Original subtitles

This is where you feel vulnerable, swimming in with a chunk of bait.

A Dunkleosteus. This is what we came for!

Oh!

This is Nigel Marven.

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

But his latest adventure is really 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 the Earth has ever known.

He's experienced three of the deadly seas,

and from here on it's only going to get worse.

He's about to meet the owner of these jaws,

and worse still, the most lethal shark the world has ever seen.

But only if he can escape the Devonian seas

and an armored fish called Dunkleosteus.

He's coming in again, he's fast this time.

Ah! Slammed the cage again.

This is getting serious. He really walloped the cage.

Dented the bars there. He really wants this bait.

I want to win the bet I had with the crew.

This sea monster, I'm sure he can slice through chain mail.

He's coming closer.

Ah, God! Nearly wrenched my arm out of the socket.

And he's chomping through now.

Slicing through it, chain mail and all.

And I have won my bet.

There's a little Dunkleosteus here. Right underneath me.

He's looking for little tidbits.

These armored fish flourished for around 50 million years,

then all of them became extinct.

Whaa!

Wow!

Listen to that.

It makes you shudder.

The big predator is crunching that juvenile,

crunching the plates.

The Dunkleosteus was certainly showing its true form.

It's not just a predator, it's a cannibal as well.

And as for its table manners...

Believe it or not, this is normal behavior.

The Dunkleosteus isn't being sick.

A fish like this that feeds on armored food

needs to get rid of the indigestible bits,

and it's regurgitated the bits of fish armor and, in this case, the chain mail,

and this is perfectly normal.

Normal for 360 million years ago, maybe.

But there's no time to rest on laurels.

They've yet to reach the halfway mark

in their voyage through the most perilous seas of prehistory.

Ahead of them are four more deadlier encounters.

Next up, our time-traveling crew heads to an era closer to the present day.

In fact, it's a mere 36 million years ago,

which is midway between the extinction of the dinosaurs and modern day.

It's home to the meanest sea mammal that has ever lived.

This must be one of the squelchiest of habitats. Mangrove swamps.

They're lush, muddy and there's water everywhere.

As far from a desert as you could imagine.

But believe it or not, this will one day become the Sahara.

I'm on the site of what will become Cairo.

If I stood here for 36 million years,

the Egyptians would come and start building pyramids on my head.

The Eocene is the beginning of the time of mammals.

They rule the Earth, they rule the sea,

and as I was about to find out, they even rule the bit in between.

These look really promising, look.

The feet have splayed like a camel's,

to support the weight, spread the weight so they don't sink into the sand.

But it's a really curious track - they're widely spaced.

Most animals, it's one foot in front of the other.

It's as if this animal swings its weight from side to side as it's walking along.

This is really weird.

It must be a big, big animal that waddles along.

Let me see if I can...

(CHUCKLES)

Every tracker's dream, look.

A pile of fresh dung.

So fresh you can almost feel the heat emanating off it.

The Inuit, it's rumored that they eat bits of dung

to learn about what they're tracking.

I want to give that a miss, but...

If you smell that, it's sweet, not too unpleasant.

A sweet smell, and I think the animal I'm looking for is a fruit eater.

(DEEP BAYING)

Here he is, come on.

Keep quiet.

It's the only animal that waddles like that.

It is a surreal creature with a funny name. It's called an Arsinoitherium.

These creatures have extraordinary horns.

This is a male - they splay out. The females, they're much more vertical.

And this is what he uses for defense and for fighting.

They've got disadvantages, too.

He's looking at me, but he can't look because the horns are covering his eyes.

He knows we're here,

but he's not approaching or anything, not running away.

He's edgy, but I really want to get a closer look.

Come on.

I'm gonna try something.

See whether he'd like to eat something from the 21st century.

(SNORTING)

He might look like a rhino,

but this mammal is more closely related to the elephant.

More surprising still is that it lives like a hippo.

Arsinoitherium is a sea monster, after all.

Well, at least an amphibious one.

There's plentiful food in the mangroves for a huge vegetarian,

but living here is difficult. A beach in the morning is a lagoon by midday.

Arsinoitherium, though, is adapted to deal with the changing tides.

A creature that's as happy in water as on land.

In fact, probably happier.

The Eocene is a momentous time for mammals.

As well as amphibious species,

new types have evolved which are totally adapted to life in the ocean.

Here were some of them.

Dorudon.

A species of ancient whale.

And whales were the reason I'd come here, though not for these tiddlers.

I was after a far bigger, meaner whale that eats Dorudon for breakfast.

It was time to find the tyrant that rules these waters.

We're sailing right here in the middle of the Tepis Sea, between Europe and Africa.

This is a pretty unfamiliar map, because it's not like this in the 21st century.

This sea closes up and dries up,

and we're actually sailing over what will become the Sahara Desert.

And this...is the monster that we're looking for.

Basilosaurus, that name means King Lizard.

When these fossils were found in 1832, they were thought to be giant reptiles.

But this is a primitive whale.

Here's an artist's impression from around 1960.

As you can see, they thought Basilosaurus were reptilian, too,

just like sea serpents or even the Loch Ness Monster.

And this skull is what's chilling to me.

There's no whales with skulls like this in modern times.

Great peg-like teeth at the front for seizing prey.

Once in the mouth, the prey is sliced up by these big teeth at the back,

great big cusps at the top.

They are for slicing through flesh.

This is by far the biggest predator in the Eocene seas.

Drop the anchor.

But how on Earth do we find one?

The configuration of the bones in the fossil skulls of Basilosaurus

is really good evidence that they can hear well.

Modern whales are so noisy, and we hope that Basilosaurus is the same.

We've got underwater recording equipment, and if we can eavesdrop on them

we should be able to locate the whales.

Fingers crossed on this one.

(SILENCE)

Nothing, it's just shrimps and fish, no whales there.

Nothing there.

Move off somewhere else.

Nigel.

I think we've got something.

That is spooky. It's definitely a whale. Maybe we've found Basilosaurus.

(GHOSTLY CRIES)

(MOURNFUL CALLING)

The whale's still in the vicinity, but where?

Sound travels much further and faster in water than in air

and he could be miles away.

What we need to do is try to entice him to us.

That eerie sound you're hearing, that's what we recorded earlier.

We're playing his calls into the ocean with a massive speaker.

Hopefully, he'll think there's another whale in his territory and come to us.

Scientists have tried this with modern whales with mixed success.

But it was the best hope we had of bringing in a Basilosaurus.

Getting louder.

(TRILLING AND SHRIEKING)

(SHOUTING)

We don't know how long these animals have been hanging around.

We've got to be fast on this one.

I had no idea what I'd find.

This is exciting. It could come from anywhere beneath me. Behind me.

So I'm using the boat as a shield.

This big shape, it's as though there's a really massive super-predator around,

so they won't come in too close.

They haven't got as big a brain as the modern whales,

so they may treat a person as prey.

Ah, wow!

And there it was. The long, streamlined shape - this had to be Basilosaurus.

It was nothing like the sea serpent of early drawings.

It was a whale, but unlike any I'd seen before.

No blubber. In this warm water it didn't need it.

It looked for all the world like a whale on diet pills.

And look at this thing.

Compare it with the boat, that gives a great idea of scale.

And he's over half the length of this 80-foot boat. 50 feet or so.

And this really is a fearsome predator.

I'm glad I'm next to the boat. I wouldn't fancy being in open water with this one.

(EERIE CALLING)

I wish the sound technician would turn this off.

It's really starting to distress the whale. He's coming in close.

(DEEP GROWLING CLICKING)

Ah!

He's bitten the speaker off.

He's shaking it like a terrier shaking a rat.

So we've lost our speaker, but it doesn't matter.

We had a really brilliant view of a Basilosaurus.

This, though, is a world on the verge of great change.

Africa is moving north towards Asia and Europe,

causing this ancient seaway to disappear.

Basilosaurus will disappear with it.

Next in store is the Pliocene,

the time when our earliest ancestors were starting to walk upright.

It's surprising what lived in our seas just four million years ago.

We're in Peru, right on the rim of the Pacific Ocean.

And living out there, there's something terrifying.

So if you're afraid of sharks,

you'll be a gibbering wreck when you see what we're gonna try next.

Look. The most famous jaws in history, a Great White Shark's.

I've swum with those in the open ocean,

but they're minnows in comparison to the prehistoric shark I'm hoping to meet.

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

That name Megalodon, what it means, it means Big Tooth.

And I don't think I need to explain why.

By hunting a Megalodon, we were getting into ever more dangerous waters,

and caution had started to creep in amongst the crew.

There was disagreement about our course of action.

I think we should head out into the deep water. Let's look for the adults.

- No. We should start with the juveniles. - We haven't got time to do that.

We should go for the smaller ones.

We couldn't say how Megalodon would behave.

Some argued that it would be worth studying juveniles,

before risking a dive with an adult.

In the end I had to agree.

I'll do one dive with the juveniles,

and then I think we ought to head out into the drop-off and find the adults.

With sharks, it's all about diving in the right place.

Like young Great Whites,

juvenile Megalodon tend to be in shallow water, away from the adults.

Partly for their own safety, but also they do prey on different things.

There shouldn't be any adults on this dive.

I'm hugging the kelp. I don't want to be caught in open water.

Big predators don't like going into dense weed like this.

I'm hoping to find the creatures that juvenile Megalodon prey on,

and they are the oddest of creatures.

There! Odobenocetops leptodon.

That name is a mix of Greek and Latin.

It means ''the whale that walks on its teeth''.

If it turns towards us, you can see why.

One tusk is about a foot long,

but on the other side, the right-hand side, it's three feet long.

The males probably use those for jousting with each other in the breeding season,

just like narwhals.

They are superb!

Flippin' heck, look!

I can't take my eyes off that.

The biggest Great White Shark ever was just over 20 feet long.

That thing must be just three years old and that's that size already!

Just imagine diving with a full-grown Megalodon,

20 times the weight of this one.

What had I let myself in for?

We'd seen a juvenile Megalodon, but we hadn't yet learned much about them.

I specifically wanted to see how they hunted.

We couldn't just wait for an attack.

We needed to make it happen.

This Odobenocetops wouldn't fool you or me,

but as a decoy it will fool the juvenile Megalodons.

If they're like Great Whites, when they see this in silhouette,

they should come up to investigate and it will enable us to learn more about them.

Our dummy didn't swim as well as an Odobenocetops,

but the young sharks didn't seem to be put off by that.

After just 15 minutes, our onboard camera got the shock of its life.

Look what's happened to the decoy. Did it hit from below?

- Straight up from underneath. - See the damage.

Megalodon has one of the same hunting techniques as Great White Sharks.

They can't afford to be injured by their prey.

They sneak up from below and attack.

The power of that big fish, look what it's done to this decoy.

This is weaker than a real animal, real sinew and muscle,

so that's why it's smashed it in two.

But if this was a real animal, it would bleed to death.

The shark would come in when it was weak and then make the final coup de gr�ce.

Megalodon are probably relatives of Great Whites,

and we now knew that the juveniles attack their prey in a very similar way.

But what about the adults?

How did they hunt?

And what does a shark over 50 feet long prey on?

Leaving the juveniles behind, we took our boat a few miles offshore.

It was time to meet a monster.

Drop the anchor.

Anyone who's tried to get close to sharks knows this eye-watering stench -

the smell of chum. That's a mix of fish blood, fish oil, bits of fish pieces.

We throw that over the side.

A trail of odor will go for miles in the current.

A Magalodon will smell that and zigzag towards the boat.

We've got this amazing delicacy for it, a great big bag of fish chunks.

And that should entice it.

And if they do come, what we've got here is Shark Cam.

There's a camera in this. We want an insight into the world of the Megalodon.

I've got to get close enough to attach it to the base of the massive dorsal fin.

This will dissolve in a couple of days.

The camera will pop up to the surface.

We'll find it and get some insight into the behavior of the wild Megalodon.

There's something to the left over there.

- Are you sure? - Yeah, I'm pretty certain.

Look at that! It can't be anything else but an adult Megalodon.

It's more like a sail than a fin. Now we get the cage into the water.

You can see the blood and the fish oil leaking out of the chum bag.

I need to be prepared with the camera. We may only get one chance.

Who knows how long the Megalodon's gonna hang around?

This is scary. I'm scared.

It's coming straight for the cage.

Oh, look at that!

Nothing prepares you for this.

I feel like just shooting to the surface and getting out of this cage.

But I've got to pull myself together.

I must admit I am really, really scared of this.

He looks like he's taking a pass now where he's gonna be really close.

Let's see whether I can get the shark cam on.

Argh! Missed that time.

I've got to get the camera onto the fin.

Argh!

This is hopeless. This is harder than I thought.

The fin is just too high.

And he's coming straight at the cage.

I can't attach the camera from the cage, so we'll try from this platform.

The chum ball, don't put it over the side. Keep your eye on the shark.

See if you can get it in a line along here, please, and I'll be ready.