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NARRATOR: 
It's the worst day in the 
history of life on Earth.

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A cataclysm that ends 
the age of the dinosaurs.

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♪ ♪

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LINDSAY ZANNO: 
If they hadn't met 
their destruction,

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our story never 
would have begun.

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NARRATOR: 
From the ashes,

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a band of survivors rises 
to become bigger...

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nimbler...

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and smarter 
than any that came before.

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Our tribe-- the mammals.

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It was only after 
we lose the dinosaurs

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that mammals really explode

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into the diversity of forms 
that we see today.

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♪ ♪

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NARRATOR: 
What happened after the impact?

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♪ ♪

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How did life surge back?

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The clues have been elusive.

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IAN MILLER: 
You could go your entire career

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and not find a skull 
from this time period.

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That's how rare they are.

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NARRATOR: 
But now comes 
a remarkable discovery.

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SHARON MILITO: 
There's just nothing like 
picking up something

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and finding out 
it's something amazing.

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NEIL SHUBIN: 
It's like winning the lottery.

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TYLER LYSON: 
Bam! We hit it big.

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NARRATOR: 
An unprecedented trove 
of fossils

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reveals a turning point 
in the history of life.

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KIRK JOHNSON: 
That moment of rapid mammal 
evolution

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is effectively the trigger

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to our existence here 
on planet Earth.

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♪ ♪

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NARRATOR: 
"Rise of the Mammals"-- 
right now, on "NOVA."

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♪ ♪

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♪ ♪

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NARRATOR: 
We live in the age of mammals.

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All across the globe,

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they thrive in an astonishing 
array of forms...

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♪ ♪

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From the great beasts 
of the forests

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to giants that sound 
the ocean depths...

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♪ ♪

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to us,

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mammals dominate the planet.

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(grunting)

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But it wasn't always this way.

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(dinosaur screeches)

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For 150 million years,

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mammals lived in the shadows 
of the dinosaurs.

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Then, a catastrophe 
gave them an opening.

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(explosion thunders)

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For years, we've known just bits 
and pieces

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about how mammals seized 
the moment

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and made our story possible.

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But now that's changing.

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♪ ♪

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An extraordinary discovery 
in Colorado

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is revealing an unparalleled 
collection of fossils

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from the time when mammals 
began their reign.

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♪ ♪

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This hoard lay hidden 
in plain sight

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until a young fossil hunter made 
a once-in-a-lifetime discovery.

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♪ ♪

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LYSON: 
I grew up in a town 
of about 80 people,

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basically the middle of nowhere 
in southwestern North Dakota.

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♪ ♪

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NARRATOR: 
Tyler Lyson's home might look 
like other outposts

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scattered 
across the American West,

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but this place is unique.

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LYSON: 
Right by my hometown, 
about a mile away,

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are badlands that preserve 
the very last moment of time

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when dinosaurs were alive.

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As a child, I would run around 
the badlands

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and find dinosaur bone 
after dinosaur bone,

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just tons of dinosaur bones 
just tumbling out of the hills.

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♪ ♪

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NARRATOR: 
Known as the Hell Creek 
formation,

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this was the first place T. rex 
fossils were discovered

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a century ago.

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♪ ♪

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Ever since, bone diggers have 
been searching

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for more traces 
of that lost world.

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♪ ♪

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(helicopter rotors whirring)

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Even as a boy, 
Tyler was in the thick of it.

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JOHNSON: 
Years ago, I met a kid named 
Tyler Lyson.

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And he was this gangly 
12-year-old kid.

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By the time he was 13, 
he was going out by himself

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and finding amazing fossils.

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He found an entire dinosaur 
when he was, like, 14 years old.

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NARRATOR: 
Tyler even discovered 
a new species

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of feathered dinosaur.

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JOHNSON: 
He became sort 
of this dinosaur wunderkind.

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NARRATOR: 
It was a made-for-TV story.

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MAN: 
High school sophomore 
Tyler Lyson has walked

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just about every inch 
of this land,

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and has already headed 
20 dinosaur excavations.

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NARRATOR: 
His most spectacular find?

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A dinosaur fossil 
with preserved skin and muscle.

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He kept finding more fossils,

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and soon became an expert 
in ancient turtles.

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He became fascinated 
by a well-known pattern

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in where dinosaurs were 
and where they weren't.

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LYSON: 
I remember as a child crossing 
over this band

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and getting above that area 
and not finding any dinosaurs.

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NARRATOR: 
The distinct layer seemed 
to mark their disappearance.

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LYSON: 
So, this always fascinated me.

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Why, above that boundary, 
were there no more dinosaurs?

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♪ ♪

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What happened here?

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NARRATOR: 
The boundary layer, 
Tyler learned,

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was the signature of an event 
that changed the world forever.

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(roars)

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♪ ♪

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During the age of reptiles,

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dinosaurs tower over mammals.

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Other reptiles 
rule the skies and seas.

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They take on a wide range 
of shapes and lifestyles.

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Many are gigantic.

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Mammals had been around 
for millions of years.

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But in all of that time, 
most grew no bigger than a rat.

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Then, 66 million years ago, 
the cataclysm.

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♪ ♪

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A chunk of rock 
over six miles wide

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tears through the atmosphere 
and slams into the planet.

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(collision thunders)

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The asteroid blasts a crater 
20 miles deep

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and over 100 miles wide

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in the Yucatan Peninsula.

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(dinosaurs screeching 
and rumbling)

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It showers the planet 
with molten rock

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and white-hot beads of glass.

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(dinosaurs screeching 
and rumbling)

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LYSON: 
And this broils the surface 
of the Earth.

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NARRATOR: 
Creatures on the surface roast.

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(creatures roaring)

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Skies across the globe darken.

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Fire gives way to frost.

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ANJALI GOSWAMI: 
You have intense global cooling.

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You're talking about 
immediate global winter.

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NARRATOR: 
Deprived of sunlight, 
plants wither.

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Lush forests collapse.

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So the animals that rely 
on those plants for food,

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the animals that rely 
on those animals

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that rely on plants for food, 
they would all suffer.

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♪ ♪

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You really are having the 
entire food chain fall apart.

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NARRATOR: 
All of the dinosaurs, 
except the birds, perish.

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SHUBIN: 
Three out of four species

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that were alive on the planet 
before the impact

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died.

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And that's just the species.

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00:09:01,300 --> 00:09:02,666
About 90% of the creatures

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00:09:02,666 --> 00:09:04,166
that were alive 
before the impact

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00:09:04,166 --> 00:09:06,100
are dead afterwards.

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ZANNO: 
We think about 
the loss of dinosaurs,

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but dinosaurs weren't the only 
animals to suffer from this.

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Many, many groups of organisms 
took a very serious hit,

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including mammals.

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♪ ♪

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LYSON: 
It's a really bad time 
for life on Earth.

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Yet some things survive, right?

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Including some of our earliest, 
earliest ancestors.

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♪ ♪

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NARRATOR: 
We don't know much 
about these creatures.

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♪ ♪

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None was bigger than a squirrel.

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And their size and scarcity 
have made their fossils

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00:09:48,733 --> 00:09:51,333
hard to come by.

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Yet somehow, this band of 
survivors and their descendants

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00:09:57,900 --> 00:09:59,533
will claim the Earth.

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00:09:59,533 --> 00:10:02,266
(birds twittering)

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00:10:02,266 --> 00:10:05,300
♪ ♪

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00:10:05,300 --> 00:10:09,433
(animals grunting 
and chittering)

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00:10:12,500 --> 00:10:16,466
LYSON: 
Today, there are over 6,000 
species of mammals.

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00:10:16,466 --> 00:10:19,000
♪ ♪

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00:10:19,000 --> 00:10:22,066
And they range in size 
from the tiny pygmy jerboa,

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00:10:22,066 --> 00:10:25,166
which weighs about 
as much as a coin,

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00:10:25,166 --> 00:10:29,466
to the largest animal to have 
ever lived, the blue whale,

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00:10:29,466 --> 00:10:35,600
which is about 180 tons, 
the size of 15 school buses.

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GOSWAMI: 
Over the last 66 million years,

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they've evolved an incredible 
diversity of forms.

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00:10:44,566 --> 00:10:47,500
♪ ♪

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SHUBIN: 
Mammals today live in almost 
every environment on the planet,

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from the tops 
of the highest mountains

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00:10:52,366 --> 00:10:55,900
to living in the trees, 
to living in the water.

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♪ ♪

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00:11:00,366 --> 00:11:04,366
NARRATOR: 
They thrive in scorching deserts

189
00:11:04,366 --> 00:11:07,300
and across the frozen tundra.

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00:11:09,166 --> 00:11:13,433
Mammals even patrol 
the depths of every ocean

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00:11:13,433 --> 00:11:17,000
and the moonlit reaches 
of the sky.

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00:11:17,000 --> 00:11:20,066
♪ ♪

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00:11:20,066 --> 00:11:23,966
LYSON: 
All this diversity 
can be traced back

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00:11:23,966 --> 00:11:27,166
to those survivors 
of the extinction.

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00:11:27,166 --> 00:11:29,866
♪ ♪

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00:11:29,866 --> 00:11:34,033
NARRATOR: 
What happened in the wake 
of that catastrophic impact?

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00:11:34,033 --> 00:11:36,700
LYSON: 
That's what I'm interested in.

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00:11:36,700 --> 00:11:40,900
♪ ♪

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00:11:40,900 --> 00:11:43,333
How long did it take 
for ecosystems to recover?

200
00:11:43,333 --> 00:11:47,933
For habitats to reform?

201
00:11:47,933 --> 00:11:50,066
For life to get big again?

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00:11:50,066 --> 00:11:53,333
♪ ♪

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00:11:57,366 --> 00:12:01,933
NARRATOR: 
The answers require fossils.

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00:12:01,933 --> 00:12:04,533
But such relics are rare.

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00:12:06,566 --> 00:12:11,366
JOHNSON: 
I've spent much of the last 
35 years looking at rocks

206
00:12:11,366 --> 00:12:12,800
from the first million years

207
00:12:12,800 --> 00:12:16,233
after the extinction 
of the dinosaurs.

208
00:12:16,233 --> 00:12:19,200
I've studied the fossil plants 
from that time period.

209
00:12:19,200 --> 00:12:22,200
And through that entire 
35 years,

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00:12:22,200 --> 00:12:24,633
I think I've found

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00:12:24,633 --> 00:12:29,500
one or two 
fossil mammal pieces.

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00:12:29,500 --> 00:12:30,933
And I'm looking.

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00:12:30,933 --> 00:12:34,366
I'm out there looking, and I 
know how rare those things are.

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00:12:37,600 --> 00:12:39,966
NARRATOR: 
For years, Tyler and others

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00:12:39,966 --> 00:12:42,266
search for these scarce 
specimens

216
00:12:42,266 --> 00:12:44,933
in North Dakota.

217
00:12:44,933 --> 00:12:47,700
He targets the rock 
above the boundary layer--

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00:12:47,700 --> 00:12:51,466
sediments laid down 
just after the impact.

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00:12:51,466 --> 00:12:56,766
♪ ♪

220
00:12:56,766 --> 00:13:02,366
Fossil hunters had occasionally 
found mammal traces here,

221
00:13:02,366 --> 00:13:04,800
but Tyler has no such luck.

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00:13:04,800 --> 00:13:09,033
JOHNSON: 
Small animals get broken up 
into fragments.

223
00:13:09,033 --> 00:13:11,033
So, when you're looking 
for an early mammal,

224
00:13:11,033 --> 00:13:13,200
you're looking 
for effectively the tooth

225
00:13:13,200 --> 00:13:15,000
of a mouse-sized animal.

226
00:13:15,000 --> 00:13:16,766
You're looking for something 
that's about the size

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00:13:16,766 --> 00:13:17,866
of the head of a pin.

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00:13:17,866 --> 00:13:20,600
And they're excruciatingly hard 
to find.

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00:13:20,600 --> 00:13:22,366
♪ ♪

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00:13:22,366 --> 00:13:23,700
LYSON: 
Every year, I go back 
to my hometown,

231
00:13:23,700 --> 00:13:25,700
and every year, I spend time 
above the boundary

232
00:13:25,700 --> 00:13:28,333
looking for fossils.

233
00:13:28,333 --> 00:13:33,800
And I've found so few fossils, 
it's, it's pathetic.

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00:13:33,800 --> 00:13:35,666
♪ ♪

235
00:13:35,666 --> 00:13:37,666
And I was starting 
to think about, like,

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00:13:37,666 --> 00:13:39,400
"Well, where's the next area?"

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00:13:39,400 --> 00:13:42,200
I was getting ready to give up.

238
00:13:42,200 --> 00:13:47,900
NARRATOR: 
But then, Tyler gets a job-- 
and another shot--

239
00:13:47,900 --> 00:13:50,400
in Colorado.

240
00:13:52,100 --> 00:13:57,333
He joins up with Ian Miller, 
an expert in plant fossils

241
00:13:57,333 --> 00:14:00,733
at the Denver Museum 
of Nature and Science.

242
00:14:00,733 --> 00:14:06,900
Ian shares an interest in the 
extinction and its aftermath,

243
00:14:06,900 --> 00:14:10,500
and knows Colorado 
is a great place to search.

244
00:14:10,500 --> 00:14:12,166
♪ ♪

245
00:14:12,166 --> 00:14:16,000
We have this really unparalleled 
record of this period of time

246
00:14:16,000 --> 00:14:17,366
here in Western North America.

247
00:14:17,366 --> 00:14:20,966
But the best place 
is right here.

248
00:14:20,966 --> 00:14:25,700
NARRATOR: 
Together, they start exploring 
locations around the state.

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00:14:25,700 --> 00:14:27,833
♪ ♪

250
00:14:27,833 --> 00:14:30,733
One, called Corral Bluffs,

251
00:14:30,733 --> 00:14:35,833
offers 400 feet of exposed rock 
rising above the boundary.

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00:14:42,033 --> 00:14:45,366
Tyler begins by scanning 
the ground for bits of bone.

253
00:14:47,600 --> 00:14:49,700
LYSON: 
That's how we're trained 
to find fossils--

254
00:14:49,700 --> 00:14:54,300
looking for actual scraps 
of bone on the surface,

255
00:14:54,300 --> 00:14:55,866
or to see bones 
sticking out of the ground.

256
00:15:02,733 --> 00:15:06,500
NARRATOR: 
But at Corral Bluffs, 
this approach yields

257
00:15:06,500 --> 00:15:08,533
just a few scattered fragments.

258
00:15:08,533 --> 00:15:12,933
LYSON: 
I really didn't find 
a whole lot.

259
00:15:12,933 --> 00:15:16,300
You can only look for fossils 
for so long

260
00:15:16,300 --> 00:15:20,800
before you get really frustrated 
and decide to go home.

261
00:15:23,800 --> 00:15:25,966
NARRATOR: 
What Tyler doesn't know

262
00:15:25,966 --> 00:15:27,300
is that a museum volunteer

263
00:15:27,300 --> 00:15:30,533
had already found the key 
to his quest

264
00:15:30,533 --> 00:15:32,233
in this same spot.

265
00:15:32,233 --> 00:15:37,300
♪ ♪

266
00:15:37,300 --> 00:15:40,900
Long before Tyler arrived 
in Colorado,

267
00:15:40,900 --> 00:15:43,966
Sharon Milito set off to look 
for fossils

268
00:15:43,966 --> 00:15:47,600
from the plateau 
atop the bluffs.

269
00:15:47,600 --> 00:15:49,033
MILITO: 
When we first came out,

270
00:15:49,033 --> 00:15:51,933
we were just looking 
for whatever we could find.

271
00:15:53,800 --> 00:15:55,900
The important thing we wanted 
to find

272
00:15:55,900 --> 00:15:57,600
were mammal jaws 
and mammal teeth,

273
00:15:57,600 --> 00:15:59,133
but they were elusive.

274
00:15:59,133 --> 00:16:02,366
So, one day, 
I was walking along in an area

275
00:16:02,366 --> 00:16:04,333
I'd been many times before,

276
00:16:04,333 --> 00:16:05,500
and I saw this white, round rock

277
00:16:05,500 --> 00:16:08,933
sitting there on kind of 
its own little pedestal.

278
00:16:10,666 --> 00:16:14,833
♪ ♪

279
00:16:14,833 --> 00:16:16,466
And I picked it up 
and looked at it,

280
00:16:16,466 --> 00:16:20,700
and as soon as I looked at it, 
I saw these teeth

281
00:16:20,700 --> 00:16:24,000
that were just smiling out 
at me.

282
00:16:24,000 --> 00:16:28,266
And I just almost 
had a heart attack.

283
00:16:28,266 --> 00:16:31,933
NARRATOR: 
She'd found part 
of a mammal skull--

284
00:16:31,933 --> 00:16:34,600
one that could fit in the palm 
of her hand.

285
00:16:34,600 --> 00:16:36,066
MILITO: 
I was so excited,

286
00:16:36,066 --> 00:16:39,633
because it was really, really 
well preserved.

287
00:16:39,633 --> 00:16:41,666
♪ ♪

288
00:16:41,666 --> 00:16:45,933
NARRATOR: 
She brought the fossil 
to the museum,

289
00:16:45,933 --> 00:16:48,866
where it was catalogued 
and filed away.

290
00:16:52,633 --> 00:16:56,033
♪ ♪

291
00:16:56,033 --> 00:16:59,533
It was years 
before Tyler happened across it.

292
00:17:03,833 --> 00:17:07,500
LYSON: 
I was downstairs, just looking 
through the collection,

293
00:17:07,500 --> 00:17:11,466
pulling open drawers, and there, 
sitting right in the front,

294
00:17:11,466 --> 00:17:16,300
was the palate of a mammal.

295
00:17:16,300 --> 00:17:19,366
And I was absolutely astonished; 
I couldn't believe it.

296
00:17:19,366 --> 00:17:22,866
And so I was sort of thinking 
to myself, like,

297
00:17:22,866 --> 00:17:25,033
"If there's this complete 
of a skull here,

298
00:17:25,033 --> 00:17:28,333
there's got to be more."

299
00:17:28,333 --> 00:17:32,733
NARRATOR: 
Sharon's fossil had been found 
in a particular kind of rock

300
00:17:32,733 --> 00:17:36,666
called a concretion.

301
00:17:36,666 --> 00:17:40,766
Sometimes, concretions can form 
around organic material,

302
00:17:40,766 --> 00:17:43,266
like bone.

303
00:17:43,266 --> 00:17:45,400
And if conditions are right,

304
00:17:45,400 --> 00:17:50,566
they protect the fossil inside 
for eons.

305
00:17:50,566 --> 00:17:52,333
LYSON: 
Sharon's skull 
was incredibly lucky

306
00:17:52,333 --> 00:17:57,433
because it showed that, 
yes, there are fossils inside,

307
00:17:57,433 --> 00:18:00,166
and this is the type of rock 
to look for.

308
00:18:00,166 --> 00:18:01,966
♪ ♪

309
00:18:01,966 --> 00:18:04,466
NARRATOR: 
Tyler decides to change his game

310
00:18:04,466 --> 00:18:08,066
and look for concretions 
to crack open.

311
00:18:08,066 --> 00:18:11,066
(Tom Petty's 
"Runnin' Down a Dream" playing)

312
00:18:11,066 --> 00:18:14,700
LYSON: 
It was absolutely 
a light bulb moment.

313
00:18:14,700 --> 00:18:16,766
That was the game changer.

314
00:18:16,766 --> 00:18:19,633
(song continues)

315
00:18:19,633 --> 00:18:22,800
PETTY: 
♪ It was a beautiful day ♪

316
00:18:22,800 --> 00:18:25,600
♪ The sun beat down ♪

317
00:18:25,600 --> 00:18:28,566
♪ I had the radio on ♪

318
00:18:28,566 --> 00:18:32,200
♪ I was drivin' ♪

319
00:18:32,200 --> 00:18:34,366
♪ The trees went by ♪

320
00:18:34,366 --> 00:18:39,400
♪ Me and Del were singin' 
"Little Runaway" ♪

321
00:18:39,400 --> 00:18:42,666
♪ I was flyin' ♪

322
00:18:42,666 --> 00:18:46,033
♪ Yeah, runnin' down a dream ♪

323
00:18:46,033 --> 00:18:47,533
♪ That never would come to me ♪

324
00:18:47,533 --> 00:18:49,600
MILLER: 
Tyler started 
to put these pieces together,

325
00:18:49,600 --> 00:18:52,933
thinking about this new lens 
to look for these concretions.

326
00:18:52,933 --> 00:18:54,900
(song continues)

327
00:18:54,900 --> 00:18:57,433
PETTY: 
♪ Runnin' down a dream ♪

328
00:18:57,433 --> 00:18:58,633
Just saying, like, 
"We're going to go down there,

329
00:18:58,633 --> 00:18:59,733
blow the doors off 
this thing."

330
00:18:59,733 --> 00:19:00,833
Nobody believes him, right?

331
00:19:00,833 --> 00:19:02,233
And even me, who, his colleague,

332
00:19:02,233 --> 00:19:05,700
I'm just, like, "That sounds 
good, that sounds good, man."

333
00:19:05,700 --> 00:19:07,966
(song continues)

334
00:19:07,966 --> 00:19:10,600
(song ends)

335
00:19:13,566 --> 00:19:16,133
NARRATOR: 
They hit the bluffs,

336
00:19:16,133 --> 00:19:18,733
their eyes peeled 
for promising rocks.

337
00:19:18,733 --> 00:19:20,466
♪ ♪

338
00:19:20,466 --> 00:19:24,800
There's a whole hillside 
of choices.

339
00:19:24,800 --> 00:19:26,900
One catches Tyler's eye.

340
00:19:26,900 --> 00:19:30,500
LYSON: 
I see this rock, 
this concretion on the ground,

341
00:19:30,500 --> 00:19:32,766
the very first one that I pick 
up, and I crack it,

342
00:19:32,766 --> 00:19:35,066
and it was amazing.

343
00:19:35,066 --> 00:19:38,633
I just found a mammal skull! 
(laughs)

344
00:19:38,633 --> 00:19:41,366
NARRATOR: 
And that was just the beginning.

345
00:19:41,366 --> 00:19:43,133
MILLER: 
It was, it was crazy 
the way it happened.

346
00:19:43,133 --> 00:19:45,200
I mean, you could go 
your entire career

347
00:19:45,200 --> 00:19:47,733
as a mammal paleontologist

348
00:19:47,733 --> 00:19:49,000
and not find a skull 
from this time period--

349
00:19:49,000 --> 00:19:49,933
that's how rare they are.

350
00:19:49,933 --> 00:19:52,000
LYSON: 
We found, I think,

351
00:19:52,000 --> 00:19:53,300
five or six mammal skulls

352
00:19:53,300 --> 00:19:57,100
within about a ten-minute 
time span.

353
00:19:57,100 --> 00:19:58,800
MILLER: 
We were just laughing 
on the outcrop.

354
00:19:58,800 --> 00:20:00,466
Nothing like that's ever 
happened to me before.

355
00:20:00,466 --> 00:20:02,633
I mean, amazing.

356
00:20:02,633 --> 00:20:05,466
NARRATOR: 
They'd cracked the case...

357
00:20:05,466 --> 00:20:08,033
♪ ♪

358
00:20:08,033 --> 00:20:11,433
...and unearthed a trove of time 
capsules filled with clues.

359
00:20:11,433 --> 00:20:13,600
♪ ♪

360
00:20:13,600 --> 00:20:17,366
JOHNSON: 
It was like opening a door 
into a new world.

361
00:20:21,800 --> 00:20:26,133
NARRATOR: 
In the months that follow, 
Tyler and Ian scour the bluff

362
00:20:26,133 --> 00:20:28,200
and discover 
thousands of fossils,

363
00:20:28,200 --> 00:20:31,266
including plants,

364
00:20:31,266 --> 00:20:35,433
reptiles, and dozens of mammals.

365
00:20:35,433 --> 00:20:37,133
(laughing)

366
00:20:37,133 --> 00:20:42,433
NARRATOR: 
All of them lived here 
just after the mass extinction.

367
00:20:42,433 --> 00:20:43,766
GOSWAMI: 
Most of the time, you know,

368
00:20:43,766 --> 00:20:47,166
we're pretty happy 
if we find some nice teeth

369
00:20:47,166 --> 00:20:50,133
from an area that's that close 
to the boundary.

370
00:20:50,133 --> 00:20:53,500
Having this kind of record 
is really rare.

371
00:20:53,500 --> 00:20:55,633
You got the other side 
a little bit, too?

372
00:20:55,633 --> 00:20:59,100
NARRATOR: 
They had found their quarry 
at last.

373
00:20:59,100 --> 00:21:03,600
But the really hard work 
now lay ahead--

374
00:21:03,600 --> 00:21:09,433
figuring out how mammals and 
their world rose from the ashes.

375
00:21:09,433 --> 00:21:15,666
♪ ♪

376
00:21:15,666 --> 00:21:20,333
What creatures 
had they unearthed?

377
00:21:20,333 --> 00:21:22,266
What was their strange world 
like?

378
00:21:22,266 --> 00:21:24,200
♪ ♪

379
00:21:24,200 --> 00:21:26,466
And how did they establish 
a foothold

380
00:21:26,466 --> 00:21:27,866
in a planetary wasteland?

381
00:21:27,866 --> 00:21:29,666
♪ ♪

382
00:21:29,666 --> 00:21:31,866
To answer these questions,

383
00:21:31,866 --> 00:21:36,233
Tyler and Ian needed to assemble 
a crack team of experts.

384
00:21:36,233 --> 00:21:40,666
ZANNO: 
The fossils are not just the 
biological remains of animals.

385
00:21:40,666 --> 00:21:42,833
They are also buried 
in a geological system,

386
00:21:42,833 --> 00:21:47,866
and so no one person can really 
understand all the data

387
00:21:47,866 --> 00:21:49,266
that we can get from a fossil.

388
00:21:49,266 --> 00:21:50,300
We need experts

389
00:21:50,300 --> 00:21:51,800
to really be able 
to piece together

390
00:21:51,800 --> 00:21:53,700
what the entire ecosystem 
would have looked like.

391
00:21:55,033 --> 00:21:58,666
NARRATOR: 
Each fossil contains 
a wealth of information,

392
00:21:58,666 --> 00:22:02,500
but it's hidden in the rock.

393
00:22:02,500 --> 00:22:06,333
The first step is to free it.

394
00:22:08,966 --> 00:22:12,366
So, they reach out 
to a virtuoso.

395
00:22:13,533 --> 00:22:16,033
ROBERT MASEK: 
I love working on fossils.

396
00:22:16,033 --> 00:22:18,433
It's so rewarding 
when you start a fossil and,

397
00:22:18,433 --> 00:22:20,800
that you really can't see.

398
00:22:20,800 --> 00:22:23,933
It's, it's almost 
like a piece of art, sometimes,

399
00:22:23,933 --> 00:22:27,800
and it also is contributing 
to scientific knowledge.

400
00:22:27,800 --> 00:22:31,800
(tool buzzing)

401
00:22:31,800 --> 00:22:35,333
NARRATOR: 
Bob Masek spent his early career 
working in factories,

402
00:22:35,333 --> 00:22:37,200
but he found he had a knack

403
00:22:37,200 --> 00:22:40,566
for releasing captives 
from rocks.

404
00:22:40,566 --> 00:22:44,266
MASEK: 
When I was little, 
I used to work on models.

405
00:22:44,266 --> 00:22:47,800
So, I did learn to do 
detailed work.

406
00:22:47,800 --> 00:22:49,600
It was sort of in me.

407
00:22:52,933 --> 00:22:54,866
My contribution as a preparator

408
00:22:54,866 --> 00:23:01,566
is to make the fossil readable 
so it can be used for science.

409
00:23:01,566 --> 00:23:03,433
GOSWAMI: 
And you can imagine, you have 
to be incredibly careful

410
00:23:03,433 --> 00:23:05,666
that you don't break your 
fossils while you're doing that,

411
00:23:05,666 --> 00:23:07,966
or even shape them 
with your own ideas

412
00:23:07,966 --> 00:23:09,133
of what they should look like.

413
00:23:10,666 --> 00:23:15,066
NARRATOR: 
The painstaking process can take 
months for a single fossil.

414
00:23:15,066 --> 00:23:21,700
But it reveals secrets held 
tight for millions of years.

415
00:23:21,700 --> 00:23:24,633
MASEK: 
As you're working, 
you do start to realize

416
00:23:24,633 --> 00:23:28,333
that this was a living animal, 
a living thing.

417
00:23:28,333 --> 00:23:31,966
I'm bringing it sort of 
back to life.

418
00:23:31,966 --> 00:23:36,166
♪ ♪

419
00:23:36,166 --> 00:23:39,966
NARRATOR: 
One by one, the fossils emerge.

420
00:23:39,966 --> 00:23:43,500
Each is exquisitely preserved.

421
00:23:43,500 --> 00:23:46,800
But what are they, 
and what do they reveal

422
00:23:46,800 --> 00:23:49,900
about the mammals' rise?

423
00:23:49,900 --> 00:23:55,666
♪ ♪

424
00:23:57,000 --> 00:23:59,233
LYSON: 
Stephen Chester is a vertebrate 
paleontologist

425
00:23:59,233 --> 00:24:02,566
who specializes in mammals.

426
00:24:02,566 --> 00:24:06,466
So when I made this discovery, 
I needed to bring him on board

427
00:24:06,466 --> 00:24:10,500
to help me identify all these 
mammals that I was finding.

428
00:24:12,566 --> 00:24:16,933
NARRATOR: 
Stephen examines each fossil 
to find details that reveal

429
00:24:16,933 --> 00:24:19,533
what it's related to.

430
00:24:19,533 --> 00:24:24,200
Not an easy job so far back 
on the mammalian family tree.

431
00:24:25,433 --> 00:24:28,666
CHESTER: 
We're talking about species 
that can be

432
00:24:28,666 --> 00:24:31,433
very difficult to identify,

433
00:24:31,433 --> 00:24:34,366
because they don't look exactly 
like what you might expect

434
00:24:34,366 --> 00:24:36,700
for, for living mammals.

435
00:24:36,700 --> 00:24:39,033
♪ ♪

436
00:24:39,033 --> 00:24:43,666
NARRATOR: 
It's a common problem 
in tracing ancestry.

437
00:24:43,666 --> 00:24:48,833
Consider how different 
an elephant is from a hyrax,

438
00:24:48,833 --> 00:24:51,833
or a manatee.

439
00:24:51,833 --> 00:24:53,766
GOSWAMI: 
You might not think 
that they are closely related.

440
00:24:53,766 --> 00:24:56,133
They are incredibly different 
animals.

441
00:24:56,133 --> 00:24:58,000
But their DNA shows us

442
00:24:58,000 --> 00:24:59,866
that they are actually 
really closely related.

443
00:24:59,866 --> 00:25:02,033
♪ ♪

444
00:25:02,033 --> 00:25:03,800
NARRATOR: 
Descendants of a common ancestor

445
00:25:03,800 --> 00:25:08,166
don't always look like each 
other, or the ancestor,

446
00:25:08,166 --> 00:25:10,466
because they've evolved 
in their own directions

447
00:25:10,466 --> 00:25:13,500
for millions of years.

448
00:25:13,500 --> 00:25:18,100
But they're bound to share 
some common traits.

449
00:25:18,100 --> 00:25:23,733
That's why Stephen examines 
each skull feature by feature.

450
00:25:25,700 --> 00:25:27,766
His first task is to figure out

451
00:25:27,766 --> 00:25:31,366
what kind of mammal 
they've unearthed.

452
00:25:31,366 --> 00:25:35,966
(birds chirping)

453
00:25:35,966 --> 00:25:39,400
All mammals share 
a few key features.

454
00:25:39,400 --> 00:25:40,933
They're warm-blooded,

455
00:25:40,933 --> 00:25:44,700
grow hair,

456
00:25:44,700 --> 00:25:49,600
and have bigger brains 
than other animals their size.

457
00:25:50,700 --> 00:25:53,700
They also give their young 
a jump start in life

458
00:25:53,700 --> 00:25:57,566
by nursing them.

459
00:25:57,566 --> 00:26:01,966
But how they have these babies 
sets them apart.

460
00:26:03,766 --> 00:26:07,566
Some, like kangaroos and 
opossums, use a pouch

461
00:26:07,566 --> 00:26:10,333
to bring their embryos to term.

462
00:26:11,933 --> 00:26:15,900
A handful-- platypuses 
and echidnas-- lay eggs.

463
00:26:17,933 --> 00:26:20,666
(chitters)

464
00:26:20,666 --> 00:26:25,000
But what about the biggest group 
of mammals alive today--

465
00:26:25,000 --> 00:26:29,633
those that carry their offspring 
in the mother's womb?

466
00:26:29,633 --> 00:26:32,533
Like us,

467
00:26:32,533 --> 00:26:36,200
they're called placentals.

468
00:26:36,200 --> 00:26:39,600
And they include the mammal 
Stephen examines

469
00:26:39,600 --> 00:26:41,600
from Corral Bluffs.

470
00:26:44,300 --> 00:26:48,100
It's one of the oldest placental 
fossils ever discovered.

471
00:26:49,666 --> 00:26:53,800
A creature called loxolophus.

472
00:26:53,800 --> 00:26:59,233
It's not yet clear if it has 
any living descendants.

473
00:26:59,233 --> 00:27:05,133
But the fossil hints 
at a highly adaptable creature.

474
00:27:05,133 --> 00:27:08,500
CHESTER: 
This mammal is probably 
about the size of a skunk.

475
00:27:08,500 --> 00:27:10,833
It has teeth in the front 
of its mouth

476
00:27:10,833 --> 00:27:13,033
that are probably good 
for tearing meat,

477
00:27:13,033 --> 00:27:15,766
but the back of its mouth 
has other teeth

478
00:27:15,766 --> 00:27:18,166
that would be better 
at processing plants.

479
00:27:18,166 --> 00:27:21,033
It's probably eating 
a mixed diet.

480
00:27:23,233 --> 00:27:25,500
NARRATOR: 
This versatility would have been 
a great advantage

481
00:27:25,500 --> 00:27:27,333
in a recovering world,

482
00:27:27,333 --> 00:27:31,500
where the types of food 
were probably limited.

483
00:27:33,533 --> 00:27:35,766
Team member Karen Cuevas

484
00:27:35,766 --> 00:27:37,766
finds other insights 
about how it lived

485
00:27:37,766 --> 00:27:40,300
by peering inside the fossil.

486
00:27:40,300 --> 00:27:42,266
CUEVAS: 
When I first heard

487
00:27:42,266 --> 00:27:45,800
about how mammals became 
what they are today,

488
00:27:45,800 --> 00:27:47,433
I was really excited to see

489
00:27:47,433 --> 00:27:50,633
how much we could deduce 
from these fossils

490
00:27:50,633 --> 00:27:54,800
and paint this picture 
from so many million years ago.

491
00:27:54,800 --> 00:27:58,166
One of the things that we can do 
with the CT scan

492
00:27:58,166 --> 00:28:01,333
is view the inner anatomy.

493
00:28:02,733 --> 00:28:04,766
ZANNO: 
CT reconstructions 
give us insight

494
00:28:04,766 --> 00:28:06,233
into tissues 
that aren't preserved,

495
00:28:06,233 --> 00:28:08,900
and teach us a lot

496
00:28:08,900 --> 00:28:10,600
about what those animals 
were really like

497
00:28:10,600 --> 00:28:12,166
as living, breathing creatures.

498
00:28:14,433 --> 00:28:19,000
NARRATOR: 
The data help the team imagine 
what the living animal was like.

499
00:28:19,000 --> 00:28:24,533
CHESTER: 
Based on CT scans, this animal 
had a hole underneath its eye.

500
00:28:25,800 --> 00:28:30,233
NARRATOR: 
A passage for nerves 
from sensitive whiskers.

501
00:28:30,233 --> 00:28:33,000
CHESTER: 
It also has a large portion 
of its brain

502
00:28:33,000 --> 00:28:35,766
dedicated to the sense of smell.

503
00:28:35,766 --> 00:28:38,266
♪ ♪

504
00:28:38,266 --> 00:28:40,933
NARRATOR: 
These senses would have been key 
to its lifestyle

505
00:28:40,933 --> 00:28:44,433
in this new world.

506
00:28:44,433 --> 00:28:49,866
Details from related species 
suggest how it walked.

507
00:28:49,866 --> 00:28:52,833
CHESTER: 
We would assume that this animal 
was moving around on the ground

508
00:28:52,833 --> 00:28:56,066
on all fours, probably something 
like a raccoon.

509
00:28:56,066 --> 00:28:59,066
(chittering)

510
00:29:00,633 --> 00:29:02,233
NARRATOR: 
It's a lot to have learned

511
00:29:02,233 --> 00:29:05,300
about one of the creatures 
that roamed the new world.

512
00:29:09,266 --> 00:29:12,766
But Corral Bluffs is about 
to reveal something even bigger.

513
00:29:15,166 --> 00:29:17,666
LYSON: 
The discovery here extends

514
00:29:17,666 --> 00:29:20,733
well beyond 
any one particular fossil.

515
00:29:20,733 --> 00:29:24,866
Here, we're dealing with the 
recovery of an entire ecosystem.

516
00:29:24,866 --> 00:29:27,266
♪ ♪

517
00:29:27,266 --> 00:29:31,833
NARRATOR: 
If the team can determine 
the age of each fossil,

518
00:29:31,833 --> 00:29:37,033
they can start to see how 
the mammals evolved over time,

519
00:29:37,033 --> 00:29:41,866
and how their world changed 
alongside them.

520
00:29:41,866 --> 00:29:43,366
GOSWAMI: 
When we find some interesting 
fossils,

521
00:29:43,366 --> 00:29:45,433
then the next thing that we do 
is spend a huge amount of effort

522
00:29:45,433 --> 00:29:48,766
trying to figure out 
exactly how old they are.

523
00:29:48,766 --> 00:29:54,033
But getting accurate dates on 
fossil sites is incredibly hard.

524
00:29:54,033 --> 00:29:57,000
NARRATOR: 
To estimate the age 
of their fossils,

525
00:29:57,000 --> 00:30:00,100
Tyler and Ian reach out 
to specialists.

526
00:30:00,100 --> 00:30:02,366
(people talking in background)

527
00:30:02,366 --> 00:30:07,066
Geologists Will Clyde 
and Anthony Fuentes.

528
00:30:07,066 --> 00:30:11,633
Their goal: determine the age 
of each layer in the rock

529
00:30:11,633 --> 00:30:15,766
by building a timeline 
up the cliff.

530
00:30:15,766 --> 00:30:21,066
To do it, they'll rely on clues 
forged by planetary forces.

531
00:30:21,066 --> 00:30:24,600
♪ ♪

532
00:30:24,600 --> 00:30:27,933
Earth is surrounded 
by a magnetic field,

533
00:30:27,933 --> 00:30:33,633
which creates north and south 
magnetic poles.

534
00:30:33,633 --> 00:30:37,433
These may seem permanent, 
but they're not.

535
00:30:37,433 --> 00:30:42,100
From time to time, 
the field reverses.

536
00:30:42,100 --> 00:30:43,533
And so what is today

537
00:30:43,533 --> 00:30:44,966
the magnetic north for the Earth

538
00:30:44,966 --> 00:30:46,900
sometimes flips and becomes 
the magnetic south.

539
00:30:46,900 --> 00:30:49,033
♪ ♪

540
00:30:49,033 --> 00:30:52,533
NARRATOR: 
Some rocks can record the 
direction of the magnetic field

541
00:30:52,533 --> 00:30:57,233
at the time they form.

542
00:30:57,233 --> 00:30:59,800
As these build up 
on top of each other,

543
00:30:59,800 --> 00:31:04,700
they can capture a record 
of magnetic reversals over time.

544
00:31:04,700 --> 00:31:08,200
The date of each flip 
has been firmly established

545
00:31:08,200 --> 00:31:10,233
in rocks across the world.

546
00:31:10,233 --> 00:31:11,966
CLYDE: 
Four, five...

547
00:31:11,966 --> 00:31:13,600
Four, five.

548
00:31:13,600 --> 00:31:15,033
CLYDE: 
So if we can find

549
00:31:15,033 --> 00:31:18,466
certain flip-flop in 
the polarity in the rocks here,

550
00:31:18,466 --> 00:31:22,433
then we know the date 
of that change.

551
00:31:22,433 --> 00:31:24,833
Six-four.

552
00:31:24,833 --> 00:31:26,966
To the east.

553
00:31:26,966 --> 00:31:29,266
NARRATOR: 
To look for these flips,

554
00:31:29,266 --> 00:31:31,833
they collect rocks 
along the bottom of the bluffs,

555
00:31:31,833 --> 00:31:34,433
where the impact boundary is,

556
00:31:34,433 --> 00:31:37,200
and work their way up.

557
00:31:39,200 --> 00:31:41,666
They then bring each sample back 
to their lab

558
00:31:41,666 --> 00:31:44,500
to measure 
its magnetic orientation.

559
00:31:46,966 --> 00:31:48,733
NARRATOR: 
Near the bottom of the bluffs,

560
00:31:48,733 --> 00:31:54,033
they find a flip 
from 350,000 years after impact,

561
00:31:54,033 --> 00:31:56,266
and trace it across the land.

562
00:31:58,533 --> 00:32:02,066
But a single date isn't enough.

563
00:32:02,066 --> 00:32:05,333
MILLER: 
If you get one date 
in a pile of rocks,

564
00:32:05,333 --> 00:32:07,066
you know where that one date is.

565
00:32:07,066 --> 00:32:10,533
But above it, you don't know how 
fast the rocks are accumulating.

566
00:32:10,533 --> 00:32:12,366
There could be a ton of rock 
in a short period of time,

567
00:32:12,366 --> 00:32:15,333
or it could be a small amount of 
rock in a long period of time.

568
00:32:15,333 --> 00:32:17,766
♪ ♪

569
00:32:17,766 --> 00:32:20,566
NARRATOR: 
Most of the bluffs, 
and the team's discoveries,

570
00:32:20,566 --> 00:32:23,733
lie above the flip 
they've found.

571
00:32:23,733 --> 00:32:28,433
They need a second one higher up 
to bracket the dates

572
00:32:28,433 --> 00:32:30,666
of their fossils.

573
00:32:32,533 --> 00:32:36,800
They work their way up, 
one layer after another.

574
00:32:37,966 --> 00:32:39,333
MILLER: 
As we went up the hill,

575
00:32:39,333 --> 00:32:40,800
you know, you're sampling, 
you're sampling,

576
00:32:40,800 --> 00:32:41,966
but there's no flip, 
there's nothing,

577
00:32:41,966 --> 00:32:44,366
and we're just running 
out of rock.

578
00:32:44,366 --> 00:32:48,366
NARRATOR: 
They test samples 
right up to the top.

579
00:32:48,366 --> 00:32:50,533
Still...

580
00:32:50,533 --> 00:32:52,566
No flip.

581
00:32:52,566 --> 00:32:56,766
No way to place 
their discoveries in time.

582
00:32:56,766 --> 00:32:59,066
♪ ♪

583
00:32:59,066 --> 00:33:01,966
Then, they find 
a small outcrop

584
00:33:01,966 --> 00:33:05,233
perched above 
the rest of the bluffs.

585
00:33:05,233 --> 00:33:09,733
It's one last chance 
to catch the flip.

586
00:33:09,733 --> 00:33:14,666
♪ ♪

587
00:33:14,666 --> 00:33:16,833
And it delivers.

588
00:33:16,833 --> 00:33:19,533
♪ ♪

589
00:33:19,533 --> 00:33:23,566
They've found 
the second date they need.

590
00:33:23,566 --> 00:33:25,366
MILLER: 
That allowed us to place 
all these fossils

591
00:33:25,366 --> 00:33:27,333
in this incredible time frame.

592
00:33:28,433 --> 00:33:29,666
We had the whole thing,

593
00:33:29,666 --> 00:33:32,033
and that was a shock.

594
00:33:32,033 --> 00:33:33,766
We didn't expect that.

595
00:33:33,766 --> 00:33:35,500
We thought we might be missing 
a part of the record,

596
00:33:35,500 --> 00:33:36,833
but it's all there.

597
00:33:36,833 --> 00:33:39,233
♪ ♪

598
00:33:39,233 --> 00:33:41,200
NARRATOR: 
The towering face of the bluffs

599
00:33:41,200 --> 00:33:45,233
chronicles the first one million 
years of the recovery.

600
00:33:45,233 --> 00:33:46,700
SHUBIN: 
If you were to choose

601
00:33:46,700 --> 00:33:49,766
any one-million-year sliver 
of time

602
00:33:49,766 --> 00:33:52,966
in the four-and-a-half- 
billion-year history of Earth,

603
00:33:52,966 --> 00:33:55,066
it's an enormously lucky event 
to have one that happens

604
00:33:55,066 --> 00:33:56,833
right after a giant asteroid 
impact.

605
00:33:56,833 --> 00:33:59,266
It's like winning the lottery.

606
00:33:59,266 --> 00:34:00,866
♪ ♪

607
00:34:00,866 --> 00:34:04,166
NARRATOR: 
Now all the extraordinary 
fossils of Corral Bluffs

608
00:34:04,166 --> 00:34:09,366
can be placed in time.

609
00:34:09,366 --> 00:34:12,966
But what story do they tell?

610
00:34:12,966 --> 00:34:16,266
Another fossil 
reveals a turning point.

611
00:34:16,266 --> 00:34:19,900
♪ ♪

612
00:34:19,900 --> 00:34:22,333
LYSON: 
In the middle part 
of the bluffs,

613
00:34:22,333 --> 00:34:25,600
I found a much larger skull.

614
00:34:25,600 --> 00:34:29,700
NARRATOR: 
This creature lived 300,000 
years into the recovery.

615
00:34:31,466 --> 00:34:33,000
LYSON: 
What's interesting about it

616
00:34:33,000 --> 00:34:38,133
is that it has 
these really large teeth.

617
00:34:38,133 --> 00:34:43,900
NARRATOR: 
Mammals today use teeth like 
these to grind leaves and stems.

618
00:34:43,900 --> 00:34:49,500
It suggests this creature dined 
mostly on plants.

619
00:34:49,500 --> 00:34:52,266
LYSON: 
And this is really the first 
major specialization that we see

620
00:34:52,266 --> 00:34:54,900
in the mammal fossil record

621
00:34:54,900 --> 00:34:57,000
right after the extinction 
of the dinosaurs.

622
00:34:58,766 --> 00:35:02,100
NARRATOR: 
Just after the impact, 
the mammals that survived

623
00:35:02,100 --> 00:35:05,733
had been opportunistic 
scavengers.

624
00:35:05,733 --> 00:35:10,200
But now, mammals were 
specializing in eating plants

625
00:35:10,200 --> 00:35:13,733
and seizing a niche 
long held by dinosaurs.

626
00:35:13,733 --> 00:35:17,033
♪ ♪

627
00:35:17,033 --> 00:35:20,200
It's a major milestone.

628
00:35:20,200 --> 00:35:22,533
But how did it happen?

629
00:35:25,233 --> 00:35:30,666
The answer could lie in the 
story of the plants themselves.

630
00:35:30,666 --> 00:35:36,366
And Colorado's rocks 
are packed with clues.

631
00:35:41,666 --> 00:35:43,433
MILLER: 
A lot of leaves.

632
00:35:43,433 --> 00:35:46,233
But just two species right here.

633
00:35:46,233 --> 00:35:49,233
NARRATOR: 
Some leaves are 
so beautifully preserved,

634
00:35:49,233 --> 00:35:51,966
they look as if they had 
just fallen.

635
00:35:51,966 --> 00:35:53,800
♪ ♪

636
00:35:53,800 --> 00:35:58,600
But other telling fossils are 
invisible to the naked eye.

637
00:35:58,600 --> 00:36:02,066
Like pollen.

638
00:36:02,066 --> 00:36:04,633
A thimble-sized chunk of rock,

639
00:36:04,633 --> 00:36:08,166
it might have 100,000 
pollen grains in it.

640
00:36:08,166 --> 00:36:11,500
Each of the different kinds 
of trees, the little shrubs,

641
00:36:11,500 --> 00:36:16,166
produce different kinds of 
pollen based on who they are.

642
00:36:16,166 --> 00:36:20,300
NARRATOR: 
Ian and scientists around 
the world have documented

643
00:36:20,300 --> 00:36:22,433
the microscopic record 
from this time.

644
00:36:22,433 --> 00:36:24,366
♪ ♪

645
00:36:24,366 --> 00:36:25,500
MILLER: 
Take a chunk of rock,

646
00:36:25,500 --> 00:36:26,800
you dissolve it,

647
00:36:26,800 --> 00:36:28,300
you take all the pollen spores 
out of it,

648
00:36:28,300 --> 00:36:31,600
put it on a slide, and you see 
many different types of plants.

649
00:36:31,600 --> 00:36:33,500
And then you can sort of paint 
this image

650
00:36:33,500 --> 00:36:36,966
of what these worlds were like.

651
00:36:36,966 --> 00:36:38,466
♪ ♪

652
00:36:38,466 --> 00:36:40,833
And so right at that mark 
where we see the evidence

653
00:36:40,833 --> 00:36:41,966
of this extraterrestrial impact,

654
00:36:41,966 --> 00:36:45,366
the pollen just dives right off.

655
00:36:45,366 --> 00:36:47,666
Everything seems to die.

656
00:36:47,666 --> 00:36:49,500
NARRATOR: 
After the impact,

657
00:36:49,500 --> 00:36:52,300
one primitive form of life 
resurges,

658
00:36:52,300 --> 00:36:56,500
and it's a sign 
of a devastated world.

659
00:36:56,500 --> 00:36:57,966
MILLER: 
Right after the boundary,

660
00:36:57,966 --> 00:37:03,400
there's an explosion 
of fungal spores.

661
00:37:03,400 --> 00:37:06,900
The thing is that fungus grows 
on things that are dead.

662
00:37:06,900 --> 00:37:09,900
So most of the world 
must have been rotting.

663
00:37:11,833 --> 00:37:16,100
NARRATOR: 
Forests destroyed 
by heat and darkness

664
00:37:16,100 --> 00:37:21,033
decompose 
beneath this fungal carpet.

665
00:37:21,033 --> 00:37:24,266
But then some plants rebound.

666
00:37:24,266 --> 00:37:28,200
♪ ♪

667
00:37:28,200 --> 00:37:30,900
MILLER: 
Following immediately on top 
of the fungal world,

668
00:37:30,900 --> 00:37:32,733
we see a spike in fern spores.

669
00:37:32,733 --> 00:37:35,733
♪ ♪

670
00:37:35,733 --> 00:37:40,566
Ferns are this group of plants 
that come back after disasters

671
00:37:40,566 --> 00:37:45,066
before the rest of the forest 
is able to re-establish itself.

672
00:37:45,066 --> 00:37:48,500
First thing that comes back 
are a blanket of ferns.

673
00:37:48,500 --> 00:37:52,333
And that probably lasts 
for a few thousand years.

674
00:37:52,333 --> 00:37:54,566
♪ ♪

675
00:37:54,566 --> 00:37:57,133
NARRATOR: 
The world is green again,

676
00:37:57,133 --> 00:38:01,366
but ferns are a limited source 
of food.

677
00:38:04,966 --> 00:38:09,300
New options arise 
as the landscape evolves,

678
00:38:09,300 --> 00:38:12,333
and long-dormant seeds 
spring to life...

679
00:38:15,433 --> 00:38:18,866
A new forest.

680
00:38:18,866 --> 00:38:21,133
MILLER: 
One of the big surprises 
was this incredible abundance

681
00:38:21,133 --> 00:38:25,000
of palm pollen.

682
00:38:25,000 --> 00:38:30,933
And we get tons of palm fronds-- 
huge, beautiful palm fronds.

683
00:38:30,933 --> 00:38:35,966
They're so dominant, it feels 
like the world is all palms.

684
00:38:35,966 --> 00:38:41,833
And it probably lasts 
about 100,000 years.

685
00:38:41,833 --> 00:38:44,366
What I'm thinking right now is 
that if you were a mammal,

686
00:38:44,366 --> 00:38:48,366
there would have been a big 
canopy of palms above your head.

687
00:38:48,366 --> 00:38:51,833
But there still wasn't 
that great source of food.

688
00:38:51,833 --> 00:38:54,500
(insects chirping)

689
00:38:54,500 --> 00:39:01,100
NARRATOR: 
The habitat looks lush, 
but still lacks diversity.

690
00:39:01,100 --> 00:39:04,800
That, in turn, limits 
the variety of animals,

691
00:39:04,800 --> 00:39:08,233
as a close look 
at the team's fossils reveals.

692
00:39:12,333 --> 00:39:14,166
When there's an extinction,

693
00:39:14,166 --> 00:39:17,000
it kind of ripples from the 
bottom of the ecosystem,

694
00:39:17,000 --> 00:39:22,100
starting from the plants, 
up into all of the other levels.

695
00:39:22,100 --> 00:39:25,900
NARRATOR: 
Gussie Maccracken deciphers 
what happened

696
00:39:25,900 --> 00:39:28,066
to some of the smallest 
creatures:

697
00:39:28,066 --> 00:39:31,366
insects.

698
00:39:31,366 --> 00:39:35,300
Insects don't fossilize well,

699
00:39:35,300 --> 00:39:38,200
but what they do to plants can.

700
00:39:38,200 --> 00:39:40,300
MACCRACKEN: 
Insect damage on a leaf 
can tell us

701
00:39:40,300 --> 00:39:43,600
about the ecology 
of the ecosystem in the past

702
00:39:43,600 --> 00:39:48,833
in a way that no other types 
of fossils can.

703
00:39:48,833 --> 00:39:51,466
NARRATOR: 
Some insects are generalists,

704
00:39:51,466 --> 00:39:55,166
and feed on many types 
of leaves.

705
00:39:55,166 --> 00:39:58,900
They carve signature marks that 
can be preserved in fossils.

706
00:39:58,900 --> 00:40:00,833
♪ ♪

707
00:40:00,833 --> 00:40:02,600
Simple holes,

708
00:40:02,600 --> 00:40:06,233
or chunks bitten 
from the leaf's edge.

709
00:40:06,233 --> 00:40:08,666
♪ ♪

710
00:40:08,666 --> 00:40:11,833
But other kinds of damage 
are caused by insects

711
00:40:11,833 --> 00:40:15,066
that specialize 
in certain plants.

712
00:40:15,066 --> 00:40:19,133
MACCRACKEN: 
They leave these wild patterns

713
00:40:19,133 --> 00:40:22,766
and we can tell things 
like if it's a moth,

714
00:40:22,766 --> 00:40:26,200
or if it's a fly,

715
00:40:26,200 --> 00:40:29,000
or sometimes a beetle.

716
00:40:29,000 --> 00:40:31,000
NARRATOR: 
Before the asteroid struck,

717
00:40:31,000 --> 00:40:34,866
the insect world was filled 
with specialists.

718
00:40:34,866 --> 00:40:39,466
But that changes abruptly.

719
00:40:39,466 --> 00:40:44,700
MACCRACKEN: 
During recovery, a lot of the 
specialist insect damage types,

720
00:40:44,700 --> 00:40:49,066
like from leaf miners 
and galling insects,

721
00:40:49,066 --> 00:40:50,433
just disappear.

722
00:40:50,433 --> 00:40:52,166
♪ ♪

723
00:40:52,166 --> 00:40:55,900
NARRATOR: 
The specialists were doomed.

724
00:40:55,900 --> 00:41:00,700
In a world with only 
a few kinds of plants,

725
00:41:00,700 --> 00:41:04,166
insects that can live on 
anything have an advantage

726
00:41:04,166 --> 00:41:06,700
over pickier eaters.

727
00:41:06,700 --> 00:41:12,600
It echoes what happened 
to the mammals.

728
00:41:12,600 --> 00:41:15,600
Only the generalists survive.

729
00:41:15,600 --> 00:41:18,000
ZANNO: 
At the time 
of an extinction event,

730
00:41:18,000 --> 00:41:21,066
any species that's highly 
dependent on a single lifestyle

731
00:41:21,066 --> 00:41:24,200
or a single location 
or a single food source

732
00:41:24,200 --> 00:41:28,033
is likely going to go extinct 
when those ecosystems collapse.

733
00:41:28,033 --> 00:41:30,900
♪ ♪

734
00:41:30,900 --> 00:41:33,300
NARRATOR: 
But in time, new plants arise

735
00:41:33,300 --> 00:41:36,633
and chances to specialize 
return.

736
00:41:36,633 --> 00:41:40,566
MILLER: 
The forests become 
more and more diverse.

737
00:41:40,566 --> 00:41:44,566
We get different kinds of trees 
growing on the landscape.

738
00:41:44,566 --> 00:41:48,766
♪ ♪

739
00:41:51,066 --> 00:41:54,266
NARRATOR: 
300,000 years 
after its collapse,

740
00:41:54,266 --> 00:41:56,433
the forest has recovered.

741
00:41:56,433 --> 00:42:00,333
♪ ♪

742
00:42:00,333 --> 00:42:02,766
MILLER: 
And it's right there 
when the animals can specialize

743
00:42:02,766 --> 00:42:05,533
in eating certain kinds 
of plants.

744
00:42:05,533 --> 00:42:08,366
NARRATOR: 
And get bigger.

745
00:42:08,366 --> 00:42:11,833
These new plant-eaters 
were now larger

746
00:42:11,833 --> 00:42:13,200
than mammals had ever been

747
00:42:13,200 --> 00:42:17,466
in over 100 million years 
on the planet.

748
00:42:17,466 --> 00:42:19,866
♪ ♪

749
00:42:19,866 --> 00:42:24,933
They've shattered their record 
in just a fraction of that time.

750
00:42:24,933 --> 00:42:28,133
And their growth spurt 
was just beginning.

751
00:42:34,066 --> 00:42:36,233
LYSON: 
In the very upper part 
of the bluffs,

752
00:42:36,233 --> 00:42:43,100
I started to find a whole array 
of large and diverse mammals.

753
00:42:48,733 --> 00:42:52,533
One of the mammals that we found 
is called taeniolabis.

754
00:42:52,533 --> 00:42:57,133
This is about 80 pounds, 
so really a large animal.

755
00:42:58,933 --> 00:43:01,300
NARRATOR: 
It was ten times the size

756
00:43:01,300 --> 00:43:05,566
of the omnivore 
they'd found earlier.

757
00:43:05,566 --> 00:43:08,966
LYSON: 
It had these really big 
incisors,

758
00:43:08,966 --> 00:43:11,166
much like modern-day beavers 
have.

759
00:43:14,033 --> 00:43:17,633
We think this animal was living 
in or near the rivers,

760
00:43:17,633 --> 00:43:22,400
because we only find this animal 
in riverine sediments.

761
00:43:22,400 --> 00:43:25,733
♪ ♪

762
00:43:28,200 --> 00:43:29,833
NARRATOR: 
Near this fossil,

763
00:43:29,833 --> 00:43:34,433
Tyler finds the skull 
of an even bigger mammal.

764
00:43:34,433 --> 00:43:39,566
LYSON: 
This is a large animal 
that was about 100 pounds,

765
00:43:39,566 --> 00:43:42,666
so almost the size of a wolf.

766
00:43:42,666 --> 00:43:47,100
And this animal had really big, 
flat back teeth,

767
00:43:47,100 --> 00:43:51,633
and it seems to be eating seeds 
and other plants.

768
00:43:51,633 --> 00:43:55,000
NARRATOR: 
In less than a million years 
since the extinction,

769
00:43:55,000 --> 00:43:59,933
mammals have exploded 
from just a couple of pounds.

770
00:43:59,933 --> 00:44:02,366
Some are 50 times bigger.

771
00:44:05,566 --> 00:44:12,200
It would take nearly 20 million 
years to make such a leap again.

772
00:44:12,200 --> 00:44:15,900
But what might have fueled 
this dramatic change?

773
00:44:19,566 --> 00:44:22,133
An intriguing clue 
lay just a few feet

774
00:44:22,133 --> 00:44:24,433
from the beasts' remains.

775
00:44:24,433 --> 00:44:28,600
(kids talking in distance)

776
00:44:28,600 --> 00:44:30,766
Ian was leading a group of teens

777
00:44:30,766 --> 00:44:33,566
studying at the museum 
for the summer.

778
00:44:33,566 --> 00:44:36,533
Probably about... 
I'd say about the same...

779
00:44:40,033 --> 00:44:41,466
MILLER: 
We were doing all kinds 
of different things,

780
00:44:41,466 --> 00:44:44,566
and it wasn't a terribly 
exciting site.

781
00:44:44,566 --> 00:44:47,733
A lot of fossils people hand you 
are just sticks.

782
00:44:47,733 --> 00:44:48,900
So, a lot of people are just, 
like,

783
00:44:48,900 --> 00:44:50,000
"Oh, this is 
an incredible fossil!"

784
00:44:50,000 --> 00:44:51,033
I'm, like, 
"Yeah, it's just a stick,"

785
00:44:51,033 --> 00:44:52,133
you know, "throw that back."

786
00:44:52,133 --> 00:44:56,766
But this one student, 
her name is Aeon.

787
00:44:56,766 --> 00:44:58,866
We're thinking about moving on, 
and going somewhere else,

788
00:44:58,866 --> 00:45:03,133
and she hands me this rock 
and she's, like, "What's this?"

789
00:45:03,133 --> 00:45:06,933
Did you get something? 
I don't know.

790
00:45:06,933 --> 00:45:08,000
And so I took it up, 
looked at it in the light,

791
00:45:08,000 --> 00:45:09,300
and lo and behold,

792
00:45:09,300 --> 00:45:12,066
it was the middle part 
of a bean pod.

793
00:45:12,066 --> 00:45:14,933
Um, I found this legume 
two seconds ago

794
00:45:14,933 --> 00:45:16,866
from this rock 
that's sitting in my lap.

795
00:45:16,866 --> 00:45:20,933
MILLER: 
Right here, 700,000 years 
into the recovery.

796
00:45:20,933 --> 00:45:23,700
This is the earliest record 
of the legume family ever

797
00:45:23,700 --> 00:45:25,200
in the fossil record.

798
00:45:25,200 --> 00:45:28,700
So that's pretty cool.

799
00:45:32,966 --> 00:45:35,466
NARRATOR: 
Aeon's legume was alive 
right at the time

800
00:45:35,466 --> 00:45:40,200
when mammals' size 
was exploding.

801
00:45:40,200 --> 00:45:43,133
A new food for a new world.

802
00:45:43,133 --> 00:45:46,566
♪ ♪

803
00:45:46,566 --> 00:45:51,133
Legumes are very special plants.

804
00:45:51,133 --> 00:45:54,466
Today, there are almost 
20,000 species of them,

805
00:45:54,466 --> 00:45:59,333
including peanuts, 
lentils, and soybeans.

806
00:45:59,333 --> 00:46:03,500
Their signature pods 
are packed with nutrients.

807
00:46:03,500 --> 00:46:07,033
♪ ♪

808
00:46:07,033 --> 00:46:08,333
MILLER: 
Legumes are like

809
00:46:08,333 --> 00:46:11,200
these protein bars for 
the mammals on the landscape,

810
00:46:11,200 --> 00:46:16,633
and at that same moment, we see 
all these new and large mammals,

811
00:46:16,633 --> 00:46:18,100
and we think 
that they're taking advantage

812
00:46:18,100 --> 00:46:19,866
of this new food source.

813
00:46:23,300 --> 00:46:27,100
NARRATOR: 
Taken together, the many fossils 
of Corral Bluffs

814
00:46:27,100 --> 00:46:32,500
suggest plants were helping 
to drive mammal evolution.

815
00:46:32,500 --> 00:46:37,100
And a final piece of evidence 
reveals how plants, in turn,

816
00:46:37,100 --> 00:46:39,733
were being driven 
by something else.

817
00:46:39,733 --> 00:46:41,400
♪ ♪

818
00:46:41,400 --> 00:46:45,733
Ian uncovers clues to one of the 
planet's most powerful forces--

819
00:46:45,733 --> 00:46:48,466
climate.

820
00:46:48,466 --> 00:46:53,266
He zeroes in on the shape 
of the leaves he's unearthed.

821
00:46:53,266 --> 00:46:55,266
MILLER: 
The more species you have 
with serrations,

822
00:46:55,266 --> 00:46:56,866
the cooler it is;

823
00:46:56,866 --> 00:47:00,666
the more smooth leaves you have, 
the warmer it is.

824
00:47:00,666 --> 00:47:03,200
And so we can use that to tell 
temperature in the past.

825
00:47:03,200 --> 00:47:05,266
♪ ♪

826
00:47:05,266 --> 00:47:08,433
NARRATOR: 
The size of the leaves 
can reveal rainfall.

827
00:47:08,433 --> 00:47:11,000
(thunder booms)

828
00:47:11,000 --> 00:47:13,200
MILLER: 
If you've got a really big leaf,

829
00:47:13,200 --> 00:47:15,866
it means that you're growing 
in a world that rained a lot,

830
00:47:15,866 --> 00:47:17,800
and so the forest 
was really dense.

831
00:47:19,633 --> 00:47:22,700
NARRATOR: 
Most of the fossil leaves 
from Corral Bluffs

832
00:47:22,700 --> 00:47:25,033
are smooth and large.

833
00:47:27,733 --> 00:47:31,866
Together, they paint a picture 
of a very different Colorado

834
00:47:31,866 --> 00:47:34,366
65 million years ago.

835
00:47:34,366 --> 00:47:38,700
♪ ♪

836
00:47:40,833 --> 00:47:44,966
MILLER: 
We're probably looking at a 
world that's more like Florida.

837
00:47:44,966 --> 00:47:47,933
It's pretty wet, pretty humid, 
and pretty darn warm.

838
00:47:50,533 --> 00:47:54,466
NARRATOR: 
This climate shaped the plants 
and the creatures

839
00:47:54,466 --> 00:47:55,800
that evolved here.

840
00:47:55,800 --> 00:47:59,900
♪ ♪

841
00:47:59,900 --> 00:48:04,033
GOSWAMI: 
No organism evolves or lives 
in isolation, right?

842
00:48:04,033 --> 00:48:07,133
Everything about them really 
reflects their interactions

843
00:48:07,133 --> 00:48:08,766
with their environment, 
with other species.

844
00:48:08,766 --> 00:48:13,100
We really need to understand 
those relationships.

845
00:48:13,100 --> 00:48:16,900
We want to build up a picture of 
how life evolved in this period.

846
00:48:16,900 --> 00:48:19,600
♪ ♪

847
00:48:19,600 --> 00:48:25,300
NARRATOR: 
In the first two years after 
Tyler and Ian made their find,

848
00:48:25,300 --> 00:48:29,266
their team collected 
over 1,000 vertebrate fossils.

849
00:48:29,266 --> 00:48:31,866
♪ ♪

850
00:48:31,866 --> 00:48:34,166
Some 6,000 plants.

851
00:48:34,166 --> 00:48:35,866
♪ ♪

852
00:48:35,866 --> 00:48:38,200
And the end is nowhere in sight.

853
00:48:38,200 --> 00:48:43,033
♪ ♪

854
00:48:43,033 --> 00:48:46,966
LYSON: 
The discovery at Corral Bluffs 
is remarkable for many reasons.

855
00:48:46,966 --> 00:48:49,066
We have the whole ecosystem,

856
00:48:49,066 --> 00:48:51,066
and we have it 
at different intervals of time.

857
00:48:51,066 --> 00:48:54,200
I mean, we're dealing 
with the entire story here.

858
00:48:55,666 --> 00:48:59,000
NARRATOR: 
So far, that story includes

859
00:48:59,000 --> 00:49:03,166
16 different mammal species 
they've found.

860
00:49:03,166 --> 00:49:07,566
It's an extraordinary record 
that unites plants, animals,

861
00:49:07,566 --> 00:49:09,666
climate, and time

862
00:49:09,666 --> 00:49:11,900
in a single picture.

863
00:49:11,900 --> 00:49:14,933
♪ ♪

864
00:49:14,933 --> 00:49:19,200
SHUBIN: 
So, what Tyler and Ian have 
discovered is a Rosetta Stone.

865
00:49:19,200 --> 00:49:22,000
And Corral Bluffs is telling us 
something very important.

866
00:49:22,000 --> 00:49:25,400
It's telling us about ourselves, 
how we got to be here.

867
00:49:28,666 --> 00:49:30,400
(rock cracks loudly)

868
00:49:30,400 --> 00:49:33,033
♪ ♪

869
00:49:33,033 --> 00:49:36,400
NARRATOR: 
The team's discoveries, 
along with other evidence,

870
00:49:36,400 --> 00:49:40,900
trace the beginning 
of the mammals' fateful rise.

871
00:49:40,900 --> 00:49:42,066
♪ ♪

872
00:49:42,066 --> 00:49:44,233
(explosion booms)

873
00:49:44,233 --> 00:49:47,966
Few survived the impact winter.

874
00:49:47,966 --> 00:49:53,566
But as the climate warmed, 
plants regained lost ground.

875
00:49:53,566 --> 00:49:58,366
Small creatures endured, 
eating whatever they could find.

876
00:49:58,366 --> 00:50:01,000
Forests recovered,

877
00:50:01,000 --> 00:50:05,800
and fueled mammals 
as they exploded in size

878
00:50:05,800 --> 00:50:09,233
and took on new forms...

879
00:50:09,233 --> 00:50:12,133
All in less 
than a million years.

880
00:50:12,133 --> 00:50:16,400
♪ ♪

881
00:50:16,400 --> 00:50:20,700
In the ages that followed, 
mammals seized empty niches.

882
00:50:20,700 --> 00:50:22,700
(large cat growls)

883
00:50:22,700 --> 00:50:27,666
Our ancestors scaled the trees.

884
00:50:27,666 --> 00:50:30,633
Others took to the air,

885
00:50:30,633 --> 00:50:35,100
or became giants of the seas.

886
00:50:35,100 --> 00:50:38,566
Mammals rose 
to dominate the planet.

887
00:50:38,566 --> 00:50:41,500
♪ ♪

888
00:50:41,500 --> 00:50:43,833
All this diversity

889
00:50:43,833 --> 00:50:47,866
sprang from the band 
of humble creatures

890
00:50:47,866 --> 00:50:50,733
that emerged from the cataclysm.

891
00:50:50,733 --> 00:50:53,266
♪ ♪

892
00:50:53,266 --> 00:50:55,933
JOHNSON: 
They inherited a whole world

893
00:50:55,933 --> 00:50:57,600
and they had the planet 
to play in.

894
00:50:57,600 --> 00:51:02,866
And that moment 
of rapid mammal evolution

895
00:51:02,866 --> 00:51:04,700
is effectively the trigger

896
00:51:04,700 --> 00:51:06,666
to our existence here 
on planet Earth.

897
00:51:06,666 --> 00:51:09,433
♪ ♪

898
00:51:09,433 --> 00:51:13,266
NARRATOR: 
By unveiling the start 
of the mammals' explosion,

899
00:51:13,266 --> 00:51:17,066
Corral Bluffs seems destined 
to join the ranks

900
00:51:17,066 --> 00:51:20,300
of other celebrated 
fossil sites,

901
00:51:20,300 --> 00:51:23,933
like Tyler's back yard 
in North Dakota.

902
00:51:23,933 --> 00:51:25,833
LYSON: 
I can trace those same questions

903
00:51:25,833 --> 00:51:28,133
that I'm asking today 
out on the bluffs

904
00:51:28,133 --> 00:51:31,500
all the way back to when I was 
six or seven years old,

905
00:51:31,500 --> 00:51:35,566
running around the badlands 
looking for fossils.

906
00:51:39,366 --> 00:51:41,300
NARRATOR: 
By pursuing those questions,

907
00:51:41,300 --> 00:51:44,633
Tyler and his colleagues 
are helping us understand

908
00:51:44,633 --> 00:51:49,400
how the planet recovered 
from catastrophe.

909
00:51:49,400 --> 00:51:54,766
They're illuminating 
the dawn of a new world.

910
00:51:54,766 --> 00:51:56,966
Our world.

911
00:51:58,766 --> 00:52:01,800
♪ ♪

912
00:52:16,933 --> 00:52:24,466
♪ ♪

913
00:52:28,300 --> 00:52:35,833
♪ ♪

914
00:52:37,466 --> 00:52:45,000
♪ ♪

915
00:52:46,633 --> 00:52:54,166
♪ ♪

916
00:52:59,900 --> 00:53:07,133
♪ ♪