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Michelle Barboza-Ramirez:
Here in the West Texas desert,

a fossilized wonder
of the ancient world

juts out from the dry
and rugged landscape.

These towering mountains,

known as
the Guadalupe Mountains,

were formed through biology
becoming geology.

Once upon a time,
they were alive.

See, the Guadalupe Mountains
are built from the ruins

of a vast tropical barrier reef.

Blake de Pastino: In the middle
of the Permian Period,

around 270 million years ago,

this reef flourished
along the edges

of a shallow inland sea

that filled a basin
close to the equator

on the supercontinent Pangea.

The reef is hundreds
of kilometers long

and curves into
what's now New Mexico,

and it once teemed
with countless species,

big and small,

that thrived
in the habitat it provided.

Gabriel-Philip Santos: That
massive fossilized ecosystem

is a spectacular relic
of the Permian,

the final chapter
in the Paleozoic,

and it's been on
quite a journey since then.

When a climate crisis
dried up the inland sea,

the reef became buried
in sediment

for over 200 million years,

locked in time as the world
changed around it.

Pangea broke up,

the dinosaurs rose and fell,

and whole eras of deep time
came and went,

with this Permian reef
staying hidden underground

through it all,

until, starting around
25 million years ago,

tectonic forces
from deep within the Earth

lifted it up,

allowing erosion to reveal

the towering, fossil-strewn
cliffs we see today.

It's a grand,
one-of-a-kind window

into a fascinating time

in the story of life on Earth,

but a time
that would end in disaster.

Because this reef,
along with a great deal

of Middle Permian life,

was doomed.

Kallie Moore: The same crisis
that dried up the inland sea

and buried the reef

was only part of a much wider
climate catastrophe

that devastated life on Earth

as the Middle Permian
drew to a close.

And it hit our proto-mammal
relatives on land

pretty hard, too.

But their story,
and the story of the reef,

shows that while
the Permian period is long gone,

its legacy can still be found
in our modern world,

if you know where to look.

The Middle Permian stretched

from about 273
to 260 million years ago,

and it's formally known
as the Guadalupian Epoch,

named for the mountain range
containing the reef.

And during this epoch,

life on Earth was a blend
of both strange and familiar.

The vast tropical barrier reefs

of the Middle Permian,
for example,

are a feature
of the modern world, too.

But the reef
in the Guadalupe Mountains

wasn't built
primarily by corals,

like most of today's reefs are.

Instead, it was
the multi-generational project

of an array
of other ancient reef builders,

including mound-building
algae and microbes,

as well as sponges
and other invertebrates.

As they died, the remains
became cemented together,

building up a framework
for each new generation

to grow on and expand further.

So, we're in
the Guadalupe Mountains,

which are mountains,
in terms of,

they are tall pieces of land,

but when people think
of mountains,

or at least when I talk
to my students,

a lot of the times, folks
don't know what that means.

In this case,
this mountain is a reef.

Look at this, look at this.

There is a sea urchin

that is just perfectly
fossilized here.

You can see
each individual spine

still attached to the urchin.

And as you give yourself
some time to get used to

what the fossils
look like in an area,

the longer you're there,
the more they're gonna

start popping out
before your eyes.

So, let's move over
just a smidge.

Every single little line
you're seeing here,

every line here,
every line here,

all of this beautiful stuff
is shells.

OK, where are you at,
my friend?

I know I saw... Ah!

Oh, my god, OK,
here it is, here it is.

Check this out.

So, this little, like,
line of Cheerios

are called crinoids,

and crinoids are related
to sea lilies,

which are still around today.

All of these little white lines
that you're seeing

are the outlines
of the fossil shells.

Just shell, shell,
fossil, fossil, fossil.

We're in the Middle Permian
Sea right now,

traveling in time,
with the fossils below me.

This reef was just
one of many complex

and multilayered ecosystems,

similar in structure
to the ones we know today

that had formed
by the Middle Permian,

both in the water and on land.

But, in many cases,

the species that filled
those ecosystems

were unlike
anything alive today.

Throughout the marine realm
of the Permian,

trilobites scurried
across the sea floor,

ammonoids bobbed
through the open waters,

and bizarre sea monsters lurked.

I love the ocean.
I love ocean life.

It's always been something
that I've been interested in.

Ever since I was a little kid,

I would do
marine science programs.

I went to aquariums.

I loved whales

and all those really cool
marine creatures.

And that really led
into how I got started

as a paleontologist.

There's just
so many cool stories

when it comes to the ocean

and things that
we can learn about

when it comes to our story,

or just the story
of life itself.

Take Helicoprion, for example,

a huge, ancient,
shark-like predator

that swam through the waters
of the Guadalupian Epoch.

Some estimates have placed it
at over 8 meters long,

making it possibly

the largest-known animal
of its day,

though,
like all shark relatives,

Helicoprion had a skeleton

made up almost entirely
of cartilage,

which often
doesn't fossilize well,

leaving us with a lot
of open questions about it.

But it's the one piece
of literal hard evidence

that we have found of them

that has ended up
leaving paleontologists

especially puzzled.

Giant whorls of teeth,
unlike anything seen

in the animal kingdom today.

Helicoprion is
one of these animals

that just has an anatomy
that really challenges us.

Obviously,
this animal existed.

Obviously,
it existed well.

It was evolved to live
in its habitat.

It lived
for quite a long time.

There's many species of it.

And now it's our job
to try to figure out,

like, what this thing is,
what it's doing.

It's really crazy.

Where exactly these whorls fit

and what Helicoprion
was using them for

were debated
by paleontologists

for decades.

Hypotheses range from
the whorls coiling upwards

from Helicoprion's snout

to hanging downwards
from the lower jaw,

to maybe even sprouting
from Helicoprion's fins

as defensive structures.

It wasn't until
scientists studied

an especially well-preserved
tooth whorl

with bits of fossilized tissue
still attached, that in 2013,

they were actually able

to reconstruct it
with confidence.

This is one of the specimens
that's been CT scanned

and shown us
the actual structure

of the jaws.

So, we know now

that this great, big,
weird circle of teeth

is, like, set
right in the middle

and only on the lower jaw.

Another thing that's
kind of interesting

is that we see these teeth
are quite sharp,

and throughout
the animal's life,

they're never worn down.

So that helps us understand
it's probably eating, like,

really soft things,
like the relatives of squids

and things like that.

That's Amazing.
So, definitely,
no spinning buzz saw.

Definitely no, like,
rum-rum-rum-rum-rum spinning.

But, like, unless
you count, like,

the whole animal
putting in new teeth

throughout its life,

the whirl does--you know,
it doesn't rotate, like,

with a click like this,

but it does kind of
always grow out.

And so, there is
a bit of a spin

over the course
of a lifetime.

All right. So
Fred Flintstone
wouldn't have used it

as, like, a tree cutter.

It would be
very ineffective.

Ah, OK.

So, species
across the tree of life

were evolving all sorts
of innovative adaptations

as they became specialized
for particular ecological niches

within their environment,

often ones that no animal
had filled before.

It's a recurring theme
of the Permian Period.

And on land,

our proto-mammal relatives
were no exception.

They, too, were specializing
in weird and wonderful ways.

Terrestrial life
in the Middle Permian

had just undergone

an important
evolutionary turnover.

In the Early Permian period,

the more reptile-looking
pelycosaurs

had their golden age.

They were an early wave
of synapsids,

the side of
the amniote family tree

more closely related
to mammals than to reptiles.

And they had pioneered

many of the first
ecological niches on land

for big vertebrates,

including everything
from herbivores

to apex predators.

But as the Early Permian
drew to a close,

the pelycosaurs
mysteriously declined,

and by the Middle Permian,

a more advanced wave
of synapsids had risen

to ecological prominence
in their place--

the therapsids.

Therapsids were often
faster and more agile,

with a greater range of motion
in parts of the spine and legs

that held their bodies
higher off the ground,

though some still had
sprawling limbs

like the pelycosaurs.

Plus, they had
more robust skulls,

more complex types of teeth,

keener senses,

and a faster growth rate.

These adaptations allowed them
to not just pick up

where the earlier pelycosaurs
had left off ecologically,

but to evolve in ways
that had never been seen before.

So, these animals are
definitely more mammal-like

than, like, the pelycosaurs
that came before them.

They're really helping us
understand bits and pieces

of how the mammal body plan
kind of came to be,

but they're certainly not, like,
on the way to "mammalness,"

if that makes sense.

Yeah, they're just, like,
experiments along the way.

Yeah, and there's
so many of them,

and there's, you know,
big ones and small ones,

herbivores and carnivores.

The most prominent
early therapsids

that roamed the landscape
of the Middle Permian

belonged to a group
called the dinocephalians,

who experienced
a dramatic rise and fall

across the Guadalupian Epoch.

And their name, which literally
means "the terrible heads,"

refers to the group's
big, thick skulls

that sometimes featured
elaborate bony ornamentation.

It's thought that
many dinocephalians

used these skulls
for headbutting each other

in competition for territory,
mates, and social status,

like many modern mammals
do today.

This makes the dinocephalians

perhaps the earliest
terrestrial animals

to show specialized traits

for highly-complex
social behavior.

Complex traits of behaviors

that we now think of
as typical of modern mammals,

from our physiology
to our sociality,

were emerging for the first time
here and there

across the synapsid family tree.

The origin of true mammals

was still a long way off,
though,

and the dinocephalians
themselves

wouldn't be directly involved.

They went totally extinct

at the end
of the Middle Permian,

dying out around
the same time as the reef.

But during the 13-million-year-
long Guadalupian Epoch,

the dinocephalians flourished.

They radiated into
a diverse array of herbivorous,

omnivorous,
and carnivorous species

across the food chain,

with some being among
the biggest land animals

of not just the Permian Period,

but the entire Paleozoic Era.

These giants included
Moschops, for example,

a dinocephalian herbivore

that grew up to
around 2 meters long.

Moschops had a thick skull,

specialized
for head-butting rivals,

and a bulky, lumpy body
with a huge gut,

for fermenting plant matter.

And its front legs
sprawled at its sides,

while its hind legs were
more upright beneath its body,

which is pretty weird.

Moschops had
a strange mosaic of traits

that are individually found
across the tree of life

but have never come together
in a single animal

in quite the same way,
before or since.

Moschops
is really interesting,

because it really
helps demonstrate

how you can have traits

that you didn't expect
would be in the same organism,

absolutely
in the same organism,

and living really successfully
in its environment.

And odd combinations of features

turn out to be
pretty characteristic

of life in the Permian Period.

Another striking dinocephalian
from the Guadalupian Epoch

is named Estemmenosuchus
or "crowned crocodile"

for its elaborate
bony skull projections.

As with many other
dinocephalians,

Estemmenosuchus probably used
these antler-like structures

for its own particular style
of head-butting combat,

likely locking heads with rivals

and pushing against them.

And these projections
may have also been

a more general form
of sexual display,

signaling health and fitness
to potential mates.

So, if you think about,
like, horns or antlers

on big, herd-living,
plant-eating animals,

that's really familiar.

Horned dinosaurs,
elk, whatever.

And so, it's interesting
and fun, I think,

to see it way back there
in the Middle Permian.

Like, one of the first times
life is playing

with this sort of
suite of characteristics

that kind of go together
really nicely.

And higher up on the food chain
were dinocephalian carnivores,

including some of
the biggest and most dangerous

terrestrial apex predators

of the entire Permian Period.

Take Anteosaurus, for example.

Anteosaurus reached
around 5 meters long

and 1.5 meters high,

with a thick, bumpy,
and crested skull,

powerful jaw muscles,

big, sharp canines,

and bone-crushing teeth.

And it was like nothing
the world had ever seen before.

Older terrestrial apex predators
had been slower

and ambushed their prey,

like Dimetrodon
from the Early Permian.

But recent reconstructions
of Anteosaurus have suggested

that it may have been
a much faster

and more agile kind of predator.

Think of,
like, a lion today.

This is a very capable cat

that can have
fast bursts of speed,

can chase you down,
is really agile.

And Anteosaurus has a lot,
kind of, more in common

with something like a lion
than it does with Dimetrodon,

even though they're both
in the Permian.

This is an animal that's,
like, standing more upright.

We know it's capable
of moving pretty quickly.

It has some sensory adaptations
that give us an idea

that it was, like,
a pretty agile animal.

When we see these, like,
different features altogether,

you know, here
in the Middle Permian,

Anteosaurus is just

a very competent
apex predator.

And Anteosaurus was probably

among the very first
land animals

to ever live like this--

one of evolution's
first attempts

at a terrestrial carnivore
that was both big and swift,

a combination that's proved
successful ever since.

While the Guadalupian Epoch

was the heyday
of the dinocephalians,

they weren't
the only land animals,

or even the only therapsids,

that roamed Pangea at this time.

The supercontinent was huge,
and its habitats were varied,

meaning that all sorts
of ecological niches existed

and were filled by
other strange Permian species,

like another group of therapsids
called the therocephalians,

who also emerged
in the Guadalupian.

Some of the earliest
therocephalians were

medium-sized predators,
including Lycosuchus,

whose name means
"wolf crocodile."

This up-to-three-meter-long
carnivore

had a relatively short
and broad snout,

featuring two sets
of large, sharp canines.

How exactly they used
these double fangs

when hunting their prey

is hard to know for sure.

We have no modern equivalents
to compare them to.

But it's thought that
Lycosuchus hunted smaller prey

than the giant apex predator
Anteosaurus,

probably including
juvenile dinocephalians.

And so, you are seeing
in the Middle Permian

kind of the development
of these, like,

tiered structures
to ecosystems.

It's not as simple
as plant eater, meat eater.

There's gradations
within the trophic hierarchy

for some
of these carnivores.

And so, something
like an Anteosaurus

is going to maybe be
your apex predator.

Animals like Lycosuchus,

very successful
in that ecosystem,

a different group
of animals altogether,

but still, again,
a very competent predator.

And from the sauropsid,
or reptile, side

of the amniote family tree
came the pareiasaurs--

bulky herbivores similar to
their dinocephalian counterparts

like Moschops,

though lower to the ground
and with bony armor.

Pareisaurs represent
an early experiment

in reptile gigantism,

long before
the first dinosaurs emerged--

a completely independent
and much more ancient branch

of big, lumbering reptiles.

One of the earliest
and most common

of these bulky ancient
pareiasaur reptiles

was Bradysaurus,

which weighed about as much
as a large modern cow.

The success of Bradysaurus

in this large-bodied
reptilian herbivore niche

paved the way for around
20 other pareiasaur species

to evolve over the course
of the Permian.

It was Earth's first wave
of giant reptiles,

but certainly not its last.

It seems that wherever you look

in the fossil record
of the Middle Permian,

you find examples of species

breaking
new evolutionary ground,

developing traits,
behaviors, and lifestyles

that had never been
tried before,

but have re-emerged
many times since.

So, life on Earth
in the Guadalupian Epoch

was flourishing,

from gigantic reef complexes
that stretched

for hundreds of kilometers
through the water

to the diverse
and often huge synapsids

and reptiles on land.

But it wasn't to last.

So, right at that
Middle-Late Permian boundary,

we have
this extinction event,

and really maybe even
a mass extinction event.

Much of this biodiversity
died off at the transition

from the Middle Permian
to the Late Permian,

victims of an extinction event

that hit around
260 million years ago.

This mass extinction
at the end of the Guadalupian

is often forgotten about
in natural history,

though some researchers argue

that it,
and potentially others too,

should actually be added

to the Big Five
mass extinctions,

making it part of a Big Six,
or Seven, or Eight.

And it doesn't get
the credit it deserves,

probably because a mere

8 million years
or so afterwards--

a blink of an eye
in geologic time--

another, even more
severe one followed--

the Great Dying at the very end
of the Permian Period,

the worst mass extinction ever.

We'll get to that story later,

but the size and scale
of the Great Dying

tends to overshadow

the End-Guadalupian extinction
that preceded it.

In fact, it was only in 1994
that researchers first proposed

that the End-Guadalupian event
was its own separate crisis,

making it one of
the most newly-recognized

mass extinctions
in paleontology.

The once-diverse
dinocephalian therapsids

disappear entirely
from the fossil record

around this time.

Some of the biggest
and most successful land animals

the world had ever seen so far--

gone in an evolutionary instant.

At the genus level,

the diversity of vertebrates
may have dropped as much as 80%,

and nearly half
of this diversity decline

comes from the total extinction
of the dinocephalians.

But while not every group
disappeared entirely

like the dinocephalians,

it seems that all groups
of land animals

lost at least some lineages.

The therocephalians, as a group,
survived through the crisis,

for example,

but their early members,

like the lycosuchid
wolf-crocodiles, did not.

Pareiasaurs survived
as a group too,

although they lost some members,

like Bradysaurus
and its relatives.

So, what could have caused
this catastrophe

at the end of the Guadalupian?

Well, it's still the subject
of a lot of debate,

and few things about it
are known with certainty.

But, tantalizingly,
it coincides with a period

of volcanic activity
in what's now China

that may have rapidly altered
the global climate.

Evidence of these huge
ancient eruptions

can still be found
in southwestern China today.

It takes the form
of a geological feature

called the Emeishan Traps--

layers of hardened volcanic rock

stretching
over 250,000 square kilometers

and averaging 700 meters thick.

It was probably caused
by a superheated plume

from within the Earth's mantle,

melting and bursting
through the crust.

And while the debate
is still ongoing,

some researchers have argued

that this dramatic
geological event

is the most likely culprit
behind the mass extinction.

These eruptions
around 260 million years ago

would have released
enormous quantities

of greenhouse gases
into the atmosphere

over the 2 million years
or so that they lasted,

potentially warming the planet
by around 4 degrees Celsius.

Many ecosystems
may have become unstable

under such significant
and relatively rapid warming,

which would explain
the loss of biodiversity

seen in the fossil record
around the same time.

And it may explain
why the biggest animals--

the dinocephalians,

along with Bradysaurus
and its relatives--

disappeared so completely.

Larger animals need
more resources

and generally struggle to cope

with dramatic shifts
in their habitat.

In the marine realm,

these eruptions would have also
had disastrous consequences,

increasing the water's
temperature and acidity

while reducing oxygen levels.

And this might explain
the extinction

of a range of species
in the marine fossil record

at the end of the Guadalupian,

marking a major shift
in ocean life.

And like
all mass extinction events,

we know about it best

from the ocean,
oceanic fossils.

So, the kinds of animals
that are making reefs

literally out of the seawater
with their bodies.

We can track changes
in diversity really well

with animals like that.

And as we go
from the Middle Permian

into the Late Permian,

we see one of
those big turnovers,

and we see
a big loss of species.

And the reef
in the Guadalupe Mountains

had an especially
dramatic downfall.

Right around the marine
and terrestrial mass extinctions

and the eruptions
of the Emeishan Traps

some 260 million years ago,

this reef was frozen in time.

A global drop in sea levels,

possibly driven by
the sudden climate disruption

caused by the eruptions,

eventually cut
the shallow tropical sea basin

off from the ocean.

The seawater evaporated,

leaving the reef high and dry

until it was gradually
buried by minerals,

mud, and sediment.

We still have a lot
of questions left to answer

about the mass extinction
that ended the Guadalupian Epoch

and the Middle Permian
as a whole.

Since it's a relatively newly
recognized mass extinction,

it's also among
the least understood.

But the fact that it coincided
with the Emeishan eruptions

is hard to ignore,

because it's exactly
the kind of trigger

that we know is powerful enough
to destabilize the biosphere.

This seems to be a recurring
pattern in paleontology

that's only become clear
over the last few decades.

The majority
of mass extinction events

in the fossil record

match up with periods
of intense volcanic activity.

And it's not hard
to imagine how this could be

more than just coincidence
but causation.

The biosphere
is pretty resilient.

Given enough time,
life can adapt

to all sorts of global changes
and conditions.

But adaptation takes time,
and if change comes too quickly,

mass extinction follows.

And, other than the occasional
unlucky asteroid impact,

massive volcanic eruptions
are among the few events

known to be capable
of rapidly triggering

intense and global
environmental changes.

By destabilizing
the global climate

through their mass release
of greenhouse gases,

eruptions of this size
also end up destabilizing life.

Today, another force has emerged

that's capable of triggering
sudden global change

in a disturbingly
similar way--us.

And if our actions
trigger changes

too intense and too quick
for a species to adapt to,

we may have to add a new
mass extinction to the list.

The fossilized reef
here in the Guadalupe Mountains

and the volcanic rock layers
of the Emeishan Traps

can be thought of as a pair

of contrasting geological
windows into the past,

allowing us to glimpse
the ups and downs

of life in the Middle Permian.

They're two ancient relics

that have survived
over 260 million years,

each telling fragments
of the same story

to those who know
how to read the rocks.

On the one hand, the reef shows
how Middle Permian life thrived

and created magnificent
complex ecosystems,

rivalling those of today.

And on the other side
of the world,

the flood basalts
of the Emeishan Traps

may show precisely how and why

many of those ecosystems
collapsed.

But this crisis
at the transition

from the Middle to Late Permian

was only a warm-up act

for something
much bigger to come.

Because, as we'll see,

life will find its feet again
in the Late Permian,

adapting, innovating,
and recovering

from the extinction event,

only to be hit by a catastrophe
of even greater proportions

that will end the Permian Period

and the era
of ancient life itself.

Complex life would soon have
its closest-ever call

with total extinction.

And just like
the Middle Permian extinction,

it would begin with a rumbling
from deep within the Earth.