Nova (1974–…): Season 48, Episode 24 - Alaskan Dinosaurs - full transcript

Paleontologists discover that dinosaurs thrived in unlikely places such as the cold and dark Arctic Circle.

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The Arctic Circle,

Northern Alaska.

In one of the most
inhospitable places on Earth,

scientists search for clues
to a mystery

70 million years in the making.

They're on the hunt for
a lost world of polar dinosaurs.

This is not the paleontology

you normally see in books.

What we're learning about
dinosaurs

from these discoveries,

it's just really
unparalleled and unprecedented.



♪♪

Alaska is the last place
on Earth

one might expect
to find large reptiles.

But the discovery of fossils has
revealed dinosaurs could live

farther north than what
was once thought possible.

Oh, we got a sweet layer
right here.

Now this team hopes to

answer some
fundamental questions.

What kind of animals lived here?

How did they survive
the Arctic winters?

How were they able to
endure the cold?

How were they able
to endure the darkness?

Where do they get their food?

If they were up here year-round,



were they really
warm-blooded animals?

Their journey will take them

from the frozen wilderness
of Northern Alaska

to the mountaintops

of Denali
National Park and Preserve

to the south.

If we can understand

how they survived here,

we might be able to understand

why they dominated the planet
for over 100 million years.

♪♪

A surprising story...

of adaptation and survival...

against the odds.

"Alaskan Dinosaurs."

Right now, on "NOVA."

♪♪

Late March,

Alaska's North Slope.

28 miles
south of the Arctic Ocean,

a team of paleontologists

is on the final leg of
a 600-mile journey

from Fairbanks to
one of the northernmost reaches

of North America.

They're part of a long-term

joint research project
studying polar dinosaurs.

Their plan is to

spend the next several days
searching for dino bones.

What makes these dinosaurs
amazing is the fact that

they lived in an
extreme environment.

This isn't the sort of thing

we typically associate
with dinosaurs.

So the fact that they lived
at these latitudes

tells us a lot about what
dinosaurs were capable of doing.

It shows them at their extremes.

Over the past 13 years,

paleontologist
Pat Druckenmiller has made

11 expeditions
to the North Slope

in search of fossils.

He's joined by paleobiologist
Gregory Erickson,

also a veteran
of this field work.

Alaska is really
paleontology's last frontier.

Dinosaurs were living in the
coldest environment

in the Cretaceous,
and it's a mystery as to,

you know, how they were making
it up there.

How did they survive?

♪♪

Here, temperatures drop to
50 below at night,

with wind chills plunging
even lower.

But despite these challenges,

this is the ideal time
to go fossil hunting

on the North Slope.

The hillside we're trying to
dig out

likes to slump on us
in the summer.

But in the wintertime,
it's frozen solid

and we can safely excavate
into the layer.

Along with excavation equipment,

they'll be carrying everything
they need to survive,

including 100 gallons of
gasoline to run generators,

one ton of wood for fire stoves,

and enough food to last for
over a week.

It's been three days of travel
just to reach this point,

and we're not over yet,
because we now have to travel

about 30 miles by snow machine
to get out to the Colville River

and reach our actual dig site.

♪♪

The team is heading to
a fossil site

in the Prince Creek Formation

on the North Slope of Alaska.

Through this remote,
awe-inspiring landscape

winds the Colville River,
flowing north from

the slopes of the Brooks Range
to the Beaufort Sea.

Along the bank
of the frozen river,

steep cliffs rise 100 feet.

This is where
geologist Robert Liscomb

came across mysterious bones

while working for an oil company

in 1961.

Later identified as
dinosaur bones,

the find was a surprise.

Dinos,
thought to be cold-blooded,

shouldn't be able to survive
in the cold and dark.

Polar dinosaurs weren't really
on paleontologists' radar

for most of the 20th century.

When you had a picture of

what a dinosaur was
and where they lived,

it was often thought to be
an equatorial sort of creature,

a creature of warm environments,

of these swampy sort of
lowland environments.

Thinking of dinosaurs living
in the polar north,

that wasn't something that was
even considered.

♪♪

The discovery of
Alaskan dinosaurs

astonishes
the scientific community...

and puts the
Prince Creek Formation

on the map for paleontologists.

♪♪

To find them in
a place like this,

where the environment is
so dramatically different,

it really does challenge what
we thought about these animals.

So far, scientists have
identified

over a dozen species,
both large and small:

herbivorous beasts
such as Pachyrhinosaurus,

a formidable horned ceratopsid;

and Ugrunaaluk, a duck-billed
dinosaur over 25 feet long;

as well as predators
like Nanuqsaurus,

a fearsome tyrannosaur and
close cousin to T. rex;

and a troodontid,
a lightly built horse-sized

dinosaur with
deadly slasher claws.

The team finally arrives

at base camp,
half a mile from the dig site.

It's getting dark and
the temperature is dropping,

now down to
minus-four degrees Fahrenheit.

The site that we're
interested in

is at that point over there.

But some of our crew is
getting cold,

and so it's important
to get our tents up and,

you know, get our stoves going.

Working on the North Slope
in the late winter

means the days are
still short and cold.

Scientists agree,
70 million years ago,

the Earth was
generally much warmer.

The dinosaurs
living here, however,

would have faced
the same inescapable reality.

As the Earth orbits the sun,
it rotates on a tilted axis.

During summer in
the Northern Hemisphere,

the North Pole is
angled toward the sun.

Areas above the Arctic Circle

receive 24 hours of sunlight.

But when Earth arrives at
the opposite side of its orbit,

the pattern reverses,
and the north is tilted

away from the sun.

Because during the Cretaceous,

Alaska was even farther north
than today,

the North Slope experienced
four months of total darkness.

The best indications

from all of the geological
and fossil evidence

is that during that darkest,
coldest winter months,

it would have gotten
below freezing.

It would have been much colder

than almost anywhere else

dinosaurs
would have been living.

♪♪

Early the next morning,

Pat and Greg visit the site

where the first Alaskan
dinosaurs were discovered:

the Liscomb Bone Bed.

We have somewhere around

6,000 catalogued bones
in our collection

from this one layer alone.

And it's also the same layer

that provided most of the
material

from which we named
a new species

of duck-billed dinosaur

called Ugrunaaluk kuukpikensis.

The areas that we work in

have been long occupied
by Indigenous peoples,

and we think it's only fitting

that when we construct
a new scientific name,

that we incorporate
words from those languages

from the areas in which we work.

Ugrunaaluk kuukpikensis
has its origin

in Inupiaq words
that mean, roughly,

"ancient chewer
of the Colville River."

Close cousin to Edmontosaurus
found to the south,

Ugrunaaluk kuukpikensis

is a four-ton herbivore.

Its discovery
in Alaska's North Slope

created a puzzle for scientists.

How did these large animals
manage to survive so far north?

Did they migrate to and from
lower latitudes each year...

like caribou do today?

If they weren't migrating,

how did they make a living
up here?

You can't imagine
there was enough to eat,

so it's just, you know,
a bit of a mystery.

♪♪

To find clues,

the scientists hope
to recover more bone material.

During the Cretaceous, some 145
to 66 million years ago,

the section they're planning to
dig was a river floodplain.

Over millennia,
some remains of dinosaurs

find their way into rivers.

Bones and other material
from different species

pile up at the bottom of
the river channel.

Layers of sediment bury
the remains.

Millions of years later,
a new river, the Colville,

carves through these layers,

exposing the edge of
the fossil bone bed

along these cliffs.

Pat examines the spot
where they found bones before.

They've come back
to continue the work,

but the familiar
landscape has changed.

Huh.

That's kind of scary.

It might have gone bye-bye.

On first inspection,
things don't look promising.

It's all slump.

Yeah.

The layer's gone.

In the summer,
the faces of these cliffs

regularly slump or
slide down into the river,

making it dangerous
to work here.

That process can expose fossils
that had been hidden.

But it can also bury
the bone layer...

And paleontologists...
Under tons of rock and mud.

The team fears its bone bed
may have been washed away.

The hills are ungluing
themselves.

Rack it up to

climate change or whatever,
but you never know.

The slumps can randomly just

take out your
favorite dinosaur site.

Yeah, that's not good.

Then, after further exploration,

they find
a newly exposed outcrop.

Oh, it's kinda got some slump
on it.

All right, I'm going up
and have a look.

Just when it looks like

the trip may have been
for nothing,

the team has a stroke of luck.

Look at that.

Right there.

Woo-hoo!

Found the first bone!

Oh, we got a sweet layer
right here.

That's good.

Pieces of bone are
clearly visible,

sticking out of the frozen rock.

I whacked right through
one here.

It's classic bone texture.

For Pat, this layer is

a paleontological gold mine.

That's what this
bone layer is all about.

It's just dripping with bones.

The challenge now

is to safely extract
the samples.

No one's ever tried this
up here before.

Digging these animals up here,

you know, basically
the end of wintertime,

we're gonna take
the whole layer,

rock and the bones,

and try to extract it.

Gotta find the sweet spot.

- Yep.
- There it is.

They have just six days left
to collect specimens

before they need to return.

The next steps are to break up
the frozen mud and rock

below the bone layer
with jackhammers

to create a working platform.

Then carve out several blocks
with chainsaws.

Each chunk will be
about three feet across

and weigh up to 200 pounds.

It's five days into
a ten-day expedition.

They still haven't extracted
a single block.

And then they suffer
another setback.

The chainsaws break down.

It's up to head of operations
Kevin May to fix the equipment.

It is.

We have been presented with

some significant challenges here

with the temperatures.

If he can't get the chainsaws
back up and running,

the expedition could be over.

Where's the other...

Pal, you're too soon.

How long do you need?

I was really hoping
to get over here

and work on the chainsaws
by myself, so...

You get too many PhDs
in a small area

and nothing gets done.

Kevin soon discovers
a possible solution.

Yep, that's what
shut us down last night.

Look at that.

Can you thaw that, please?

The friction from the chainsaws
melts the permafrost,

which seeps into the mechanics
and immediately refreezes.

Turns out that

because of these temperatures,

we're gonna have to
repeatedly warm our chainsaws

and get the chains
thawed out a bit.

After a thorough cleaning,

the team tries again.

Four more days
in the biting cold

digging,

sawing,

sleeping,

and more sawing

before the first block
is finally freed.

It's coming, it's coming.

Well done, Pat.

We have success!

Yeah, that's
a really nice, big chunk.

There's a big one right there.

Big, very dark,
there's one right here.

There's one there,
there's one there.

It's full of bones.

After all that time...

We've got it.

We're hitting the jackpot
right now.

This is gonna pay off.

Let's bring it in for a landing.

In total,

the paleontologists manage
to extract eight frozen blocks,

1,000 pounds to haul home.

And now it's just a matter of

bringing home a bunch of rock,

and we'll get that stuff
back in the lab,

and we can prepare it out
and we'll see what we find.

♪♪

They hope the samples will

contain fossils that can
fill out their understanding

of the animals that lived here
and help answer the question

at the heart of
the Alaskan dinosaur mystery:

how did they survive
the dark polar winter?

That's a tough place
to make a living.

How were dinosaurs
able to do that?

Did they have to leave,

maybe migrate south?

Or were they able to
park themselves

in the poles year-round?

If we have evidence that they
were staying year-round,

it really has a powerful impact

on what we expect of
dinosaur physiology.

♪♪

Early July.

At the University of Alaska

Museum of the North in
Fairbanks,

the blocks from
the Prince Creek Formation

are in the prep lab.

♪♪

It's not just the big bones

the scientists are after.

Even the tiniest
unassuming crumbs

could hold vital pieces
of the Alaskan dinosaur puzzle.

♪♪

To ensure the tiniest fragment
isn't overlooked,

the scientists scrutinize
buckets of material

grain by grain.

It's a process of

finding a needle in a haystack,
or...

I liken it more
to panning for gold.

♪♪

Three years earlier,

on their previous expedition
to the Prince Creek Formation,

Pat and Greg find
something exceedingly rare

and a potential clue to
the mystery of the lifestyle

of polar dinosaurs:

very small bones they suspect
are from a very young dinosaur.

Some are no larger than
the head of a pin.

Small size alone doesn't
necessarily mean that

this is from a very young
individual dinosaur.

For that information,
I look at other clues.

And one of the best clues

can be seen
in the surface texture.

♪♪

What I'm seeing is a surface
that's highly porous,

as if somebody took a little pin
and pricked the surface

over and over and over again.

And each of those holes
represents places

for little vascular canals

where nutrients
were flowing into a bone

at a stage of rapid growth.

That sort of surface texture is
highly indicative of

animals' very early stages
of development.

And by that we mean days, weeks,

maybe as much as
a couple of months,

meaning that
this is a great clue

to help identify baby bones.

♪♪

It's an unprecedented find.

Baby dinosaurs have never been
found this far north before.

This was a totally unexpected
discovery.

When we first started to see

these, these small teeth and
bones,

it was, it was really a
jaw-dropping experience.

Further investigation reveals

remains of the teeth and bones

of seven different species
of dinosaur,

all in their very
earliest stages of development.

It's evidence
that 70 million years ago,

several species of dinosaurs
nested in the Arctic,

not only living in Alaska
during the mild summer,

but breeding here, as well.

It raises a whole bunch of
really interesting questions.

One of the most important is,

if they reproduced
in the Arctic,

is it actually possible for them
to have also had time

to migrate to lower latitudes?

If migratory, dinosaurs
would have to move north,

incubate and hatch their eggs,

and then return to the south,

2,000 miles away,
with baby dinosaurs in tow,

in order to escape the depth of
the polar winter shadow...

And all between
spring and early fall.

Could the hatchlings
have managed it?

♪♪

One important clue can be found
inside specimens like this,

less than
an eighth of an inch long.

It looks like a drill bit,

but it's actually
a tooth from a baby dinosaur.

When teeth form, daily growth
lines are laid down.

And by counting those up,
one can figure out

how long it took dinosaurs
to incubate their eggs.

So we looked
at really small embryos,

animals that were
just about to hatch out,

and we were able to figure out
really large dinosaur eggs

took six months to incubate.

♪♪

If it took large animals
such as Ugrunaaluk

six months to hatch,

and eggs were laid
during the spring,

the dinosaurs would have
only one month to move south

before the onset of polar
winter.

There's no way that
those dinosaurs

could have hatched out
and made a 2,000-mile trek

all the way down to Alberta
to warmer climatic conditions.

It just wasn't possible.

It's just unavoidable...
They were up there year-round.

♪♪

The idea that dinosaurs
lived in cold darkness

challenges previous assumptions
about dinosaur biology

and the traditional view
that they were

giant cold-blooded animals
like today's reptiles,

relying on ambient temperature
to warm their bodies.

What we don't find in
the Prince Creek Formation

is evidence for
cold-blooded animals

such as crocodiles and turtles,
lizards, amphibians.

It's almost like they
were physiologically limited.

What we do find up there
are birds

and mammals

and dinosaurs.

That alone suggested
that they were warm-blooded.

♪♪

Even if they weren't
cold-blooded,

how did herbivores like
Ugrunaaluk find enough food?

Without sunlight,
many trees shed their leaves.

During these winter months,
food for the plant-eaters

would have withered or died.

♪♪

If we think about those
Alaskan ecosystems,

we have to address the fact...

Where do they get their food?

Karen Chin is one of the world's
leading experts

in dinosaur dung.

She's been investigating
hadrosaur diet

by studying the fossilized
remains of their feces,

known as coprolites.

♪♪

At 100 times magnification,

even the individual
fossilized cells

of the dinosaur's last meal
are visible.

Investigating coprolites
from non-polar dinosaurs

living in
Southern Utah and Montana,

Karen finds something
intriguing.

We can see chunks of intact
wood,

and that's where you see
all of the cells

are almost glued together.

They're glued together
with lignin.

But then you can also see
all of these loose cells

all over the place,
in no particular order,

scattered all around.

♪♪

And that indicates rotting wood.

To break down lignin,
it requires oxygen,

so that can't happen
in an animal's gut.

It has to happen outside,
where there's access to oxygen.

So we know that the wood
was degraded, decomposed,

before it was ingested
by the dinosaur.

I was quite surprised...

Why were they eating
so much wood?

The incredible new evidence

suggests the southern hadrosaurs
could diversify their diets,

feeding on rotting wood
to survive.

Where are you going to get
protein if you're an herbivore?

You can go to a rotting log

where there's lots of
creepy crawlers

like beetles and
millipedes and pill bugs.

It raises the tantalizing
possibility

that this could have been a
winter food source

for Alaskan dinosaurs, as well.

Herbivorous dinosaurs
like Ugrunaaluk

might also have
been feeding on rotting wood

during the four months of the
year or so when

they had the polar winter.

With the arrival of winter,

darkness is one problem
for the Alaskan dinosaurs.

They also face much colder
temperatures.

What in their
physiology allowed them

to remain in Alaska,
shielding them

from the elements?

So for a long time, the image of
a traditional, classic dinosaur

was of a very scaly,
very reptilian,

almost a monstrous
sort of creature.

But lately, dinosaurs have been
getting softer,

they've been getting fuzzier.

Like, dare I say it,
they're getting cute.

There was a early tyrannosaur

that lived about 125 million
years ago named Yutyrannus

covered almost head to tail

in fluffy feathers, and this
was not a small animal.

This animal was
about 30 feet long.

Intriguingly, Yutyrannus
lived in a part of China

during the early Cretaceous that
had a cool climate

similar to Alaska
70 million years ago.

Most dinosaurs had simple
feathers that looked like hair.

Our hair keeps us warm,

that's what hair does
in mammals,

and for many dinosaurs,
they had these simple feathers

probably to keep their bodies
warm.

If dinosaurs that were living
in an area

of similar temperatures
earlier in the Cretaceous

had all of these
thick coats of feathers,

then probably a lot of
the Alaskan dinosaurs did, too.

In addition to feathers,

Alaskan dinosaurs may have
had other adaptations

for surviving
colder temperatures.

One of the interesting groups
of dinosaurs

that we have represented in
our fauna

in the Prince Creek
Formation are thescelosaurids.

♪♪

Thescelosaurids are dwarves

in a land of Alaskan giants.

The smaller of two Arctic
species

is just 18 inches tall
at the hip.

Small creatures lose heat
more rapidly,

and they freeze a lot faster.

So how did these
small dinos survive the cold?

A clue can be found

in their Montana cousins.

♪♪

Some species of thescelosaurs

were found actually preserved
in a burrow.

Up until about 20 years ago,

that's not something that
we thought dinosaurs did.

That raises the exciting
possibility that

perhaps the species
of thescelosaurid in Alaska

might also have been capable
of burrowing,

and potentially
over-wintering by hibernating.

♪♪

Feathers and the ability
to burrow

aren't the only adaptations that
may have helped polar dinosaurs

survive the cold temperatures.

We're finding a very exciting

number of bones from troodontids
in the bone bed layer

we excavated this winter.

And because they're so rare,

every single bone that we find
is providing

another new piece of the puzzle

in understanding
what this animal was.

♪♪

Troodontids were lightweight,
fast-moving,

and agile predators

with eyes set towards the front,

a common adaptation in predators
giving them binocular vision

to triangulate small,
scurrying prey.

They're raptors, so to speak,

and had giant sickle claws on
their second toe,

and clawed hands,
and menacing teeth.

In many ways,
this was a roadrunner from Hell.

♪♪

But the Alaskan troodontid

has one noticeable aspect
that sets it apart.

So I'm looking at

a adult troodon tooth from
the Prince Creek Formation.

And this is a monster,
it's a big one.

This tooth is probably
50% longer than we see in

Troodon formosus, which is a
species found down in Montana.

That suggests this is a
different species,

or same species
got larger up here.

♪♪

Troodontids that lived elsewhere

stood three feet at the hip.

But the Alaskan troodontid
was twice as tall.

Why would living in a harsher
environment

lead to a larger size?

It's been shown with some
mammals and few other birds

and a few other creatures
that they get larger

when they live closer
to the poles.

It's a thermal advantage to
be bigger in a cold environment.

You're, you're less likely to
cool down, so to speak.

So far, from the
Prince Creek Formation alone,

scientists have identified

at least 13 unique species
of dinosaurs specially adapted

to life in the Arctic.

But among all the species found
there,

one is of particular interest
to the team.

It's an animal that was
originally thought

to have evolved to be smaller,
not larger, like the troodontid.

That animal came to light
in 2014,

when another team of scientists

working at the
Prince Creek Formation

announced the discovery
of Nanuqsaurus,

the Arctic's apex predator.

Ultimately, what this comes down
to is this.

T. rex, the most iconic dinosaur
of all,

how do you take that type
of animal

and move it into the Arctic?

What does it become?

Estimated to be half the size
of an adult T. rex,

it's labeled a dwarf species.

Mysteriously, it comes from
a lineage of giants,

but when first discovered,

it was thought to have bucked
the evolutionary trend

that suggested
tyrannosaurs evolved

to become larger
over millions of years.

If it's tough to survive there,

animals often get smaller.

It's easier to cope
with limited resources

if you're getting smaller,
so maybe because the Arctic

was a tough place to live...
It was cold, it was dark...

The tyrannosaurs could not
get as big there.

But these initial findings are
made

on just a handful of
bone fragments.

Leading them to wonder, was it
really as small as it looked?

♪♪

Pat and the team
haven't identified

any new Nanuqsaurus bones

from the Colville this time.

But there is another place

they hope to find evidence.

Not with bones, teeth, or
dinosaur droppings, however,

but thanks to a different record
of the past

preserved in the very ground
they walked on.

Their footprints.

It's not just finding
new species.

It's not just tracking these
animals.

It's really revealing a world
that we know very little about.

It's a unique ecosystem

that really doesn't have an
equivalent on our modern planet.

Using geological maps,
Pat identifies several

new sites in
Denali National Park where

dino prints might be preserved

in its Cretaceous rock.

Dinosaur tracks were first
catalogued

here in 2005,

but they've never been fully
surveyed.

Pat and his team

will systematically explore
these sites,

deep into the backcountry.

One of the things we're
interested in investigating is,

are dinosaurs
that lived in the polar regions

slightly larger than their close
relatives at lower latitudes

or even smaller?

♪♪

450 miles south of
the Prince Creek Formation,

in the Alaska Range, is Denali
National Park and Preserve.

Its six million acres
of tundra, boreal forest,

and ice-capped mountains
cover an area

equivalent in size
to the state of Vermont.

To get to the suspected track
sites, it's a six-mile hike

through unforgiving terrain.

The only way in is by foot.

There are so many things
that can go wrong.

You just gotta be really
on top of it.

This wilderness is, is
beautiful,

but it's beautiful because
it's a very raw place.

♪♪

During the late Cretaceous,

Denali looked
completely different.

♪♪

Millions of years of uplift
and faulting

have created the stunning
landscape seen today.

♪♪

On Pat's last expedition
to Denali,

they located
a huge vertical wall,

riddled with thousands of tracks
preserved for millions of years.

It's multiple layers of rock,

and there's over 100 feet

of vertical rock section
exposed here, and now

tilted up on end.

So we're seeing a story told at
different levels

and through time.

Each depression on what
was once flat ground

represents a footprint.

Occupying an area
over a football field in size,

it's the largest dinosaur track
site in Alaska.

Most prints come from one
species,

a duck-billed dinosaur
like Ugrunaaluk.

Graduate student
Evan Johnson-Ransom

examines a trackway.

One of the most fun things about
duck-billed dinosaurs is

that they may have had different
forms of locomotion.

Some think that bipeds may have
been for the juveniles,

but for the larger adults,

it would have been, like,
quadrupedal, however.

But the jury's still out,
though.

It's really cool to, cool to see
these all in person, though.

As well as providing clues
to the animals' locomotion,

for science writer Riley Black,

trackways also provide
a fascinating glimpse

into their behavior and world.

These tracks themselves are
fascinating

because they're fossilized
behavior.

In places like this, where
we have multiple tracks

on any given slab,
you start to ask yourself,

"Okay, well, why is that?"

Oftentimes, you'll have
something like a sandbar

or the edge of a lake.

That's the best place to sort
of skirt around it,

and you'll have animals going
back and forth

over time, making these
dinosaur dance floors.

♪♪

Over the next several days,

the scientists continue to probe
the surrounding area.

Because not all tracks are easy
to identify with the human eye,

the paleontologists use a tablet
equipped with the latest

lidar technology to document
each track they find.

Scanning the surface of the
print produces

a 3D model the scientists
can analyze further.

As well as prints that preserve
the impression of a foot,

tracks can also survive

as natural casts,
made by the material

that filled the original
imprint,

like this outcropping
that once filled a footprint.

These are classic

ceratopsid, or horned dinosaur,
footprints.

The only kind of ceratopsid
dinosaur that we know of

in Alaska is Pachyrhinosaurus
from Northern Alaska.

♪♪

Ceratopsids are large
plant-eating dinosaurs

that stand on four sturdy legs.

Pachyrhinosaurus perotorum
is a unique species to Alaska,

lacking the large horns typical
of this group.

At seven feet high
and 18 feet long,

it could weigh up to four tons.

It's bulky and muscular,
like a modern rhinoceros.

So far, the scientists

have found numerous footprints...
Not just from dinos,

but also of flying reptiles
and birds.

And they've discovered

an abundance of tracks
from plant-eaters,

sharing the land and the food

it has to offer.

Where there are herbivores,
there are usually predators,

but where are they?

The team ascends
the mountains of Denali,

looking for evidence of Alaska's
Cretaceous carnivores.

The more different

track types that you can record,

the more likely you
are to figure out

at least some
broad sense of diversity

of the dinosaurs

and of other creatures,
like birds

and possibly flying reptiles.

And that's one of our
big questions at this site,

is, who was here?

♪♪

In Denali, the team

identifies a promising site.

The surface appears

to have been trampled on by
a large creature.

To get a closer look,

Pat and Greg decide
to descend the cliff face.

♪♪

They scan the trackway.

Look at that.

It's almost like we, we use our
eyes to find them,

and that to actually see them
better.

Back at the top,

Pat measure the dimensions
of the prints.

Yeah, 59 centimeters,
so that's a big footprint.

If I measure the width,
we'll see what we get.

33 centimeters.

So the footprint is longer than
it is wide,

and each foot was laid down,

they're almost purely in a
straight line.

All the evidence appears
to point to one creature.

This could very well be from
a tyrannosaur.

Which is pretty exciting,
'cause if that's the case,

this is, this is the longest
tyrannosaur track site now

we've found in the park.

♪♪

But the findings are
inconclusive.

The prints lack detail

to positively identify
the track maker.

For a better indication of
a large predator,

the scientists need to find
a track

that has preserved
the original features

of the dinosaur's foot.

We got a good one!

Exploring the summit
of an outcrop,

graduate student Tyler Hunt
makes a surprising discovery.

So we have one toe here,
one toe here, and one toe here.

There's a pretty prominent
claw impression here,

and then I'm seeing some pads
with a raised area in between.

So this count of pads is pretty
indicative

of a theropod, along with the
shape of the toes.

Its three skinny toes with claws
at their tips

points to a carnivore.

But which meat-eater is it?

The middle toe right here
is really long.

Along with this asymmetry,

it's pretty indicative of
a tyrannosaurid.

It would have been a very big
tyrannosaurid, as well.

It's an extremely rare find:
a detailed footprint

of a tyrannosaur.

At least we got the one.

Now we know they're here.

Absolutely.

Got really lucky there.

Why couldn't you find it in
a more accessible place?

I know, right?

♪♪

Back at base camp,

Pat and theropod specialist
Evan Johnson-Ransom

analyze the track.

Measuring the print reveals
the size of the creature.

50 centimeters, so that is
a very big theropod.

That's a big theropod.

Doing the standard method

of four times the foot length

would put us at at least a
two-meter hip height.

In that other track site,

you found footprints of a large
duck-billed dinosaurs,

and so those duck-billed
dinosaurs were probably prey

to this large tyrannosaurid.

They, they were top dog, right.

Oh, definitely.
Yeah.

That was no small predator.

Yeah.

There's no way this is
a pygmy tyrant.

Cretaceous Alaska's apex
Arctic predator

is the so-called dwarf
tyrannosaur Nanuqsaurus.

Over the last several years,
researchers at

the Museum of the North have
collected and catalogued

dozens of its bones from the
Prince Creek Formation.

Their new investigations in
the North Slope

shed light on the true size of

this mysterious carnivore.

In the imaging lab,

researcher Zack Perry scans
a vertebra by laser.

Then digitally enlarges it.

What we've noticed
is that these are

much larger
bones than initially thought.

These would not fit a dwarf
tyrannosaur model.

So just how big is Nanuqsaurus?

Zack examines a tooth

also recovered from
the Prince Creek Formation.

This is about
a three-inch-long tooth.

This is a massive tooth.

It is more the size of an
Albertosaurus

or a Gorgosaurus tooth,

which are definitely not
dwarf tyrannosaurs.

From this, we can infer a
similar size to those species

which are about 30 feet long,

maybe about
a two-meter hip height,

so much, much larger

than the initially described
size Nanuqsaurus.

♪♪

This is a tyrannosaur to rival
the biggest carnivores.

Nanuqsaurus would have had a
mouth full of these teeth.

They're very large

and they have these serrations
for tearing flesh

off of its prey.

♪♪

With an estimated bite force

of 4,000 pounds, Nanuqsaurus is

the top predator in the Arctic.

To catch its food,
it could use its serrated teeth

to tear flesh off its prey,
likely causing it

to bleed to death.

♪♪

For the dino hunters, the new
finds

help illuminate this lost world

and paint a picture
of its wider ecosystem.

♪♪

To support such
a big apex predator,

the environment must have had
more food,

more flora and fauna,

than thought possible
at such an extreme latitude.

♪♪

Pretty much everything we found

bones of in Northern Alaska,

we're finding footprints of very
similar-looking creatures here.

We see things like duck-billed
dinosaurs,

horned dinosaurs, small and
large meat-eating dinosaurs.

And even things like birds.

This must have been a very
productive landscape,

home to a really interesting
and diverse set of organisms

that called Denali home
70 million years ago.

♪♪

The fossils recovered

from the Prince Creek Formation,

along with the Denali tracks,
give us a compelling glimpse

of a rich ecosystem

and the incredible adaptability
of these Arctic dinosaurs.

Here during the warmer months,

the landscape is a spectacular
sight,

covered in hundreds of
dino nests.

With thousands of dinosaurs

of different species feasting
on an abundance of plants

and animals, with extraordinary
adaptations

to survive and thrive

in this lost world

of Alaskan dinosaurs.

♪♪

Evolution is always

operating to fine-tune organisms

to their environment.

The finds here

are going to help us zero in on
what made

these animals so flexible.

They weren't really constrained
by the temperatures

on the planet
to a particular zone

or a particular range.

They lived in almost every
conceivable environment

on land, that was one of the
keys to their success.

So these Alaskan dinosaurs
are a prime example

of life finding a way.

♪♪