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[narrator] Seventy million years ago, the mightiest dinosaur

that ever lived, roamed the earth.

Its name was Tyrannosaurus Rex.

[roars]

[growls]

It was 13 meters long, and weighed six tons.

This awesomely creature, was king, of the dinosaurs.

Much about T-Rex has been shrouded in mystery.

Now with modern technology, a clear picture is taking shape.

Remarkable physical capabilities that defy conventional wisdom.

[powerful music]

An advanced brain, and intellect, for hunting.

We look at their brain and wonder whether that

enlarged cerebrum may have actually had the capacity,

to be involved in, sort of a coordinated

group hunting effort.

[narrator] In addition, new fossil finds from around the world,

are revealing the origins of this enormous predator.

It turns out, that T-Rex's ancestors were actually small,

and frail.

They weren't, you know, the big bears, with the big

lions, with the big tigers, at the top of the food chain.

They were something much smaller, much weaker.

[narrator] Somehow Tyrannosaurus

transformed from small creatures,

threatened by their enemies, into the most powerful

dinosaurs of them all.

Starting with the very earliest ancestors,

we'll explore an amazing tale of evolution.

Siblings on a journey in search of new lands,

they cross paths with a fearsome carnivore.

Which will reign supreme?

The king of kings, Tyrannosaurus Rex.

This is a story of 100 million years of remarkable evolution.

The first Tyrannosaurus fossils were discovered

in the United States, in the early 20th century.

[soft music]

The dinosaur's monstrous appearance inspired its name,

Tyrannosaurus Rex.

Tyrant, lizard king, or T-Rex, for short.

For more than a century, scientists have been working

to piece together T-Rex's evolution.

Stephen Brusatte, is one of the top researchers

in the field.

So everybody in the world, has heard of T-Rex.

But for a long time, there have been some big mysteries,

about where T-Rex came from, how it evolved,

how it got so big.

And these have been mysteries for many decades.

But finally, over the last 15 years, people all over

the world have been finding older, smaller, more primitive

Tyrannosaurus, that tell us, where the big ones came from.

[upbeat music]

[narrator] Scientists are zeroing in, on T-Rex's roots.

[growling]

They've determined, that its earliest ancestors

first emerged far from North America.

This is the Junggar basin, in the Xinjiang Uyghur,

autonomous region of China.

Now dry, this landscape was once home to many different types

of dinosaurs.

In recent years, excavations have unearthed a wide variety

of fossils.

Xu Xing, has led some of these digs.

Inside a 160 million year old soil strata,

they found a completely new, meat eating dinosaur.

A crown like appendage, on its head inspired its name.

Guanlong, or "crown lizard".

Xu and his team, conducted a detailed analysis

of the teeth, and bones.

They determined that Guanlong, was T-Rex's ancestor.

[mysterious music]

[dinosaur] Ahh, there they are.

[narrator] A group of Guanlong siblings, they're on the hunt.

One takes off, perhaps he's the oldest.

He closes in on his prey,

but he's no match.

At this point in time, the Guanlong was just

three meters.

Dwarfed by the thirteen meter long T-Rex.

It weighed only 75kg, 1/80th of the weight,

of its massive cousin.

The very oldest Tyrannosaurus were much, much different,

much smaller, but they didn't have anywhere near

the firepower of a T-Rex.

They were kind of like, you know, cats or dogs,

kind of that type of animal.

They weren't you know,

the big bears, or the big lions, or the big tigers at the top

of the food chain.

[narrator] How did such a small, and relatively weak creature,

eventually lead to T-Rex?

The largest dinosaur of them all?

[growling]

The story of Tyrannosaurus, is really a story

about evolution. And one of the things

that it tells us, is that evolution is unpredictable.

When those very first Tyrannosaurs like Guanlong,

entered the scene, 175 million years ago,

you never would have thought that they would ultimately

evolve, into giant monstrous animals like T-Rex.

But that's what happened.

How were they able to survive for so long, for 80 million

years, as these small, human sized carnivores?

And then maybe the biggest mystery of all,

how were those small Tyrannosaurs, able to switch

and become these giant, dominant, super predators?

[narrator] The keys to unlocking these mysteries, are newly discovered

fossils from around the world.

Researchers have discovered 28 species, related to T-Rex.

[suspenseful music]

Brusatte has conducted detailed analysis of the bones of some

of these specimens.

his goal was to clarify the process behind

T-Rex's evolution.

The approach he used, is called Phylogenetic analysis.

We have hundreds and hundreds of those features,

that vary in these dinosaurs. Some have the bones,

some don't. Some have small muscle

attachments, some have big ones.

Some have triangle shaped bones, or projections, others have

square shaped ones. Those kind of features

that are variable.

[narrator] Brusatte's analysis have illuminated 366

distinctive characteristics of Tyrannosaur bones.

And the data he's amassed form the basis, for mapping

T-Rex's family tree.

The results confirm that the diminutive Guanlong,

was indeed the most primitive species of Tyrannosaur.

From the time the first Guanlong emerged, until T-Rex appeared,

took 100 million years.

Over this time, dramatic evolutionary advances,

created a creature of unparalleled dominance.

So it is an unusual animal, a freak of nature,

a feat of evolution.

And I'm fascinated to learn, to try to understand

how evolution makes an animal, like T-Rex.

That's the mystery that drives me, and the research that I do.

[narrator] 160 million years ago, China's Junggar basin, was home

to the Guanlong.

This species then migrated to North America.

And about 70 million years ago, T-Rex appeared.

The question is, why T-Rex's ancestors left

their familiar environment, and set out,

on their epic journey.

A clue can be found in the southern reaches,

of the Pacific ocean.

5,000 meters beneath the surface lies an enormous Java Plateau.

Naohiko Ohkouchi, has studied the formation.

This huge lava mass, was created by a major geological event

120 million years ago.

Deep inside the earth is a swirling mass of matter,

called the mantle.

Magma suddenly surged up, erupting through fissures

in the ocean floor.

[explosion]

The Pacific ocean wasn't the only place this occurred.

All over the world, volcanoes violently burst to life,

these major eruptions also occurred

on the Eurasian continent. Where the primitive

Tyrannosaurs lived.

[fire crackling]

They had no choice but to flee.

[ethereal music]

Leaving familiar territory behind, they began a journey,

into the unknown.

They headed toward the North,

for a reason.

Climate change, the gases released by volcanic

eruptions contained large amounts of carbon dioxide.

This triggered global warming.

As the earth warmed, lush forests sprouted up

from Siberia, to the Arctic.

Xu Xing believes this greening of the North, encouraged

the Tyrannosaurs migration.

Triceratops fossils have been found from Eurasia,

to North America.

And they're often found together with fossils of Tyrannosaurs.

As the forests spread further North,

the plant eating dinosaurs' range, expanded.

Scientists believe this is what prompted T-Rex's ancestors

to begin their migration.

Into the unknown, searching for a new home,

with bountiful game, they start out on their epic journey.

They arrive on the Eastern edge of the Eurasian continent,

in front of them, is a vast ocean.

And just when it seems they can't go any further,

something incredible happens.

Tectonic shifts bring the Eurasian, and American

continents closer together.

Then, a land bridge appears,

closing the gap between them.

A path has opened.

The two siblings make their way toward it, and head

to a new land.

The pair arrives, in North America.

It's a vast expanse of land, covered in lush forests.

But, it turns out,

large, meat eating dinosaurs also live here.

[growls]

Before T-Rex, other carnivorous dinosaurs ruled the Americas.

Scientists have found fossil remains in the deserts of Utah.

Lindsay Zanno is a Paleontologist who has

explored the area.

She had been excavating for five years,

then, in 2013, she made a significant discovery.

And I was coming around the corner, on a low hill

and spotted some bones sticking out of the hill,

so I got down and looked at the bone, and could tell

instantly that it was a Theropod bone.

A very large Theropod bone by the looks of it.

And we got very, very excited right away, that we'd found

a very large species, that had never been seen before.

[narrator] Now, the real work began.

Team member, Peter Makovicky took the fossil to Chicago,

for further study.

His specialty is analyzing dinosaur bones.

[Peter] The bones we have here, are parts of the skeleton

of a large carnivorous dinosaur, even though it's big,

and superficially might look like Tyrannosaurus,

it actually belongs to

a very different lineage

of meat eating dinosaurs.

[narrator] The size of the bones, suggested the dinosaur measured about

11 meters, from head to tail.

It's a relative of Allosaurus, from the Jurassic era,

and is known as Siats.

Experts believe this dinosaur had razor sharp claws,

and teeth like knives.

Such features point to a mega predator.

The name "Siats" actually comes from the Ute Indian language.

It refers to sort of a cannibalistic clown monster.

Sort of a dangerous creature, in their legends.

And it is by far the biggest Theropod, and would likely have

been the top predator in its ecosystem.

[narrator] Close to the Siats fossil find, Zanno has recently discovered

a relative of Tyrannosaurus.

This is a tooth from one of the mysterious, small,

Tyrannosaurs we find here, in these rocks that are about

98 million years old.

We find the tantalizing remains of tiny little Tyrannosaurs,

about the size maybe, of a small horse.

[narrator] A tooth from this dinosaur is just about 1/10th the size

of that of a T-Rex.

[mysterious music]

So the Tyrannosaurs living here were quite small,

they were living in the shadow of dinosaurs like Siats.

[narrator] The weak, Tyrannosaur siblings were now living side by side,

with this formidable beast.

[screeching]

[growl]

They were absolutely outrivaled in size, and in power.

Well, I think you know, if...

the small Tyrannosaurs

that were alive at this time, would have run into Siats,

it would have been sort of like a fox meeting a lion,

or a tiger.

There's no doubt that there's a very vast difference

in body size, uhm so basically what we have

is evidence that Tyrannosaurs were present at the time.

But would have occupied a much lower tropic level,

among the carnivores, than Siats.

[soft melodic music]

[narrator] Siats stood atop the ecosystem.

It was a dangerous environment for the much

weaker Tyrannosaurs.

But somehow, they managed to survive.

To find out more, Brusatte has done research all over

the world.

In 2016, he came across one fossil that provided

some clear answers.

It was found in Uzbekistan, in central Asia.

An analysis revealed that it was from a new species

of Tyrannosaur.

It's called Timurlengia, and measured three meters long.

At a glance, it doesn't seem too different from its

its smaller ancestors.

But, internally, it's dramatically different.

We're able to look into its brain,

into the ear, using cat scans.

And we can see it had a big brain,

very intelligent animal. We can see it had an ear,

that was really sophisticated, really good at hearing

a wide range of sounds.

[narrator] Brusatte and his colleagues took scans of the cranium.

Inside the inner ear, is the cochlear duct,

which is responsible for picking up faint sounds.

They found that in Timurlengia, it had significantly evolved.

So what this is telling us, is that these small Tyrannosaurs

were evolving, bigger brains, greater intelligence,

better senses; when they were living, in the shadows.

When they were trying to survive, in a world dominated

by the Allosaurs, and other big predators.

[narrator] Early, small Tyrannosaurs developed a keen sense

of hearing,

that allowed them to quickly sense enemies, and escape.

Helping them to survive.

But fleeing wouldn't have been enough to challenge,

and overtake Siats' dominant position.

There's more to the mystery of how descendants of these

diminutive siblings, would have gone on to rule

the dinosaur world.

For many years, the evolutionary path from Guanlong,

to the giant T-Rex, contained puzzling holes.

So we know a lot about the very earliest Tyrannosaurs,

now we know they were small, we know a lot about

the latest Tyrannosaurs, we know they were huge.

But in the middle, there's a gap in the fossil record,

a dark period of Tyrannosaur history, where we know nothing.

No fossils.

[narrator] The Tyrannosaurs 100 million year evolutionary history,

contains an intriguing hole.

It was during this time, that the spectacular advances

that led to T-Rex, occurred.

Mark Loewen, has been researching this mystery.

He's focused in, on an ancient land mass

on the North American continent, called Laramidia.

The real changing point, of Tyrannosaur evolution,

was the isolation, and evolution that happened on Laramidia.

Isolated populations of dinosaurs,

could evolve in isolation from other dinosaurs.

[soft mysterious music]

[narrator] Around 90 million years ago, global warming,

caused sea levels to rise.

This lead to monumental flooding of the North American continent.

causing it to become divided.

The dinosaurs lived in the Western part

of the continent. Much of the land was covered

with steep mountain ranges.

Rising waters drove the dinosaurs to narrow strips

of level land, where they became isolated.

In these densely populated areas, meat eaters would have

a significantly greater chance of finding prey.

Loewen believes this is precisely what sped up

the dinosaurs' evolution.

[dinosaur grunting]

This crucible of evolution, that is Laramidia,

the small populations were able to undergo dramatic change,

and rapid evolution.

[narrator] Revolutionary advances took place in many

different creatures.

Ankylosaurus evolved thick, bumpy skin,

like protective armor.

Members of the Ornithomimus family, developed the ability

to run 60 kilometers per hour, to escape predators.

Similarly pronounced changes occurred among

the Triceratops' ancestors, hunted by Tyrannosaurs.

They adapted for survival, by becoming massively large.

This gave them the power to repel attacks.

From early ancestors weighing only 100 kilograms,

They developed into creatures weighing more than six tons.

But many uncertainties still remain about

T-Rex's predecessors.

In 2013, Loewen discovered a fossil, that answered

some questions.

It's from a previously unknown species of Tyrannosaur,

called Lythronax.

The fossil was buried in soil deposited 80 million years ago.

During the evolutionary gap period.

The name we chose, Lythronax, means "gore king",

in ancient Greek. And, we chose this name because

Lythronax really was, the top predator in its ecosystem.

[narrator] The fossil indicates that Lythronax measured about

eight meters in length.

That represents a remarkable jump in size, from Guanlong,

its weak ancestor.

This new Tyrannosaur was large enough to battle

with the massive Triceratops.

Conditions were right for different species

to influence one another's evolution.

This phenomenon is known as coevolution.

[soft ominous music]

[Mark] So Tyrannosaurs were exploiting these prey species,

and also undergoing rapid evolution themselves.

So it's really an arms race between the predators,

and the prey species.

And all of these animals

are evolving to have larger body size.

Both to defend themselves from predators,

and for the predators to be able to attack the herbivores.

[narrator] Researchers believe that one factor supporting

the Tyrannosaurs growth, was a jump in their

hunting skills.

Their heads, relatively delicate up to then,

widened by about three times.

That made astonishing improvements in eye

sight possible.

[Mark] One of the things that's unique about Lythronax,

is the fact that it has forward facing eyes.

Forward facing eyes, occur in modern animals

that are predators.

And the ability to have forward facing eyes,

allows you to have overlapping field of vision,

and perceived depth.

So depth perception, clearly was possible in this dinosaur,

and it's something we associate with hunting.

[narrator] Depth perception makes it possible for a hunter,

to accurately grasp, the distance to its prey.

That would have allowed Tyrannosaurs to catch prey,

more easily, and turned them into much more

successful hunters.

[dinosaurs growl]

They would have gotten plenty of nutrition,

enabling massive growth.

These changes culminated in the mightiest

dinosaur of all, T-Rex.

[Stephen] By about 80 million years ago,

a whole new world of dinosaurs had dawned.

and this was a world that was dominated by the Tyrannosaurs.

They were the biggest predators, and they ruled at the top

of the food chain. And these were the Tyrannosaurs,

that we're all familiar with.

The ones like T-Rex,

the ones that grew so fast, that they put on five pounds

of weight every day, during their teenage years.

And they were utterly in control, they were the kings,

of the late Cretaceous.

[narrator] Overwhelming size wasn't the only result

of the Tyrannosaurs continuous evolution.

Lawrence Witmer, is a paleontologist,

who has studied the brains of T-Rex.

[soft mysterious music]

He's used CT scans of fossils, to analyze their

brain structure.

The scans point to new developments

in sensory faculties.

One thing we saw when we started to reconstruct the brain

of T-Rex, is that the olfactory, bulbs of the brain,

the part of the brain that's involved

in processing odors, or smells, were really quite enlarged.

What that told us, is that the sense of smell, is very

important for T-Rex.

Uhm, it was potentially important for locating its prey.

[narrator] Signals from the sensory organs were sent to, and analyzed

by the Cerebrum.

An index measuring intelligence based on brain to body size,

suggests T-Rex was more advanced relative to other dinosaurs.

[Lawrence] The Cerebrum, which in mammals like us,

is the seat of intelligence.

and planning, and problem solving.

Uh, the Cerebrum in Tyrannosaurs was actually fairly expanded.

We look at their brain and wonder, whether that

enlarged cerebrum may have actually had the capacity,

to be involved in, sort of a coordinated group

hunting effort.

Such that maybe some animals, would actually drive the prey,

towards other animals, other Tyrannosaurs, that were

laying in wait.

[suspenseful music]

[narrator] There he is, T-Rex.

He's not only smarter,

but also has a superior sense of smell.

Even in the dark of night, he's able to locate his prey.

[growling]

Aiding his ability to track game, is his keen eyesight.

The Triceratops tries desperately to get away,

but there's another T-Rex waiting in an ambush.

[bones cracking]

Feasting on kills, fuel growth.

The Tyrannosaurs now measured 13 meters.

Their bones grew harder, and stronger,

and their bodies were covered in muscles like steel.

Some experts have questioned whether creatures this big,

had the speed needed to run down prey?

The conventional belief was that T-Rex ran

at a speed of 18 kilometers per hour, that would make

it slower than a human.

Tyrannosaurs were thought of as slow, and clumsy.

Paleontologist Bill Sellers, challenged that view.

So it's very hard, when all you've got is bones,

to try and work at how fast, an animal would run.

So what we were trying to do, was come up with evidence

from living animals, that we could use to work out

how fast fossil animals would move.

[narrator] Sellers and his colleagues looked for present day animals,

that would approximate the movements of a Tyrannosaur.

They zeroed in on the ostrich.

[Bill] And these ostriches, are as close as we can get,

in terms of a modern animal that's a bit like a T-Rex.

So they've got two legs, they've got very large bodies,

and they're high speed runners.

A lot of the basic anatomy, is exactly the same,

so they do make a very good model.

[melodic music]

[narrator] Using the ostrich's movement as a reference, Sellers made

a computer simulation of how a T-Rex might have run.

The models show which muscles a T-Rex would have used

when running.

Sellers took particular notice, of the muscles connecting

the thighs, and the tail.

Previously, experts thought these muscles were merely

for tail movement.

But it became clear, that they also played a key role

in helping the T-Rex, to run fast.

[Bill] What it does, is it pulls the thigh bone backwards.

And so obviously, this is the main powerhouse.

Even though it's a very heavy animal, it can obviously

generate the force that it needs to go at a good speed.

[soft ominous music]

[narrator] With this model, the average T-Rex's top speed

increases to 30 kilometers per hour.

And the strongest could run, as fast as 50.

The descendants of the primitive Tyrannosaur siblings,

have acquired speed, size, and intelligence.

But, there's more.

Karl Bates is an expert, on the bite force of dinosaurs.

[unsettling music]

With an enormous bite force, and enlarged neck muscles,

it probably clamped onto its prey, and pulled away

at the flesh.

There have been quite a few fossils found of plant eating

dinosaurs, with T-Rex bite marks in them.

Where the bite marks go very deep into the bones.

[loud growl then bones crack]

[narrator] A huge jaw powered this deadly bite.

Bates has studied the structure of T-Rex's skull.

He recreated the muscles that connected the upper

and lower jaws.

Then, he used the computer simulation to quantify

the strength, of its bite.

Bite force, is measured in newtons.

The lion, known as the king of the Savannah,

has a bite force of 4,000 newtons.

The bite force of alligators, fearsome killers near water,

is around 6,000 newtons.

Compare this to the dinosaurs, the Allosaurus is considered

to have been the strongest dinosaur, before T-Rex.

Its bite force, was about 9,000 newtons.

According to Bates, the T-Rex, had a bite force

of some 60,000 newtons.

That's seven times greater, than the Allosaurus.

[Karl] 60,000 newtons is a huge amount of force.

So we're convinced that T-Rex had a very large bite,

in absolute terms.

And was probably one of the fiercest biters,

of all time.

[narrator] When a T-Rex bit into its prey, it exerted six tons of force.

That's equivalent to the weight of an African elephant.

[mysterious music]

In theory, such heavy loads could cause the jawbones

to break.

But something protected T-Rex from this.

So the skull was very important for capturing prey,

and consuming prey.

And we were just interested in how this huge structure,

performed mechanically.

[narrator] A T-Rex skull is made up of more than 40 different parts.

Here and there are gaps measuring just

a few millimeters.

These gaps released force when the T-Rex bit,

and helped to soften the shock.

The T-Rex has this reputation of being such a deadly,

fearsome creature.

And so we're pretty much convinced that T-Rex was one

of the most ferocious biters of all time and worthy

of the title "King of the dinosaurs".

[narrator] A creature with both extraordinary physical

capabilities and, sophisticated intelligence.

After 100 million years, the T-Rex had reached

the pinnacle of its evolution.

A pair of T-Rex siblings,

even if they were to meet up with Siats, former ruler

of the dinosaurs, they would have no reason

to flee.

[growls]

[growls]

They are no longer the small, weak, Tyrannosaurs of old.

[both growling loudly]

The siblings set off, on a new journey.

In search of more prey.

They are heading back to the Eurasian continent.

Along the way, they pass through areas inhabited

by many relatives from the Tyrannosaur family.

[ethereal music]

T-Rex was the king of the late Cretaceous, no doubt about that.

But not all Tyrannosaurs that lived at that time,

were big, top of the food chain predators, like T-Rex.

Some of them were actually quite a bit smaller.

So even when T-Rex was ruling the world, there were other

close cousins of T-Rex

were doing other things,

filling other roles in the ecosystem,

and doing a very good job at it.

[narrator] In 2014, in Northern Alaska,

researchers found a new species, of Tyrannosaur.

They called it Nanuqsaurus, after the Inuit word,

for Polar bear.

At six meters, it wasn't even half the size of T-Rex.

Experts attribute its small size to a lack of game.

The same year, in Jiangxi Province,

in Southern China, a team dug up an unusual fossil.

The most noticeable feature, is its long, thin, nose.

It's been nicknamed Pinocchio Rex, in reference

to the beloved character.

Outwardly, it looks nothing like T-Rex.

But a bone analysis confirmed it as a new Tyrannosaur species.

Then, in July 2015, scientists made a discovery in Japan.

Up until then, no one thought large Tyrannosaurs,

had lived there.

The team found fossils, of two large teeth.

Each measuring eight centimeters.

Their size suggests they came from an animal, 10 meters long.

Finds like these, illustrate the distinctive evolutionary

paths, taken by Tyrannosaurs, all over the world.

So far, experts have identified 28 individual species.

[unsettling music]

At one point, T-Rex truly dominated the dinosaur world.

But in the end, it would meet a cruel fate.

Evidence of this emerged, in 2015.

Scientists were excavating in Alberta province,

in Western Canada.

They found this fossil, a cousin of T-Rex,

called Daspletosaurus.

Here and there, researchers spotted telltale signs

of battle.

A wound deep enough to pierce the bone.

On the back of the skull, a part had been bitten off.

Scientists wondered what kind of creature, could have

inflicted such wounds, on the mighty Tyrannosaur.

Paleontologist David Hone, points to an unlikely suspect.

So you immediately have only one credible candidate,

for these kinds of injuries, and these kinds of bites,

and that's another large bodied Tyrannosaur.

[narrator] Hone says the shape and size of the bite marks,

indicates a fight between two members

of the Tyrannosaur family.

They're gonna hunt at the same time,

or die in the same place, and have similar territories.

And they're going to come into these conflicts.

Well I'm sure, every so often there were fights to the death.

And certainly we actually see evidence of cannibalism

among Tyrannosaurs, they do kill each other.

[narrator] In turf battles, even siblings could become rivals.

And if one refused to back down,

[growling]

[loud growl]

Two frail T-Rex ancestors set out on a grand journey,

in search of new lands.

On the North American continent, they confronted

countless beasts.

But they managed to thrive.

Their descendants continued to evolve, eventually becoming

the undisputed rulers, of the dinosaurs.

But once at the top, these powerful killers,

turned their awesome power, on one another.

66 million years ago, the reign of the dinosaurs,

came to a sudden end.

Experts believe the reason, was a gigantic asteroid,

that smashed into Earth.

[explosion]

Resulting climate change, wiped out the dinosaurs.

Including Tyrannosaurus.

[ominous music]

But, was that really the end of the dinosaurs?

Stephen Brusatte's research, provides evidence

that it wasn't.

Certain creatures alive today, are descendants from a branch,

of the Tyrannosaur family.

Birds.

Once the dinosaurs died out, birds underwent

a spectacular evolution.

New species appeared, and they became the rulers

of the skies.

They were able to do this, because of strengths

they inherited from their Tyrannosaur ancestors.

We always talk about dinosaurs going extinct

66 million years ago, when the asteroid hit.

But really not all dinosaurs went extinct, most of them did,

but one type of dinosaur survived, and those

are the birds. So birds evolved from dinosaurs,

and they're actually a type of dinosaur.

And they live out today, there's over 10,000 species of birds.

There's birds flying around here.

And so these birds

are living dinosaurs

and so birds today,

carry on the genes, of T-Rex.

[powerful music]

[narrator] Creatures unlike any seen before or since.

The free spirit of T-Rex, lives on.

[music continues]