Original subtitles

Megalodon. The biggest carnivorous fish that's ever lived.

And it would be so fantastic if I could get this camera onto this guy.

I'm gonna try from the platform.

Keep the bait ball above. Watch the shark. Get it in a line.

This is Nigel Marven.

He's a zoologist, and an expert in tackling dangerous animals.

His latest adventure is testing his nerve.

He's left the safety of the 21st century behind and traveled back to prehistory.

His mission, to visit the seven deadliest seas of all time,

and to come face-to-face with the most terrifying sea creatures ever known.

So far he has made it through four prehistoric oceans,

but ahead lie the two most dangerous,

inhabited by the nastiest collection of predators nature has yet assembled.

And he still has to get past a 50-foot shark called Megalodon.

You idiot.

Don't move that chum bag till you can see the shark.

Winch it up quick.

(CLAPPING)

I'm sorry I called you an idiot. I was scared when I fell in.

- Well done. - I hope we get some shots with that.

The camera was designed to break away from the shark and pop up to the surface.

After a couple of days, we picked up the signal.

There it is, just ahead of us.

Come on. You should have a precious and unique cargo.

The camera seems OK, no damage.

Just a bit of shark fin.

It's rubbed this off on rocks on the bottom.

I just hope it was on long enough to get some great footage.

This was so exciting.

The camera had survived whatever ordeal the shark had put it through.

We were in the Pliocene, observing a day in the life of a Megalodon.

And if that wasn't fantastic enough, this happened.

There's a silhouette. Whether it's an Odobenocetops or whatever...

Can you see that?

This could be great. If we got a kill...

He's going down. He is attacking, look!

Crikey!

Wow. Let's see that again.

The footage we got with the shark cam, it's better than I could have ever hoped.

Just watch this.

There's a shape up there.

It's not an Odobenocetops, it's actually a species of whale.

The shark's gone down so it can get more momentum.

It's accelerating now...

And the violence of this impact... Look!

A cloud of blood. That knocked the camera off.

And Megalodon, it's a species of shark that actually attacks living whales.

And pretty big ones at that.

But even this, the ultimate shark,

will be unable to defend itself from the coming Ice Age.

As the oceans turn colder,

whales, with their high body fat, will adapt and move to the icy polar regions.

Megalodon will be forced to stay in the warmer water around the Equator.

Deprived of its prey, it will be starved into extinction.

It's time for Nigel to leave this, the third most dangerous sea, behind.

Next lies the Jurassic.

To reach it, he has to travel back from four million to 155 million years ago.

The Jurassic is right in the middle of dinosaur time,

and it's home to some of the most colossal animals ever to live on land,

outweighed only by the monsters that live in the water.

I've come to the Jurassic 'cause this is a land of monstrous creatures.

On the land there are giant dinosaurs, and here in the water...

Well, look at that!

That's a shoal of Leedsichthys, the biggest fish that have ever lived.

As big as those fish are,

there are predators nearly as large that attack them.

That's what I'm here for,

to see some of the most massive marine reptiles that have ever lived.

Well, they must be 75 or 80 feet long.

These shoals of giants

are sustained by the tiniest creatures that live in the sea.

They filter out any tiny plankton, any small animals floating in the ocean.

At this time of year though, they're living on their fat reserves.

And that really sorts out the healthy fish from the sick ones.

You can see over there, there's one that can't quite keep up with the shoal.

It's just at the edge there.

Already it's attracting some of the smaller predators in these Jurassic seas.

And there, over there, Metriorhynchus. You just wouldn't expect that.

It's a kind of marine crocodile.

It's totally adapted for a life in the sea.

Great paddle-like feet, nothing like modern crocs.

Look at the tail. There's no armor plating.

This creature has sacrificed defense for speed.

Wa-hey, that's just a bit close.

Go away.

Look at that...below me.

It's a most bizarre shark, called Hybodus.

See those strange horns on the top of its head.

It's going in to feast now.

Look at him twisting. Twisting to get a chunk of flesh.

And, oh, you feel sorry for the Leedsichthys.

They're actually eating it alive.

It is pretty unnerving, being here right next to the shoal.

You've got to worry about sharks, marine crocodiles.

And I haven't even seen the really massive reptile I've come here for.

But I wouldn't have long to wait.

No large predators on the first dive, but there's potential prey.

This is the injured Leedsichthys. We're tracking it with an acoustic tracker.

It's bouncing back off the injured fish.

Not moving very fast, but we need to move to starboard now.

As we saw, the injured Leedsichthys is drawing in crocodiles and sharks.

And before long, something much bigger is bound to come in.

This is it! Four flippers, that short compact neck.

It's approaching the Leedsichthys.

That is colossal, and I'm sure this is Liopleurodon.

The biggest carnivorous reptile ever, and it is closing down on the Leedsichthys.

Peter, can you get the pole cam, mate?

As quick as you can.

It's deep. I'll look on the monitor, see if I can guide you.

Move to the left, mate.

Deeper.

As I thought. It's a Liopleurodon.

Look at those flippers. It's really had a go at the Leedsichthys.

It's not moving a fin. It must be dead now. We've scared it.

It's disappearing into the murk, Pete.

Fantastic. Well done, mate.

Those Liopleurodon are awe-inspiring sea monsters,

and it would be a thrill to see them under the water.

But I'd need protection. The technicians and I have come up with this smell suit.

Liopleurodon have an acute sense of smell, and we'll use that to protect me.

What we do is put a bottle on here, a bottle of noxious chemical,

and if the Liopleurodon get too close, if things get hairy,

I'll switch a valve, there'll be an explosion of chemicals into the water.

The chemical is called putricine. That's essence of rotting reptile flesh.

Hopefully, that will keep them away from me.

Why did we decide on putricine?

We did some field trials with young Liopleurodon in shallow water.

We put the smell suit around a dummy, weighted it down, put it on the bottom.

You can see they're putting squid in the suit.

That's to get the Liopleurodon excited, get a feeding frenzy

and see how they'll react to the smell suit.

And now it was a matter of waiting.

In the first experiment, the suit had a deterrent that keeps sharks away.

We wanted to see what would happen with these reptiles.

They're very curious about these squid.

See the release of the chemical? Had absolutely no effect.

You'd have had your head bitten off.

The next experiment, we filled the smell suit with putricine.

There's still squid on the dummy, they know it's not a danger.

Here come the Liopleurodon. See that, the putricine's released.

Another one comes in, mouth open, gives it a whack.

I hope it doesn't whack me like that!

But hopefully that will give me some protection when I go in with the adults.

Two...three, four, five.

A Liopleurodon, perhaps even a pair, have come back to the carcass.

We've lost the light, but that doesn't matter, they live in a world of smell.

We've got light so we can see. It's gonna be spooky though.

I'm relying on the smell suit. The cameraman's got one, too.

And we'll swing her out.

Oh! Goodness!

It's enormous.

Well, I am so glad the camera's here. Nobody would believe me back at home.

That's a cracking view of those teeth. They are so distinctive,

that rosette of really sharp teeth at the front of the jaws there.

They are like knife blades.

They are piling into that fish carcass,

slicing through the flesh of that Leedsichthys.

That short neck, that helps them to be more powerful.

That's why they can twist off chunks of flesh.

They're not paying any attention to me.

That food is really keeping them occupied.

So I think I can take a calculated risk.

If they do go for me, I've got the smell suit.

So I'm gonna move in as close as I dare.

I am just 20 feet away

from a feeding frenzy of some really ferocious sea reptiles.

But I am petrified watching this.

Ah, it's coming in so close.

Argh!

Thank heavens this smell suit works.

But it's time to get out of here.

Hold on, Nigel, you're not done yet.

That was the second most dangerous sea,

which means it's time to enter Hell's Aquarium, the most dangerous sea ever.

It's just a short hop forwards from the Jurassic to 75 million years BC,

not long before a massive meteor ploughs into the planet

and marks the end of the dinosaurs.

That same cataclysmic event

will also be the end of most of the sea monsters that we're about to meet.

(DIN OF SQUAWKING)

A familiar sight on the coast of the Cretaceous.

These birds are called Hesperornis.

They are so vociferous it's deafening being in a colony.

They're flightless, like penguins, but they're far from as cute.

Look at those dagger-like bills, and inside there they've actually got teeth.

But just to hold their own, Hesperornis have to be tough.

They're around at a time when there are truly awe-inspiring predators.

On the land, there's T-rex.

In the water, well, every time Hesperornis go on a fishing trip

they have to enter the deadliest sea of all time.

Why is this sea more deadly than the others?

There's not just one predator, there's a whole suite of them.

There's frightening sharks, terrifying sea reptiles...

Even the fish. You couldn't imagine them in your worst nightmares.

I call this Hell's Aquarium, it's so jam-packed with killers.

This is where Hesperornis spend much of their life.

They're amazingly adapted for diving,

with specially heavy bones to stay submerged.

But few Hesperornis live to a ripe old age,

because in this sea there are so many ways to get eaten.

To the right a bit.

Oh, my goodness.

Keep going right.

There's a real blood patch.

Pass the periscope, please.

With this, I should be able to have a peep into this bloodbath.

I'd love to see what's going on. It's such a flurry of activity down there.

There's a shark right in the middle of the feeding frenzy.

Don't know what species.

What is that?

That is one grotesque fish.

That's more like a bulldog than a fish.

If the devil kept fish, this would be one of them.

Xiphactinus, a predatory fish over 20 feet long.

There's a big one coming right at the periscope.

It's got a Hesperornis in its mouth.

Hesperornis are over six feet long, and it's swallowing it down in one go.

Something else there looked familiar:

the ominous shape of a Mosasaur.

These I'd read about.

They're the ruling class of marine reptiles in the Cretaceous.

Their serpentine shape is no accident, as they're closely related to snakes,

but they're far more ferocious and way bigger.

This species near the coast is just a tiddler, a mere 10 feet long.

But offshore lurk 60-foot giants.

And that's where we were heading.

We're going into deeper water on our mission to find giant Mosasaurs.

We're sailing right over the top of Kansas, which sounds weird.

This is the map of the US that we're used to,

but now in the Cretaceous it's totally different. Look at that.

The central United States are covered by a vast inland sea.

I can't dive in that sea. Mosasaurs are much too dangerous.

And up here, to give us early warning, the acoustic tracking device.

We've got cameras on the prow. This is the view from the forward-facing one.

This is the backward-facing one.

If the Mosasaur comes near, we'll get views on video.

This is something we are particularly proud of.

This is a remote-operated vehicle with a superb camera.

It would be foolhardy for me to swim with Mosasaurs,

but we're hoping we can get this right alongside them.

We soon had company.

With its huge size and characteristic crest, this could only be one thing.

Not a bird, but a flying reptile called Pteranodon.

They catch fish in these waters, but this is Hell's Aquarium,

so occasionally the fish catch them.

The next morning, we were in for a nasty surprise.

(CRASH)

What the heck was that?

We hit something with a tremendous clunk.

And, look, it's the body of a turtle, like no turtle alive in the 21st century.

It is huge. I think it's an Archelon.

And you can see it has been bitten in two.

It's a shame. I'd love to see one of those alive.

But it proves that we're in giant Mosasaur country.

Nothing else could have done damage like that.

On we sail through Hell's Aquarium, watching and waiting for giant Mosasaurs.

(GROWLS)

(CREWMAN) Nigel, this is interesting.

Those creatures are going right under the boat. This could be it.

Not a Mosasaur. Some of the most exciting of sea reptiles.

I've always wanted to see these.

Elasmosaurus. That was the front camera.

This is the camera facing backwards. Look.

They're riding our bow wave, just like dolphins.

Maybe these are migrating.

Can we stop the boat?

This was a perfect opportunity to try out the ROV,

with its remotely-operated camera.

They're not scared of it. They're diving, can you go deeper?

They're coming really close.

Look, this one's investigating.

Look!

Those small heads on those long necks may be a way to deceive prey.

Fish will be frightened by big bodies,

but the Elasmosaurus can sneak those heads into a shoal,

and then strike.

Gosh, a living Archelon!

One of those giant turtles.

I said I couldn't dive in this sea. It's just too dangerous,

but I've got to get in with that.

It's a bit risky going in here, but the ROV should be guarding me,

keeping an eye out for any predators lurking around.

And I just can't resist a ride on an Archelon.

He must come up again for air soon.

(SONAR BLEEPS)

What was that?

- Where is he? - Is Nigel back, Pete?

Get him out. There's something big on the tracker.

OK, just got to find him first.

We've got to find Nigel. There's something down there.

I'm so relieved to be back on here.

I'll tell them we're coming.

Ancient Mariner, Nigel here.

How was the dive, Nigel?

It was a thrill to be riding the turtle, but at the end, that was scary.

We're on our way back now.

OK, Nigel. Over and out.

(SQUAWKS)

The rope's what...?

Can you see him on the ROV?

(NARRATOR) The ROVhad seen it all.

Perhaps mistaking the boat for a turtle,

the top predator of the Cretaceous had homed in on the crew.

If there's one thing worse than swimming with a 60-foot carnivorous reptile,

it's swimming with its family.

Giant Mosasaurs often travel in groups to protect their young.

Move away from the boat.

They will attack anything that moves -

sharks, turtles, giant squid,

even other Mosasaurs.

With three humans and an upturned boat, they were spoiled for choice.

So far, they were choosing the boat.

Of the seven deadliest seas of all time, this was the worst.

Thanks. Everyone OK?

And the worst was over...

That shook me up. There's still blood in the water.

..almost.

(SONAR BLEEPS RAPIDLY)