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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.