-blooded metabolism." "There is usually plenty of prey down by the lakeside, but, this morning, there is only trouble." "There is a newcomer down by the lake." "Stirring in the morning's early rays is an Ambulocetus, a bizarre beast that has swum up the river from the nearby coast." "He is a predator." "Her hunting is interrupted once again." "She must move on, and quickly." "The three-metre-long carnivore waddles awkwardly towards the lake." "Although his ancestors hunted on land," "Ambulocetus has evolved to be far more at home in the water." "In fact, his descendants will take this to a greater extreme." "You are looking at the very earliest form of whale." "Ambulocetus in fact means "walking whale"." "But with another 10 million years of evolution, the limbs will become flippers and the tail will become a fluke." "His style of swimming already has the look of a whale or a dolphin - his body moves up and down, and not side to side like the fishes or crocodiles he shares the water with." "He is the most powerful predator in this lake... ..but he is far from safe here." "There is a hidden peril." "Huge quantities of volcanic gas are trapped in the lake bed." "If enough of this gas were to escape at one time, it would suffocate the animals for miles around." "The lake is a time bomb." "But the Ambulocetus thinks he has found the ideal spot for practising his deadly speciality..." "..ambush." "A Propalaeotherium, an early form of horse, presents the day's first good chance of a kill." "This time, the Ambulocetus fails, but the day is long and he will try again and again." "For the Leptictidium, the forest is now too dangerous and the time for hunting is over." "The mother returns to the safety of her nest." "She has not done well this morning, and it is vital her next hunting trip is more successful." "She will sleep now until the evening, when hunting will be easier and the low light will help her evade the sharp-eyed birds." "Noon, and temperatures climb above 30 degrees." "The only movement is the Gastornis chick, starting to break free from the egg." "Not far away, the Leptictidium family are still in their nest." "But, in their sleep, they are totally defenceless against one particular predator." "Ants... ..giant carnivorous ants." "This is the largest species of ant ever." "They are on the lookout for prey - any creature that can't get away in time." "(SQUEALING)" "This is the vanguard of an ominous killing machine." "Behind them is an army of half a million others, marching through the forest, stripping its prey to the bone." "(SQUEALING)" "The ants have their next victim." "Mid-afternoon, and the Propalaeotherium are busy foraging for grapes from the forest floor." "By modern standards, these primitive horses are tiny, but this is how horses started out - small forest-dwelling animals." "At this stage, they are not much bigger than cats, and have yet to even develop hooves, having instead four hoof-like toes." "In a forest where every tree could hide a predator, the horses live on a knife edge, ready to spring at the slightest sound." "(SQUEALING)" "(SQUAWKING)" "As the light drops before sunset, the Leptictidium stirs from her nest." "It's time to hunt again." "But first she must clear away escape paths around the tree." "This will give her a slightly better chance of outrunning any predators she meets, and every little bit counts." "Her young are eager to join her this evening." "Until now, she has managed to keep them safe from the dangers of the forest by suckling them in the nest, but there comes a time for all mammals when they can no longer rely on their mother's milk." "The young must now learn to find food for themselves, and their only hope is to follow their mother's example." "These are important lessons." "By smelling the insect she has caught, they can recognise what is safe to eat." "However, their chances of survival are slim." "Most won't make it to adulthood." "As dusk approaches, the predators are still out in numbers." "The Ambulocetus has yet to make a kill today, and is preparing another ambush near the shore of the lake." "Although he has no ears, he listens for approaching prey by putting his jaw to the ground and detecting vibrations." "It is the same mechanism that allows him to hear underwater." "If any animal strays too close, he'll be waiting." "The Propalaeotherium appear less alert than usual." "Throughout the afternoon, they have continued to eat the fermenting grapes off the ground." "They contain only the smallest amount of alcohol, but it is enough to dull their usually sharp senses." "This is a bad time to get careless." "The Leptictidium scurry to safety... ..just." "This is a world where birds eat horses." "At dusk, the Gastornis returns to her nest." "Only now does she discover the fate of her offspring." "The biggest predator here, humbled by the smallest." "Her size forces her to nest on the ground, and now she has paid the price - months of dedication wasted." "Despite everything, this evening the Leptictidium have fed well and all the young have survived their first outing." "The night is usually a safe time for them." "Tonight will be different." "After a day of slumber, this nocturnal Godinotia is stirring." "This is a type of primate, a new group of mammals that specialise in living in trees." "Primates possess keen vision and amazingly dexterous hands which not only help them to move among the branches, but also to wheedle out their favourite insects, even when they're beneath the bark." "They are inventive and resourceful animals and, although these Godinotia are solitary, primates have a sociable future." "Among their descendants in millions of years' time will be a hairless type of ape called Man." "At the lakeside, the Ambulocetus is still maintaining his patient vigil, waiting for prey." "At night, a whole different cast of animals comes down to the water's edge." "Eventually, a small predator chooses the wrong bit of lake to drink from." "The Ambulocetus's killing technique is simple." "His vice-like jaws hold the struggling prey until it drowns." "The dark hours go by and some of the Godinotia are becoming less solitary." "Copulation among these primates is all part of the normal rhythm of the night." "But this is not a normal night." "(SHRIEKING)" "(RUMBLING)" "An earth tremor." "These are common here, but this one is bigger than normal." "The gas at the bottom of the lake is suddenly shaken free, releasing a deadly cloud of carbon dioxide." "(SCREECHING)" "Driven by the wind, the gas sweeps through the forest undergrowth, suffocating every animal in its path." "The day has come full circle." "The poisonous cloud has cleared, leaving a trail of corpses." "The Leptictidium, however, was lucky." "She and her litter escaped death only because their nest lay away from the path of the deadly gas." "But her struggle to survive never stops." "It's time to hunt again." "Once more, the Ambulocetus is lying in her path, but she instinctively knows he is dead." "Today, the Leptictidium is the survivor, but, ironically, the future holds a different outcome for these mammals." "The Leptictidium and her kind are destined to become extinct when this hot, wet world gets cooler and drier and the world's forests start to disappear." "Ambulocetus is the one with the big future." "He is the ancestor of the whales, the most magnificent dynasty of mammals, and mammals are about to take over the world." "Next time, we move forward 15 million years to when the descendants of the Ambulocetus become the true masters of the oceans." "On land too, mammals shrug off their small beginnings to evolve into the largest and fiercest animals on the planet."