All language subtitles for Monsters.of.the.Deep.20000.Leagues.Under.the.Sea.S01E02.1080p.MY5.WEB-DL.AAC2.0.H.264-RAWR_track3_[eng]

STEVE BACKSHALL:
Deep in the ocean's dark abyss,

20,000ft below the surface,

in the freezing depths,

lurks a strange, unexplored world...

..where alienlike creatures...

..grow to terrifying sizes

and are the ruthless predators...

of the abyss.

Many look like something
from our darkest imaginations...

..while some create
the myths and legends of the deep.

Weird creatures
with alien ways to hunt... and kill.

It's said we know more about Mars
than we do our deep seas

and the strange life forms
within it.

This series will uncover
the great unknown,

come face to face with some of
the sea's most elusive creatures...

..and use cutting-edge technology...

..to reveal behaviour
that has never been captured.

These are the unknown and unseen
monsters of the deep.

In this programme,
we meet the giants.

From the massive monsters
living in the deepest oceans

to the strange creatures that live
longer than any other animal.

It's a giant isopod.

That is extraordinary.

From the most voracious
super-predators...

..to the enigmatic giants
that haunt our subconscious.

How did you feel when you saw that
for the first time?

It was such an incredible
"It's happening" moment.

Today, lurking in the dark abyss,

at depths of 1,000m or more,

are giants that are rarely seen.

Their presence revealed only
through tantalising glimpses.

One, more than any, has gripped the
dark recesses of our imaginations.

One of the most fascinating things
about our seas

is that so many of its monsters

remained hidden
for hundreds of years.

Tales of the giant squid
go back centuries,

and usually
from first-hand narratives

of sailors who encountered them
while they were far out at sea.

And these gave rise to legends
of mythical beasts like the kraken,

a creature that could engulf ships
and drag them down to their doom.

In the mid-1800s,
a ship's captain even described

three men being seized
off the coast of Africa.

But hard evidence of these enigmatic
monsters was difficult to come by.

Then, in 1873, a Newfoundland
fisherman, Theophilus Picot,

had an actual encounter
with a giant squid.

He spotted something
floating at the surface,

and as he approached,
realised that it seemed to be alive.

So he prodded it with his boat hook,

and, as he writes,
that aroused the creature's fury.

And so it engulfed his boat
with its tentacles and arms

and started biting with its beak.

And so he responded
by hitting it with an axe.

This severed
one of the feeding tentacles,

which was 19ft in length,

as long as a giraffe is tall.

Finally, it had been established
without doubt

that the giant squid was real.

So what is the truth
behind the legend?

It was only in 2004 that a complete
giant squid was finally recovered.

It resides in a tank deep below
the Natural History Museum.

Up to 13m in length,
weighing more than half a tonne,

this is Archie,
the female giant squid...

..deriving from the scientific name
Architeuthis.

The person responsible
for preserving Archie

is curator Jon Ablett.

So, to get a complete,
intact specimen is incredibly rare.

I was contacted back in 2004

by a fisheries agency
in the Falkland Islands,

and some fishermen
pulled up their nets

and they found this in it.

And they caught her
at a depth of about 200m,

which is probably
near the kind of limit

to where giant squid occur
towards the surface of the water.

We froze it on the Falklands
and shipped it over

all the way back to the UK.

Then I defrosted it.
It took about four days to defrost.

Because giant squid contain ammonia,

I basically made the whole building
smell of urine.

So, now she is stored
in the basement, in the tank room,

of the Darwin Centre at the
Natural History Museum in London,

and the tank
is actually manufactured

by the same people that make the
tanks for Damien Hirst's artwork.

So I think
she's my own piece of art.

Finally, we are able to examine
the elusive giant.

So, at the end of Archie,
at the tentacle,

it's an expanded area at the end
called the tentacle club,

and this is where
the largest suckers are found.

These suckers are about 2cm, 2.5cm,
so really quite large.

And if you see,
on the edge of each of the suckers,

it has this sawtooth firm edge,

which really helps it to dig in
and grab its prey

when it shoots out its tentacles.

And if you move further back,
you can see,

not only does it have
the two long tentacles,

but back here,
it has the shorter eight arms.

And these arms
are much more muscular.

And there's quite a big difference
between them,

because on the arms,
you find suckers

along the whole length
of the appendage,

whereas on the tentacles,

you only find these suckers
right at the very end.

This is the head,

and the beak is actually
at the top of the arms here.

Then behind it, you've got the eye,

and the brain is situated
sort of just below the eye,

and it's doughnut-shaped
to let the food pass through.

This is a beak from a giant squid,

and they're made of chitin,

a very strong substance,
and incredibly sharp at the tip,

and allows to cut through bone,
flesh, shell, whatever it's eating.

So, when a giant squid
feeds on its prey,

grabs it with its large,
fast-moving tentacles,

pulls it in to the much stronger
arms where it can hold it,

and then you basically get nibbled
to death.

It's kind of a death
by a thousand nibbles,

macerating the food
before it swallows it.

Because Archie is so precious,

to see the inner workings
of the giant squid,

we need to examine
a less complete specimen.

This is actually
another specimen of giant squid.

This one came from Canada.

So, this area here is the mantle,

and this is where
all the organs are stored.

So kind of everything
that would be in our body.

We've got here one of the gills.

They actually have two large gills
to extract the oxygen.

And they actually have three hearts.

So they have
a central systematic heart,

and each gill
has its own little heart.

So this whole mantle area
fills up with water.

So it sucks the water
in through here

and then pushed at great pressure
through this funnel

to allow it to move very quickly,
just like a jet ski.

So, giant squid normally live
deep in the ocean.

So we're talking maybe over 1,000m,

and we don't think they can
actually survive above 150m.

And what about the giant squid
at the surface,

encountered by Theophilus Picot
in 1873?

It seems likely that the "attack"

was simply the squid
in its death throes,

as they only come to the surface
when they're dying.

Archie,
no matter how large and impressive,

is still a dead squid
and can only tell us so much.

In life, is it
an aggressive hunter-predator

or a passive opportunist?

No-one had seen the animal alive...

..because,
unlike 90% of life in the sea

that lives in the upper two layers,
in the sunlight and twilight zones,

the giant squid usually lives
at great depth,

nearly a kilometre down,

near a layer
called the midnight zone,

where light can no longer penetrate.

'It was while exploring these depths

'that marine biologist
Nathan Robinson

'had only the second-ever
squid encounter of the giant kind.'

I'm meeting him in the workshop

of the UK's home
of deep-water exploration

at the National Oceanography Centre.

So, talk us through how
you actually captured these images.

OK, so, this is a visual lure.
This is our e-Jelly.

When we're trying to attract
an animal like a giant squid,

you've got to think
like a giant squid.

A giant squid has the largest eye
in the animal kingdom.

They have an eye that can be around
12 inches, like the size of my head.

A giant squid's world is visual.

So, there's a deep-sea jellyfish

that creates a blue pinwheel
bioluminescent display,

and it does it
to attract other big animals

to eat the animal that's eating it.

So we create
this biomimicked display,

and then that seems to be
the perfect lure

to bring in a giant squid.

So, the imagery is very fleeting,

but you see this sinuous serpentine
shape coming out of the darkness.

So, at this point, we'd reviewed
about 120 hours of footage,

and so much of this is nothingness.

And then finally,
this object came in

and then just unfolded
its tentacles, attacked the bait.

It was such an incredible,
like, "It's happening" moment.

And how deep down is this?
This is at 750m.

It's surprisingly tentative,
isn't it?

It's tasting.

It's figuring out,
"Is this something I can eat?"

And the second it realises
that it isn't what it thinks it is,

it just says,
"No, I wanna go somewhere else."

What do you think this tells us

about how the giant squid
is likely to hunt

and the kind of things that it's
likely to have as its main prey?

So, there's big debate
for a long time

as to whether giant squid
are active predators.

This footage shows
that it can actively pursue prey.

We have that five minutes

of it slowly just trailing
behind our bait.

If you're actively hunting down
your prey,

you're gonna need to eat more.

I've been underwater
with Humboldt squid, big ones,

and one of the first things
that they very obviously target

is other Humboldt squid.
Yes.

Do you think that that is likely
with the giant squid?

Could they be cannibalistic?
I definitely think they could.

And when you're a deep-sea animal
like the giant squids,

anything you find that's
a potential meal, you're gonna eat.

So if they're encountering smaller
and younger giant squid out there,

they could see that
as their next big meal.

That's life in the deep sea.

A giant squid
that washed up recently in Spain

showed signs of a lethal struggle.

Its injuries revealed
it had been attacked

and mortally wounded
by another giant squid.

It would appear that giant squid
are not only aggressive hunters,

they are cannibals.

It's astonishing to think
that this huge giant...

..despite being known about
for centuries,

has only ever been filmed twice
in the wild.

The biggest animal alive today,
the blue whale...

..can be more than 30m in length
and exceed 200 tonnes in weight.

And yet,
encounters with them are rare.

And this raises
an interesting question -

could our seas be hiding
even greater mysteries?

And could the seas of the past
hold even bigger monsters?

STEVE BACKSHALL:
The biggest creatures on the planet

are found in our seas.

Some, hidden in the dark abyss,
like the elusive giant squid.

Others, close to the surface,
like the great whales.

The world's biggest animal
is the blue whale.

But how and why do they get so big?

Baleen whales feed on prey that is
the tiniest fraction of their size.

And in the seas of the past,

there were monsters
that were almost as big...

..but far, far more ferocious.

One strategy to allow an animal
to grow big

is to be able to take on big prey.

And to do that, it really helps
if you have fearsome teeth.

That way, you get more bang
for your bite.

So, this is the tooth
of a great white shark.

It is scalpel-sharp,
serrated at the edges.

Found throughout the oceans
of today,

the biggest have been
over six metres in length

and weighed as much as two tonnes.

With a mouthful of 300 teeth,

the great white shark
is a formidable killer.

But this is the tooth of Otodus.

It is one of its relatives.
It's extinct.

And I guess we know it better
as the megalodon.

Megalodon lived in seas
not so different from today

until around 2.5 million years ago.

For the most part,
all we have of them is their teeth,

which grew up to 18cm in length.

The ancestors of our own great white
shark were around at the same time.

But megalodon
was only a distant cousin.

A much, much bigger cousin.

This tooth is a similar profile
in shape but far, far bigger.

And there is no doubt that this had
one of the biggest bites

on the planet.

Megalodon shares the sea
with eight-metre whales.

The question is: how big is the prey
that a megalodon can tackle?

At London's Natural History Museum,

Curator of Palaeobiology
Emma Bernard has evidence

that could provide an answer.

This is a piece
of fossilised whale bone

that's five-and-a-half million
years old.

And this would belong
to a whale about seven,

maybe eight metres in length.

So quite a big animal.

It's got these strange markings
all the way across the bone.

They're actually bite marks.

And because of the depth
and the distance between them,

it would have had to be
a very large predator.

And that predator
would have been megalodon.

The teeth of megalodon
are the stuff of legend,

and the museum has over 300 of them
collected from all over the world.

So, the name megalodon
actually means "big tooth".

And I think that's quite clear
to see with this one here.

And this would have been from
a fully grown large megalodon.

It's also got this serrated edge
all the way down the tooth.

And this serrated edge
is very similar to a knife.

So, a megalodon tooth
is really like a dagger

and a steak knife
all rolled into one,

into an amazing,
effective killing tool.

So, as it's biting down on its prey,

these teeth would often come
in contact with the bones.

Like all sharks,

megalodon's skeletons are made of
cartilage rather than bone,

so fossils are extremely rare.

Previously,
megalodon's size estimates

were done by simply upscaling
a great white shark

and were believed to be around
14m in length.

A megalodon backbone was discovered
in Belgium in 1843.

But when Jack Cooper
from Swansea University

re-examined it in 2022,

he made an incredible discovery...

..that changes everything
we thought we knew about megalodon.

Jack Cooper is more familiar
with the meg than just about anyone,

including Jason Statham.

He's reconstructed the monster
using its backbone

and discovered something
about the meg

that makes it even more terrifying.

You know, a shark can replace

tens of thousands of teeth
during its lifetime,

and those are so well represented
in the fossil record.

But to find a vertebrae,
I mean, that's really special.

Even one vertebrae
is incredibly rare.

And this spinal column from Belgium

is the only one of its kind
in the world.

But when we reconstructed the spine,

we found that
that alone was over 11m long,

and that brought the whole
total length closer to 16m.

But even that is not the biggest
sizes we know of a megalodon.

We have estimated that megalodon
could get as big as 20m.

That is gigantic.

Well, should we get an idea
of that size?

So, five metres.

I've swum alongside great whites
at that kind of size,

but six metres.

So around about there.
Let's keep going.

If we get a bit bigger still,
we're going on

and up to our biggest fish species
in the world today.

12m is a pretty good size
for a whale shark.

But that is not a fierce predator
like a megalodon.

It's, you know,
feeding on plankton and small fish.

By comparison, megalodon was eating

almost 100,000 kilocalories
every single day,

and that is about 20 times
the amount of food

that a great white needs.

Megalodon was consuming whales
up to seven or eight metres long.

That is insane.

But we're not there yet.
They get bigger still, right?

16.

So, 16.

Length of the shark
measured by its vertebrae.

That is the size of our model shark.

Already about three times bigger
than our great white sharks.

But we still have some growing to do
for our megalodon.

17, 18.

And, unbelievably...

..is there, 20m.

That's vast.

You could fit almost ten people
in line,

and that would still have room
to spare for megalodon.

So, what, then, were the main
benefits of this enormous size?

Well, one of the key benefits
of being so big

is that you have less competition
by eating such big prey.

So that allows megalodon to eat
pretty much whatever it wants

and not have to worry
about that many competitors.

A 20-metre megalodon,
how big is its mouth gonna be?

That mouth is going to be
well over 1.8m tall,

so it can easily swallow a person.

You and me could both stand
in a shark's mouth at that size.

'Jack's work on megalodon
gives us the best picture ever

'of this super predator.'

Unlike most other fish,
this is warm-blooded.

They can cruise faster
than any other shark,

able to cover vast distances
in search of prey.

It was a whale killer.

Megalodon could dispatch
an eight-metre whale

in five or six bites.

Giant predators like megalodon
are truly awesome.

They are dominant super killers.

And yet megalodon went extinct.

It turns out giants have
an inherent weakness.

So long as prey is abundant,

being a giant apex predator
means you rule the seas.

But if prey becomes scarce...

..all of a sudden,
gigantism can be a big problem.

All it took was a slight change
in the climate...

..which made their main prey
harder to find.

Very quickly,
one of the most gigantic predators

the world had ever seen disappeared.

But you can't keep gigantism down
for long.

The loss of megalodon
left a vacancy.

An opportunity for another animal
to become a giant.

It was only after the extinction
of megalodon

that baleen whales evolved
into today's generation of giants.

Today's baleen whales
can grow even bigger.

Because even though they feed
on small prey,

by lunge feeding,

they can eat huge amounts

in what is effectively
a single bite...

..and so can grow to enormous sizes.

The only limit is the availability
and concentration of their food.

They're so big,
they're virtually invulnerable.

But there is one monster
that rises from the deep

to attack the giants of today.

From sperm whales...

..to orca and great white sharks,

alarming injuries have been seen
on giants.

But just what is responsible
for these bizarre wounds?

STEVE BACKSHALL:
Becoming a giant might be difficult,

but the rewards justify the efforts,

making the animal
pretty much invulnerable.

But given their vast size,

is there anything hidden
in the depths of our seas

that poses a threat
to today's ocean giants?

Well, there might be.

Strange injuries on some
of our ocean's biggest animals

suggest a mysterious assassin
lurking in the depths.

Even humans have been attacked.

What kind of monster is responsible
for these vicious attacks?

Marine researcher Jethro Reading

at the National Oceanography Centre
could have the answer.

These wounds are bizarre
because they don't look natural.

They look surgical.

We find these injuries
on large predators.

Here, we've got an injury
on the side of a sperm whale.

Similarly, we've got injuries
on orcas...

..great white sharks.

And something is attacking them.

Among the NOC's
deep-water specimen collection,

Jethro suspects
he knows the culprit.

This is the bizarre
cookiecutter shark.

Here she is.

She's got this, like,
little smiley mouth.

That mouth is actually concealing
quite a sort of nasty little secret.

It's only half a metre long
but packs a fearsome bite.

The cookiecutter shark
has the largest teeth

for its body size
of any shark that we know of.

This whole section
would sort of hinge down

to create this circular mouth.
And on the lower jaw,

these huge teeth are fused into
this single saw-like structures.

The cookiecutter shark spends most
of its time deep in tropical oceans,

up to 3,500m down
in the midnight zone.

But to feed, every dusk,

it rises three kilometres
to the sunlight zone.

It's rarely seen
and has never been filmed feeding.

Having impressive jaws is only part
of the cookiecutter's secret.

While it may look sort of
rather drab and brown here,

this animal glows.

It shines a bright blue light
out of its underside.

These dark spots all over the body
are photophores.

That's organs in the skin
that produce light.

They are bioluminescent,

and they're missing
from this collar around the neck.

It uses this bioluminescence
to hunt,

making its profile smaller,

trying to lure in potential victims.

Here, we've got a little setup
that gives you an idea

of what you might be seeing if you
are a predator in the deep sea.

So, it has a very,
very strong silhouette

against the sunlight from above.

But with its glowing disguise,
it looks much smaller.

This dark colour really stands out,

and it's thought that
this dark colour

is going to resemble a small fish.

By luring their victim close,

the cookiecutter gets its prey
just where it wants them.

And it may be that
when these predators

investigate the cookiecutter,

lured in by
this false fish silhouette,

the cookiecutter turns it around
on them

and takes a chunk out
of them instead.

And the hunted
very quickly becomes the hunter.

Deploying its razor
saw-like teeth...

..the shark latches onto its prey

and creates a suction seal
with its lips.

It pivots around in a circle,

using the saw-like lower teeth

to cut a near perfect plug
of muscle from its victim.

While the cookiecutter shark takes
advantage of giants at the surface,

to find the biggest giants of all,

we need to descend
into deeper waters.

Because it's here
that we find abyssal giants

or the giants of the deep.

The Greenland shark is found
in the North Atlantic

up to 2,000m deep...

..with temperatures around freezing
in total darkness.

Here, food is very hard to come by.

And yet the Greenland shark
grows to seven metres in length

and can live up to 500 years.

Some of the sharks living today

could have been around while
Shakespeare was writing his plays.

They are the longest-living
vertebrates on Earth.

They do so by taking things easy.
They slow their metabolism.

They take their time
over everything.

It takes 150 years
to become an adult.

Greenland sharks
are deep-sea giants.

But the most extreme examples
of so-called abyssal gigantism

are not sharks.

And they're not squid either.

Tammy Horton at
the National Oceanography Centre

is no stranger to deep-sea giants.

But first,
she has a miniature to show me.

This is a shallow-water sea spider.
And they're called sea spiders...

People might think they're quite
closely related to spiders,

but they're actually quite distant.

It doesn't actually have
much of a body.

The trunk is pretty small,

and the majority of the animal
is legs.

This is a female specimen,
and you can see its eggs,

which are held inside its legs
all the way down there.

Oh, are they really?
STEVE GASPS

That's amazing.
So they're absolutely amazing.

What's this here?
That's an egg mass?

Yes. We can zoom in a little bit
to show you that.

Because there's so little space
in their trunk,

their digestive systems, everything,
their reproductive systems

stretches down into their legs.

This one here is about the size
of my little fingernail.

Yes, but they can get
a hell of a lot bigger.

To find the giants,
you need to go deep.

That one's heavy, too.
Oh, you're not lying.

After you.
Thanks.

So, these were collected at 2,600m?

Yes, at the Mid-Atlantic Ridge.

And these are...
STEVE GASPS

No.
..giant sea spiders.

That's insane!
Yeah.

So, the deep-sea version

of that teeny-tiny fingernail-size
sea spider is a giant.

That's right. These are true giants.

And I think the largest specimen
of this ever recorded

had a 70-centimetre leg span.

70cm?
70cm.

Can I take one?
Yes, please do.

Wow.

So, it's the same animal,
but a whole different scale.

There are instances where
deep-sea or abyssal giants

are 700 times bigger than
their shallow-water equivalents.

And some look like
they're from another world.

So, this is a giant isopod.

That is extraordinary.

What an alien.

This is the largest isopod known
on this planet.

It looks like
a super-sized woodlouse.

That's right.

I would imagine to many people,
that would be their worst nightmare.

That is absolutely extraordinary.

It's grotesque
but absolutely fascinating.

It's amazing, isn't it?

So, do you have a shallow-sea one
for size comparison? Yes.

So, that's the same creature,
just on a whole different scale.

This is effectively a shallow-water
version of this giant isopod.

This is only found in deep sea.

'Proportionally,
these deep-sea monsters

'are the biggest giants of all.'

This whole idea of deep-sea
or abyssal gigantism,

the capacity to get really,
really big,

are there any ideas
of why that might happen?

One of the things to remember
about living in the deep sea

is that food is really scarce,

and that means that these animals

have to really wait out long periods
of time in between meals,

and then they have to travel
longer distances to find their food.

Being larger, then, would give them
a competitive advantage.

It's quite counterintuitive,
isn't it?

It is quite counterintuitive
that there are some animals

that are really, really big
in this food-poor environment.

So they live a very slowed down
sort of lifestyle.

Their metabolic rate is slower.

So, living slow, living long,

these can be a real advantage.
Absolutely.

Animals with a low metabolism
that live life in the slow lane

can make the best of meagre
resources in their environment

and grow to become giants,

while those at the surface,
like the great whales,

become giants
by feeding efficiently.

The sea continually produces giants.

And a recent discovery might be
about to dethrone the blue whale

as the largest giant
that has ever lived on our planet.

STEVE BACKSHALL: The biggest giant
on our planet is the blue whale.

Averaging 24m long
and weighing 180 tonnes...

..it was thought that no animal
had ever grown bigger.

But hiding in rocks
laid in ancient seas are clues

that could change all that.

Despite their size,
today's giants of the sea

can be surprisingly elusive
and difficult to find.

It raises a fascinating question.

Just how big
do these sea monsters get?

Some recent clues
have given us the idea

that the biggest giants of all time
lived in the seas of the past.

That monsters existed
in the dim and distant past

has been known about
for a long time.

In fact, the first discoveries
of ancient marine reptiles

was right here on this stretch
of coastline, the Jurassic Coast.

This was one of those monsters,
as was this.

These exquisite ichthyosaurs are
at the Etches Collection in Dorset.

The thing that strikes you
is how similar they are

to a modern-day dolphin.

So, first of all, you've got
this extended beak-like rostrum,

and inside there,
rough, cone-shaped teeth

which would be perfect
for catching slippery,

fast-moving prey
like squid and fish.

And you can tell
that's what it was eating

because its last meal
is fossilised inside it.

The stomach contents are here,

and you can see little bits
of fish bone.

So exactly the kind of thing
that a modern-day dolphin would eat.

Ichthyosaurs, like dolphins,
are air-breathing animals

and evolved from a land-living
relative to live in the sea.

They were both shaped by evolution,

becoming streamlined
for a life in the ocean.

It's a classic example
of what biologists call

convergent evolution.

It has these four limbs here,

which are adapted
into paddle-like flippers.

So those could be used
to give it lift

and perhaps to move them
in the water like rudders.

And this is truly remarkable.

On some ichthyosaur species,

they had the biggest eye socket
of any known vertebrate.

So it's likely that those huge eyes
drag in the light,

and they're used when they're
hunting at depth in the darkness

for fast-moving prey.

From the largest-eyed species,

it's thought they could hunt
by sight as deep as 500m.

Ichthyosaurs were one of
the apex predators of their day.

And this one here
was just a youngster.

They got to be much,
much bigger than this.

Very recently,
amateur fossil hunters

discovered a huge chunk
of fossilised bone

on a beach in Somerset,

a fragment that hinted
at something extraordinary.

Dr Dean Lomax is an expert
on extinct marine reptiles.

He instantly recognised
the significance of the discovery.

This is a giant jawbone
from an ichthyosaur.

Now, it's just one bone,
and this is... all together,

when we lay this out correctly,
is over two metres long.

But it's incomplete.

We've got a much smaller skull

of an ichthyosaur that was probably
about two metres long,

about the size
of a modern-day dolphin.

And you can pick out
this gigantic bone,

the very same bone
in the bottom of the jaw here.

By comparing the fossils,

Dean can estimate
the size of the giant's skull.

If you imagine,
this is just one jawbone.

If you add all the other bits
and pieces to this,

you can estimate that the skull
might have been...

possibly up to five metres.

Truly a gigantic animal.

In 2024, Dean and his team named
the new monster Ichthyotitan.

And when Dean looks at the jaw
more closely,

there's another
surprising discovery.

Not only can we learn a lot
about bones from the outside,

but also on the inside.

So by taking this core sample,

you can see the structure
of the bone inside here.

And all of these individual details

tell me that this animal
was still growing,

and that potentially was probably
something like a very late juvenile,

maybe, say, a teenager
or an early subadult.

So an early adult.

So just how big is Ichthyotitan?

Based on the jawbone, Dean can
estimate and plot out its size.

20, 21, 22.

We estimate that Ichthyotitan
is about 25m long.

'That makes our Ichthyotitan
longer than the average blue whale

'and a contender for one
of the largest animals

'that ever lived.'

Because this individual
was still growing when it died...

..it's possible that
a fully grown adult Ichthyotitan

could reach 30m or more.

If Dean's calculations are correct,

he believes that Ichthyotitan could
have been a real record breaker,

potentially able to challenge
our very own blue whale

for the title of the largest animal
ever known to have existed.

Just how do these monsters
of the sea grow to be so immense?

One part of the puzzle
is that seawater

will do the heavy lifting,
quite literally.

Let's imagine that our water balloon
here is a giant marine creature.

Well, its body will be supported
by the water,

which is a denser medium than air.

It can hang here neutrally buoyant,

with no expenditure
of energy whatsoever.

But take that same animal
out of the water,

and it'll need a hefty
so-called graviportal skeleton

just to stay upright.

Moving around requires
an enormous amount of energy.

And at a critical mass, it'll simply
collapse under its own weight.

As a result, it's only in the oceans

and in the deep, dark abyss
where such huge animals can live.

One of the key advantages
of reaching a huge size

is that you're pretty much
off the menu for any other animal.

And in the sea, being bigger

means you can move through the water
more efficiently.

From their eyes, we know
ichthyosaurs were deep divers.

And a bigger body means
a bigger oxygen-carrying capacity

and an ability to dive deeper
for longer.

Today's deep-diving sperm whale can
hold its breath for over 90 minutes.

For Ichthyotitan, getting big
means not only is it a top predator,

but it can also hunt at depths

few other air-breathing animals
can reach.

Today's giants, the great whales,

cover vast distances
during their lives...

..and help perpetuate gigantism
in the seas.

They circulate nutrients
in the oceans they move through,

fertilising and boosting
plankton production as they go.

Turbocharging the food chain,

ultimately enabling the giants
at the top.

It's likely that
all the giants we've seen

play a similar and critical role,

circulating and spreading nutrients
through our oceans.

From megalodon
to the modern whales of today.

Giants are not just inevitable
in our oceans, they're essential.

Our oceans are the cradle
of life on Earth.

Throughout history,
they continually produce

the most formidable killers...

..the most immense giants.

And the more we explore,

the more of the ocean's weird and
wonderful secrets we will discover.