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Kallie Moore:
We mammals are the result

of a long and winding
evolutionary journey.

Hundreds of millions of years

of mutation,
selection, and chance

have brought us
from humble beginnings

as small and obscure
lizard-like insect hunters

to the diverse and spectacular
modern mammals of today.

In fact, the Cenozoic Era
that we currently live in,

the era of recent life

that covers
the last 66 million years,

is sometimes referred to
simply as "The Age of Mammals."

Though, considering it's
us mammals doing the referring,

there may be
a little bias involved.

Blake de Pastino:
But we really do have

some justified bragging rights
in this era.

Because for much
of the Cenozoic,

from the end of the reign
of the dinosaurs

right up to the modern day,

the largest animals
in most environments

have been mammals of some sort.

From bears to bison
to blue whales,

big, conspicuous mammals
exist almost worldwide.

And we come in all kinds
of shapes and sizes,

filling all kinds
of ecological niches, too.

So, it does seem like something
of a golden age for us.

But the story of how mammals
came to be so successful,

diverse, and charismatic

stretches back
well before the Cenozoic,

before the rise and fall
of the dinosaurs,

and even before the first
true mammals themselves.

Our family tree has deep roots,

and they reach back to
the world of the late Permian,

more than 252 million years ago.

This was the final chapter

in the era of ancient life,

the Paleozoic,

when the synapsid
ancestors of mammals--

specifically, a group of them
known as therapsids--

were in a much older golden age,

one that's often
forgotten about.

These therapsids,

our direct ancestors
and cousins,

are separated from us
by such a long expanse

of evolutionary time

that, in a lot of ways,

the family resemblance
is often hard to see.

They laid eggs, they had
no visible external ears,

and they were probably
hairless, leathery,

and couldn't regulate
their body temperatures

like we do.

But scattered across
the therapsid family tree,

a mosaic of increasingly
mammal-like traits

was gradually emerging, too.

Michelle Barboza-Ramirez:
From saberteeth and tusks,

to versatile limbs,

to impressively
complex behaviors--

features that in many cases
had never been seen before,

but have reemerged in mammals
many times since.

In fact, for quite a while
in paleontology,

therapsids were referred to
as mammal-like reptiles,

on account of their blend

of seemingly ancient
and modern traits.

The Late Permian Period
was a critical chapter

in our evolutionary story,

albeit for two wildly
different reasons.

On the one hand, it was a time

when therapsids
thrived, diversified,

and, in some cases,
became more mammal-like.

But, on the other hand,

this first golden age
of therapsids

would come crashing down
by the Permian's end.

Almost all of this diversity
would be wiped out,

along with nearly
all other Permian life,

in the biggest mass extinction
of all time--the Great Dying.

And it's only thanks
to a lucky few survivors

from this event

that true mammals, including us,

ever had a chance
to eventually shine.

Gabriel-Philip Santos:
The fossil record of
synapsid evolution

is a tale written
mostly in teeth.

That's partly because
they fossilize better

than most other body parts,

and they can tell us a lot

about an animal's
identity and lifestyle.

But it's also because

one of the most unique
characteristics of us mammals

and our ancient
synapsid relatives

is that our teeth are
highly specialized

for multiple roles,

sometimes
in pretty elaborate ways.

The story of synapsid evolution
leading to true mammals

is innately a story
in large part about teeth

and the weird things
we evolve to do with them.

It might not seem like
a particularly important

or radical trait

compared to our big brains
or our complex behaviors,

but from
an evolutionary perspective,

having a bunch
of different kinds of teeth

is one of the most remarkable
adaptations we possess.

Christy Rettenmund:
We're currently

at the Animal Health Center,

where we provide
health care to animals

at the Milwaukee County Zoo.

Today, we'll be anesthetizing
a North American river otter

to do an examination on it.

So, river otters
have 36 teeth.

They're composed
of incisors, canines,

premolars, and molars.

So, they're a fairly typical
carnivore species

with their dentition.

Not only do our teeth
differ from each other

within our mouths--

think of your molars,
incisors, and canines,

for example--

but the mammalian
dental setup as a whole

can radically evolve

to better specialize
on certain diets.

Probably
a good example of that

would be if you compare
giant pandas to brown bears.

So, their diets are
radically different.

Giant pandas are gonna be
eating bamboo,

and because of that,

most of their teeth
look more like molars.

So, they don't have a need

for very well-developed
canines.

Their molars are definitely
much flatter and stronger

for eating that bamboo

as compared
to brown bears,

where their teeth tend to be
a little bit more ridged,

so that they can grab
onto their prey

and kind of chew their prey
a little bit easier.

Joan Stasica:
Giraffes are ruminants,

so they eat
a bunch of food at once,

and then
they bring up a cud,

and they chew it again
and swallow it again,

and they might
bring it up again,

in order to get
all of the nutrition

out of all those plants
that they're eating.

And so,
those big, flat molars

in the back
of their jaw help

with the grinding
of the cud

every time they bring up
that cud to chew.

So, just like a cow.

Exactly.

Giraffes actually
have 32 teeth,

just like people do,

but most
of a giraffe's teeth

are in the back
of their mouth.

They have these big,
flat molars.

And then in the front,

they have incisors
on the bottom,

but on the top,
they just have

kind of
a hardened gum plate.

They don't actually have
any front teeth

on the top.

They can use
the bottom incisors

and then the gum plate

to kind of strip bark
off of branches

or to strip leaves
off of branches.

So, they're really good
at using their tongue

and their lips
and those bottom incisors

to do everything
they need to do.

In contrast, fish,
amphibians, and reptiles

mostly have sets
of pretty uniform teeth

that only really vary
in each mouth by size.

They tend to have
less different types of teeth

as compared to mammals.

So, for instance, sharks,
they're carnivores,

so they have pretty much
all canine teeth.

So, because
they don't really need

any molars for grinding,

they're not eating plants,

reptiles, amphibians,
and fish tend to have

maybe one type of tooth
in their entire mouth,

because they just don't need

all of those different
specialized teeth

like mammals do.

But our uniquely
adaptable dentition

has allowed us to become
so diverse and successful

by opening the door
to new abilities

and specializations

that weren't possible before.

And our new tools couldn't
have come at a better time,

because Late Permian Pangea
had plenty of challenges

for those ancient
therapsids to solve.

The supercontinent's habitats

varied from patches
of tropical equatorial swamps,

to vast arid deserts,

to towering forests of conifers,

gingko relatives,
and other ancient seed plants.

There were a lot of open niches
and ecological opportunities

for our Permian relatives
to sink their teeth into--

so to speak.

And in the fossil record
of Late Permian therapsids,

the relatives and forerunners
of true mammals,

we see familiar mammalian
dental setups emerging

again and again.

OK, so we are here

at the Burke Museum
of Natural History,

which is my local museum.

I come in once a week

to volunteer
in the fossil prep lab.

So, we're at the Burke,
because we are learning

about Permian Age fauna,

and some of the best
Permian Age fauna are found

in Russia and Africa.

We are at a place
that has already gone

and brought those fossils
back for us to take a look at.

At the top of
the Late Permian food chain

was a group of therapsids
called the gorgonopsians,

the first known
sabertoothed animals

that the world ever saw.

Their fossils are mostly found
in South Africa and Russia,

which were both
at the high latitudes

on the supercontinent
of Pangea at the time.

So, what are we
looking at here?

This is a gorgonopsian
from Africa named Lycaenops.

They're a fascinating
transitional animal

that's kind of halfway
between a reptile

and halfway
between a mammal.

Those first gorgonopsians

lived and hunted in the shadows

of another group of therapsids
called the dinocephalians

that dominated
the large animal niches

of the Middle Permian.

But during
the chaotic transition

from the Middle
to the Late Permian,

the dinocephalians
disappeared entirely,

allowing gorgonopsians to fill

many of their former
ecological niches.

Early on, they were
a lot smaller.

Towards the end
of the Permian,

they get
really, really big.

And by the time
they get really big,

they ate everything
and anything.

Is this the really big?

No, this is
the really small.

While some
late gorgonopsian species

remained small,

others took the extinction
of the dinocephalians

as an opportunity to supersize.

Kind of like modern cats,
they all kept

the same basic body plan
and predatory lifestyle,

with only modest
physical differences

across species,
other than their size.

By the Late Permian,
some gorgonopsian species

reached over 3 meters long,

about the size
of a large tiger,

making them
the biggest predators

of the Late Permian.

They specialized
as hypercarnivores,

capable of hunting
even big and powerful prey

that could put up a fight.

Like the pareiasaurs,
for example--

heavily armored,
cow-sized reptiles

that also reached
up to 3 meters

from head to tail.

More ancient
apex predator synapsids,

like Dimetrodon
from the Early Permian,

had jaws optimized for grasping

and holding onto
struggling prey--

long and lined
with lots of teeth.

But the gorgonopsians
of the Late Permian had evolved

their own distinctive
approach to predation--

maximum damage.

Reptiles walk
with their legs

out on the side
of their body.

The sprawl, right?

Yeah. And then their hands
are also turned sideways,

pointing sort of
to the back of them.

Now I'm a reptile.
You're a reptile.

Meanwhile, I am
a synapsid like Lycaenops,

and my limbs are
underneath my body,

and my hands point forward
when I walk.

So, we go
from this to this.

To this.
And it's helpful,

because when your limbs
are under your body,

and your feet
are pointing forward,

you're a lot more active
and quicker

than some of the animals

that might be waddling
around you

with their legs
on the side.

So, he's like...
beast mode.

They were very active
hypercarnivores.

They were chasing
and running down each other

and other animals
in the environment.

Their jaws
were more squared off

at the front with a chin,

and they had fewer
but more specialized teeth,

mostly towards
the front of their mouths.

This suggests
that they were adapted

for inflicting deep wounds

and ripping chunks of flesh

so that their victims
were killed or subdued quickly,

before they had
much chance to resist.

This was probably a kind
of arms race response

to the species they preyed on,

evolving bigger body sizes

in the Middle and Late Permian.

And perhaps
the most iconic adaptations

of the gorgonopsians

for this hypercarnivorous
lifestyle

were their saberteeth.

Now, earlier predators
had experimented

with enlarged canines too,

like Dimetrodon, for example,

but none had evolved ones

quite this exaggerated
and specialized before.

Based on the size,

we think it's
the African species

of Inostrancevia,

which is one of
the largest gorgonopsians,

typically found
in Russia and Siberia.

Oh, my God.

Wow, you can really see
the serrations here.

These sabers were
a first for their time,

but they're a trait
that would pop up

over and over again
in later mammal evolution.

You might have even
seen them before

in the famous sabertoothed
cats of the Cenozoic Era.

They were also apex predators
that could quickly overpower

big and potentially
dangerous prey.

And the gorgonopsians
didn't just use their teeth

to bite prey.

They may have had
a social function too.

That evidence comes in the form

of a fossilized
gorgonopsian snout

with what might be
a healed bite mark

and tooth fragment
embedded in it.

I have another jaw
of a gorgonopsian

right here.

It's another lower jaw,
different size.

Right here...

That's not his tooth.

It's not his tooth.
Ew...

That is probably the tip

of another
gorgonopsian's tooth,

embedded in the side
of the denary, or lower jaw.

And it's got signs
of healing around it.

This wasn't a killing blow.

There's a couple different
ways to interpret this.

One could be that
it wasn't attacked

by another gorgonopsian

that was seeking to end
this gorgonopsian's life

and make it food.

It could have also been
a social behavior,

like asserting dominance.

So, is that idea because
modern animals today

also do that sort
of social biting?

We see in
a couple different groups,

like canids
and modern dogs,

they have
a dominance behavior

where they will bite
each other

without the intent to kill.

It can get a little rough.
Yeah.

It's a rare snapshot
into the complex social life

of a Late Permian gorgonopsian,

and a reminder that behaviors
we think of as advanced

can sometimes be found
in surprisingly ancient places.

I think they would have
looked terrifying

with those huge canines
coming at you.

But I think they would have
looked somewhat like a mammal.

They would have had
characteristics

that would have
connected you to them.

They might have had
a little fleshy nose

at the front,
kind of like a dog's.

They might've had whiskers

or some primitive
hair-like structures
on their face.

They would've started to look
kind of fuzzy and lovable.

Almost there.
Almost there.

I think gorgons
should be talked about more,

because no one knows
about them.

They get
so little attention

in terms of
popular culture and TV.

I think they're
the coolest thing

you've never heard of.

It wasn't just
the carnivorous therapsids

that were specializing in
increasingly mammal-like ways.

Many of the herbivores
were doing it too,

and alongside
the first saberteeth

came the first tusks.

Tusks evolved for the first time
in the Late Permian,

in a group of
barrow-bodied herbivores

called dicynodonts,

which literally means
"two-dog teeth."

Dicynodonts were one of
the most successful

therapsid groups of the time,

radiating into
nearly 100 species,

ranging from small,
gopher-sized burrowers

to big and bulky grazers
and browsers

spread across
the supercontinent of Pangea.

Like the saberteeth

of the gorgonopsians
who preyed on them,

the tusks of dicynodonts
are the first of their kind

in the fossil record,

but they've convergently evolved

again and again in mammals.

Here you go.

I got to feed an elephant.

You're joining us in
our Elephant Care Center.

We're home to three
African savanna
elephants.

What are elephant tusks?

Elephant tusks are
elongated incisor teeth

from an elephant.

Elephants naturally
use them

for debarking logs,

digging holes,
fighting, defense,

shows of dominance,
if you're a male.

But dicynodonts were
the original pioneering tuskers,

probably using them for things
that modern tusk animals do,

like rooting around
for plant material,

defending against predators,

and for social display.

Now, despite so many typically
mammalian adaptations emerging

for the first time
in the Permian,

therapsid evolution was not
a single linear pathway

towards true mammals.

And true mammals ourselves
were not destined to end up

with the particular
combination of features

that we did.

Evolution is much more
branching than that.

And many ancient branches
of our family tree,

like the dicynodonts,

also evolved in ways unlike
any other mammal relatives,

past or present.

Over the course
of their evolution,

many dicynodont lineages
actually replaced

most of their teeth,
other than their tusks,

with a turtle-like beak
made of keratin.

It's an unusual
and kind of ironic form

of dental specialization,

losing your teeth
almost entirely.

And permanently
trading teeth for a beak

is a unique trait in therapsids
that had never been seen before,

and has never been seen
again either.

And the story
of the dicynodonts' beak

shows us that although
these ancient therapsids

seem more and more
like later true mammals,

in a lot of ways,
they were evolving

in completely
different directions, too.

But in the Late Permian,
dicynodonts' beak and tusk combo

seems to have paid off big time.

Perhaps the single
most impressive therapsid

of the Late Permian

was a small, cylindrical,

and extremely abundant
dicynodont

called Diictodon.

So, this is a skull
of Diictodon.

And Diictodon,
in South Africa,

at least,
in the Karoo Basin,

there's at least 3,000
of these specimens.

Most other species
are known from a handful,

like two or five or ten.

So, I know of a couple
of localities where you'll find

100 Diictodons
for every gorgonopsian,

for example,
that you might find.

Wow.

So, it gives you an idea
of how abundant they are

on the landscape.

Diictodon's success
probably came down

to the ecological niche
it filled.

It was a gopher-like burrower

that dug spiral tunnels
with chambers.

Diictodon's beak
and tusks were adapted

for clipping tough vegetation

and pulling fibrous roots
and tubers from the soil.

And this would have helped them
access nutrients,

even in pretty harsh
environments,

on the increasingly hot and dry
supercontinent of Pangea.

Plus, their burrows would
have provided shelter
from the elements,

helped them regulate
their temperature,

escape from predators,

and possibly even
raise their young.

So, we haven't found
the babies yet inside there,

but you definitely find
multiple skeletons

of the same species
living together.

So, they were social.

Perhaps.

I mean, if you look
in cynodonts in the Triassic,

you definitely see burrows

where they're creating,
like, a network of burrows.

Little underground city.

Little meerkats, right?
Wow.

Diictodon and dicynodonts

don't seem to be doing
that specifically.

They are doing
individual burrows,

perhaps with multiple animals
living in them.

Although, I should say,
when you find one burrow,

you almost always find more.

So they are perhaps
living in the same area.

The property value,
they could still afford
their own home.

They hadn't quite moved
into condos yet.

Exactly.

The complex
and dynamic ecosystems

of Late Permian Pangea sparked
an evolutionary arms race

between predators and prey,

pushing species
to innovate to survive.

And one of the most intriguing
adaptations to emerge

from this coevolutionary dance

came from a therapsid group
known as the therocephalians,

or "beast-heads."

Therocephalians were
a diverse group that ranged

from small insect-eaters
to large predators

that almost rivaled
gorgonopsians

in the Late Permian food chain.

But it's from the smaller side
of the family

that an especially
impressive weapon

may have emerged
for the first time

in vertebrates--
a venomous bite.

Now, venom is something
usually more associated

with the reptile side
of the vertebrate tree,

but it may have actually
first emerged in the mouths

of these very ancient
relatives of mammals.

Because in the Late Permian,

around 100 million years
before the first snakes evolved,

the earliest potentially
venomous vertebrate

was a therocephalian
around the size

of a small dog,
called Euchambersia.

There are only two of these
known in the world.

And we have one?

Well, we have a 3D print.

OK, so this is finally

where I get to talk
about my earrings.

These are a cast

of an actual
gorgonopsid skull.

We have technology now
that is allowing us

to 3D scan
and CT scan fossils

that are in
our collections.

The fossil was CT scanned,

the data was converted
into a digital format,

and then
you can send that data

to a 3D printer

and print
a new version of it.

I mean, for a paleontologist,
this is an amazing thing,

because there are only
two of them in the world,

and we can now print
one here at my museum

for teaching, for research,
for whatever we want.

Right behind the canines

on the upper jaws
of Euchambersia's skull

are a pair of huge
deep hollows in the bone.

No other animal has
anything like this

in the fossil record.

And the question is,
what fills that big gap, right?

Could it be a scent gland?

Could it be, you know,
some other type of gland,

maybe something
for digestion?

We don't know.

And so, is it possible
that this housed a venom gland?

That's
a definite possibility.

But I think there's still

lots of other possibilities
out there.

Whenever you're talking
about soft tissue

in the fossil record,

you have to make
inferences.

And our best inferences
come from animals

that are alive today.

And despite being
much more common

on the reptile side
of the family tree,

venom has evolved a few times,
at least in modern mammals,

including the platypus,
the slow loris,

and the shrew-like solenodon.

But none of them house
the venom glands in the snout

below the eye,

as Euchambersia seems to have.

It's still sort of
an open question, I would say.

Is this an experiment
that didn't work out?

Or are we
misinterpreting this?

But if this animal
did have venom,

that would open up a lot

of really interesting
possibilities, right?

The extraordinary diversity
of ways that therapsids

were experimenting at this time

means that there's
always the possibility

that the truth
is actually so strange

that we would never guess it
in a million years,

or 255 million years,
in this case.

Somewhere in this
therapsid golden age,

dodging saberteeth,
tusks, and possibly venom,

were our direct ancestors.

We mammals trace back to
just a sliver of this diversity,

and those other
therapsid cousins of ours--

the gorgonopsians,
the dicynodonts,

and the therocephalians--

would eventually
disappear entirely.

But we belong
to the one and only lineage

of therapsids--

and synapsids as a whole--

that did survive all the way
from the Paleozoic era

through the Mesozoic
and into the Cenozoic--

the cynodonts.

So, this is a cynodont

from the Late Permian
of Zambia.

And cynodonts among
the Late Permian therapsids

are the closest relatives
of mammals.

This will give rise
to the animals

that cross over
that major mass extinction

at the end of the Permian,

and then eventually
give rise to mammals later on.

And so, a lot of the features
that we think about mammals

actually have their origins
way back in the Late Permian.

The cynodonts
of the Late Permian

were not the biggest, strongest,
or most successful group

of therapsids around.

They were just a new and
relatively obscure side branch

of the family tree,
with early cynodonts,

like this Procynosuchus,
for example,

being small generalists
up to a meter long at most.

And their toolbox of traits
was much less flashy

than many other therapsids.

They evolved cusped teeth

and specialized
jaw muscle attachments

that made their chewing
more effective,

which was useful for
feeding on things like insects

and other arthropods.

And changes
in their skull structure

allowed them to chew their food

and breathe at the same time,

a trait that we mostly
take for granted today,

but which was a pretty big
innovation at the time.

The early cynodonts
also show adaptations

for a greater range of motion

and an increased use
of their forelimbs

for capturing
and manipulating their food.

This agility and dexterity meant
that their range of movement

and style of foraging

were probably more mammal-like

than any of
their therapsid cousins.

The cynodonts were still
very much side characters

in Late Permian ecosystems

compared to
the sabertoothed gorgonopsians

or the ridiculously
abundant Diictodon,

but their legacy has outlasted

all of the other
Permian therapsids

and can still be found
in the form of you, me,

and all other true mammals
around today.

These animals are
really poorly understood,

and they're
a really good snapshot

into the evolution
of mammals

and how we developed

the features
that we have today.

So many things
that we think of

that are characteristics
of mammals

actually evolved
before dinosaurs evolved.

You can trace some features
to such an ancient point

in Earth history,

250-plus million years ago.

The array
of Late Permian species

that thrived across
the supercontinent of Pangea

were the product of
one of the most dynamic

and ecologically complex periods

of the planet's history so far.

It was a time that saw

our therapsid ancestors
and relatives

evolve brand-new traits
and behaviors

that have been part
of life on Earth

in some form ever since.

And it's precisely
because life was doing so well

that the Great Dying at
the end of the Permian Period

was such an unparalleled
evolutionary tragedy.

This proto-mammal heyday
was on the cusp

of a catastrophic change

that would bring
the other branch

of the amniote family tree,
the reptiles,

to the forefront for an era.

And while a lucky few therapsids

would make it through
the coming apocalypse unscathed,

it would be another
nearly 200 million years

before their descendants,
true mammals,

regained our place
in the ecological spotlight.