When Dinosaurs Roamed America (2001) - full transcript

They were the most extraordinary
creatures ever to walk the land.

Some were huge,

some were terrifying...

...and some were downright bizarre.

But they all had one thing in common.

They lived in our own backyards.

Now, journey back to a time when the
world was a jungle primeval

and Dinosaurs Roamed America.

To most New Yorkers,

the hustle and bustle of downtown
Manhattan is where the action is.

But 225 million years ago,
this was no-man's land,



smack in the middle of nowhere.

All the continents...

...were joined together in one giant
super-continent called Pangea.

Now it was breaking up. North America
was tearing away from Africa

along a rift parallel to the present
day East Coast.

As the rift widened it gave birth to
the Atlantic Ocean

and created a string of freshwater
lakes scientists call,

the Newark Supergroup.

Back then an evening on planet earth
looked like a scene out

of science fiction.

On the surface, an eerie gloom
pervades the atmosphere.

About 20 million years earlier,

evidence indicates an asteroid crashed
to earth.

The collision triggered the Permian
extinction,



which wiped out over ninety percent
of all living things.

Out of the disaster, a new world was
born.

It's the Triassic period.

After millions of years of evolution,
conditions are ripe

for something new, something
different, the dinosaurs.

A freshwater lake is the local
watering hole.

But the customers don't always mix.

For Coelophysis, danger lurks just
below the surface.

Rutiodon is quick,
but Coelophysis is quicker.

The Triassic Period is the heyday
of the reptiles.

To exploit the vacuum left by the
Permian extinction,

reptiles evolved into a variety of
different species.

Now, they come in all different shapes
and sizes.

Some are docile plant eaters.

Others like Coelophysis are predators.

Coelophysis may look like your average
reptile, but it's not.

It's unusually fast on its feet,
curious and alert.

Icarosaurus is the first reptile to
learn how to glide.

A hungry dinosaur will try anything
once.

Traversodont is a mammal-like reptile.

To improve its chances for survival it
feeds at night,

and sleeps all day in a burrow.

Demastosuchus is a docile plant eater.

It uses its snout to nip ferns and
root out tubers.

The armor is for protection.
Even its belly is plated.

The spikes on its shoulders are a foot
and a half long for good reason.

At 20 feet, Rutiodon is one of the
largest predators around.

Its legs are short and project outward
from its body, which inhibits speed.

Demastosuchus is fair game for a
worthy predator.

But it's too much for Coelophysis.

Insects have been around for over 100
million years

and some are huge.

This locust can usually fly its way
out of trouble.

Coelophysis is built for speed.

Its limbs are powered by a large
muscle that extends from its

thighbone to its tail.

Its anklebones are designed to keep
its feet straight while walking

or running.

A right angle hip joint and an open
socket positions its legs under

its body,

so it stands upright and moves fully
erect.

Its neck is long and shaped like an
"S",

lifting its head above it's body for
greater visibility.

Its fourth and fifth fingers are short;

turning forelimbs once used for
locomotion into hands that can

manipulate food.

With its long legs and erect gait

it can run longer and faster than any
other reptile alive.

Soon the old order will slip away

and the dinosaurs will inherit the
earth.

45 million years after the Permian
extinction,

the earth is once again under siege.

Evidence suggests a comet entered the
earth's gravitational pull

and disintegrated,

hurling a stream of fragments toward
the surface along latitude 23 degrees.

Two fell on Canada, one in France,

forming a chain some 3000 miles long.

Two more strayed into Minnesota and
the Ukraine.

With each impact, clouds of vaporized
rock billowed into the atmosphere

blotting out the sun.

Here the Triassic Period ends and the
Jurassic begins.

Now the land belongs to the dinosaurs,

and in time, they'll be bigger and
better.

This is one of the most dramatic kinds
of transitions we can see in all of

Earth's history,

and in this particular outcrop is we
actually have the boundary between

the Triassic down here and the
Jurassic up here.

This layer, these layers, especially
this white layer and this little

black layer, which is a coal,

extend for miles around in this area.

Within this white layer we found
elevated amounts

of the element iridium,

which is relatively rare
in the earth's crust

but relatively more abundant

in asteroids and comets.

My colleagues and I have concluded
that

this white layer is evidence of the
impact of a giant asteroid on earth.

Now, there are very few places
in the world that

you could see anything like that,

and it makes this spot absolutely
unique.

A group of flesh eaters is on the
prowl.

This is Syntarsus.

At ten feet from head to tail, they're
about the same size as their

forerunners in the Triassic.

But these guys aren't chasing bugs.

They're stalking dinosaurs.

Anchisaurus is a plant eater.

Although it walks on all fours,

it spends most of its time on its hind
legs browsing in the trees.

A claw on its thumb is its only
protection.

Syntarsus and Anchisaurus may look
similar now,

but in the future they'll go their
separate ways.

Anchisaurus will evolve into Sauropods,
the largest plant eaters of all time.

Its leaf-shaped teeth are well
suited for plucking vegetation.

Its neck is long for reaching into
trees,

and the claw on its foot is ideal for
digging or pulling down branches.

Syntarsus will evolve into Therapods,
like Allosaurus and T-Rex.

Its jaw is designed to absorb the
stress of struggling prey.

Its wishbone, only found in birds,
helps make its arms more flexible.

And its three-toed feet allow for
faster running than the plant eaters.

Anchisaurus is clearly out-classed.

Only one thing intimidates a predator,
a bigger one.

Dilophosaurus towers over its
competitors, and its prey.

This is no ordinary predator.

It's a triple threat. It can slash,
bite and run.

A meal comes none too soon when
there's a hungry mouth to feed.

But there's no time to relax when a
stranger is sneaking around.

The carcass of Anchisaurus is too
large for one sitting.

The dinosaurs will eat their fill,
then they'll be back.

This is one of the most amazing slab
of footprints I've ever seen.

The tracks are raised because it's the
mud that filled in the tracks

rather than pushed down as it would
be if they were the actual tracks.

But more abundant on this slab are
various different sizes

of dinosaur footprints,

particularly Theropod dinosaur
footprints.

There are small individuals like
this one here;

you can see its three toes right there.

It was a carnivore, you can see from
the very sharp and large claws.

This is about as large as late
Triassic dinosaurs footprints get,

not all that much bigger than the palm
of my hand.

When we get over the Triassic-Jurassic
boundary however,

we see an immediate and abrupt
increase in the maximum size of

Theropod dinosaur tracks.

We get up to the size of truly large
carnivorous animals.

There aren't many other kinds of
footprints around.

Gone are tracks of things like
Desmatosuchus,

and in their place is an almost
completely uniformed assemblage of

various sizes of Theropod dinosaur
footprints,

basically large and small versions
of this.

The rules of the forest are simple,

kill or be killed,

or steal.

Syntarsus may be a hunter,
but it's also an opportunist.

Ironically, Dilophosaurus and
Syntarsus are family;

they're both Ceratosaurs.

But you'd never know it.

Dilophosaurus is still a primitive
dinosaur.

In the future, carnivores will have
three fingers instead of four.

Their heads will grow larger, their
bodies more massive, and the crest

will disappear.

Dilophosaurus may be top dog for now,

but when predators get bigger

so does the prey.

The descendents of Anchisaurus have
nowhere to go but up.

Salt Lake City, Utah lies nestled in a
valley at the foot of the Wasatch Range.

But 150 million years ago these
snow-capped mountains didn't exist.

Instead, the climate was warm and
seasonal,

and the land was a vast Savannah that
stretched from Canada,

south to New Mexico,

and from Idaho east to Nebraska.

It's the dry season.

As far as the eye can see

the once verdant plain has shriveled
to a few scattered trees and

drought-resistant plants.

An empty streambed is a highway to
nowhere.

No rain has fallen for months and
the heat is relentless.

In times of drought dinosaurs,
like Dryosaurus,

flock to the their favorite river.

Here, water usually flows year round.

But now its gone dry and the ponds
have turned to salt.

This Stegosaurus is looking for a seep.

Like African elephants, digging for
water sometimes pays off.

But scratching out a living in the dry
season is hard on the dinosaurs,

big and little.

When times are tough and life is
under stress,

anything can happen.

Finding water is critical for
Dryosaurus.

Her offspring are less than a year old.

They've never experienced a drought.

Today is a lesson in survival.

They don't know they're being watched.

Ceratosaurus is the last of its kind,
but more dangerous than ever.

Dryosaurus is too small to defend her
brood against a hungry predator.

All they can do is run for their lives.

Dryosaurus's extra-long legs make for
speed,

but one of her offspring lags behind.

Now the only hope is to find cover.

In the Jurassic world there's
something even bigger than Ceratosaurus.

The Jurassic river bottom preserved
here at Dinosaur National Monument

contains an extraordinary diversity of
dinosaurs.

There are four kinds of Sauropod
dinosaurs, three kinds of meat-eating

dinosaur,

there are two kinds of bipedal plant
eating dinosaurs,

and of course there's Stegosaurus,
the great plated dinosaur.

Now these animals when we look at
their carcasses,

we can see they're of the same
condition of preservation.

This suggests they all died pretty
close to the same time.

But what brought all these animals
here?

Most bone beds are of just one
species.

We believe that this was a location

where there was a perennial
river flowing

through the Savannah of the upper
Jurassic of western north America,

and it dried up.

Animals would come to this place
during the dry season

where seeps would bring water to the
surface where everywhere else was dry.

But on one particularly bad year the
river dried up completely.

The animals, not wanting to leave
their only known source of water,

stayed until they finally died.

We're looking at the deaths of the
predators, the prey, young and

old animals alike.

Truly an extraordinary dinosaur
deposit.

Like a caravan in the desert, a group
of Camarasaurus lumbers

towards an oasis, a grove of conifer
trees.

Long ago the plant eaters found a way
to co-exist with nature and each other.

When it comes to food, they live in a
vertical world.

Dryosaurus is tagging along.

Without rain, the pickings are slim.

But where the big Sauropods go,

Dryosaurus knows a feast
is in the making.

Camarasaurus thrives on the boughs of
evergreens, high in the trees.

Their strong teeth and powerful jaws
literally rip the branches off.

To reach them, Camarasaurus can do
something most other Sauropods can't.

The vertebrae in its neck are strong
yet hollow,

which makes them lightweight.

A network of cable-like ligaments

helps Camarasaurus hold its head in an
almost vertical position.

Sauropods don't chew their food.
They gulp it.

To digest it, they swallow stones
called gastroliths, which grind the

food in their stomach.

Because Camarasaurus consumes large
quantities of vegetation faster than

it can process it, its belly is huge.

The Dryosaurus make short work of the
scraps.

They chew their food to speed
digestion.

A Sauropod is a virtual bulldozer.

They can wipe out a forest in no time
by uprooting trees and plants.

In the days to come herds of Sauropods
will scour the landscape,

but for now, its one tree at a time.

Two other local residents,

a male and a female Stegosaurus
are also scrounging for food.

For an animal the length of a bus and
the weight of a rhino,

its snout is small and toothless.

Still, it's the largest dinosaur of
its kind in the world.

The plates on its back and its tail,
bristling with four-inch spikes,

are designed to repel the most
aggressive attacker.

Flushed with victory, the male
Stegosaurus begins to strut.

His back plates are like feathers to
a peacock.

They're priceless when it comes to
mating.

The female's not ready.

For the male, there's always tomorrow.

The dry season is now in its fourth
month, but a change is in the wind.

Storm clouds bring the promise of
needed rain.

The monsoon will last for days.

By storm's end, the landscape is
transformed.

Torrents of water cascade from the
hills, and rivers begin to flow.

Seasonal lakes and ponds magically
reappear.

Their muddy banks are a maze of
footprints left by thirsty dinosaurs,

large and small, both predator and
prey, running helter-skelter together.

But the coming of the wet season
ushers in more than just rain.

Apatosaurus has arrived.

This is Dino of the Flintstones,
in the flesh, all 30 tons.

With legs the width of tree trunks
and feet almost as big as bicycle tires,

Apatosaurus is the elephant of the
Jurassic, only 12 times heavier.

Sauropods, like Apatosaurus and
Camarasaurus,

are the largest land animals the
world has ever seen.

This is the most complete Sauropod
dinosaur ever found.

It's a Camarasaurus about two years
old and already about 19 feet long.

The Sauropod dinosaurs are the kind
of thing we always think about

when we hear the word dinosaur.

I grew up with Brontosaurus,
now correctly called Apatosaurus.

If we look around the world in the
upper Jurassic,

Sauropods are the dominant dinosaur.

In fact, in North America in any
particular dinosaur quarry

we find we usually see as many as four
different types,

some feeding high in the trees, some
feeding low, grazing on the surface.

They're an immense part of the fauna,
very important to the eco-system.

You would think we'd know a lot about
these dinosaurs,

however young and their eggs are
virtually unknown.

In fact, in all of western
North America, extending from Canada

down to central New Mexico,

we have not found a single Sauropod
eggshell fragment in the Morrison Basin.

If we look at eggs from South America
or from Europe,

we see that Sauropods laid eggs as big
as soccer balls with eggshell about

a quarter inch thick.

While in western North America in the
Morrison we do get dinosaur eggs,

some of which are only two millimeters
thick,

so you would certainly think
we'd be finding Sauropod egg if it

was here at all.

This tells us that these animals were
migrating into and out of the Basin.

Perhaps, they were nesting in the
lowlands of the mountains to the west,

or perhaps to the north in Canada
along the coast of the sea.

Certainly they weren't nesting
and reproducing

within the Rocky Mountain region.

When Apatosaurus moves the earth
begins to tremble.

Like elephants, these Sauropods
migrate long distances, following

the rainy season.

Along the way they graze on ferns
and low-lying plants.

To accommodate their immense size,

Apatosaurus has perfected a way to eat
the most amount of food with the

least amount of effort.

Sweeping its neck in an arc from side
to side,

it scours the ground like a giant
vacuum cleaner.

Apatosaurus is the length of a tennis
court.

Its tail alone is 30 feet long and
ends in a whiplash.

To carry the weight, Apatosaurus'
backbone has tall vertebral spines

over its hips.

Attached to the spines
are ligaments

that hold its neck and tail up.

At the front of its body, the spines
are forked to brace its neck when

moving it over the ground.

A healthy adult has no enemies.

Its size alone protects it.

But stalking the herd is Allosaurus,

the most advanced flesh eater of its
day.

This youngster has strayed from the
center of the herd.

Allosaurus is no quitter.

There's plenty more fish in the sea.

Ceratosaurus has also been stalking
the herd.

Danger has a whole different meaning
for Stegosaurus.

For days the male has been trying to
lure the female into mating.

Now his persistence finally pays off.

A season of Sauropods has wreaked
havoc on the land.

For Apatosaurus, it's time to go.

Dinosaurs this big are constantly on
the move.

Having eaten their fill, they head for
greener pastures.

Felled by a broken leg, Apatosaurus
is mortally wounded.

Today, Allosaurus is the victor.

The Sauropods will live on,

and a whole new generation of titans
will leave their footprints in the mud.

Allosaurus will vanish into extinction.

In Utah, the seasons come and go.

Once again the dry spell returns.

Now all that hints at the passage of
time are bones bleaching in the sun.

Tomorrow, the curtain will rise on
the Cretaceous,

and a new cast of characters will
appear.

Some are sinister, some are strange,
and some have never been seen before.

Were it not for the Rio Grande River,

New Mexico's largest city would be
bone dry and uninhabitable without

a drop of water to drink.

But 90 million years ago, the land
beneath Albuquerque

was a tropical swamp.

During the Cretaceous, sea level began
to rise,

slowly flooding the interior of
North America.

In time the Arctic Ocean joined the
warm waters of the Gulf of Mexico,

creating a shallow inland sea that
split the continent in two.

On the southwestern shore of the sea,
cool summer breezes and warm

winter rain

nurtured the seeds of a different kind
of forest.

For the first time, ancient stands of
conifers and palms were joined by

broad-leafed trees

like sycamores, magnolias

and poplars along with a new crop
of dinosaurs

that had
never been seen before.

This is Zuniceratops,

the first dinosaur with horns and
frills to appear in North America.

Although they're small now,
about the size of a cow,

in a few million years their
descendants will be four times as big.

Until then, these docile plant eaters
need protection.

Where a herd of Zuniceratops goes,
danger can't be far away.

Lurking about are predators,

and now they're more cunning than
ever.

Coelurosaurs are too little to be a
threat to Zuniceratops.

But nearby, what looks like a flock
of weird birds

is actually a band of Dromeosaurs
already lunching on a carcass.

The odor of a fresh kill lures an
uninvited guest.

The intruder is a loner out for a free
meal.

The carcass is carefully guarded,

and the leader of the pack, the alpha
male is in no mood to share.

Outnumbered three to one, the intruder
knows when to quit.

A Dromeosaur or raptor is the
smartest, quickest, and most

dangerous dinosaur alive.

Alone or in a pack, it's well equipped
to deliver a lethal blow.

The nasty claw on its foot works like
a switchblade.

A tendon attached to the calf muscle
pulls it into the attack position.

Its legs are strong yet lightweight
for speed.

Its tail is stiffened by bony rods for
balance.

And its arms and hands are extra long
for grappling with prey.

Good eyesight, a keen sense of smell,
and a big brain

make the raptor a daunting predator.

The escape from the pack was a close
call.

To keep on running is playing it
smart.

But the raptor's not out of the woods
yet.

Something's hiding in the bushes,

but it's too large to elude detection.

The raptor's leery.

These are the claws of a carnivore.

They look lethal,

but looks can be deceiving.

It may have the claws of a killer,

but its long neck and small head
belong to a plant eater.

This is Nothronychus.

The raptor's never seen a dinosaur
like this before. Is it a predator,

or is it prey?

No other creature in the world looks
like a half-plucked turkey

and walks like a pot-bellied bear.

Still, an oddball can be dangerous.

Raptors seldom make mistakes.

But Nothronychus is rare in
North America.

Like Zuniceratops, its ancestors
also migrated from Asia.

Therizinosaurs such as Nothronychus
were once streamlined predators,

until they evolved into plant eaters,
unlike the raptors.

In 1996, we began to find evidence of
dinosaur bones here.

After several months of exploring,
we discovered a little bone bed

and it was in that bone bed we found
an animal that has never been seen

in the New World before.

It has claws as you see here,
and it's barely non descript,

you'd think it's a meat eating
dinosaur.

It told us we had a Therizinosaur.

These are amazing animals,
only known from Asia,

very poorly understood

and we now know they're extremely
bird-like dinosaurs.

But unlike the other bird-like
dinosaurs

they're not meat eaters,
they've become plant eaters.

And right behind me here we discovered
this small skull.

This little skull belongs to a small
Therapod or meat-eating dinosaur

and we believe it belongs to a group
of dinosaurs called the Coelurosaurs.

A brand new dinosaur from 90 million
years ago.

Yeah, at first when we were looking at
the teeth,

which are very well preserved here,
we thought we might have a

Dromiazaur or as many people know
the raptors.

But as we uncovered the skeleton,

we began to realize we had a more
primitive animal, a basal Coelurosaur.

This animal may help unravel
the origin

of our classic cretaceous dinosaurs.

Once a year, come spring,

some dinosaurs have more on their
minds than food.

For Zuniceratops, it's the rutting
season

and this young male is in his prime.

The challenge is to entice a female
into mating.

Horns and frills evolved to scare off
predators and discourage rivals.

But to a female, they're sexy if she's
impressed.

The female's not interested.
But someone else is.

Only the leader of the herd can mate
with the females

and he's not about to relinquish his
control.

The object isn't to kill,

it's to win by intimidation.

For Nothronychus, the noise is a minor
distraction.

For the raptors, it's a trumpet
sounding roll call.

There may be injuries, and a wounded
Zuniceratops is an easy kill.

The opportunity is too good to pass up.

Raptors share over 30 anatomical
features with birds,

which is why they look more like birds
than primitive reptiles.

Claws to the ready, the raptors are
patient.

The old male's been bested.

His wound is minor, but his pride's
been dealt a stinging blow

and the excitement's not over yet.

When it comes to survival, the bonds
of kinship transcend a family feud.

The skirmish over, the raptors retreat.
But they'll be back.

For the once proud leader of the herd,
time is running out.

In the lush forests of New Mexico an
experiment in evolution is underway.

Fleet footed predators aren't new.

But Coelurosaurs are different.
They're on the fast track.

Their bones are lighter, which makes
them even more agile and quick.

They're also more active and better
coordinated.

The primitive feathers are for
insulation.

This is the body plan of the future.

On the inland sea the days are hot and
humid and the atmosphere unstable.

But deep in the forest, it's business
as usual.

Deep in the forest, the dinosaurs are
unaware a storm is brewing.

Zuniceratops live most of their lives
eating.

They mate yearly.

They're vulnerable when they're
young and old or injured.

The encounter with the raptors has
taken its toll on the old male.

Since the attack, the raptors have
been stalking the herd.

They're here to finish what they
started.

Spooked by the lightening the herd
scatters and runs.

But the old male lags behind.

The tinder is dry.

Within seconds sparks leap through
the underbrush,

setting the forest floor on fire.

Soon the flames leap from tree to
tree, igniting a firestorm.

As it races through the forest, some
creatures ignore the peril.

When it comes to food, danger has
no meaning for the raptors.

Zuniceratops has been on the run
since the first bolt

of lightening struck.

Now, what remains of the herd heads
for safety as fast as

their legs can carry them.

Nothronychus is not far behind.

But the flames overtake the raptors'
escape route.

Now nothing can outrun the fire.

In this area here, we have coaly
material coming out

of this sediment here.

It's very likely that this material
is actually,

was actually produced by a fire.

There are several lines of evidence
including the structure

of the coaly material,

but also not far from here we have an
upright charcoalified stump

that was probably burned in place.

When you have forest fires you often
have the roots burning down

into the soil.

And if this is the case,
this is really exciting

because this is not just a vague time
when the dinosaurs lived,

this is an actual event that would
have happened

when the dinosaurs were here.

In nature, disaster is a constant
companion

and death comes in many guises.

Dinosaurs not trapped by the fire,
flee in panic.

Most will survive.

For the creatures that perished,
the conflict is over.

For those that remain, what lies ahead
is 30 million years of evolution.

Triggered by unseen forces, the
environment will gradually change and

so will the dinosaurs that live here.

In the distant future, the offspring
of Nothronychus

will grow bigger, weirder, and even
more perplexing.

The raptors will stay small, agile and
quick.

But they'll get smarter.

And the kin of Zuniceratops will
become one of the most famous

dinosaurs in North America.

The granite faces of the presidents
on Mount Rushmore in South Dakota

celebrate two hundred years of
American history.

But not far from here is another
important landmark.

65 million years old, it's some of
the last ground

the dinosaurs ever walked on.

During the late Cretaceous,
the Great Inland Sea retreated,

causing a dramatic shift in the
environment.

Now forests and fields stretch for
hundreds of miles in every direction.

Grass has yet to evolve,

so the plains are covered with ferns
and herb-like plants.

In the twilight of the Cretaceous,
evolution is in overdrive.

After 160 million years, the size and
sophistication

of the dinosaurs is breathtaking,

but these creatures are the last of
their kind.

Triceratops is one of the largest
animals on the northern plains.

Although it's related to Zuniceratops,
time has made a dramatic difference.

These are giants, twice the size of
a rhinoceros.

Their heads are huge,
up to 11 feet long,

and their frills are seven feet wide.

Triceratops are plant eaters.
They roam the plains in herds,

grazing on ferns and small trees like
palmettos,

while keeping an eye on their young.

Of all the plant eaters, Anatotitan,
is the most efficient

because of the way it processes food.
Members of the Hadrosaur family,

they're famous for their bills,
which look like a duck's.

Hadrosaurs tend to be big up to 30
feet long.

But Anatotitan is even bigger;
they range up to 40 feet,

the length of a bus.

Here, size is no accident.

Three million years ago a monster
arrived in South Dakota.

Now it's the scourge of the American
west,

Tyrannosaurus Rex.

T- Rex is the consummate killing
machine.

Its skull is a lethal weapon.

Although it's 40 feet long,

it's not the size of the animal that
makes it deadly;

it's the size of its mouth.

The bigger the mouth, the bigger
the bite.

Towards the end of the Cretaceous

the Tyrannosaurs produced their
largest version, an animal called

Tyrannosaurs Rex.

And other families of dinosaurs did
much the same things like triceratops,

because the inland sea withdrew from
North America.

And as it withdrew, we had the
introduction of a continental climate.

The summers were hotter, the winters
were colder, the days were warmer,

and the nights were cooler.

And under this kind of climatic
regime, selection tends to favor large

size in animals.

Quetzalcoatlus, the king of the
Pterosaurs.

Named after an Aztec god,

with a wingspan of 40 feet,

this is one of the largest animals
that ever flew.

A Pterosaur has no feathers.

Its wings are made of a single
membrane

that stretches from the elongated
fourth finger of its hands

to its ankles.

Its arm bones are hollow and thinner
than a postcard.

Tiny fibers called actinofibrils
stiffen the membrane

to give its wings lift.

Although Quetzacoatlus can fly under
its own power,

more often it glides on thermals,
scanning the ground for a meal.

Today, the carcass of a dead dinosaur
proves irresistible.

Quetzacoatlus may soar like an eagle,

but on land it's a fish out of water.

Nearby, Triceratops is feasting on
shrubs.

The last in a long line of horned
dinosaurs,

their ancestors migrated from Asia.

With horns as long as broom handles
and hides as tough as a rhino's,

these dinosaurs have only one known
enemy.

Sensing danger, the group closes ranks.

Head on, nothing could be more
menacing than the frill and horns

of an angry Triceratops.

At 17 feet from tip to tail,
this T-Rex is a teenager,

less than half the size of its
parents.

The herd can wait.

At a mere 200 pounds, Quetzalcoatlus
is hamburger for this youngster.

At a top speed of 30 miles an hour,

a young T-Rex is one of the fastest
dinosaurs around.

Chasing prey for a living is a chancy
business.

Even carnivores like T-rex are not
always successful.

At dusk the odds are even poorer.
Daylight favors the predators.

As night falls, colors fade, depth
perception decreases,

and familiar images begin to blur.

Without a kill, this youngster flunked
its first test as a solitary hunter.

But in a pack, a family of T-Rex's is
a force to be reckoned with.

A male stands twelve feet tall.

The female is even bigger.

A veteran of the combat zone,
she bears the scars of a hard life.

Her leg's been crippled by a painful
injury.

Still, she rules the roost.

A young T-Rex still relies on its
parents for support.

T- Rex's skull is huge, over five feet
long,

filled with air spaces to accommodate
an elaborate network

of nerves and muscles.

Its brain is the size of a gorilla's.

Its teeth are serrated for shearing
meat,

and its jaw is powerful enough to
crush bone.

While its arms are too short for
grasping prey,

its body is massive, and robust.

Its ribs are an interlocking array of
bones designed to help it breathe.

Equipped with strong, sturdy legs,
T- Rex is braced to spring to the attack.

Tomorrow the youngsters
will learn to hunt

from the deadliest predator
of them all.

The discovery of juvenile Tyrannosaur
bones lead to some surprising

changes in how we think about these
animals.

First of all, when we looked at the
juveniles it turned out that they

weren't built the way we originally
thought they were.

They did not look like the adults;

the legs were longer and more slender
compared to their body size.

Given that we know these animals
were extremely fast.

This led to some speculation
concerning the behavior of the

juveniles in the pack structure.

If we compare those dinosaurs to
modern animals we have analogues.

When you look at a pride of lions,

the female lions are generally much
faster than the males because they're

lighter weight,

and very often they're used to scare
up the prey and chase them back into

the jaws of the male lion.

Tyrannosaurs may have done something
very similar.

Because of their speed, they may have
moved into a herd

of duckbill dinosaurs,

scared up an individual or two, and
these came back into the jaws of

the adults who killed them.

Contrary to popular opinion, life in a
primeval forest is filled with

endless days of boredom.

Moments of terror are only fleeting.

Anatotitans are peaceful creatures.

They'd like nothing more than to be
left alone.

Although they're almost as large as
Tyrannosaurus Rex,

they have few defenses against a
hungry predator,

especially when they're old or sick.

To protect themselves,

Anatotitans congregate in herds and
post sentries to lookout for danger.

Equipped with good eyesight,

acute hearing and a keen sense of
smell, they're constantly on alert.

Hadrosaurs seem to prefer a diet high
in fiber.

But unlike Sauropods, that rely on
stones and chemicals in their gut

to breakdown vegetation,

Anatotitans have the most
sophisticated food processor yet

devised by nature.

The front of their muzzles are
toothless and rigid for shearing plants.

When chewing, their jaws move
from side to side

allowing a battery of hundreds of
tightly packed teeth to grind the

food to a pulp.

Hadrosaurs are one of the most
successful dinosaurs that ever lived.

Scores of different species once
inhabited North America,

from Texas to as far away as Alaska.

From birth, a baby Anatotitan clings
to its mother for protection,

a behavior passed from generation to
generation.

As adults, Hadrosaurs cling to each
other.

But it's not always fool proof.

The Anatotitans have walked into
a trap.

The young T-Rex leaps like a bird
dog flushing prey.

The Anatotitans bolt for safety,

unaware a second youngster is lying
in wait.

There's one more surprise in store.

Mom.

Tyrannosaurus Rex has terrorized
the land for the last time.

An asteroid bigger than Mount Everest
streaks across the sky

and slams into Mexico's Yucatan
Peninsula at

an angle of about 30 degrees.

The impact gouges out a crater 120
miles wide

and sends an incandescent plume

of vaporized rock
arcing towards the Northwest

at speeds close to ten miles per
second.

In minutes everything for hundreds
of miles is incinerated.

In South Dakota plants and animals
suffer a different fate.

Some are scalded by the heat,

others succumb to shock waves
generated by the collision.

An hour after impact

a cloud of dust and debris settles
over North America.

Temperatures drop, and acid rain
begins to fall

as nitrogen burned by the heat is
washed out of the atmosphere.

The sun won't shine again for months.

First light reveals the devastation.

90 percent of all leaf-bearing trees
and plants have been obliterated,

and 70 percent of the animals have
vanished.

Most of the dinosaurs are now extinct.

There are many theories that try to
explain why dinosaurs suffered

such a massive extinction 65 million
years ago.

The evidence in the rocks here
suggests that 65 million years ago

something major happened.

We have iridium, we have shocked
quartz, we have micro diamonds.

Along the Red Deer River of Alberta
though we have some of the best

evidence anywhere for showing us

what was going on in those last few
years that the dinosaurs ruled.

For example, as we follow the Red
Deer River upstream we're literally

going up in time.

Ten million years before the dinosaurs
disappeared there were 35 species of

dinosaurs living in this area.

Five million years before the end
there was only 20 or 25 species left.

And just before the great extinction
event there was only about half a

dozen species of dinosaurs in this,
in this area.

Not since the great Permian extinction
gave rise

to the dinosaurs had an event been so
catastrophic and so final.

But life is resilient.

In South Dakota, a turtle angles for
a perch in the sun.

A primitive mammal comes out of
hiding.

The only dinosaur visible,

a bird soars overhead to remind us
of the giants that are gone.

The dinosaurs are one of life's great
success stories.

From Alaska to Mexico,
Maine to California,

they roamed North America
in huge numbers

for a staggering 160 million years.

In their day they were the largest,
brainiest, and most sophisticated

creatures on earth.

It's unlikely anything

so huge or captivating
will ever pass this way again.

But for a tiny mammal called,
Purgatorius, the future belongs to them.

Someday their children will walk
on the moon

and think back in awe to a time
When Dinosaurs Roamed America.