Australia's First 4 Billion Years: Monsters

RICHARD SMITH: Over four billion years in the making.

An island adrift in southern seas.

It's Australia, the giant Down Under.

A young nation, with all the gifts of the modern age.

But move beyond the cities and an ancient land awaits... One nearly as old as the Earth itself.

Australia is a puzzle put together in prehistoric times.

And the clues that unlock the mystery can be found scattered across Australia's sunburnt face.

I'm Richard Smith, and this is an amazing country.

I'll show you that every rock has a history, every creature a tale of survival against the odds.

Join me on an epic journey across a mighty continent, and far back in time.

Of all continents on Earth, none preserve the great saga of our planet and the evolution of life quite like this one.

Nowhere else can you so simply jump in a car and travel back to the dawn of time.

In this episode... Out of the chaos of disaster rises a new world order, ruled by reptilian tooth and claw.

It's the Age of Dinosaurs Down Under.

Join me as I retrace the footsteps of predators and prey and dive into a long-lost sea.

From Australia's ancient stones comes the story of our world.

"Australia's First Four Billion Years: Monsters."

Right now, on NOVA.

Major funding for NOVA is provided by the following: SMITH: It's a long journey back to our modern world from distant ancient Australia.

From the birth of the Earth to the present day, the road of time stretches a mind-boggling 4.6 billion years.

It helps to imagine, just for a moment, that this car can travel through time.

SMITH: I've set the controls for a million years per minute.

That's 60 million years of history for every hour we travel down the road.

You want to see the real, old Australia?

It's quite a ride.

GPS VOICE: Your destination is the Mesozoic.

SMITH: Traveling at a million years per minute, the entire story of Australia-- and the planet-- is condensed into a little over three days of solid driving.

And for most of those first three days, we've roared through the infancy and childhood of the Australian continent.

Now, with 70 hours of my journey behind me and only another four to go, we've arrived at the start of Australia's wild adolescence.

It's the Mesozoic.

(insect buzzing by) (roaring) SMITH: It's the most familiar of all geological eras.

(dinosaurs burring) And for good reason.

It's in the Mesozoic, home of the Triassic, Jurassic and Cretaceous periods, that dinosaurs ruled the Earth.

But despite such world domination, evidence for their conquest of Australia has been a little thin on the ground.

Until now.

Time for the Age of Dinosaurs... Down Under.

The Triassic, the first of the three great periods that made up the Mesozoic, got off to a pretty shaky start.

The Permian Crisis, the world's most catastrophic extinction event, was over, but gone with it was perhaps 95% of the biological diversity of the planet.

Around the world, life had been all but wiped out in the sea... and devastated on land.

Yet somehow, out of the carnage and confusion of that devastated world rose a new one, and with it, the dramatic sandstone landscape of Sydney.

TIM FLANNERY: I think, Richard, this would have to be one of the best places to see the Sydney sandstone.

There's the Pacific Ocean.

There's North Head over there.

There's the entrance to Sydney Harbor just behind us there.

Over here is the Gap.

And a lot of rock underneath us.

There's about 250 meters of solid sandstone.

SMITH: Biologist Tim Flannery knows the landscape of my hometown well.

Sydney, it seems, was built on the aftermath of disaster.

FLANNERY: We would have been standing when this sandstone was laid down in a post- catastrophic world.

We've had the great disaster of the Permian extinction with life almost extinguished, 95% of all species gone.

SMITH: Even plants struggled to recover.

The colorful forests and rich coal swamps of the Sydney basin had gone.

And over the next 20 million years, the lush world of the Permian was buried deeper and deeper in sand.

FLANNERY: There have been some recent studies suggesting this sand here particularly may have come from as far away as east Antarctica and that is a massive distance.

SMITH: Storms raged on those distant mountains.

And rivers thundered from their denuded slopes, carrying unimaginable quantities of sand northwards across vast, spreading floodplains.

FLANNERY: This rock talks to me of a time when life was slowly recovering, but there's not even enough life and vegetation to hold the banks of the river together.

It's just this great braided system flowing across the landscape.

I can just imagine standing there, seeing these ripples six meters high, imagining this world where the physical processes of the planet are just laid so bare.

These sand grains saw that.

They... the sun that was shining down on the planet then struck those sand grains that we are standing on now and it's that great physical reminder-- that's why I love geology, you know-- that you know that that rock was there at the time, 230 million years ago.

(machine hammering) SMITH: Shifting sand has turned to solid stone, and the debris from the end of the Permian world is now the foundation for a new one.

(jack hammering) (beeping) Now after waiting quietly in the dark for some 230 million years, the lost sands of Antarctica have a new job: as the bedrock and building blocks of a great global city.

SMITH: Sydney is defined by its Triassic geology.

From the warm glow of its stone buildings, to the shape of its harbor.

The sandstone dictates everything, from the flow of traffic to the form of its native flora.

The sandstone cliffs stand hard and proud against the Pacific Ocean and weather into the soft golden sands of the surf line.

The sand also buries the Permian peat lands, allowing them to become the coal that powers the city.

And rising to the west, this same sandstone forms the rocky ramparts of the Blue Mountains and the Great Dividing Range.

All of this, a legacy from the dark days when the Earth nearly died.

It was the sudden lurch into an intense greenhouse climate that seems to have triggered the initial disaster at the end of the Permian.

A series of wild climate swings then plagued the early Triassic before the planet finally stabilized.

And even when it did, temperatures still simmered.

SMITH: Conditions would have remained pretty hot and dry no matter where you went on the planet.

Australia was still part of the supercontinent Gondwana, but Gondwana was now part of the super, supercontinent called Pangea, where all lands were one.

And given a decent four-wheel drive, you really could have gone just about anywhere.

SMITH: Australia had joined the wild bunch, though it was very much at the bottom of the continental pack.

Australia lay near where Antarctica does today.

But this was a south pole in an ice-free greenhouse world.

There were ferns and ginkgo trees.

Freshwater fish and giant carnivorous amphibians.

But the Triassic Earth belonged to reptiles.

Some were taking to the air, others to the sea.

Walking the land were lizard-like reptiles, mammal-like reptiles, and the first dinosaurian reptiles as well.

Though we know these early dinosaurs roamed across southern Gondwana, they've left almost no trace here in Triassic Australia.

(crunching) But the evidence for Australian dinosaurs is out there, if you know where to look.

The old gold mining town of Mount Morgan in Central Queensland is one such place.

When the old miners excavated clay from a nearby hill, what they dug away was the mud that once filled a Jurassic lake.

So this was all a lake deposit here?

HEICKE: Yes, so we're in underneath where the dinosaurs walked on the edge of that freshwater, shallow lake.

SMITH: Left behind in the rocky ceiling are the three-toed imprints of dinosaurs that walked on the lake's muddy fringe.

The ghosts of dinosaurs past still haunt these caverns.

They're still up here... Ah, yes, yes.

SMITH: These footprints-- and those from other mines- help flesh out a Jurassic Australia rich in forests and waterways.

I'm standing in what was the muddy edge of a lake, and up there on the lake's surface, a therapod once walked above me, about 190 million years ago, an imprint as clear as day.

SMITH: But Australia is big and old and red and flat.

This is a geological landscape that has kept its Mesozoic secrets well hidden.

The botanical landscapes Australia's dinosaurs walked in, though, are much easier to experience.

You can still walk in them today.

The Mesozoic was a great time for plants.

The Earth was an ice-free, greenhouse world, warm and wet.

Thick forests spread around the globe, and the southern lands of Gondwana were no exception.

Cycads, ferns and ginkgoes were common and had now been joined by the tree ferns that still abound in the rainforests and gullies of eastern Australia.

But the standout trees of Mesozoic forests worldwide were the giant conifers.

Luckily, some of those giant conifers are still with us.

This towering sentinel is a Queensland Bunya Pine.

And it's remarkable not only for its great size, but because it's so little changed.

The bunya, hoop and kauri pines of Eastern Australia are well-known living fossils from the days of the dinosaurs.

But in 1994, the ultimate pineosaur was discovered-- the wollemi pine, a green giant 130 feet tall and hiding only a hundred miles from Sydney.

Here, in a couple of secret canyons, are less than a hundred of perhaps the oldest surviving tree species in the world-- the spitting image of fossils from as far away as Antarctica.

Today the great conifer forests of Australia are gone, but the few surviving pockets allow you to dream of the days when you could have driven from coast to coast with not a eucalyptus leaf in sight.

The Mesozoic Earth was restless.

Like a teenager with a growth spurt, it was on the move again.

The supercontinent Pangea was breaking up, leaving Australia still attached to a remodeled Gondwana in the southern hemisphere.

And around the end of the Jurassic, a little extra remodeling was applied from space.

A falling rock in the shape of an asteroid or comet slammed into Central Australia.

(thunderous crash) It was a bull's-eye that you can still see almost bang in the middle of the continent.

As impressive as it is, Gosses Bluff-- or Tnorala, to give it its indigenous name-- is a shadow of its former self.

Most of the original 13-mile- wide crater has been worn away.

What's left is merely the bowl punched deep into the Earth below ground zero.

Still, the ring of low hills gives a pretty good hint of the scale of utter devastation that must have been visited upon the land for at least 60 miles in every direction.

Sometimes you get a chance to truly grasp the scale of past geological events.

And when you do, it's truly humbling.

It wasn't the Gosses Bluff impact that did in the dinosaurs.

But it was a portent of dangers to come.

(birds and insects chirping) When dawn broke on the Cretaceous, dinosaurs still had their claws on the continent... (roar) ...from one side of it to the other.

It's been a long wait, but finally the 21st century is throwing new light on the Australian dinosaur story.

For years, the ancient secrets of the Kimberley coastline near Broome have been guarded by extreme tides and extensive, crocodile-inhabited mud flats.

It makes for an easy place to imagine what might have been walking the land in the primeval past.

Wonderful.

But imagination alone is not required here.

The giant beasts of the early Cretaceous have made their presence clear to us.

(muffled roaring) The first clear chapter in Australia's rather secret history of dinosaurs starts here-- on the beaches near Broome in the Kimberley.

Back then, this was a vast coastal forest running down to floodplains and estuaries near the sea.

Not radically different from the tropical mudflats of today, except for the 15 or so species of very large dinosaurs that have left their marks in the rocks here.

A rich reptilian community once stomped this landscape.

Dinosaur footprints stretch over 60 miles of coast.

They must have been everywhere.

Even a suspected Stegosaur left its mark here... One of only a handful of such five-toed prints in the world.

But the largest and most abundant footfalls belong to towering vegetarian sauropods.

And this is the trackway of one large sauropod that came wandering past Broome around 132, 135 million years ago.

Big footprints.

One there.

Another one there.

Big footprint here.

And interspersed amongst them some smaller footprints thought to have been made by a calf wandering with its mother.

(dinosaurs roaring, calves squealing) There's little evidence, though, for parental care in sauropods and, once you reach this sort of size, little need for it.

Finding enough to eat was probably a bigger concern than avoiding predators.

But for most Australian dinosaurs, day-to-day life was a hazardous experience-- as a small herd discovered 95 million years ago near Winton, in Queensland.

That moment is frozen in time here at Lark Quarry...

The site, it's been thought, of the world's only recorded dinosaur stampede.

Picture the scene here one ordinary day in the Cretaceous.

This was a broad, muddy spit running down into a lake just over there.

Now, sometime during the day, a mixed herd of small dinosaurs wandered across the mud to take a drink at the water's edge.

Here you can see the very clear footprints of a small, chicken-sized meat-eater, and here the emu-sized tracks of an ornithopod dinosaur.

But behind me, probably more or less where the wall is, was the start of a forest of tree ferns and ginkgo trees.

These rich forests, dominated by conifers, provided shelter and food.

And cover for a meat-eater.

Even for a wary dinosaur, the Cretaceous was no time for complacency.

Now if you popped your head up and looked back this way, you would have seen one very large, very hungry theropod head down and heading your way.

(scuffling and squealing) In the pandemonium that followed, 150 terrified dinosaurs scattered in all directions, sliding on the mud and crashing into each other as they raced to reach the relative safety of the forest beyond.

(birds squawking) Footprints can only ever tell part of the story.

Bringing Australia's true blue dinosaurs to life needs bones.

And finally, those bones have also started turning up.

DAVID ELLIOTT: Here's your coffee.

Oh, thank you.

How's it going?

Slowly coming together.

Very, very slowly.

SMITH: They've come to occupy a very special place in the lives of sheep farmers David and Judy Elliott.

You've only got 10,000 pieces to go.

Yeah, I'm doing really well.

SMITH: And yes, that is a dinosaur, on their kitchen table.

JUDY ELLIOTT: It's a pile of rock that's got tiny bones in it.

And we've dubbed it Chook or Chooky because that is about the size of the animals that the bones relate to.

So it's Chooky.

SMITH: Hunting dinosaurs was never part of the Elliotts' business plan, but they're fast becoming experts.

DAVID ELLIOTT: This dinosaur site that we are going to is probably the most exciting and it's definitely the most significant of what I've found so far.

It's a place that's produced a tremendous amount of material in quite a short time.

SMITH: The Elliotts began their dinosaur odyssey by accident, pretty much by tripping over the bones of some dead ones on their property.

So Dave, this is a big hole in the ground?

Yeah, here we are.

This is where it all started.

If you can imagine 95-100 million years ago we were sitting in a lush rainforest area.

If you look back in the north and where we have nice flat open grassland, that would have been an inland sea.

And what we had were these big rivers coming in and bringing silt and just depositing silt.

So slowly that sea was being pushed back to the north.

So this country here was cool, it was lush, it was green.

The rivers would have been full of lungfish and turtles and big crocodiles and freshwater fish.

SMITH: From what they've seen so far, David's convinced the dinosaurs being unearthed have a unique Australian pedigree.

DAVID ELLIOTT: The dinosaurs out here are totally different.

And that's so true for just about everything Australian, isn't it?

Even us, you know, we're a little bit different, aren't we?

SMITH: Before the dinosaurs showed themselves in Western Queensland, Winton was most famous for a song.

(man singing, echoing in background) A visit to this billabong-- an Outback waterhole-- inspired bush poet Banjo Patterson to pen the country's most famous national tune.

That legacy lives on.

Each animal being revealed to us bone by ancient bone is given a local nickname.

DAVID ELLIOTT: If there's a dinosaur, say, that comes from the Winton area, then it needs to have that context.

One of the strongest contexts, of course, with Winton is Banjo Patterson, "Waltzing Matilda" and that link.

SMITH: Not exactly waltzing, but here's one big-boned girl: the sauropod Matilda.

Matilda stretched 60 feet tip to tail and stood 13 feet high at the hip.

And then there's Banjo himself, the fearsome southern hunter.

DAVID ELLIOTT: You look at these things and they're just skinny bones really.

They don't look all that significant.

But you start fleshing these bones out and putting sinews on them, putting muscles on them, and then you put that leg on that animal as it would have stood, and you can see that what we're dealing with isn't any spring chicken.

It is one hell of a big and very dangerous dinosaur, and it's not the sort of thing that you'd particularly like to have chasing you up the garden path or down the hallway.

What you've got is an animal that didn't rely on its teeth to kill.

Massive claws.

Massive beefed-up arms.

So you imagine just getting its claws in, driving them in and just tearing it apart.

It would have had that strength.

(roaring) SMITH: In an extraordinary twist of irony, it now turns out that the spot where the bones of both Banjo and Matilda were found was indeed a billabong.

It's not quite Jurassic Park, but after years languishing as a dinosaur backwater, Outback Australia is opening up as the hot new Cretaceous playground for palaeontologists.

It's always been a big country out here, and after an unusually wet year, this red landscape is so green it even looks like it could carry some pretty large livestock.

A 500-mile drive south of Winton brings you to the site of some of the biggest dinosaur discoveries yet, near the small town of Eromanga.

Population: 171.

A warm summer's day here is 117 degrees.

As far as towns go, Eromanga is no titan, but that's not so true of the bones found on nearby Plevna Downs Station.

In a thundering echo of the Winton story, ranchers Robyn and Stuart McKenzie have been unearthing bones belonging to some of the largest dinosaurs to have ever shaken the planet.

This enormous drumstick is over six feet long-- a giant leg bone from an as yet undescribed species of Titanosaur, a big bloke called Cooper.

ROBYN McKENZIE: Cooper is approximately 95 million years old.

And so what we've got here is the largest bone of the largest animal that ever walked around on Australian soils and is actually up there in the top ten in the world.

SMITH: At over 100 tons, and with a hip height as high as the hotel roof, this giant would have barely fit in Eromanga's main street.

SCOTT HOCKNULL: Australia is really in a natural history revolution.

There's dinosaurs being found all over Queensland, central Queensland from Winton down to Eromanga and even in southern Australia.

So in the last decade, we've found hundreds and hundreds of dinosaur bones from the smallest dinosaurs to the largest.

There's no stop to it now.

SMITH: For a tiny town, Eromanga can make some big claims to fame.

Being the furthest town from the sea in Australia is another one.

But it wasn't always so.

Ask a geologist, and they'll tell you the town has lent its name to the largest inland sea in Australian history.

By the middle of the Cretaceous, ocean levels were on the rise again, climbing 600 feet above today's levels.

With the center of the continent already subsiding, the sea flooded in to central Australia.

Today, Eromanga's only reliable source of water comes from underground: the Great Artesian Basin.

1909, it was first sunk.

SMITH: It's one of the largest artesian basins on the planet.

It's 160 PSI of pressure at 100 degrees Celsius.

You got to be very careful working around it.

SMITH: The heat comes from the warmth of the Earth over half a mile below us.

It's smelly because it's been trapped down there for a million years.

Of course, this isn't stinky prehistoric seawater coming out.

Rather, it's fresh groundwater that's taken an age to seep deep into the porous stone that was once the sand at the bottom of the Eromanga Sea.

Without the Eromanga Sea, there wouldn't be a Great Artesian Basin.

It's the fine muds of the old Eromanga seafloor that seal the top of the artesian basin.

Mark out the boreholes that tap into it and you can pretty much draw a map of where the ocean used to be.

About 120 million years ago, the Eromanga Sea spread out over a quarter of the continent.

I'm heading to Coober Pedy, on its southern shoreline.

Scattered on the outskirts of town are strange clues to its past.

Petrified driftwood.

The salty glint of gypsum.

Even rocks dropped from winter ice that once rafted overhead.

(fly buzzing) Today's mysteriously beautiful landscape was once a seascape.

When the first European explorers made it out here to Central Australia, some of them expected to find an inland sea.

Now we all know they failed, but not because it was a silly idea.

They just got here 120 million years too late.

Arrive when the tide was still in and you would have found the Eromanga Sea full of monsters: toothy marine reptile monsters like plesiosaurs and ichthyosaurs.

Air-breathing animals that had returned to the sea, both these types of reptiles are known to have hunted in Eromanga waters.

And they died here, too.

Sometimes, a corpse sank to the seafloor and fell all the way to the future.

These days, Coober Pedy bakes in the heat.

It might look like a ramshackle collection of mineshafts, underground houses and tourist traps, but this is opal central.

The diggings here produce over 70% of the world's supply of this rainbow-hued treasure, so it's no surprise opal is Australia's national gemstone.

Brothers Steve and Drago Marjanovic make their living prising these precious stones from the ancient seabed on the outskirts of town.

This is their daily commute: a tight fit dangling on a wire 70 feet down a giant wormhole.

Wow!

Hi, Drago.

Drago has offered to lead marine reptile expert Maria Zammit and I deep into the prehistoric Eromanga seafloor.

The brothers have dug an extraordinary catacomb of shafts and tunnels into a Cretaceous marine graveyard.

So Drago, is it hard to tunnel through this?

Oh, yeah.

SMITH: Opal formed here, it's thought, when silica-laden water leached through the rock, pooled where it met resistance, and then slowly evaporated.

Occasionally, when this mineral-rich water encountered a fossil, a biological treasure became a mineralogical one as well.

Wow, that is just beautiful.

That green one is stunning.

And it's clearly a shell.

MARIA ZAMMIT: You're absolutely right.

You can really see that they're shells.

That tells us a little bit about the sea bed that was here at the time.

However, for me of course, the favorite are the vertebrate fossils, so the parts of those marine reptiles that you do occasionally get opalized.

SMITH: These are some of the opalized body parts recovered so far.

Back bones, rib bones, tail bones and flipper bones, near-complete skeletons from long-dead reptilian sea monsters.

(hissing) ZAMMIT: I've heard of some descriptions of them being like a snake threaded though the body of a turtle, and that's really what they look like.

They've got these gigantic flippers attached to this body, and then you've got this long neck stretching out in front.

SMITH: Enough plesiosaur remains have now been found to determine that many found in the area were juveniles.

You do see some that are only about this big.

So they are obviously juveniles.

How young?

We don't know if they are just newborn babies or if they are slightly older than that, but it is suggested that, because we see so many specimens that show these signs of being quite young, that it was a nursery.

SMITH: Plesiosaurs could calve and fatten up in the nutrient-rich summer waters, heading north again before the winter returned.

It might have been a safer place than most to raise a youngster in a dangerous ocean.

(squawking) Sail out into the Eromanga Sea and you would have encountered a host of strange Cretaceous sea creatures.

And it's highly unlikely that they were all as friendly as dolphins.

MARK NORMAN: What I think is amazing is if this was a hundred million years ago, we'd be traveling over very similar seas to this, but when we got there, we wouldn't be looking for these strange animals.

They'd be looking at us.

SMITH: Marine biologist Mark Norman and I are off to meet one of the strangest survivors from these Cretaceous seas.

It's the nautilus.

No, it should have been straight through here.

SMITH: It's not easy to find.

These days, this ancient mollusk hides away far below the reach of daylight and divers on the deepest reef walls in the Coral Sea.

A trap has been sitting at depth overnight, set with some unusual bait.

Their taste for chicken went against them.

The phrase "living fossil" gets used a lot for these long-lived ancient groups of animals.

These went through seven mass extinctions.

The dinosaurs didn't make it through one.

The nautilus and their relatives over 500 million years are the great survivors.

SMITH: Modern-day relatives of the nautilus are squids, cuttlefish and octopus-- all cephalopods, a clan with a long and proud history.

Meet a face from the distant past.

Eyes for seeing, and hidden within a nest of 90 tentacles, a mouth for eating.

Primitive it may be, but this whole prehistoric package is jet-propelled.

The distant ancestors of the modern nautilus were the nautiloids.

We know them from their fossil shells, which in the early days were mostly straight.

MARK NORMAN: For hundreds of millions of years, these sorts of animals dominated our oceans and got to massive sizes.

Some of the straight ones got to ten meters long, so they were like giant telephone poles bobbing along, hoovering up trilobites.

SMITH: By the Cretaceous, it was the nautiloid's coiled cousins, the ammonites, who ruled the molluskan world.

Some grew larger than tractor tires, and they must have had an appetite to match.

Rich pickings were to be had throughout the Eromanga for mollusk and reptile alike.

Out here, even a long-necked plesiosaur needed eyes in the back of its head, for the Eromanga was the hunting ground of perhaps the greatest sea monster of all time: the pliosaur Kronosaurus.

So here we have just the skull of kronosaurus queenslandicus, the largest marine predator of all time.

We start at its snout, we go past these amazing teeth, these bone-crushing teeth, back to the back of the skull.

Here is where the actual eyes would have been, and right where I'm standing, two meters away is the back of the skull.

SMITH: This toothy monster was a meat-eating machine.

And we can even see what its last meal was.

SCOTT HOCKNULL: Right here is a rib cage of Kronosaurus, and inside its stomach we can see the vertebrae of its meal.

This is a long-necked plesiosaur, and it even preserves the stomach stones from this animal.

On top of that, we have turtle.

So this animal was eating long- necked plesiosaurs and turtles.

SMITH: These were the dying days of Gondwana.

Africa had long ago slipped off to the west.

Now India was gone, too.

Even at the bottom of the world, the strain between Australia and Antarctica was beginning to show.

Marking the boundary between the separating continents was a rift valley, rich in forests, lakes and rivers.

But this entire landscape lay within the Antarctic Circle, so close to the South Pole that in the summer the sun never set, and mid-winter would be dark for months on end.

And that made it interesting when dinosaurs started turning up here as well.

For over three decades, paleontologist Tom Rich has been on the hunt for bones of animals that lived in these primeval polar forests.

TOM RICH: There aren't many places anywhere in the world where you get polar dinosaurs, so that makes this site and this area particularly important.

Australia was one of the most isolated blocks of land at that time in the world, so things we might find out about this are things we won't find anywhere else.

It's almost as if there's an independent experiment in evolution going on here.

(dinosaur squawking) SMITH: Some of these experiments were small ornithipod species like these.

Outwardly conventional, these were rare dinosaurs, thought to be permanent polar residents.

Their bones lack signs of a hibernating lifestyle, suggesting they remained active right through the long, chilly gloom of the sunless winter.

But the dinosaurs weren't the only polar pioneers living in these dark forests.

Some had fur.

While reptiles may have ruled the world from the poles to the tropics, it's easy to forget they didn't have the planet all to themselves.

There was another type of animal hiding in these prehistoric forests.

They're still here, and there's one just over there.

The ancestors of the platypus have been poking their mammalian noses into the billabongs and waterways of Australia for at least 120 million years.

Proof is kept locked in this safe at the Australian Museum in Sydney.

It's another opalized national treasure: a tiny lower jaw from an ancestral platypus, a wonderful iridescent gem recovered from a Lightning Ridge opal mine.

Warm-blooded, furry, and for the most part small, the mammals we know existed at the time could hide and hunt in the shadows of the giants.

They were born survivors.

It went with the territory.

Like all empires, the reign of the dinosaurs was coming to an end.

And they might have seen it coming if they looked to the sky.

(explosions) (roaring) SMITH: When an asteroid slammed into Mexico's Yucatan at the end of the Cretaceous, the repercussions were felt around the world.

Though Gondwana and Australia escaped a direct hit, within an hour of impact, bits of pulverized Mexican seafloor flung into space began raining back down all over the planet.

In places, it would have turned the sky as hot as a giant rotisserie.

No good record of this bad day on planet Earth has been found yet in the rocks of Australia, but step across to the south island of New Zealand and you'll find hard evidence for the blanket of cosmic dust that settled over the planet.

This, believe it or not, is the moment that the world changed forever.

Now, it might not look like much, but this thin grey band of rock found around the world offers a remarkable window into one of the most dramatic events in the planet's history.

Below this boundary lie dinosaur bones, and rising in the rocks above is a world clearly recovering from a catastrophe.

The days were numbered for any Australian dinosaurs that clung on after the initial impact.

A tremendous darkness, it's thought, in the form of soot, dust and smoke settled over much of the world in the immediate aftermath, lasting months, years or even decades.

Temperatures plummeted.

Plants withered.

Dinosaurs disappeared.

The great lizards were gone, but the show was far from over.

The tremendous calamity at the end of the Cretaceous had cleared the global stage, though this time not simply for the next scene in the great drama of life on Earth, but for the appearance of the Australia we know today.

of "Australia's First Four Billion Years," The adventure co an adventure way down under... Blimey, this is tight!

...reveals the key to the kangaroo's story and the giant evolutionary leap that led to a continent of strange creatures.

Huge wombats, huge kangaroos and giant koalas.

Now, this little guy, he's a truly famous Australian.

The story of Australia is written not only in the rocks, but on them as well.

Next time on "Australia's First Four Billion Years" on NOVA.

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Episodes of "NOVA" are available with Passport.

"NOVA" is also available on Amazon Prime Video.

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