Original subtitles

The congo basin, central africa,

One of the wildest, most remote parts of the planet.

Within these waterways lives a predator few have heard of,

Ancient,

Cold-blooded,

Yet intelligent.

Little is known about it,

Because few have dared to explore here.

But recently, humans did,

And they made an astounding discovery.

They found deep caves riddled with swarms of bats,

And staring back at them,

Crocodiles,

Living in the bowels of the earth.

These crocs had weird orange skin and huge eyes.

Now some of the original explorers are back.

To uncover the mystery of the cave crocodiles of gabon.

The strange orange creature that they saw

Was a dwarf crocodile.

Of the 27 species of crocodilians,

This has got to be the most elusive.

Dwarf crocs only grow to six feet,

But what they lack in size, they make up for in attitude.

Like a heavily armored komodo dragon,

Equipped with reinforced bony-plated skin,

Razor-sharp teeth, giant eyes

And powerful long legs that propel it in water and on land.

Dwarf crocs live in small streams and flooded forests,

But this is the first time

They've been found living in caves.

Crocs regulate their metabolism using sunlight,

So how are they surviving underground?

We all know their cousin, the nile croc,

A giant, up to 22 feet long.

It's a predator that launches its attacks from water.

Dwarf crocs are totally different

In that they spend much more time on land.

They stand higher, on long legs.

Front claws and rock-hard nails

Give traction across forest terrain.

This raised body enables them to push through mud

And scramble over logs and exposed roots.

But like all crocodilians,

It's totally at home in water too.

At night, the dwarf croc reveals

Its terrestrial hunting powers.

Its pupils, which are narrow, vertical slits during the day,

Are now wide open, letting in more light,

Allowing it to see in the dark.

It sweeps the leaf litter with its tail,

Disturbing grubs underneath.

Despite their venom,

Centipedes make a great high-protein snack.

This flexible hunting style may explain

How this species is able to survive in deep caves.

But what drew them in there in the first place?

It's the dry season in gabon,

The best time of the year

To try and solve some of these riddles,

Because the water level is low and the caves are accessible.

Since herpetologist matt shirley first saw

Orange crocodiles in the caves,

It's been his quest to unravel this mystery.

Expert caver olivier testa has

Also been to the caves before.

Olivier will be in charge of safety and cave navigation,

While matt attempts to catch and study the orange crocs.

Dwarf crocodiles are considered to be

One of the least known crocodilians of the world,

As are most of the crocodilians in west and central africa.

As this is one of the only known populations

Of crocodiles in the world of any species

That inhabits full time a cave ecosystem,

Our objective is to better understand

How are they surviving in there

And what is this lifestyle doing to them as a population?

Is it driving them down another evolutionary path

Away from their forest neighbors?

The objective is to find out as much

As we can about these animals.

It's just a really fascinating system.

Crocodilian ancestry

Dates back further than you think.

65 million years ago,

A catastrophic event wiped out most of the dinosaurs,

But crocodilian ancestors survived

Within their aquatic habitats.

Today there are 27 different species,

Ranging from the alligators and crocodiles in america

To gharials in asia and nile crocodiles in africa.

Previously, it was thought there was

One species of african dwarf croc,

But in the last decade, scientists discovered

There were actually three distinct species.

Matt wants to know if this cave population

Could be showing signs of diverging again.

There's a reason why these crocs

Were only recently discovered.

This is one of the most inaccessible

Places on the planet.

A land of snaking rivers and forests.

Below the canopy lies a secret world rarely seen by humans.

The only way in is by boat.

Matt and olivier catch a ride upriver as far as they can.

Then they'll hike.

To find and catch a crocodile in a pitch-black,

Confined space requires a certain skill set.

Matt's called in backup from wildlife guide kharl remanda.

He knows the terrain better than anyone.

The team don't have long.

It's called a rainforest for a reason.

The dry season is short.

A deluge will flood the caves,

Making them impossible to access.

Olivier has gps coordinates,

But the jungle has consumed any previous paths.

If they get into trouble here, no one can help them.

They're in africa, and that means forest elephants,

Driver ants, whose bite feels like a hot poker to the flesh,

And secretive leopards.

The constant heat and high humidity

Can lead to rapid exhaustion.

It's these threats that have kept explorers away.

For most, a pitch-black, stinking cave system

Full of crocodiles is a nightmare.

This is not going to be an easy search.

Finally they reach one of the cave entrances.

Few humans have set foot in here

And there's a good reason why.

As the men walk deeper, they are overrun with insects,

Cave crickets, spiders and tens of thousands of bats.

The air is thick with ammonia fumes

From tons of rotting bat feces.

There could be fungal spores

And dangerous pathogens down here too.

They check for crocs along the edges of the cave walls.

The tunnel narrows.

If matt finds a croc now, he'll have to face it head on.

His years of catching crocs has led him to this moment.

The dwarf croc is compact,

But their strength can't be underestimated.

Their bite force is almost as strong as a nile croc.

The solid ground turns to bat guano sludge.

Fresh tracks...

Here's lots of tail drags,

Footprints and body drags of crocodiles.

So for example, this track right here,

It's quite big, it's quite fresh.

Let's go.

If they meet a large croc now,

They won't be able to run!

They're crawling through guano soup.

Suddenly, a strange noise,

The distinctive sound of baby crocs.

Mother could be close by.

Matt could be in big trouble.

Little one.

It's a juvenile, maybe three years old,

And the mother is nowhere to be seen.

This youngster is an exciting find.

It proves the cave crocs are reproducing.

Matt needs to study it,

But getting out of the tunnel is another story.

Matt's still never seen any evidence of nesting down here.

He thinks the mothers are leaving the caves

During the rainy season to lay eggs in the forest.

He's seen remnants of nests just outside the caves.

Dwarf crocs are very particular when it comes to their eggs.

They gather a large mound of leaves from the forest floor.

Within this, they lay up to 20 eggs.

This building happens in the dead of night

And it's never been filmed until now.

This dwarf croc is busy tending to her nest.

She's laid her eggs inside this mound.

For the next 100 days, her sole job

Is to make sure the nest stays intact,

Tidying any leaves that may have gone astray.

The leaves decompose, generating heat,

Which keeps the eggs warm until they're ready to hatch.

Down in the caves,

Matt's recorded the data. Here.

Now he releases the young croc.

He still hasn't found any of the legendary orange adults,

But his luck could be about to change.

In a tunnel filled with bats,

The team close in on much bigger tracks.

They lead through a narrow bottleneck.

Can you see him?

No.

Matt is too big to get through.

The passageway curves

And kharl follows the tracks as far as he can.

The croc has gone into a small crevasse.

That crocodile is way out of our reach.

He took this tunnel down here to the right,

So let's get outta here.

The cave system is made up of large tunnels,

Intersected by narrower passages

That the crocs travel through.

Their only chance is to try and catch it on the other side.

Matt heads around to try and intercept the croc.

Kharl, yo, the groove.

It's a big one, around five feet long.

To study it properly, he has to catch it.

He uses a soft noose.

Now he has to get close enough to grab it.

Matt's noosed a cave croc, but it's lodged in a crevasse.

Crocodiles have incredibly strong tails.

This one has wedged itself like an anchor.

Kharl tries to free the tail.

Eh, eh, eh, eh, eh, okay.

But it's locked on tight.

He tries from another angle.

Eventually his plan works. Okay, go.

Yep, yep, he's out!

Okay. Nice.

Okay, I got him now.

They need to be as careful as possible.

It's a big one, aye?

It's one of the biggest dwarf crocodiles I've ever seen.

Matt quickly secures its jaws.

The croc can lunge and clamp onto prey

With bone-crushing force in microseconds.

The capture was exhausting.

They're now deep inside the caves.

It's sweltering.

Air is heavy with gases from the decomposing guano,

And breathing is getting difficult.

They need to get to the surface as quickly as possible.

Okay.

The croc is safely secured for the journey.

By studying each croc he finds,

Matt hopes to understand more about their unique lifestyle.

Dwarf crocodile populations are threatened

Across their range from gambia in the west

To the congo in central africa

Due to habitat loss and bushmeat hunting.

From the data he's collected, matt believes there could be

Up to 200 crocs living in these caves.

Finding out how they're surviving is vital

To protecting this isolated population.

Voila.

Above ground, he can finally get

A good look at this mystery creature.

This is a fully-grown adult,

Which might seem small for a crocodile,

But at around five feet long,

This is larger than most of the dwarf crocs

Living in the surrounding forest.

He checks its sex.

Definitely male.

It's in good condition.

Cave life is obviously treating these crocs well.

It weighs in at 53 1/2 pounds,

A little over average for a dwarf croc.

Some of the specimens found on previous expeditions

Had a strange orange coloration.

A quick scrub down reveals this one

Is the common black color.

It's not an orange croc.

The burning question remains.

How does a creature evolved for forest life

Survive in the harsh cave environment?

Above ground, dwarf crocs live

By the rule of little and often,

Snacking on frogs, fish, crustaceans and insects.

They adapt their diet to what's in season.

What will it be today?

Catfish.

Lightning-quick,

He knows chasing them down would be fruitless,

So he opts for plan b.

Sit and wait.

Let the fish come to you.

He can hold his breath for over four hours.

A flap of skin in the throat

Closes his windpipe so he doesn't drown.

Sensory pits around the jaw and along his sides

Detect tiny pressure changes in the water,

Allowing him to feel the movements of his prey.

What the catfish thinks is a submerged log

Is actually a camouflaged killer.

Crocs can't swallow underwater.

He has to surface to eat.

His highly acidic stomach will do the rest,

Able to break down flesh, scales and bones.

Nothing is wasted.

Their skin is another asset in surviving cave life.

In latin, their name osteolemus means bony.

Their tough skin is reinforced with osteoderms,

Free-floating pieces of bone,

Making them invincible to even the strongest jaws and claws.

But in this forest, the most deadly attacker

Is no bigger than your fingernail:

Driver ants, swarming in their millions.

These vicious carnivores attack

And consume anything in their path.

The croc goes into lockdown,

Shutting down all vulnerable parts of its body.

The ants seek out any weak spots they can attack,

But evolution has ant-proofed this croc.

He just has to sit it out.

Eventually the ants give up.

In the caves, this armor could seal the crocs off

From the rocks and acidic bat guano.

Crocs typically need the sun

To regulate their body temperature.

Voila.

So what caused these crocs to move

Into the pitch-black caves?

Matt's about to find out.

He prepares the croc for a stomach contents test.

He's never seen the cave crocs hunting.

This is the most reliable way

To find out what they're surviving on.

Stomach contents are about to reveal

How the crocs are surviving in the dark caves.

It doesn't harm the croc,

And each sample collected will contribute

Towards the conservation of this unique population.

Okay.

Cricket, some kind of.

A big beetle.

Matt finds the remains of crickets and beetles,

And something more unusual.

Those are small rocks that crocodiles ingest

That helps them do the mechanical digestion,

And then the rest is, yeah, it's all bat hair,

Eating tons and tons and tons of bats.

The big mystery is, how can a rugged reptile

Catch such fast, airborne prey?

Matt's hoping to find out.

Dwarf crocodiles are territorial,

So he makes sure to return the croc

Exactly where he found it.

This cave offers shelter and protection from predators,

But the stomach contents show

What they really came here for:

Bats.

So how do they catch them?

It's late afternoon and the bats are stirring.

They would be easy pickings, if only the croc could climb.

They start to leave the caves en masse.

Fruiting trees in the forest are a dinner bell.

The sweet smell of ripe mango

Lures them out in their droves.

Matt waits for any evidence of hunting.

In the traffic jam, some bats collide and are grounded.

Thin wing membranes clog with slimy guano.

A croc waits in the shadows, but it knows matt's there.

He's seen enough.

It seems likely this abundant food source is what

Attracted the crocs to the caves in the first place.

So far, the crocs matt's found are living in caves

That have free access to the forest,

And they're all the regular colored dwarf crocs.

He's yet to find the legendary orange crocodile.

The network of underground passageways

Extends over one square mile.

That's around 200 american football fields.

An underground metropolis, carved out over time by water.

In horizontal channels,

The crocs are able to come and go freely,

But where the water has cut vertically through the rock,

The result is a cavern you can only fall into.

Once inside, crocs can become trapped.

The orange croc found on the previous expedition

Was in a deep cave below a vertical shaft.

They'll have to rappel in,

Feet first into the unknown.

Olivier has located one of these shafts.

If there's something down here,

It's probably been there a long time.

A long rope is secured,

Which will be their lifeline in and out of the dark depths.

The tunnel below is teeming with bats.

Kharl.

Yeah?

At the end of the cavern, matt sees something.

Not one, but two crocs.

And in the light of his headlamp,

That could be an orange tint!

Matt's seen two crocs,

But they're retreating into the stinking mud.

If they wedge themselves in that tunnel,

He won't be able to get them out.

He grabs the closest one.

It's big, and a pale orange hue

Glistens under the guano slime.

He's found one!

The first one is bagged.

He goes in for the second.

It's bigger, and it's orange too.

The questions on matt's mind?

How did they get here and how long have they been down here?

Long enough to change color.

Okay!

One theory is they found their way in

Through small fissures,

Which then filled up with sediments, trapping them inside.

These crocs could have been in here for decades.

Okay, take it up!

These two specimens

Will be critical to matt's mission.

that's a nice...

The goal now is to get the pair

Back to the makeshift lab.

Each orange croc he finds

Adds to the limited data on this rare population.

Their orange hue could be a result

Of being pickled by bat guano for years.

Largely comprised of urea,

The nitrogen-rich chemical is highly alkaline

And over time is effectively tanning the skin.

But it could also be from lack of light.

Matt takes measurements to see

If there are any other physical differences.

Yeah.

It turns out these individuals are broader

Than their forest relatives.

Trapped in the dark caves,

These crocs are in the process of adapting.

Dna results show the cave crocs

Have a distinct genetic signature.

They are not yet different enough

To be considered a new species,

But this population is slowly separating

From their forest cousins.

This is adaptation in motion.

Matt notches its tail.

This way he'll be able to identify

The animal if he finds it again.

The crocs have given matt the information he needs.

They are quickly returned to their dark lair,

Where their move toward a new species can continue.

There are still miles of caverns to explore,

But nature has other ideas.

The deluge begins.

This is no place for a human.

The expedition is over.

Fortunately, the crocs have mastered this realm.

On this trip, matt's discovered young crocs,

So the cave population is growing,

He's found evidence that the crocs are hunting bats,

And he's found the fabled orange crocs,

Which he now knows are unique to these caves.

These crocs could have been here for thousands of years,

Yet their world is only just being revealed.

The dwarf croc is truly a survivor.

It's no surprise they out-survived the dinosaurs,

And they're not done yet,

Not by any means.