ever made by an animal.

They are gorgeous in their complexity,

delicate in their construction,

and yet strong enough to hold a bird

thousands of feet in the air.

Like all things in nature,

feathers evolved over millions of years

into their modern form.

It could be hard to imagine

how this could have happened.

After all, what did the intermediate forms look like?

What good is half a wing,

festooned with half-feathers?

Thanks to science,

we now know that birds are living dinosaurs.

You can see the kinship in their skeletons.

Certain dinosaurs share some anatomical details with birds

found in no other animals, such as wish bones.

And in the late 1990s,

paleontologists started digging up

some compelling support for that idea:

dinosaurs with bits of feathers

still preserved on their bodies.

Since then, scientists have found

dozens of species of dinosaurs

with remnants of feathers.

Some were as small as pigeons,

and some were the size of a school bus.

If you look at how they are related on a family tree,

the evolution of feathers

doesn't seem quite so impossible.

The most distant feathered relatives of birds

had straight feathers that looked like wires.

Then these wires split apart,

producing simple branches.

In many dinosaur lineages,

these simple feathers evolved

into more intricate ones,

including some that we see today on birds.

At the same time,

the feathers spread across the bodies of dinosaurs,

turning from sparse patches of fuzz

into dense plumage,

which even extended down to their legs.

A few fossils even preserved some of the molecules

that give feathers color.

They reveal a beautiful range of colors:

glossy, dark plumage, reminiscent of crows,

alternating strips of black and white,

or splashes of bright red.

Some dinosaurs had high crests on their heads,

and others had long, dramatic tail feathers.

Now, none of these dinosaurs

could use their feathers to fly -

their arms were too short

and the rest of their bodies were far too heavy.

But, birds don't just use feathers to fly.

A woodcock uses feathers to blend in perfectly

with its forest backdrop.

An ostrich stretches its wings over its nest

to shade its young.

A peacock displays its magnificent tail feathers

to attract peahens.

Feathers could have served these functions

for dinosaurs too.

Exactly how feathered dinosaurs took flight

is still a bit of a mystery.

But if a small-feathered dinosaur flapped

its arms as it ran up an incline,

its feathers would have provided extra lift

to help it run faster.

This accident of physics might have led

to the evolution of longer dinosaur arms,

which would let them run faster

and even leap short distances through the air.

Eventually, their arms stretched out into wings.

Only then, perhaps 50 million years

after the first wiry feathers evolved,

did feathers lift those dinosaurs into the sky.