All language subtitles for Megafauna What Killed Australias Giants S01 E01_track4_[eng]

HUGH JACKMAN: Ice Age Australia.

Home to giant and bizarre animals
known as megafauna.

Herds of wombat-like herbivores
run vast grasslands.

Living alongside kangaroos,
with strange short faces.

And ruling this land,
the apex predators.

Heavily armoured giant lizards

and a marsupial-killing machine
Heavily armoured giant lizards

and a marsupial-killing machine
armed with bone-crushing jaws.

These majestic animals lived here
for millions of years.

But in a blink of time...

..they were wiped
from the face of the Earth.

So what happened?

Today, experts are gathering clues

from remote and inhospitable parts
of Australia.

There's been 12 people on the moon
and 10 people in this cave.

This place is like nowhere else
in the world, really.

This is pretty bloody good.
(CHUCKLES)

These scientists are testing
the leading theories

behind this disappearance.

Is this the smoking gun that
explains the megafaunal extinctions?

New evidence will rewrite
Australia's Ice Age cold case.

What killed Australia's giants?

Deep within the Naracoorte Caves
in South Australia

lies the ultimate megafauna
crime scene.

WOMAN: This is one of the largest
deposits of megafauna fossils

anywhere in the world.

In this tomb are the fossil remains
of 26 species of extinct megafauna.

So we've got in front of us bones
of a giant marsupial browsing animal

that was called Zygomaturus,
weighed half a tonne.
So we've got in front of us bones
of a giant marsupial browsing animal

that was called Zygomaturus,
weighed half a tonne.

that was called Zygomaturus,
weighed half a tonne.
We have Thylacoleo carnifex,
the gigantic marsupial predator

We have Thylacoleo carnifex,
the gigantic marsupial predator

which really did rule the jungle
around here.

And we can see also skulls
of gigantic kangaroos

that had short faces and ate leaves
instead of grass.

For palaeontologist Liz Reed,

this crypt offers rare insights
into the creatures' final moments.

These caves have literally acted
as death traps

for hundreds of thousands of years,
and we call them pitfall traps.

If you can imagine a small entrance
on the surface,

If you can imagine a small entrance
maybe concealed by vegetation,

maybe concealed by vegetation,

which leads down a relatively
maybe concealed by vegetation,

which leads down a relatively
narrow deep hole into a cave.

So animals are hopping around,
moving around the surface.

They don't see this entrance
until it's too late

and they'll just plummet down
into these caves.

But their brutal deaths provide
a treasure trove of information,

including a time line
to their extinction.

What we're looking at here is what
we call a stratigraphic section,

which is basically a series
of sediment layers

that have washed into the cave
over time.

At the same time that animal
remains were accumulating.

At the same time that animal
This is a classic fossil deposit,

This is a classic fossil deposit,

and we've dated this deposit from
around 13,000 to 65,000 years ago.

If we look at a particular layer
in time,

if we come down here
to around 42,000,

if we come down here
we see something quite remarkable.

we see something quite remarkable.

We see the last appearance
we see something quite remarkable.

We see the last appearance
of the megafauna.

And these were animals
that had a long evolutionary history

And these were animals
of millions of years,

of millions of years,

but that came to a halt
of millions of years,

but that came to a halt
for many of them

around this time
when they became extinct.

Back then, the world was
in the grip of an ice age.

While Australia stayed mostly free
of glaciation,

the climate went through periods
of rapid and extreme changes.

Dominating the country were huge
species, weighing up to 2,500 kilos,

known today as megafauna.

So what could have caused almost 90%
of these animals to disappear

by 40,000 to 50,000 years ago?

Many scientists around the continent

are trying to look at different
lines of evidence

to understand what may have driven

these magnificent creatures
to extinction.

One is whether climate
had some kind of role to play.

So changes in the environment
and the climate

did not favour
those particular animals.

Everyone's aware that there
is some dramatic changes happening

Everyone's aware that there
on the Earth at the moment.

on the Earth at the moment.

One is biodiversity loss,
on the Earth at the moment.

One is biodiversity loss,
the other is climate change.

But we can't really get
a long perspective on that

by just looking
at what's happening now.

So studying megafauna helps us
understand

So studying megafauna helps us
what drives animals to extinction.

what drives animals to extinction.

So that the dead are actually
helping us inform

So that the dead are actually
about the future of our planet.

about the future of our planet.

PILOT: Traffic Arkaroola helicopter
hotel alpha becoming airborne.

Tracking to the north-east
for Lake Callabonna.

Tracking to the north-east
Not above 2,500. Traffic Arkaroola.

Not above 2,500. Traffic Arkaroola.

Palaeontologist Aaron Camens
Not above 2,500. Traffic Arkaroola.

Palaeontologist Aaron Camens
is travelling deep into the outback

to an ancient lake bed
that could contain important clues

about whether climate change
caused the demise of the megafauna.

Lake Callabonna is like nowhere else
in Australia or the world, really.

Lake Callabonna is like nowhere else
It's a huge salt lake today,

It's a huge salt lake today,

It's a huge salt lake today,
but 50,000 years ago,

but 50,000 years ago,

there was a lot more water around.

And literally thousands
of megafaunal animals

And literally thousands
got stuck in the mud.

got stuck in the mud.

And what this means is that we see,
got stuck in the mud.

And what this means is that we see,
rather than just one or two bones,

complete skeletons preserved
where the animal got stuck.

And because they're stuck
in the mud,

they're essentially partly buried
as they die,

which means that the fossilisation
detail is much higher.

And that is something that we do not
see anywhere else in Australia

And that is something that we do not
for any of these species.

for any of these species.

It's been four years since
Aaron's last visit to the lake.

Ah, it's exciting to be back here.

These shifting sands continually
reveal new megafauna remains,

while earlier discoveries disappear
forever,

eroded by the harsh desert
conditions.

Finding valuable evidence here
is a race against the elements.

So here we can see that
we've got to this one too late.

So here we can see that
So the bone is reduced to powder.

So the bone is reduced to powder.

If it's in that weathering zone,
it can be eroded or weathered

If it's in that weathering zone,
very, very quickly.

very, very quickly.

But amidst the crumble remains
very, very quickly.

But amidst the crumble remains
is a precious discovery.

Wow, this looks great.

It's quite extensive too.

So what we've got here is the
skeleton from Diprotodon optatum,

the thing that has made Callabonna
famous.

Up at this end, we've got the
fragmented remains of the skull.

This is so well preserved
that we can see the body

still as it was
when the animal died.

We've got the spine down the middle,
the pelvis at the back,

and the legs are still
in the position

where this giant marsupial fell
over on its side.

This is the biggest marsupial
that ever lived.

Stood about two metres tall
at the shoulder,

3.5m long, weighed over two tonnes.
at the shoulder,

3.5m long, weighed over two tonnes.

So it's about the size
of your urban SUV.

Five lumbering giants have gathered
by the water's edge.

There is a new member of the family.

At nine months, this joey
is exploring his surroundings,

spending less time
in his mother's protective pouch.

Diprotodons were widespread
across much of Ice Age Australia.

Diprotodons were widespread
Males were much larger than females,

Males were much larger than females,

suggesting they could have lived
in small family groups

suggesting they could have lived
characterised by one dominant male.

characterised by one dominant male.

(ROARS)

Their large nasal cavities
might have been used

to make deep grunting calls.

Like koalas today, low frequencies

would have allowed them to maintain
social communication

over long distances.

This is one of the most exciting
parts of Callabonna for me.

The lake bed has safeguarded
the most precious of details.

Nowhere else in Australia
do we see the soft tissue

Nowhere else in Australia
of megafaunal animals preserved.

of megafaunal animals preserved.

If we have a really close look here,

we can see this kind
of dimpled surface.

Now that is actually recording
the foot pads of Diprotodon.

So where Diprotodon got stuck
in the mud here,

the mud has wrapped around its foot,

and that impression of the soft skin
of the foot

has been preserved
for over 50,000 years.

Staggeringly, the remains
of nearly 900 Diprotodons

Staggeringly, the remains
have been found at Lake Callabonna.

have been found at Lake Callabonna.

So why did so many
take their last steps here?

If we go back 50,000 years,

Lake Callabonna
is progressively getting drier.

We're talking about a time
of extreme climatic variability,

and that change in climate

could be one of the driving factors

in what led to
the megafaunal extinction.

As the lake contracted over time,

animals were forced
to move through the mud

animals were forced
to get to the shrinking water supply.

to get to the shrinking water supply.

And the heavier the animal,
the more likely it was to get trapped

in a muddy grave.

Fortunately, for this family
of giants,

they've safely navigated the perils
of the lake.

But there may have been another
deadly consequence to being so large

in a drying environment.

So one of the theories is that
because these animals were so big,

they may have been very slow
to breed.

They might have only had one joey

as opposed to two, three, four,
or even ten,

like some of our
carnivorous marsupials have.

There might have been a need
for many good years in a row,

so maybe four or five years
of good vegetation

to be able to raise a young
to maturity.

As temperatures become more extreme
and rainfall changes,

what was a fertile landscape
dries out completely.
As temperatures become more extreme
and rainfall changes,

what was a fertile landscape
dries out completely.

The lake and its vital water
has disappeared.

Despite its mother's best efforts,

this baby Diprotodon cannot go on.

Now out at Lake Callabonna,
we have a drought period,

but that doesn't mean that that was
what drove the megafauna extinct.

At one area, we might see
what's called extirpation,

which is the local extinction
of a group of animals.

But that doesn't mean
that they've gone extinct

But that doesn't mean
on a continental scale.

on a continental scale.

So was drought driving extinctions
in other parts of Australia?

Over 1,300 kilometres
to the east of Lake Callabonna,

researchers are trying to determine

researchers are trying to determine
if climate change could have caused
megafauna to die out

if climate change could have caused
megafauna to die out

if climate change could have caused
in other parts of the continent.

in other parts of the continent.

The back yellow one should be
loosened, John.

Haidee Cadd is a palaeoecologist
who studies environments of the past.

Haidee Cadd is a palaeoecologist
Flip it.

Flip it.

She's part of a team

aiming to reconstruct
the environmental conditions

present here at Welsby Lagoon during
the time of megafauna extinction.

Welsby Lagoon is a really
interesting and important site.

It's one of the few sites
that we've got in Australia

that hasn't dried up
during the last 80,000 years.

So we've managed
to get a continuous record.

It's disconnected
from the regional water table

and it also has no inflowing
or outflowing streams.

So it provides a really great
natural case study

for us to look at things like
changes in environment and climate.

That's Litoria cooloolensis,
which is one of the acid frogs

That's Litoria cooloolensis,
that only live in Wallum wetlands.

that only live in Wallum wetlands.

It's an endangered species.

They're very common in this wetland.

They're jumping everywhere
off the reeds in front of me.

They're jumping everywhere
It's quite amazing.

It's quite amazing.

That's all untangled, Pete?
Yep.

Let's put them on.

Today, the team will drill down deep
Let's put them on.

Today, the team will drill down deep
enough to extract sediment layers

Today, the team will drill down deep
dating back 40,000 to 50,000 years.

dating back 40,000 to 50,000 years.

Yep.

OK.

When we take our cores
out of the sediment,

we see often just brown mud.

Ready?

OK. Slow.

But when we take those cores back
OK. Slow.

But when we take those cores back
to the laboratory

But when we take those cores back
and we start to analyse them,

and we start to analyse them,

that's how we can get
a precipitation record.

So that's how we can start
to work out

whether the changes we're seeing
in the environment
So that's how we can start
to work out

whether the changes we're seeing
in the environment

are related to changes in climate
as well.

are related to changes in climate
as well.
For the first time in tens
of thousands of years,

For the first time in tens
of thousands of years,

the lagoon's hidden history
is revealed.

It's quite fibrous and peaty
at the top here

and it looks like it changes
gradually through here.

Much finer here.
But look down there.

Yeah.

That last five centimetres
or so is very different, isn't it?

Like you can feel an edge there.
Yep.

This is very much lake sediment.

The sediment core tells a story

of significant environmental
and climactic change.

The first part of our record,
we see quite wet conditions.

There's rainforest growing
around the site.

But as we move through between
60,000 and 50,000 years ago,

we start to see
some really dry conditions

that shifts the vegetation into this
open grassland kind of environment.

Shall we wrap it?
Yep. Let's wrap her up.

We've looked at other records
along the east coast of Australia,

and we've managed to find changes
in the vegetation

in a lot of these other records that
corresponds to the climate changes

in a lot of these other records that
that we're seeing at Welsby Lagoon.

that we're seeing at Welsby Lagoon.

Forensic analysis
of these sediment cores

has produced some of the most
profound evidence

of the existence and disappearance
of megafauna in the area

through, of all things, their poo.

What we have here are some photos
from one of the cores

that we've analysed
from Welsby Lagoon

and what we see at the start of the
record,

so from 80,000 to 60,000 years ago,

is sporormiella spores.

These are the dung fungi
that come from megafauna.

These are the dung fungi
And we can see that

And we can see that

during the time period
And we can see that

during the time period
where it's dominated by rainforest,

we get quite a high abundance
of these dung fungi.

And then as we move forward
through time,

we start to see this drying of the
climate just after 50,000 years ago.

And we also see a change
in the vegetation.

And you can see we still
see some spores

of our sporormiella in this period,

suggesting that megafauna
were still around,

but the amount of the sporormiella
is much lower.

And then again,
at about 40,000 years ago,

we start to see really dramatic
changes in rainfall.

we start to see really dramatic
So quite dry conditions,

So quite dry conditions,

which is also changing
the local environment.

And this also coincides
with the time that we see

And this also coincides
the disappearance of Sporormiella.

the disappearance of Sporormiella.

By 40,000 years ago,

it looks like there was no
By 40,000 years ago,

it looks like there was no
megafauna living around this site.

How did this changing environment

lead to the disappearance of
megafauna here on Minjerribah?
How did this changing environment

lead to the disappearance of
megafauna here on Minjerribah?

The drying conditions that we see
from Welsby Lagoon

The drying conditions that we see
from Welsby Lagoon
probably wouldn't have suited
the megafauna particularly well,

probably wouldn't have suited
the megafauna particularly well,

so they would have started
to see changes

in the food sources
that they've been eating

if the vegetation
is starting to change.

But we'd also be seeing a lot
of the fresh water sources

on Minjerribah and North Stradbroke
Island start to dry up,

and the megafauna would
have been struggling to find

and the megafauna would
food to eat and water to drink.

food to eat and water to drink.

And perhaps this catastrophic drying
that happened

during this 50 to 40,000 year period

might have been enough to push
the megafauna over the edge.

But why is it that some species of
megafauna still walk the Earth today

But why is it that some species of
while others perished?

while others perished?

As the climate rapidly changed,
only the hardy could survive.

It's possible that those animals

capable of travelling
great distances

capable of travelling
between diminishing water supplies

between diminishing water supplies

had a better chance of survival.

There is a group of megafauna
who could do just that.

Today's kangaroos
are the great survivors.

Kangaroos that we know today

have got a really beautiful,
Kangaroos that we know today

have got a really beautiful,
streamlined body shape.

have got a really beautiful,
They've got a small head

They've got a small head

and what we'd call
a gracile upper body

coming down to really big,
powerful hip and thigh muscles

and long, thin legs and feet.

All of these are adaptations for
really efficient bipedal hopping.

Comparative anatomist Natalie
Warburton studies living animals

to learn more about
their extinct relatives.

So, our big red and grey kangaroos,
that get up to 70 kilos or more,

So, our big red and grey kangaroos,
that get up to 70 kilos or more,
were hopping around
at the same time as Diprotodon

were hopping around
at the same time as Diprotodon

and the giant extinct goanna
megalania.

There was also a lot of diversity
in kangaroos.

But one of the biggest of all
of the extinct kangaroos

But one of the biggest of all
was Procoptodon Goliah.

was Procoptodon Goliah.

Standing over two metres tall
and weighing up to 240kg,

this was an enormous beast moving
through the Australian landscape.

A pair of Procoptodon feast
before the heat of the day.

Unlike today's kangaroos,
who feed on grass,

they prefer bushes and leaves.

Their distinctive short face
gives the jaw more strength

Their distinctive short face
to chew the tougher plants.

to chew the tougher plants.

Procoptodon was the largest
of the extinct short-faced marsupials

Procoptodon was the largest
known as sthenurine kangaroos.

known as sthenurine kangaroos.

But could this giant do

what its modern-day relative
takes for granted -

what its modern-day relative
hop?

hop?

The hopping at high speeds
is actually really efficient.

These really long tendons
and muscles in the leg

stretch like elastic bands
and then recoil.

That helps to transmit some
of that stored elastic energy

That helps to transmit some
into the hopping.

into the hopping.

So what about
a 240-kilogram Procoptodon?

Were they able to hop or were
they doing something different?

And was that the difference
between life and death?

Today, a team of scientists

is putting an eastern grey's tendon
to the test

to understand
how its ancient relative got around.

MAN: So this is a sub alpha male.
They get bigger than this.

But this guy has probably been
in a fight.

He's been forced
to leave his territory,

He's been forced
he's had to cross the road,

he's had to cross the road,

and unfortunately
he's had to cross the road,

and unfortunately
he's been hit by a car.

And that's how he's ended up here
today.

I'm just going to cut this skin away
so we don't damage the tendon.

Christopher Clemente is
a comparative biomechanist.

So when a kangaroo hops,

all that force has got
to pass through the tendon.

And we think this might be
one of the limitations
all that force has got
to pass through the tendon.

And we think this might be
one of the limitations

to the maximum body size
And we think this might be
one of the limitations

to the maximum body size

or the maximum speed that these
kangaroos are capable of moving at.

or the maximum speed that these
kangaroos are capable of moving at.
WOMAN: Yeah. Like cleaning up
that cross and then it looks...

WOMAN: Yeah. Like cleaning up
that cross and then it looks...

Yeah. Oh.

See all the individual muscles,
Yeah. Oh.

See all the individual muscles,
yeah.

It's nearly as thick as your finger,
which is incredible.

For an animal that's a fourth...
a quarter of the weight of a human,

these tendons are incredibly big.

Would a tendon like this be strong
enough to support a hopping Goliath?

Would a tendon like this be strong
Here you can feel it's quite tough.

Here you can feel it's quite tough.

It's basically this rubber band.
You know.

They really have this unique
tendinous structure.

Ah, yeah. There we go.

Once the tendon is removed,

it's secured in a specialised
engineering rig,

where it will be stretched
to the point of failure.

Can you feel it? Is it taut?

Yeah, it's very taut.

OK. We're going to do
our failure test.

So we're going to pull it up
all the way until it breaks.

Alright. And starting.
Starting.

Alright. And starting.
(BEEP!)

(BEEP!)

Perfect.
That's...four.

Five.
Now it's going to go.

Five.
Six.

Six.

And now it's going. Now it's going.

300 newtons.

500 newtons. That's insane.

700 newtons.
500 newtons. That's insane.

700 newtons.
800 newtons.

700 newtons.
Oh! Now it burst.

Oh! Now it burst.

You can see it at the top here
it slipped.

So at 880 newtons...

There. It's about to go
at the very top.

Sliding out.

The eastern grey's tendon
withstood an immense 880 newtons

The eastern grey's tendon
until it failed.

until it failed.

That's the equivalent of
until it failed.

That's the equivalent of
more than 80kg of force.

The force that this tendon
can withstand

was about four times the body weight
of this kangaroo,

in just one tendon of one leg.

We were able to get huge forces
out of these tendons,

We were able to get huge forces
and that's a little bit surprising.

and that's a little bit surprising.

So we think these tendons are
and that's a little bit surprising.

So we think these tendons are
actually able to withstand

So we think these tendons are
higher forces than we thought.

higher forces than we thought.

I'm just going through
today's simulation.

The team have used their knowledge
of the eastern grey's anatomy

The team have used their knowledge
to build a computer model.

to build a computer model.

So you've got the 50-kilogram model
hopping at multiple speeds.

Is that right?
I have.

This model can be scaled up

to test if kangaroos can become
too big to hop.

So this one here is the 200.

By building these models

that are heavier and heavier
than the animals we actually see,

we can make predictions about the
ways in which they would have moved.

OK, so what happens when we get
to 250 kilos?

This is about the mass
of a Procoptodon.

This is about the mass
Could it hop?

Could it hop?

(GROANS) It's an effort.
Oh!

(GROANS) It's an effort.
He's not doing very well.

He's not doing very well.

How much more the torso has to move.

So it really flings its body up.

And see how the ankles
touch the ground?

Right. And what speeds is it capable
of hopping at?

Right. And what speeds is it capable
Just one.

Just one.

It can only hop
at 2.6 metres per second.

It can only hop
So it's now highly constrained...

So it's now highly constrained...

Yes.
..in the speeds that it can hop at.

Hopping at one speed is hardly
a practical way of getting around.

So if hopping is off the table,
how did Procoptodon move?

Deep in the vaults
of the Melbourne Museum

are some of the best preserved
Procoptodon fossils on the planet.

By comparing these ancient bones
to those of modern kangaroos,

scientists may have found
the answer.

MAN: Independent lines of evidence
all seem to roughly

MAN: Independent lines of evidence
be pointing in the same direction,

be pointing in the same direction,

that there were these giant striders
in the Australian landscape.

NATALIE: This is
an incredible specimen.

There's so many bits here.
It's so amazing.

Today, Tim Ziegler
and Natalie Warburton

have the bones of three kangaroo
skeletons for comparison.

Laid out on the table is
a box of eastern grey bones,

Laid out on the table is
the giant Procoptodon fossils,

the giant Procoptodon fossils,

and an impressive,
the giant Procoptodon fossils,

and an impressive,
almost complete skeleton

of a 50,000-year-old
Sthenurine kangaroo.

It's a typical-sized kangaroo.

It is, but it's very, very chunky.

Yeah.
It's got amazing bones.

This short-faced kangaroo lived
at the same time as Procoptodon.

It's a close relative,
so can provide the best evidence

as to how Procoptodon
might have moved around.

So when we look at these hips...

You know, in our grey kangaroo,
we've got almost a straight line.

And when we look at this one...

You know, we've got this flexed
angle probably corresponding

to a posture that's more upright.

There are several telltale signs
within this skeleton

that prove these ancient kangaroos
walked instead of hopped.

In terms of the shape,
it's so different.

You can run through the entire
skeleton of a short-faced kangaroo

to find features
pointing towards striding.

The joint surface
is just so much bigger,

The joint surface
and big joint surfaces mean

and big joint surfaces mean

spreading of load
to reduce the stress.

That's something a hopping kangaroo
just doesn't have to worry about.

That's something a hopping kangaroo
They're exceptionally adapted for

They're exceptionally adapted for

supporting their weight
on one leg or another,
They're exceptionally adapted for

supporting their weight
on one leg or another,

rather than spreading their body
mass across both feet at once.

rather than spreading their body
mass across both feet at once.
This is even more pronounced
in the leg of the Procoptodon.

This is even more pronounced
in the leg of the Procoptodon.

The knee joint at the end
of the bone as well is interesting.

The knee joint at the end
It's very broad.

It's very broad.

It's supporting
It's very broad.

It's supporting
spreading that weight

and spreading stress from movement,
side-to-side movement,

and spreading stress from movement,
really effectively.

really effectively.

This is a knee for an animal

that is moving its body side to side
This is a knee for an animal

that is moving its body side to side
as it walks.

One of the strongest signs
a short-faced kangaroo didn't hop

One of the strongest signs
was the length of its tail.

was the length of its tail.

In living kangaroos,

their long tails act as
a counterbalance when they take off.

This means their body doesn't tip
forward or sideways.

There's fewer vertebrae.

You know, it looks like it's
probably going to get to about here,

which is much shorter than we would
expect in a hopping kangaroo.

That's really suggesting that this
is moving in a really different way.

That's really suggesting that this
Sure.

Sure.

These bones paint a picture
of a very different kangaroo...

..one with a short tail
that walked upright like a T-rex,

rather than hopping like
a contemporary kangaroo.

Could this difference in locomotion
have played a part in its extinction?

In terms of climate,

unpredictability has become
an advantage in some ways

for living kangaroos.

Because they can move such vast
distances in a short amount of time

with their incredibly efficient
hopping locomotion.

That's a response that just wouldn't
have been available to Procoptodon.

Once those distances are too great
for this animal to move,

Once those distances are too great
well, then, it's kind of stuck

well, then, it's kind of stuck

and therefore at more risk
to local spontaneous events

like the decline in regular
seasonal water or disease.

The ultimate proof to whether these
prehistoric kangaroos strode

The ultimate proof to whether these
prehistoric kangaroos strode
may lie in the sands of Lake
Callabonna in South Australia.

may lie in the sands of Lake
Callabonna in South Australia.

MAN: To unpick what happened
over 40 to 50,000 years

MAN: To unpick what happened
in the past is a major challenge.

in the past is a major challenge.

What we have, though, in Australia

is that opportunity
What we have, though, in Australia

is that opportunity
to do more discovery

to identify fossil deposits
is that opportunity
to do more discovery

to identify fossil deposits

no-one has seen before

no-one has seen before
to look for that unexpected piece
of evidence.

to look for that unexpected piece
of evidence.

This is pretty bloody good. (LAUGHS)

Completely unexpected.

Aaron Camens has discovered
Completely unexpected.

Aaron Camens has discovered
exciting new evidence.

I think that's about it.

These footprints could change
scientific theory into fact.

Yep. I think that's what we've got.

Excellent.

We have just stumbled across
this trackway.

If we have a look, we can see that

there are short oval prints.
If we have a look, we can see that

there are short oval prints.

there are short oval prints.
They're fairly wide set,

They're fairly wide set,

and the animal is taking
fairly short strides.

So this is nothing like
we would expect to see

if we were looking at an emu.

The trackways are much narrower,

and the shape of this foot doesn't
really fit with anything

except one of our extinct
short-faced kangaroos.

So, this is the first time I have
come across a trackway like this

that potentially does demonstrate
we've got a striding kangaroo.

Now, as someone who works
on fossil footprints,

Now, as someone who works
this is a pretty exciting moment.

this is a pretty exciting moment.

One of the great things about
trace fossils is that

they're an actual record
of behaviour.

And so if an animal is moving
in a specific way, in a track way,

it's not a theory anymore.

We've got actual evidence that
that's how that animal moved.

To learn that there are preserved
striding trackways

of short-faced kangaroos in the
Lake Eyre basin in South Australia,

of short-faced kangaroos in the
Lake Eyre basin in South Australia,
that's incredible.

that's incredible.

This is the...the smoking gun

that proves these giant kangaroos
weren't hoppers, they were striders.

People wait lifetimes to see
evidence like this.

We see proof with our own eyes

because we can walk
We see proof with our own eyes

because we can walk
in their footsteps.

The shores of Lake Callabonna
provide a wealth of knowledge

on the megafauna that lived here
more than 40,000 years ago.

But there's one species
in particular that reveals

But there's one species
in particular that reveals
the fatal consequence
of a changing climate.

the fatal consequence
of a changing climate.

the fatal consequence
(THUNDER RUMBLES)

(THUNDER RUMBLES)

Aaron's colleagues, Phoebe McInerney
and Trevor Worthy,

are investigating what led
to the extinction of Genyornis,
Aaron's colleagues, Phoebe McInerney
and Trevor Worthy,

are investigating what led
to the extinction of Genyornis,

a large flightless bird that
disappeared during the last ice age.

MAN: Somewhere down here.

Yes. That's a...
Drumstick?

Yeah.
Ankle. Foot going down there.

Gizzard.
Yeah.
Ankle. Foot going down there.

Gizzard.

Yeah, that's really nice
with the gizzards.

The breastbone.
Yeah.

Across there the femur.
You can basically just see the bird.

Another femur here.
You can basically just see the bird.

Another femur here.

Another femur here.
These fossilised remains vividly
display the position of the bird

These fossilised remains vividly
display the position of the bird

at the time of death.

So we have the chest plate,
or sternum, poking up through here,

and coming down either side of it,
or sternum, poking up through here,

and coming down either side of it,

we have the two legs.

we have the two legs.
So they would start about here,
and then head down

So they would start about here,
and then head down

and going down into the mud.

And it's gotten its feet quite deep
and it hasn't been able to move.

And it's gotten its feet quite deep
And that's how it stayed since then.

And that's how it stayed since then.

Genyornis newtoni comes from a group
of birds that are all extinct today.

And this species is associated
with a family

called the Dromornithidae.

And they all managed to grow to
these really large, gigantic sizes.

So Genyornis newtoni
was kind of mid range

and was stood about two metres
to 2.5m tall at the head,

and weighed probably about
250 kilos on average.

Two of these giant birds
are in search of food

Two of these giant birds
along the lake shoreline.

along the lake shoreline.

Genyornis, also known as
along the lake shoreline.

Genyornis, also known as
the Thunderbird,

Genyornis, also known as
was heavily built.

was heavily built.

It resembled more a giant goose
than today's emu.

Like some contemporary birds,
it's believed they mated for life.

It was a herbivore and had adapted
to live on the margins of wetlands,

It was a herbivore and had adapted
feeding on fruits and reeds.

feeding on fruits and reeds.

But 50,000 years ago, as the climate
dried and the lake diminished,

so too did Genyornis's
sources of food.

In this barren landscape,

this couple will have to venture
further out onto the lake,

this couple will have to venture
where an uncertain fate awaits.

where an uncertain fate awaits.

We found a number
of these individuals

We found a number
across Lake Callabonna...

across Lake Callabonna...

..but when we take them back
to the lab, we can clean them up

..but when we take them back
and piece them all back together.

and piece them all back together.

And then that's when you start
to see these little features

that indicate that something
wasn't quite right with this bird.

Forensic analysis
of these Genyornis bones

Forensic analysis
could yield important information

could yield important information

about the condition of the big bird
at the time it died.
could yield important information

about the condition of the big bird
at the time it died.

Interestingly, while we were looking
at these bones,

we noticed that a few of them
didn't quite have

the clean, beautiful surface that
we were expecting from the bones.

So, for example, this one over here,

you can see that this region here
is really nice and smooth,

you can see that this region here
beautiful, healthy bone.

beautiful, healthy bone.

But then once you come up
beautiful, healthy bone.

But then once you come up
to the top here,

But then once you come up
all of a sudden there's this lump.

all of a sudden there's this lump.

It's a bit rugose.
There's lots of holes in it.

These clues point to one cause -
disease.

So that means that the individual
itself is probably struggling

with other things as well
in its environment.

Something else that we see, though,
is that

several individuals actually
have these symptoms.

So this bone that we have here
is the sternum or the chest plate

So this bone that we have here
on Genyornis newtoni.

on Genyornis newtoni.

And it's also an individual
that shows signs of pathology.

So you can see at the front here
that we have this extra lumpy bone,

and when we looked at this
in a scan data -

so we saw the structure
of the bone using a CT scanner -

we could actually see that
all of this is extra bone growth

we could actually see that
on the surface of the original bone.

on the surface of the original bone.

So we also see this
on the other side of this bone,

So we also see this
where we have these lumpy regions

where we have these lumpy regions

with a different texture
where we have these lumpy regions

with a different texture
to the rest of the healthier bone.

And there's this really big cavity
here as well,

which is associated
with a compromised immune system.

So we have multiple
Genyornis newtoni individuals

walking around at Lake Callabonna,

getting stuck in the mud,

and having these pathologies,

which indicates to us that
it's not an individual problem,

but it's actually
a population problem.

These birds were suffering
from a compromised immune system,

likely due to poor nutrition.

If we correlate that

with what was happening
in the environment at the time,

we start to see that

there were these major fluctuations
in the environment,

with often really severe periods
of drought,

with often really severe periods
which went for quite a long time.

which went for quite a long time.

So these birds were likely having
these environmental changes

So these birds were likely having
causing significant stress levels.

causing significant stress levels.

Those types of factors
potentially contributed

to the extinction of Genyornis
at Lake Callabonna.

Megafauna, like Genyornis, lived
in Australia for millions of years,

surviving repeated climate changes
throughout the fluctuating ice ages.

So what could have made
the environmental changes

So what could have made
40 to 50,000 years ago so different

40 to 50,000 years ago so different

that many species were
40 to 50,000 years ago so different

that many species were
wiped off the face of the Earth?

There's an extraordinary
geological phenomenon

There's an extraordinary
that some scientists now believe

that some scientists now believe

may have been the final nail
that some scientists now believe

may have been the final nail
in the coffin.

MAN: So it was only about
three or four years ago,

I was having a really detailed
conversation

with a great colleague of mine,
I was having a really detailed
conversation

with a great colleague of mine,

complaining that I could see
these major changes

in the animals and megafauna
and Australia

in the animals and megafauna
and Australia
all around 42,000 years.

all around 42,000 years.

What was happening?

Why was it all happening then?

And he said, "Well, the only thing
that happens 42,000 years ago

"in the geological record

"is the Laschamp excursion."

And I was like, "What's that?"

The Laschamp excursion was
an incredibly rare geological event

where the Earth's poles
switched places.

Normally, our Earth's core
generates a magnetic field

that protects our planet
from harmful radiation

that protects our planet
from the cosmos and our sun.

from the cosmos and our sun.

But 42,000 years ago,
as strange as this may sound,

Earth's magnetic north and south
swapped.

The change lasted
just 1,000 or 2,000 years,

The change lasted
but during that time

but during that time

our protective magnetic shield
was dramatically weakened,

resulting in a massive bombardment
of radiation from space.

Until recently, the precise timing
of this event was hard to pin down.

But in 2019, an extraordinary fossil
was discovered in New Zealand,

But in 2019, an extraordinary fossil
which held the answer,

which held the answer,

and with it perhaps the ultimate clue
to megafauna extinction.

MAN: These pieces of kauri
that we have in the archive

represent unique windows that we can
peer into for Earth's history.

This cross section of a kauri tree
is over 42,000 years old,

preserved in a bog
until a few years ago,

when it was discovered
during excavations

when it was discovered
for a geothermal power plant.

for a geothermal power plant.

Kauri tree is a unique type
of conifer

that grows in the northern part
of New Zealand,

and it's an incredibly important
tree for climate science

and it's an incredibly important
because we have preserved kauri

because we have preserved kauri

that date back
tens of thousands of years.

About 41,000 years ago is somewhere
in this range of the tree...

For climate scientist Drew Lorrey,
it's not just a tree,

For climate scientist Drew Lorrey,
it's a gold mine.

it's a gold mine.

This ancient kauri represents

the truest reflection
of atmospheric radiocarbon
This ancient kauri represents

the truest reflection
of atmospheric radiocarbon

the truest reflection
that we have on the planet.

that we have on the planet.

The rings of the kauri tree

The rings of the kauri tree
reveal significant change in the
Earth's atmosphere 42,000 years ago.

reveal significant change in the
Earth's atmosphere 42,000 years ago.

We looked at the atmospheric
radiocarbon signature

through the time period
that this tree lived,

and what we can see is
an enrichment of radiocarbon,

that spikes quite significantly
to nearly 800 per mil.

That's the strongest radiocarbon
signature that we have at any time

That's the strongest radiocarbon
in the last 50,000 years.

in the last 50,000 years.

The increase in radiocarbon was the
clue scientists were looking for,

indicating more radiation from space
was penetrating Earth's atmosphere.

The radiocarbon signatures in
the naphtha kauri tell us that

the Earth's magnetic field
weakened greatly

during the time of
the Laschamp excursion,

to the point where

we probably barely had
a protective magnetic field.

But what would a weakened magnetic
field have meant for life on Earth

during this time?

So one question is, OK,

is this the smoking gun that
explains the megafaunal extinction?

It's a controversial hypothesis,

but for evolutionary biologist
Alan Cooper,

the theory offers
an intriguing picture

of how devastating the effects
could have been.

Suddenly, with the magnetic field
turned off,

that ionising radiation
is penetrating right into the earth.

It's doing enormous damage
to the ozone layer.

We think it probably
removes it completely.

Like the ozone layer
is completely gone.

At that point, ultraviolet light
is coming...charging in,

causing major climactic shifts.

One theory, which I think
might be right,

is that ionisation in the atmosphere
causes clouds as well.

You actually get cloud cover
building up.

And clouds are a really good way
of cooling something down.

And clouds are a really good way
They reflect sunlight.

They reflect sunlight.

As a result, the surface underneath

is not getting that heat
As a result, the surface underneath

is not getting that heat
down to surface level.

is not getting that heat
Cooling and drying.

Cooling and drying.

Why would this cause
megafaunal extinctions?

Why in Australia
would the impacts be so bad?

Well, one of the things
about Australia is the aridity.

Is the difficulty of water
as a resource.

Australia is already
starting to dry out,

Australia is already
the lakes are starting to dry up.

the lakes are starting to dry up.

And one of the things
we think has happened

is that the magnetic excursion
causes sudden cooling.

Cooling is nearly always associated
with dryness.

You get less water coming
off the ocean to form rain,

You get less water coming
so the continent starts drying out.

so the continent starts drying out.

Suddenly you've got
this major impact

Suddenly you've got
of cold, dusty, sandy...

of cold, dusty, sandy...

Think of Mad Max type environment.

(CALLS)

Now, in other parts of the world,
the megafauna can move.

They can migrate to try and deal
with these changing conditions.

The problem in Australia,
you're stuck there.

The environment's shifting,

the plants changing
from trees to more grasses,

the plants changing
fires going off

fires going off

from the lightning coming down
fires going off

from the lightning coming down
from the ionised atmosphere,

and the megafauna are suddenly being
confronted with all these changes.

But there's another major change
during this time

But there's another major change
that some academics think

that some academics think

could have played a part
in megafauna extinction.

So in the next episode...

(INHALES, EXHALES)

MAN: All good?

More people have actually
been on the moon.

There's been 12 people on the moon
and 10 people in this cave.

..scientists search for clues
in an underwater lair,

once home to a fierce
Ice Age predator.

Now, this is an animal that is
like no other that is ever existed.

We discover the largest lizard
to have ever walked the Earth.

MAN: Megalania must have been
venomous,

which is a really mind-blowing
discovery.

which is a really mind-blowing
And the ultimate question...

And the ultimate question...

Well, that's the giant kangaroo
that we're looking at now.

Well, that's the giant kangaroo
That's where the head is.

That's where the head is.

..was megafauna extinction caused
That's where the head is.

..was megafauna extinction caused
by Earth's most successful predator -

..was megafauna extinction caused
humans?

humans?

Our people used to live
right through here

with the...
(SPEAKS INDIGENOUS LANGUAGE)

Captions by Red Bee Media

Copyright Australian
Broadcasting Corporation