** this script is inexact, but close enough to help you**
 

This little mammal is a scavenger called Didelphodon. She is a marsupial and specialises in raiding abandoned dinosaur nests. This evening, she could be in luck. Unfortunately, the smell of the nest blinds her senses to danger.
 
The end of the Cretaceous. The continents are taking their modern forms. But this movement of the Earth's crust has produced a surge in volcanic activity. Massive eruptions that have lasted for centuries have laid waste to landscapes, filling the atmosphere with gases and debris.
 
This desolate world is still ruled by dinosaurs, as it has been for 160 million years, but they are nearing the end of their reign. Life on earth is choking to death. Yet in the last two million years, the dinosaurs' most infamous predator has appeared. Tyrannosaurus, a five-tonne,13-metre long carnivore, specifically evolved to kill other giant dinosaurs.

This is a male. He's been drawn to this volcano by the smell of food. The area is full of geothermal springs and the air thick with sulphurous fumes. But there is another smell here. In one small valley, there is the stench of death.

Unwittingly, the Tyrannosaurus has been drawn into a natural trap. Volcanic vents are producing poisonous carbon monoxide, and because it is heavier than air, it has formed a suffocating layer close to the ground. The giant predator stands above the layer, but as he puts his head down to feed he begins to feel the effects. If he topples over now, he will never get up.

Eventually, his sheer size is his salvation. As he stands up with his prize, his head just clears the gas layer. There are still islands of greenery between the lava flows. In the warm, moist climate of the late Cretaceous, the vegetation has transformed. Instead of conifers, broad-leaved trees fill the forest canopy.

Driving this quiet revolution among the plants is the remarkable evolution of flowers. Their secret lies in their intimate relationship with insects, so close that some flowers can only be pollinated by insects and some insects, like butterflies, can only feed on flowers. Among these new plants, the birds are flourishing, and their calls for man ever-present chorus.

Millions of years of evolution have also created intimate relationships among different types of dinosaurs. Especially the delicate balance between predator and prey. One dinosaur that specialises in defence is the extraordinary Ankylosaurus. They are evolved to withstand attack even from giant predators like Tyrannosaurus. At seven tonnes, Ankylosaurus are so heavily armoured that even their eyelids are hardened. And if that wasn't enough, they have a formidable club on the end of their tails. Sadly, not even these magnificent creatures have any defence against the natural forces that are suffocating their world.

Nearby lies the Tyrannosaurus nest. These are usually closely guarded by the mother, but this nest has been abandoned, and a Didelphodon has burrowed into the side. Dinosaurs are vulnerable because they lay their eggs on the ground. But size helps, and the egg is a challenge for this marsupial. Soon the age of the mammals will dawn, and they will grow massive, but this is as big as Cretaceous mammals get.

The Tyrannosaurus embryo inside the abandoned egg is already dead. The scent is a lure to another Didelphodon. Many dinosaur embryos cannot survive in this volcanic environment because acidic pollution prevents their eggshells from forming properly. The mother is calling for a new mate. Tyrannosaurus have huge territories of hundreds of square kilometres. Her challenge is to attract a wandering male. She may have to call like this for weeks. One of the Tyrannosaurus's principal sources of prey are these bulky Torosaurus.

In the late Cretaceous, herds of horned herbivores are very common and attract many predators. It is rutting season. To display, males flush blood into their crests, creating vivid patterns. These displays help to avoid physical contact. With one-metre-long horns, fighting can easily result in bad injuries. The best and the brightest crest is all that is needed to settle arguments. Occasionally, showing off is not enough and males resort to brute force.

For this old Torosaurus, this was one fight too many. He will never again challenge for the right to mate. The mating call of the Tyrannosaurus continues to echo across the volcanic slopes. And it has been heard. A male has killed a young Triceratops. It's not just to satisfy his hunger. It is a gift. Female Tyrannosaurus are larger and more aggressive, and he courts her with food to stop her attacking him on sight.

The female arrives. She is wary. The primary weapon of a Tyrannosaurus is its mouth. The primary weapon of a Tyrannosaurus is its mouth. Its arms are tiny so it can carry a massive jaw and remain balanced. This jaw can crush bone and tear off up to 70 kg of meat with one bite. The male keeps his distance. Later that evening, they mate. This is the first of many couplings as the male stays by the female while she is receptive - ready to see off any other males.

On the lava flows, a group of Anatotitan wanders between islands of greenery. These animals are members of the hadrosaur family, the most common group of dinosaurs in the Late Cretaceous. But their kind has evolved to thrive in lush lowland swamps, not in an ash wilderness.

Three days have passed. The Triceratops carcass has been stripped and the female Tyrannosaurus is beginning to tire of her mate. The male knows better than to stay. Gliding in from the coast, a magnificent pterosaur, Quetzalcoatlus, is hunting for food. This is now a rare sight. For 20 million years, these flying reptiles have been in decline. These 13-metre giants are the only ones left. And this is a dangerous place to be.

One-tonne crocodiles live in the lake, and could easily drag the delicate glider to his death. Driven on to extinction. The skies of the future belong to the birds that already flourish around him. Months have passed, and the female Tyrannosaurus has built a new nest, camouflaged in the forest. Mother keeps watch. For the full two months of the eggs' incubation, she will not leave or even eat. She knows her nest is a magnet to scavengers.

Like this Dromaeosaur. His cautious approach is watched by the Tyrannosaurus. She judges exactly when he has got too close. As the sun sets, another threat comes out to haunt the mother. With food becoming scarce, the mammals are getting bolder. She checks to make sure more have not burrowed in, then returns to her vigil.

The weeks pass, and above the brilliant volcanic sunsets, there are signs of an even more destructive natural disaster. Showers of shooting stars herald the approach of a giant comet on a collision course with the Earth.

Far below, the dinosaurs are oblivious. The Torosaurus herd continues to feed. Nervous of moonlight predators, younger animals seek protection among the larger adults. Using the darkness, a pair of Dromaeosaurs unsettle the herd and isolate one of the youngsters. Safe. But the predators have tasted blood and will not give up easily. Morning reveals the results of last night's tussle. The little Torosaurus lost his fight with the predators. For the herd, it is a blow. Too few young are being born in this polluted environment.

A Didelphodon is already at the carcass. These little opportunists are about the only animals that are thriving. During their reign, dinosaurs have adapted to huge changes but now they face a combination of events that will spell their doom. After trekking across the ash fields, Anatotitans gather round a stagnant pool to drink and feed. Huge batteries of chewing teeth make short work of the vegetation.

Once again, the predators make the water's edge a dangerous place. The group senses danger and starts to break up. The mother Tyrannosaurus has broken her fast and is back with a vengeance. Nearby is the reason for her hunger. Three Tyrannosaurus chicks. The only survivors from a clutch of twelve. The moment they hear the kill, they start calling for food. The mother delivers a slab of Anatotitan meat. Only four weeks old and less than a metre high, competition is intense between them. One is already picked on by the others. They'll remain under their mother's protection for another two months. Soon after that, she will abandon them, or worse, view them as food. It is unlikely the outcast will last that long.

A few days later and the mother rests in the warm afternoon sun. There is no sign of the smaller runt. He may have been killed by his siblings. Increasingly, the bickering pair are happy to wander from their mother to explore their surroundings. From the undergrowth, a snake watches. These reptiles have only recently evolved from the same family as lizards, but they specialise in hunting warm-blooded creatures like mammals. They use sensory pits on their snouts as a way of detecting the heat signatures of other animals.

It doesn't like what it sees. While the chicks play, they are oblivious to approaching danger. The mother is caught completely by surprise. The Ankylosaurus has very little brain inside its reinforced skull, so when faced with danger, it reacts automatically and aggressively. Normally, Tyrannosaurus would retreat, but she will not abandon her young. The blow has cracked the mother's femur and ruptured internal organs. She limps away in agony.

That night, the usual evening chorus is joined by the whimper of a dying giant. By morning, she lies life lesson the baking ash fields. The chicks stand expectantly by the colossal corpse of their mother. Hours pass, and still they wait. But their fate will now be settled, along with all the other giant dinosaurs of the Cretaceous.

3,000 km to the south, the massive comet crashes into Earth. The light from the impact fades in silence. Then the shock waves arrive. Next comes the blast front. Finally a rain of molten rock starts to fall out of the darkening sky - this is the end of the age of the dinosaurs.

The comet struck the Gulf of Mexico with the force of 10 billion Hiroshima bombs. In the catastrophic climate changes that followed, 65% of life died out. It took millions of years for Earth to recover, and when it did, the giant dinosaurs were gone, never to return. In their place have emerged other powerful and beautiful creatures.

We now know one small group of dinosaurs did survive the extinction - and they are all around us today - the birds.