Original subtitles

(vibrant inspirational orchestral music)

- [Narrator] Dragonflies the size of hawks.

Centipedes larger than humans.

The strange menagerie of giant insects and amphibians

reigned over the earth 300 million years ago.

Over time these huge creatures

shrunk in size or disappeared.

The reasons for their progressive extinction

remained controversial.

358 million years ago the continents came together

to form the supercontinent, Pangaea.

This was the beginning of the carboniferous period.

Oxygen levels in the air were much higher back then,

35% compared to today's 21%.

For the first time on Earth

giant trees stored carbon dioxide

and released oxygen in abundance.

Human beings would not have survived

in this high oxygen atmosphere.

But for some swamp dwellers it was ideal,

like Arthropleura measuring up to 10 feet.

This long lost cousin of the centipedes was a herbivore.

Or Meganeura with a wingspan up to 25 inches.

This member of the dragonfly family

is the largest known flying insect ever discovered.

A tireless predator

who had no airborne competitors at the time

since birds and flying reptiles didn't exist yet.

The high oxygen levels in the atmosphere

give the characteristic sepia color to the sky

during the carboniferous period.

Oxygen also makes the air extremely flammable.

Such a hostile world is hard for us to imagine.

Lightning storms could set aflame the immense forests

and their inhabitants. (lightning strike)

During this period not a day went by

without huge forest fires

and yet giant insects thrived.

Later when fires became less frequent

these astonishing creatures simply disappeared.

Scientists are trying to determine

what caused their extinction.

- [Translator] There are several possible culprits.

In fact, it's a bit like an Agatha Christie novel

when there is not one but several murderers.

It's our job to take the clues we have

and reconstruct the investigations

in order to come up with the most likely scenario.

- [Narrator] While we've known about giant insects

since the 19th century

paleontologists do not understand why they have disappeared.

For a long time the change

in the composition of the atmosphere

was the only explanation.

But at the beginning of the 21st century

the discovery of fantastic fossil insects

and their predators opened up new possibilities.

- While that's a wonderful hypothesis

and assuredly something was preying upon these giant insects

we don't have great evidence for it.

- [Narrator] Around the world

American, European and Chinese scientists

confront the old theories using new fossil discoveries

unearthed by groundbreaking technology.

But try and explain why these giants became extinct.

The earliest giant insect fossils

were found in the French region of Allier in 1880.

Under the surface of this pond were the remains of animals

that had died 350 million years ago

during the carboniferous period,

Meganeuras, now extinct.

These tireless predators

are the largest flying insects that ever existed.

This abandoned industrial site

was an important coal field in the 19th century.

And as the coal was dug out

fossils were discovered close to the town of Commentry.

The owner of the coal mine, Mr. Monyi

gave his name to the specimen

that is preserved at the natural history museum in Paris,

Meganeura monyi.

Andre Nel a paleontologist whose specialty is early insects

watches over this valuable piece.

- [Translator] Miners would look for fossils

to make a little extra money.

And one day when they were opening slabs

they came across this animal.

Unfortunately when they were digging it out

they hit it four times with a pick and we lost its head.

They were the super predators at the time,

predators of other insects that were also very big.

- [Narrator] These large sized fossils

are quite exceptional.

While thousands of insects were found

on the site of Commentry

only five Meganeuras were ever discovered.

- [Translator] Meganeura, like all other insects

had four wings, two on each side

attached to the thorax in the center.

In front you had a head with big eyes

because it was a predator,

so it's eyes, just like modern dragonflies

were used to see its environment in 360 degrees,

so possibly even behind the animal.

- [Narrator] To better understand

how this extinct animal once lived

we must step back 300 million years in time.

This is what the French region of Allier

would have looked like then,

a giant swamp scattered with Cypresses.

Humidity at nearly 100% made the atmosphere dense

and allowed Meganeura to easily carry

its heady exoskeleton into the air.

It is part of a genus that is extinct today.

But it looks much like modern dragonflies

and is part of the same Odonataptera super order.

With wings that functioned independently of each other

Meganeura was agile in flight.

But unlike its contemporary cousins

it couldn't fold it's wings.

Faced with this efficient airborne predator

vegetarian insects such as Palaeodictyoptera

had to keep themselves out of sight.

By comparing its anatomy to modern dragonflies

we can guess at Meganeura's main physical characteristics.

One, it could fly over 40 miles per hour.

Two, it was a sight predator,

it's head was independent from the rest of its exoskeleton

so it could keep it still while flying

and focus on its prey.

Three, it had a huge appetite.

It could eat its own weight in food every 30 minutes.

To catch all this food

Meganeura had an array of attributes identified in fossils.

But what might explain its giant size?

Away from the public is the museum's library of species

where they keep the specimens that scientists study.

Here we find Meganeuras and their prey

both reaching impressive sizes.

- [Translator] So here you have

an example of a Meganeura

on which we see the base of its wings, the thorax.

But what is most spectacular are the forelegs

equipped with strong spines that were used to stab prey.

But the Meganeura's prey were also large sized insects

like the Palaeodictyoptera.

You just have one wing from here to here.

So you can imagine the whole thing.

These were Meganeura's prey.

They were big guys too,

big insects to escape big predators.

So in this case we have an arms race

between predators and prey.

- [Narrator] But this battle to be the biggest

between Meganeura and its prey seems to have had its limits.

Otherwise paleontologists would certainly have found

even bigger and more terrifying insect fossils.

Most of Meganeura's day was spent looking for food

since its metabolism required a lot of energy.

According to scientists the huge size of insects

during the carboniferous period was possible

because of the high levels of oxygen in the air.

Insects don't have lungs but instead use a unique system

of tubes, trachea and tracheals

to bring air directly to their organs

including their digestive system.

The downside to this system is it lacks efficiency.

Air travels through the tissues in the form of gas.

The bigger an insect is the more oxygen it needs.

- [Translator] It is very strange

that these animals reach these sizes

because nowadays we do not have such big insects.

And at the time of the dinosaurs

when we had large vertebrates insects were much smaller.

It turns out that in the carboniferous period

for reasons linked to geochemistry

the oxygen rate in the atmosphere was higher

than it is today.

Which encouraged the development of animals

such as the large insects.

- [Narrator] Meganeuras could not survive

in today's atmosphere

because not enough oxygen would reach their organs

including their brains.

And they would faint.

Since the beginning of the 20th century

scientists have proposed a link between the size of insects

and the concentration of oxygen.

But it wasn't until 2007

that an experiment finally proved it.

In the Chicago suburbs the Argon National Laboratory

houses the United States' most powerful synchrotron

a scanner that generates the brightest X-ray beams

in the northern hemisphere.

The distance around the particle accelerator

is more than half a mile.

So, Jake Socha the scientist in charge of the study

uses a trike to get around.

Today live insects are being put under the scanner.

- We use the idea that you can take living insects

and make inferences about insects that existed in the past.

What we're trying to do in this study

is to test an old hypothesis

that the amount of oxygen in the atmosphere

is what limits insect body size.

So the idea with this hypothesis is that

when you have more oxygen your insects can get larger.

And when you have less oxygen

insects will get smaller in response.

But no one had really ever tested this hypothesis before.

So we use synchrotron X-rays to look inside the animal

to study the dimensions of their tracheal system.

- [Narrator] This particle accelerator

generates extremely intense and focused X-rays

that pass through the insects body.

- Our purpose is to see the tracheal system in action.

And some of the tracheal tubes are really small.

And we wanna see it in the living animal.

So this is really the only technique

where we can do all of those things.

(alarm beeping)

- [Narrator] For the first time scientists are able

to actually observe an insect breathing.

- [Jake] Did you turn the beam on?

- [Narrator] Using this experiment

they discovered that crickets not only breathe passively

but also use their whole bodies

to carry air to their organs.

- And you can see that bubble in the gut

moves forward to the head then it moves backward.

And every time it's doing that it's synchronized

with the compression of the tracheal system.

The movements that you see here are not a passive effect.

This is an active movement by the animal.

And the ultimate cause of it are contraction of muscles.

- [Narrator] Just as this cricket

contracts its digestive system to send air to its organs

Meganeura would have contracted its abdomen

to absorb the thick carboniferous air.

The elastic exoskeleton would resume its shape

once the muscles have completed their action.

But beyond the discovery of this internal movement

what interests Jake Socha is the space occupied

by the respiratory system within the insects' bodies.

He has compared beetles of different sizes

to study the link between their size

and that of their respiratory system.

- And what we found is that the tracheal tubes

take up a larger fraction of the body

as you go from smaller to large than you might expect.

So, what we think based on the study

is that if you would make this even larger,

so we would scale this up farther and farther

eventually you reach a limit

where you can't stuff more tracheal system inside the animal

because you have to have other things like

muscles and gut and nervous tissue,

fat bodies things like that

that are all important for the physiology of the animal.

You can't just have one big tracheal system.

- [Narrator] The higher oxygen concentration

of the carboniferous period

meant that insects required fewer respiratory tubes

and could therefore grow to a larger size.

But with the modification of the atmosphere

the giant insects had to reduce their size

over millions of years of evolution.

And not all of them survived these changes.

290 million years ago during the Permian period

oxygen levels decreased from 35% to 23%,

close to today's level.

Pangaea had already formed a super continent

extending from one pole to the other

surrounded by a single ocean.

It was subject to extreme climatic conditions.

The heart of the continent

suffered drastic temperature changes and deserts appeared.

But at the equator heavy rainfall allowed the great forest

from the carboniferous era to survive.

During this period of major climate change

punctuated by the monsoons and the warming of the atmosphere

a living fungus appeared on the bark of trees.

This tiny mushroom uses an enzyme to break down wood.

Gradually plant debris and dead trees decompose

and no longer build up on the ground to form coal.

The fungus stopped the accumulation of carbon on the ground

and instead it was recycled into the atmosphere.

The proportion of oxygen in the air decreased gradually

with major consequences for the environment.

This transitional period

brought about the demise of Arthropleura,

a distant relative of the centipedes.

But why did the first giants

of the carboniferous period disappear?

Could their lifestyle be responsible?

In 1977 Arthropleura fossils were found in Altier

in the heart of the French countryside.

The slag heap surrounding this former mining town

are hallmarks of its industrial past.

In the local natural history museum

tribute is paid to the miners

who discovered fossils while they were working.

Among them this impressive set of footprints,

the most important ever found in France.

They're examined by Sylvain Charbonnier

a specialist in arthropods, the family of invertebrates

that includes insects and centipedes.

- [Translator] Here you can see a set of tracks.

You have two trails that are parallel.

This was made by an organism of quite a respectable size,

an animal that must have measured around three feet long.

It's just a fragment of the track

that was probably much bigger.

- [Narrator] Unfortunately no adult size fossil

has been discovered.

The paleontologists have found many smaller specimens

in these coal deposits.

- [Translator] You can see here

what this little creature looked like.

These are juvenile specimens which are tiny.

Here's a complete specimen

or its shell that is well preserved.

So obviously this organism as it grows

will produce larger trails when it grows.

- [Narrator] Arthropleura was rather similar

to modern centipedes.

It could reach 10 feet in length

and it crawled on the ground or up trees in search of food.

Life in the rain forest during the early Permian period

was quite similar to that of the carboniferous period.

And there was enough oxygen in the atmosphere

for Arthropleura to thrive

and face unexpected predators such as Eryops.

This amphibian locates Arthropleura using cells in its skin

that detect vibration from the tree trunk.

But Arthropleura had a considerable advantage.

The claws at the end of its articulated legs

allow it to grip the trunk.

And its protective shell shields it against attackers.

(water splashing)

Arthropleura's disappearance

may not have been caused by predators

but by decreasing food supplies.

This creature was a herbivore.

At the time it would have had plenty to eat.

- [Translator] At that time the vegetation

was equatorial or tropical

so it was an extremely lush vegetation

with a great variety of plants.

These plants are in fact the origin of coal.

Arthropleura lived in this forest environment.

You also have on the other side trees and leaves

that were found in Arthropleura's stomach contents.

So it probably fed on these tree branches.

Did they eat from trees lying on the ground

or did they climb trees?

These are hypothesis, we will probably never know for sure.

- [Narrator] These fossilized plants

have been so well preserved that they still appear alive.

But as they began to disappear Arthropleura had to adapt.

- [Translator] This forest environment will tend to dry out

at the end of the carboniferous.

The climate will change, the vegetation will disappear.

And Arthropleura will lose its food source

which is probably one reason that explains its extinction.

- [Narrator] Over a period of 10 million years

the atmosphere and the climate gradually changed

bringing about the demise of Arthropleura.

The most recent fossils we have

date from about 280 million years ago.

Evolution could have retained smaller

and more energy efficient insects.

However, in 2009 scientists were surprised to find

new Meganeura fossils in the south of France.

These specimens discovered on sites

dating from the end of the Permian period

proved that the declining oxygen rate

cannot be the sole explanation

for the extinction of giant insects.

What clues did these unexpected fossils reveal?

These deposits are scarce. (hammering)

Scientists know of about only 15 of them in the world.

And like here it not being all fully excavated.

(hammering)

This beautiful landscape with its typical red rock

is located less than an hour from the French Riviera.

This is one of the sites excavated by Andre Nel.

- [Translator] Here we are 250 million years

into the red continental Permian,

red Permian because the rocks have become oxidized.

The iron is oxidized and has become red.

So we are dealing with an environment

that is extremely rich in organisms

that have left their impact

but few visible fossils up to now,

in any case in this deposit.

But fortunately fossils have been found in other deposits.

- [Narrator] It's in a similar geological layer

that insect fossils from the Permian period

were discovered in 2009

close to the French city of Montpellier.

- [Translator] For a long time

we thought these giant dragonflies

existed during the carboniferous period

at the beginning of the Permian.

But they no longer existed towards the middle

and end of the Permian.

But we were surprised to discover dragonflies

that were as big as those from the carboniferous.

- [Narrator] Paleontologists were perplexed

since the level of oxygen

had already decreased by that period.

In theory giant insects should have disappeared

but the specimens of different sizes

conserved in Andre Nel's laboratory in Paris

prove that they were still around.

- [Translator] There are tiny wings in the Meganeuradae

like this one here.

This is the size of a modern dragonfly's wing.

We have much bigger species.

Here is the real wing of another Meganeuradae,

another species.

This one too was a giant.

We have bigger ones but only fragments.

This here is a piece of Meganeuradae's wing.

The size is comparable to that

of the Meganeuradae of the coniferous.

We estimate that its wingspan is about 23 inches.

We see that with these animals there is great diversity.

It's during this time that they become the most diversified.

We have small ones, medium one, big ones and very big ones.

This means they have not really become extinct

to this period.

This does not sit well with the scenario of extinction

due to decrease in the level of oxygen.

- [Narrator] These recently discovered species

of Meganeuras found in France

have also turned up in the United States.

Evidence of their existence is accumulating.

Here is what the Earth looked like

during the middle of the Permian period,

the hot and humid world covered with tropical forests.

With an oxygen rate just slightly higher than today.

One animal species survived against all odds, Meganeuras

represented by this Meganeuropsis.

This specimen discovered in Texas

is as large as its French cousins.

But how can an insect measuring nearly two feet

survive breathing air that was much poorer in oxygen

than in the past?

Did it have an advantage that Arthropleura did not?

The Meganeuropsis fossil was discovered in 1937

next to Kansas City in the USA.

Professor Michael Engels is a paleoentomologist

who has worked at the University of Kansas

for the past 20 years.

Author of the definitive work

on the evolution of the insects

he's also the head of this collection

containing 4.7 million specimens,

most of them contemporary insects.

- These are some of the large insects that occur today,

large moths, stick insects, beetles,

dragonflies and damselflies.

And while they're pretty impressive in their size

none of them can compare to the giant insects of the past.

- [Narrator] According to Engels

one asset which might have enabled Meganeuras to survive

during the Permian period despite the low oxygen levels

is the movement of their wings.

- You would have an easier chance

getting a large flying insect

than you would a large insect that doesn't fly.

Wings are vital not only for the movement of the organism

but as the muscles contract to move the wings up and down

they actually press up against the air sacs

and move air through the body.

Flight actually confers an advantage to the giant insects

in the fact that the actual movement of the flight muscles

helps to support the metabolically active tissue within them

by getting oxygen into an area where a wingless insect

or other arthropod would not be able to.

- [Narrator] This full body ventilation

could be the secret to Meganeuropsis' survival.

The movement of its wings quickly brings air to the trachea

which then supplies the organs with oxygen.

While the ground dwelling giants

of the carboniferous period disappeared

this advantage would have allowed Meganeuras

to continue ruling the skies during the Permian period

remaining at the top of the food chain in the swamps.

This Diplocaulus, a now extinct amphibian

has no chance of going unnoticed,

betrayed by its need for air.

Meganeuropsis sees it

as soon as it leaves the water's surface

thanks to eyes that are extremely sensitive

to movement, shapes and colors.

(water splashing)

Meganeuras were the super predators of the time.

Their wings enabled them to survive

despite falling levels of oxygen.

So what caused their extinction?

No Meganeura fossils have been discovered

from after the Permian period.

Today scientists still don't know

exactly when they disappeared.

But other, large sized dragonflies

survived the next 130 million years.

To explain the extinction of these giants

scientists are now contemplating

the emergence of new predators.

While insects were the only flying creatures

during the first part of their history

other animals took to the skies

during the later Permian period

between 300 and 250 million years ago

of what was to become eventually Europe.

Jean Sebastian Steyer, paleontologist

at the natural history museum in Paris

is the leading French specialist in early vertebrates.

He has come to the legendary paleontology gallery

to collect a very important specimen

for the study of insect predators.

Though smaller in size than many other fossils

this was the first of its species

to possess a major advantage.

- [Translator] This is the fossil of a gliding reptile

that is about 250 million years old

and has the strange name of Coelurosauravus.

This reptile actually developed gliding flight.

- [Narrator] The ability to glide

allows an animal to catch prey in the air

like the giant insects.

The planet continued to heat up

at the end of the Permian period.

Swamps, an infinite source of fossils

now have aquatic plants characteristic of stagnant waters.

Like the insects during the carboniferous period

reptiles were just starting

to try out life in the trees and flying.

Amongst them Coelurosauravus

would become an outstanding insect hunter

thanks to its retractable wings.

- [Translator] It had a very unusual

and interesting anatomy.

It's fairly small head was a triangular shape.

On its skull we can see small, conical pointed teeth

that were probably used to crack

the hard exoskeletons of insects.

And of course the main characteristic

of this gliding reptile are its stick shaped bones

that start around the armpits and enable this animal

to throw itself in the air and base jump.

We can well imagine it

climbing up this microscope for instance and then jumping.

We can even imagine it climbing with its small claws

and then unfolding its wings to glide.

So we can picture the race between Coelurosauravus

and the flying insects living at that time.

- [Narrator] Only 16 inches long,

this small reptile couldn't catch Meganeuras

but it could compete for the same prey,

the Palaeodictyoptera.

To catch its victim it has to take the plunge.

Coelurosauravus can't flap its wings.

To catch flying insects it relies on an element of surprise.

And its ability to glide.

There is no room for error.

Coelurosauravus is merely a first step

on the road to flight.

- [Translator] This gliding reptile

has no doubt played a part.

Maybe not in the full extension of giant insects

but in any case we have a super predator

regularly attacking them.

And we can therefore assume that this was one element

in the decline of giant insects at the time.

- [Narrator] If Coelurosauravus was not the only culprit

it was certainly the first

to put pressure on giant insects

before any others took to the skies.

This animal guarding the entrance

to the Karlsruhe Museum in Germany

is part of the pterosaur family.

These flying reptiles appeared 230 million years ago.

Today they are completely extinct.

But scientists have discovered

around 100 different species.

Could they, too, have been a threat to giant insects?

Professor Eberhard Frey or Dino as he is usually known

is a world specialist in pterosaurs.

- Pterosaurs are flying reptiles

and they are characterized by a flight membrane

that extended from the tip of the little finger

down to the ankle.

The interesting point with these pterosaurs is that

they have a size range which is simply unbelievable,

from about 20 centimeters wingspan

up to 14 meters wingspan which is unique.

- [Narrator] Yet according to scientists

very few of these pterosaurs were insect eaters.

The only insectivores were part of the Anurognathus family,

among the smallest pterosaurs.

- We cannot imagine really that they hunted the big insects

but probably they chased the small ones

which are not seen in the fossil record.

The big insects however also chase small insects

so they probably conquered about the same prey.

All the other pterosaurs from that time we know

likely fed on something else.

And thus did not make any concurrence to the big insects.

And probably this is one of the reasons

why they persisted such a long time.

- [Narrator] 230 million years ago

during the Triassic period pterosaurs spread around Europe

but also to what is now South America and Asia.

For the first time in the history of life on Earth

the family of vertebrates learned to master

not just gliding but flapping flight.

Like Anurognathus discovered in Germany

its Asian cousin Batrognathus is a flying reptile,

nocturnal, insect-eating and fast.

With its flat skull and big eyes

Batrognathus occupies the same

ecological niche as modern day owls.

But the comparison with birds of prey stops there.

Its enormous jaws are equipped with a dozen conical teeth.

No flying insect can hide from Batrognathus.

literally flying frog jaw.

An insect with a 10 inch wingspan take it on.

An experiment carried out in Germany

puts the theory to the test.

Dino Frey works in collaboration

with the Institute of Fluid Mechanics in Germany.

This wind tunnel is usually used

to refine the shape of airplanes

and improve their aerodynamics.

But today the paleontologist is using it

to test the pterosaur's flying abilities.

A resin and carbon fiber model of Anurognathus

is placed in the wind tunnel.

- We are the beginning of our studies.

But what we learned so far is that pterosaurs

likely were extremely slow flyers.

So they could cope with wind speeds

around 40 kilometers power or less.

But probably these guys needed to flap their wings

to stay in the air and that they were not very good gliders.

But flapping wings also means

that they were as active flyers much more maneuverable.

And this is again interesting

when they started to chase insects on the wind.

- [Narrator] When pterosaurs appeared

insects lost the monopoly on flapping flight.

Batrognathus was indeed capable

of leaving the tree-lined shore

to chase insects out in the open

which its predecessor Coelurosauravus,

the flying lizard was unable to do.

The pterosaurs seemed to have had

more of an impact on the giant insect's prey

than on the giant insects themselves

contributing to their final decline

but not fully explaining their extinction.

On the other side of the Atlantic

one American researcher suggested other culprits

in a study published in August 2012.

This paleontologist specializes in the extinction

that occurred at the end of the Permian period

250 million years ago.

More at home in front of a computer

than wielding a trow in the field

Matthew Clapham is a database devotee.

It took him a year and a half to collect the information

needed to publish a survey on the decline of giant insects.

He has undertaken a mammoth task,

gathering the sizes of all fossil wings

since the first scientific publications.

- We compiled this very large database

with nearly 10,000 insect species

by simply getting published papers

where paleontologists had found insect fossils

and described them and given them a name.

- [Narrator] Clapham discovered

that during the first part of their history

insect size changed with the level of oxygen

in the atmosphere.

As oxygen declined they diminished in size.

And as it rose their size increased.

- And so this pattern holds for the first

200 million years or so of insect history.

But then beginning in the late part of the Jurassic period

around 150 million years ago

you can see insects become smaller

even though atmospheric oxygen is going up at this time.

And this coincides quite closely

with the evolution of Archaeopteryx, the first bird.

- [Narrator] The ancient ancestors of the birds

first appeared during the Jurassic period

160 million years ago.

The oldest fossils come from China.

At that time forests of giant conifers

offered a fantastic launch pad to conquer the sky.

An ecological niche that was quickly seized

by a new generation of creatures learning to fly.

Small dinosaurs like this Anchiornis

had feathers on their arms and legs and used them as wings.

The claws on their wings enabled them to gain altitude

and get good vantage points.

Insects like this had to hide in the trees to survive.

As soon as it takes off it becomes visible

and is hunted down by Anchiornis.

While only a few pterosaurs like Anurognathus ate insects

all bird ancestors did.

Increasingly skilled at flying

they would become fierce insect predators.

- In the cretaceous period

when these first birds are evolving

there would have been increased predation and pressure

on these large insects in particular

as they were less maneuverable than the smaller insects.

In addition to this increased predation

there was likely competition between birds and insects

especially these large predatory insects

for the same food sources.

And so both of those factors

likely led to a decrease in insect size.

- [Narrator] This competition between birds and insects

still happens today.

Just like flying lizards and pterosaurs

birds would have had an influence on the size of insects.

But why have giant insects completely disappeared

leaving only today's small insect population?

Our last clue could provide an answer.

It came from a fossil rich site

close to where Anchiornis was found

in the Chinese region of Liaoning

northeast of Beijing.

The numerous eruptions that shook the region

125 million years ago

have helped preserve certain plants

from the period in volcanic ash

including the ancestors of flowering plants.

Discovered in 2002 by the paleobotanist Sun Ge

they would have had an unexpected impact

on the extinction of the last large sized dragonflies.

- But here in China

in the west we found the oldest known

and this one we call the Archaefructus.

- [Narrator] This is Archaefructus,

the first flower to appear on our planet.

On this fossil seen through a microscope

we can distinguish the male organs,

the stamens that contain the pollen

and the pistil, the female organ.

These characteristics allow Sun Ge to confirm

that this fossil belongs to the angiosperm,

the family of plants whose seeds

are enclosed inside a fruit, unlike conifers.

According to the paleobotanist these plants were aquatic

and grew on lake shores.

But what does the appearance of the first flowering plants

have to do with the extinction of large carnivorous insects.

Andre Nel believes these two events are linked.

- [Translator] Many families of insects

disappeared at that time.

And others managed to adapt to angiosperms

which proliferated and began to diversify

to produce more or less our modern forests.

The impact was also very significant

for dragonflies during that same period.

- [Narrator] Could the decline of giant insects

have something to do with the dragonflies original shape

because before they were able to fly

they were aquatic creatures.

Their life began under water.

For the first few years they existed as larvae.

And just like their cousins the mayflies

they fed on other aquatic insect larvae.

When flowering plants such as Archaefructus

appeared on the lake shores 125 million years ago

the larvaes life conditions changed.

The plants took root in shallow waters

but then opened their flowers in the air.

When they withered their petals and leaves

floated on the surface before sinking to the bottom.

This material is digested

by the microorganisms present in the water.

But to do this the organisms use the oxygen

contained in the water

leaving little oxygen available for the dragonfly larvae.

- [Translator] These dragonflies

may have disappeared at that time.

Because their larvae could not adapt

to this change in the aquatic ecosystem

and they were replaced by other dragonflies.

- [Narrator] The emergence of flowering plants

completely modified the lake's ecosystem.

And would have led to the extinction

of the last large sized insects

which had gradually declined since the carboniferous.

The extinction of arthropods and giant insects

over millions of years of evolution

teaching them that it took many protagonists

to cause the extinction of these species.

The change in the composition of oxygen in the atmosphere,

the emergence of new predators like flying lizards,

some pterosaurs and the bird ancestors

and finally the birth of flowers.

In the early 21st century

which are the largest insects that inhabit our planet?

Today insects can reach the size of a hand

but very few are bigger than this Chinese cricket.

For we are at the dawn

of a new phase of extinction caused by humans

since the onset of the Industrial Revolution.

- [Translator] The large insects live mostly in topical

or intertropical climates.

They're in danger since the habitat is a risk.

If the forest in which

the giant stick insect lives is in danger

the giant butterfly will of course disappear.

- I certainly hope that we will continue to see them

but certainly with the rate of habitat destruction

that's going on throughout the world

particularly in the tropical environments

where many of these species occur

it is very likely that a lot of them will be lost

just like the giant insects.

(vibrant inspirational music)