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We're living through THE golden age of dinosaur discoveries.

From all over the world,

a whole new generation of dinosaurs has been revealed...

from the biggest giants and the deadliest killers

to the weird and wonderful.

From the Arctic to Africa.

From South America to Asia.

With the most extraordinary fossils...

from dinosaur embryos to the exquisitely preserved.

And using the latest imaging technology,

cutting-edge research has allowed us to probe deeper

and reveal more than ever before.

It gives us our first truly global view of these incredible animals.

In this episode we look at the new, bizarre

and extraordinary feathered dinosaurs,

many of which have only just been discovered.

Some conquered new worlds.

Others grew to gigantic sizes.

As we learn more about the evolution of these feathered beasts,

they're revolutionising our understanding of life on Earth,

blurring the boundaries between dinosaurs and birds.

For over a century, the great dinosaur discoveries

came from North America and Europe,

but in the last decade or so, the focus shifted.

One country now sits at the centre of the new dinosaur revolution -

China.

In recent years, spectacular fossils have been uncovered here.

Amazingly preserved, these fossils revealed exquisite new details.

And they are giving us incredible glimpses into an alien world,

a world full of the most bizarre dinosaurs we have ever seen.

Possibly the strangest of all lived 154 million years ago,

in the late Jurassic period.

An animal that looks like nothing else on earth.

Hiding in these lush forests is Epidexipteryx.

The size of a pigeon, everything about this creature is odd,

from the length of its arms to the shape of its teeth.

This forest is home to many predators

and being small makes it vulnerable.

This is Sinraptor.

A small dinosaur like Epidexipteryx

would be of no interest to a seven-metre adult.

But this is a juvenile,

and Epidexipteryx is a perfect-sized snack.

Being small does have its advantages,

because it can escape to the safety of the trees.

Everything we know about Epidexipteryx

comes from an incredible fossil, first revealed in 2008.

It showed an animal with a small skull and large eye sockets,

and unusually long teeth.

With toes suited to gripping branches

and very long arms and hands,

it suggests that this was a dinosaur well suited

to living in the trees.

The extraordinary, elongated third finger

is another distinctive feature of the group.

With this and its projecting front teeth, Epidexipteryx

has the perfect tools to hunt for insects among the trees.

And one of its favourite foods

are burrowing beetle grubs that are hiding

within the trees themselves.

Prey like this, which is difficult to catch, is quite a prize -

a prize that can attract unwanted attention.

Here it's another, larger, Epidexipteryx.

Stealing food is a common tactic,

particularly where an animal possesses an expertise.

There is more to this extraordinary creature

than first meets the eye.

Not only was it perfectly designed for life in the trees,

but the fossil has also revealed

that it was covered in short, simple feathers.

Feathers that were likely to have evolved for just one reason -

to keep it warm.

But there is one last striking feature -

four long feathers on its tail.

These feathers aren't like those of modern birds.

These are long and ribbon-like.

Almost certainly, only for show.

They're the earliest record of ornamental feathers.

Not just for attraction

but also to threaten.

In fact, the very name Epidexipteryx means "display feather",

and they're among the most bird-like of any dinosaur.

Stealing among the trees is one thing.

Stealing on the ground is quite another.

Only among the trees can you be safe

from the large predators like Sinraptor.

On the ground, a few feathers offer no protection.

The first feathered dinosaur was discovered in 1996

but lots more would quickly follow.

It suddenly appeared as if many dinosaur species

actually had feathers.

And confirmed what had long been suspected -

a direct link between dinosaurs and birds.

A link that can be found in the dinosaurs that

lived here in the Mongolian desert 85 million years ago.

This is Saurornithoides.

It's a member of the Troodon family and we have discovered

actual fossils of these dinosaurs sitting on a nest.

It takes days to lay a full clutch of eggs

and until that's complete,

this animal won't begin its brooding behaviour

and start sitting on the next.

With the Saurornithoides off foraging,

this unguarded nest provides an invitation for predators.

This is an Oviraptorid - a bizarre-looking theropod dinosaur.

With no teeth, they were mostly plant eaters.

But that doesn't mean it won't take advantage

of a different kind of lunch.

We know Oviraptorids were mostly plant eaters

because of some amazing evidence we have found.

One fossil in particular was incredibly well preserved.

Inside its body were small stones - gastroliths.

Just like a bird,

it had swallowed these to help digest tough plants.

But when the remains of two unrelated embryos

were discovered in an Oviraptorid nest,

it suggested that some were not just plant eaters

but may have been nest-raiders as well.

With two bony projections in its upper jaw,

this Oviraptorid has the tools to break into an egg

and get at the precious contents inside.

It means that a nesting animal like a Saurornithoides

can never turn its attention away for long.

But two lost eggs are the least of its problems.

Here, some nest raiders are bigger than others.

This is Gigantoraptor.

Gigantoraptor was discovered in 2007 in the Gobi Desert of Mongolia.

The sheer size of the bones

revealed it was unlike anything found before -

eight metres long and weighing around 1.5 tonnes.

From its bones, we know

it was 35 times bigger than its closest Oviraptorid relatives.

And yet this giant wasn't even fully grown.

it was "like finding a mouse the size of a cow".

We don't know for sure

if such a huge dinosaur like Gigantoraptor

would have or need feathers.

In dinosaurs, feathers are usually found as a fine body covering

and appear to be mainly for keeping warm.

But feathers were found, and preserved on a fossil

of one of Gigantoraptor's close relatives.

And on the forearms and tail are the unmistakeable traces

of longer symmetrical feathers, similar to a modern bird's.

It seems certain that Gigantoraptor too was feathered,

making this the largest feathered animal ever discovered.

These aren't for flight - Gigantoraptor couldn't fly.

Nor are they for insulation.

These are used to intimidate or attract.

Across the world, discovery after discovery

has revealed more and more features -

from nesting to feathers - that were once thought of

as exclusively bird-like but have now also been found in dinosaurs.

But the ultimate discovery is perhaps that of a dinosaur

that lived in Northeast China around 120 million years ago.

This remote area has revealed

spectacular fossils in exquisite detail,

unearthing an astonishing diversity of animals,

many of which are well adapted to living in trees.

One particular dinosaur discovery takes this to a whole new level.

This is Xianglong.

With curved claws, it's a lizard well suited to climbing trees.

With prey like this, predators were sure to follow.

The most common dinosaur in these forests

doesn't live on the ground.

Microraptor.

The fossils of Microraptor are so well preserved

they clearly reveal every detail of its anatomy.

With distinctive claws on its first toe,

this is a member of the raptor family.

But these claws evolved for climbing, rather than killing.

At less than a metre long,

this was a dinosaur perfectly suited to live in the trees.

Microraptor is small, and perfectly adapted to chasing prey.

Xianglong, however, has a trick.

This is a flying lizard.

It seems to have the perfect skill to escape.

But the fossils of Microraptor reveal something else.

This was a feathered dinosaur,

but these feathers aren't for keeping warm or for show.

Their structure is plainly visible from the fossils.

They are very long, veined and most importantly,

their shape creates a perfect aerodynamic surface.

And they aren't confined to its forearms.

Its legs, too, had long feathers.

These feathers are designed for one thing only - flight.

Microraptor is a four-winged dinosaur...

that took to the skies.

But in these Chinese forests,

Microraptor isn't the only flying monster.

Sinornithosaurus. Closely related and larger.

More than capable of stealing prey.

But it has larger prey in mind.

Microraptor is now the hunted.

Both can fly.

But this isn't powered flight - it's gliding.

Recent research has revealed how Microraptor flew.

It didn't have the muscles for powered flight,

so instead it made the most of its four wings.

By holding its rear legs back and to the sides,

it was able to become an incredibly efficient glider...

..moving through the forest in a series of long, looping glides.

Having longer flight feathers on both its arms and legs,

Microraptor is by far the better glider.

But with no ability to gain height, the only way is down.

And once on the ground, the long feathers

turn from an advantage into weakness.

Microraptor is barely able to walk, much less run.

Sinornithosaurus has no such problem.

On the forest floor, the tables are turned.

Microraptor has a fortunate escape.

Sinornithosaurus was one of the first feathered dinosaurs found.

The fossils are so perfectly preserved

they have helped us solve

one of the great dinosaur mysteries.

For years, the colour of dinosaurs

was thought impossible to work out.

In 2010, it was discovered that the feathers on this fossil

weren't just impressions.

Under the microscope, tiny structures were revealed

identical to those found in modern birds -

structures that contain the pigment.

Remarkably, by comparing them to living birds,

we can even work out the true colours.

The feathers appear to be a combination of reddish-browns,

yellows, greys and blacks,

perfectly suited to forest life.

Another dinosaur living in this forest is Jeholosaurus,

a small plant eater.

Recent fossils indicate that this type of dinosaur

looks after and protects its young.

With feathers that allow it to blend in with the forest,

Sinornithosaurus can move, unseen, through the tree tops.

And Sinornithosaurus is a hunter with a potent secret weapon.

In 2011, a study of the eyes of this creature revealed

that it was a predator perfectly capable

of hunting equally during day and night.

And a study of its teeth, in 2009,

showed something that definitely sets it apart from birds.

Something far more deadly.

The greatest danger is not simply being outnumbered.

We have found that Sinornithosaurus teeth

have unusual and distinctive grooves along their length.

They resembled those of the venomous Gila monster,

the grooves in its teeth used to deliver venom into its victim.

The team even identified what they thought was the location

of the venom sac in the fossil.

It appeared Sinornithosaurus could kill with poison.

This is a far more deadly predator than anyone ever imagined...

and completes an extraordinary picture of a bizarre lost world.

All of these discoveries reveal the importance of feathers

to a whole host of dinosaurs -

from insulation to defence and finally, flight.

And Microraptor not only hints at how flight developed,

but also, that dinosaurs still live amongst us today,

as birds.

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