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Of all the animals
that live on our planet,

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one extraordinary
group dominates.

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It has produced the largest...

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The blue whale!

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..the fastest,

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and the most intelligent creatures

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that have ever lived.

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They're known as the vertebrates,

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and they all share
one vital feature.

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A backbone.

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Now, I want to travel back in time
to explore their ancient origins.

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And investigate the key advances
that led to their amazing success.

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Advances that can also reveal

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how we came to acquire the
characteristic features

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of our own vertebrate bodies.

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Jaws that bite, lungs that breathe,
ears that can hear.

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Because the story
of the rise of animals

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is also the story of how you
and I came to be as we are.

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I will find evidence in a series of
spectacular fossil discoveries

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around the world and
within living animals.

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That's it.

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With the latest scientific
analysis,

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we can bring our ancient
ancestors back to life.

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And understand how,
over 500 million years,

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they developed the bodily features
needed to master the seas...

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..colonise the land,
and take to the skies.

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This is the story
of the rise of animals.

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The history of life on Earth

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has been known in
outline for many years,

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but there were a number of
tantalising gaps in it,

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particularly in the history
of animals with backbones.

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When, for example, did the first
signs of a backbone appear?

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And is it really true that
dinosaurs developed feathers

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and turned into birds?

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Well, in recent decades,

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answers have been found to
those extraordinary questions,

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here, in China,
and I'm here to look at them.

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China is the new frontier
for fossil discoveries.

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Excavations here are
unearthing links in the story

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of the vertebrates that
have so far eluded us.

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I have long wanted to see this
sensational evidence for myself.

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I will be travelling to the
frozen north of the country,

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and to the capital, Beijing.

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But to search for the first
step in our journey,

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I'm heading south,
to Yunnan Province.

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This is the site of a thrilling
discovery that has given us

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new evidence for the
very first vertebrates.

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Excavators here are exposing
a rich seam of rocks

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known as the Chengjiang fossil beds.

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Remarkably, they contain the remains
of creatures that once swam

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in the ancient seas
525 million years ago.

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Palaeontologist, Hou Xianguang,
was the first to discover

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the unique features of these beds,

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an astonishing perfection
of preservation.

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Are these mouth parts?

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Yeah. That's very beautiful.

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You can see it's got
striations on it.

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To find complete bodies like
this is extremely rare.

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When an animal dies in the sea,

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normally bacteria destroy
the soft parts very quickly

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so that all we can find afterwards
are the hard parts, bone or shell.

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Why that didn't happen here
in this particular part

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of this particular sea
is something of a mystery.

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It may be something to do
with the lack of oxygen,

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but whatever it was,
it has given us a privileged view

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into one of the most
exciting chapters

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in the whole history of life.

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The beds have so far yielded
over 200 separate species.

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This was a time period
known as the Cambrian.

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The land was still
bare and lifeless,

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but, underwater, it was exploding
into a multitude of forms.

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The major animal groups we know
today were appearing on the planet

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for the very first time.

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They built their bodies
entirely of soft tissue.

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Some protected and supported
it with a hard outer casing.

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But none had anything
that resembled a backbone.

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These were the invertebrates.

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Then, Professor Hou and his team
found one intriguing exception.

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Oh, yes, yes, yes.

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It's a fossil called Myllokunmingia.

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But to examine it in detail,

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you've got to look at
it under the microscope.

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Its features reveal evidence
of a new type of support,

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not outside the body, but inside.

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This is one of about 30 specimens
that have already been found

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of this tiny little creature.

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Under the microscope, it contains
an extraordinary amount of detail.

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Those marks are marks that have been
made by the excavator's needle.

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This is the animal itself. This
is its head, the top of its back.

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And nearly every one of them have
these two little black spots

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at the front, eye spots.

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Looking farther down the animal,

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there are just some striations here,

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little bars which are thought
to have been the gill bars,

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the little constructions
that carry blood vessels

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which enabled the animal
to extract oxygen

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from the waters it flowed
over and breathe.

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And behind them, farther down the
animal, there are these bars...

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..bands of muscle, and they were
probably attached to a gristly rod

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somewhere in the middle there.

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This is called the notochord,

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which was the forerunner
of the backbone.

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Myllokunmingia is the earliest
creature we know of

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that we can truly call a vertebrate.

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And it seems clear that it
used its strong inner rod

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to move in an entirely new way.

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As the muscles contract,
they bend the rod from side to side.

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This movement pushes against the
water and creates forward thrust.

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Here was a revolutionary
new way to get around.

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It allowed Myllokunmingia to
roam far and wide and escape

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the dangerous invertebrate predators
that were prowling the seas.

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The vertebrates would diversify
over millions of years

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to create the spectacular variety of
backboned creatures we see today

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in every environment on the planet.

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Fish dominate the seas,
lakes and rivers.

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The amphibians live
in both water and land.

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The reptiles can survive
in the driest places on Earth.

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The birds rule the skies...

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..and the mammals have
insulated their bodies

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to adapt to every climate.

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We humans have used our greater
intelligence to overrun the planet.

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This astonishing journey

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was built on a series
of key evolutionary steps

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that helped our ancient ancestors
to exploit their environments

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and overcome huge challenges.

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The first of these advances was
the development

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of that inner support -
the notochord.

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Back in Europe, you can
find a creature that represents

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the next critical step in our story.

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It lives unobtrusively and
often ignored in British rivers.

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And it sheds light on the challenges
those first vertebrates faced.

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Ah, there it is!

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This is a lamprey.

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You might think at first sight that
it was a kind of fish, but it's not.

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It's something much,
much more primitive.

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It has no fins, and even its tail

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is nothing more than
a flattened blade.

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But what is most remarkable about it

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is that it doesn't
really have a true mouth.

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Its mouth is just a simple hole

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with little bristles about it.

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And it feeds by sucking
in water through that mouth

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and then filtering out
little particles of food.

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So this little animal takes us
right back to the time

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when the first animals with
backbones appeared on Earth.

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It's a true living fossil.

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The first vertebrates seem to have
had the same kind of mouth

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and they were almost
certainly limited

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to the same kind of simple food.

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Over time, other forms evolved
with different shapes and sizes,

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many of them rather
larger than Myllokunmingia,

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but all of them had
that very simple mouth,

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an opening at the front of the body
as the lamprey has today.

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If the early vertebrates were
going to really take advantage

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of the variety of food that was
available in those early seas,

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they were going to have to
develop a much more complex

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and powerful form
of eating machinery.

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Scientists on the east coast of the
United States are seeing evidence

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of this evolutionary advance, not
in fossils but in living creatures.

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Maine, New England.

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Marine biologists at the
University of New England

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are studying a group of fish
with a very ancient ancestry.

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They build their skeletons with
the same strong material

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that formed the gristly rod of the
first vertebrates - cartilage.

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They're the sharks,
skates and rays.

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This group appeared
among the vertebrates

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over 420 million years ago.

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And that means we can use them

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to examine the development before
that split of a remarkable piece

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of engineering that changed the
course of evolutionary history.

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The jaw.

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If you look back
on the evolutionary tree,

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you'd find that a jaw is a really
important feature to have

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and it's one of the features
that have made skates

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and sharks apex predators in the
environments in which they live.

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A jaw hinged to the skull brought
the new ability to grab food,

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then rip or grind
it into digestible pieces.

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But where did this amazing
piece of equipment come from?

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Scientists have found an answer

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by studying the way living
vertebrates develop as embryos.

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Skates lay their fertilized
eggs on the sea bed

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inside leathery cases
called mermaid's purses.

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Scientists can open these up
and observe them as they develop,

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fed by a generous
supply of egg yolk.

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The skate embryo has
a simple structure

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shared by all embryonic vertebrates

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that served as the basis
of the first jaw.

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What we see are these folds...

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..and what's really interesting
about this,

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is that this skate is in about...

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four months of its development.

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If we take a close look at another
vertebrate,

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we can see it looks very similar.

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Here we have the head, as you can
follow it down to the body.

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You also see the folds.

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Now, this is actually a human being.

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It's thought that the embryos
of the earliest vertebrates looked

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much like this and that each fold
developed into a gill.

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In a skate embryo, the folds
furthest from the head

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keep to their original purpose and
form the rigid arches of its gills.

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But the nearest fold has been
adapted to form

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an upper and lower jaw.

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In a human embryo, the lower folds
develop into structures that

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include the larynx and the throat.

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But the top fold, once again,

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constructs the jaw.

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The development of the jaw improved
the ability to collect food,

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and those that lacked it, with a few
exceptions like the lamprey,

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died out.

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But in order to collect food,
you have to find it

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and that led to
an improvement in swimming.

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In the Chinese capital, Beijing,

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I've been given special access

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to a newly identified missing link.

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This tiny fossil holds clues that
are just fragments and hard to spot.

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But it's the earliest example yet
found of a creature

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with two pairs of fins.

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It's called Parayunnanolepis and

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it's about 410 million years old.

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Its front part, like many other
fish at the time,

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was covered by armour plating

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to protect it from predators.

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Underneath, you can
see that it has a mouth,

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and although the lower jaw
is missing,

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you can tell from marks on the upper
jaw that it was once there.

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But what is most important about
this is its fins.

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Just their stumps are visible.

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It had two fins at the front -

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petrol fins.

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They were shaped rather
like the wings of an aeroplane,

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and they had the same effect,

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creating upwards lift through
the water.

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Front fins have been
found on older fish.

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But what's interesting is this
is the earliest example which

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has another pair of fins
at the back -

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the pelvic fins.

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This second smaller pair brought
much more stability,

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helping the fish to
hold its course through the water.

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This system was hugely successful

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and it made the sharks the skilful
swimmers that they are today.

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So now, the vertebrates had jaws
and four fins.

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To see evidence of
the next crucial development,

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I'm heading out onto Lake Fuxian,
in southern China.

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These waters are home to living
descendants of a group

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that developed a new kind of inner
support,

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a support that would have huge
significance for later life.

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Here they get a lot of fish

248
00:19:22,700 --> 00:19:24,100
like this.

249
00:19:24,100 --> 00:19:27,060
It's a carp and it's very different

250
00:19:27,060 --> 00:19:28,180
from the sharks

251
00:19:28,180 --> 00:19:29,860
we've been looking at,

252
00:19:29,860 --> 00:19:32,740
because instead of having
cartilage skeletons,

253
00:19:32,740 --> 00:19:35,820
carp and others like it, have
skeletons that are strengthened

254
00:19:35,820 --> 00:19:37,780
with calcium phosphate.

255
00:19:37,780 --> 00:19:41,780
They're bony and most fish today
have bony skeletons.

256
00:19:44,420 --> 00:19:47,540
Bone contains the main material
found in cartilage,

257
00:19:47,540 --> 00:19:50,340
a long stringy protein called
collagen.

258
00:19:52,220 --> 00:19:55,220
Hard crystals of calcium
phosphate add strength.

259
00:19:57,340 --> 00:19:59,860
But the collagen can still
flex slightly

260
00:19:59,860 --> 00:20:02,940
and prevent the bone snapping
under pressure.

261
00:20:09,860 --> 00:20:14,340
These bony fish could subject
their skeletons to the far greater

262
00:20:14,340 --> 00:20:17,980
forces that come from increases
in speed and agility.

263
00:20:22,020 --> 00:20:24,700
They added mobile fan-shaped fins

264
00:20:24,700 --> 00:20:27,100
and assumed
a multitude of different forms.

265
00:20:35,180 --> 00:20:38,500
From their simple origins
over 500 million years ago,

266
00:20:38,500 --> 00:20:40,340
the sharks and bony fish

267
00:20:40,340 --> 00:20:42,380
diversified to dominate

268
00:20:42,380 --> 00:20:44,980
every underwater
environment on Earth.

269
00:20:49,940 --> 00:20:53,900
There are over 35,000 species
alive today.

270
00:21:04,140 --> 00:21:08,380
The strong inner bony support to the
body had evolved in water,

271
00:21:08,380 --> 00:21:12,020
but it would prove most
spectacularly successful,

272
00:21:12,020 --> 00:21:14,260
in a completely new environment.

273
00:21:23,300 --> 00:21:25,980
For most of the Earth's history
until now,

274
00:21:25,980 --> 00:21:28,620
the land had been empty and barren.

275
00:21:30,700 --> 00:21:35,980
But around 450 million years ago,
first plants, then worms

276
00:21:35,980 --> 00:21:39,380
and then the ancestors of insects
began to colonize it.

277
00:21:41,100 --> 00:21:44,820
Here were rich pickings for any
vertebrate that could reach them.

278
00:21:46,340 --> 00:21:49,340
The stage was set for one
of the most astonishing

279
00:21:49,340 --> 00:21:51,180
leaps in evolutionary history.

280
00:21:53,460 --> 00:21:56,020
The vertebrates move onto land.

281
00:21:59,740 --> 00:22:03,180
But to achieve this remarkable feat,
they would need to make

282
00:22:03,180 --> 00:22:04,780
a major modification.

283
00:22:07,460 --> 00:22:11,260
To move around on land without
the support of water,

284
00:22:11,260 --> 00:22:14,340
these fish needed a way to
lift their bodies

285
00:22:14,340 --> 00:22:16,820
up from the surface of the ground.

286
00:22:16,820 --> 00:22:18,460
They needed limbs.

287
00:22:21,060 --> 00:22:24,580
Scientists have recently found
the earliest evidence for this

288
00:22:24,580 --> 00:22:26,740
key moment in Eastern Europe.

289
00:22:32,500 --> 00:22:34,700
Zachelmie, Poland.

290
00:22:38,700 --> 00:22:40,940
Once a quarry for building stone,

291
00:22:40,940 --> 00:22:44,420
today this is a hugely
significant fossil site.

292
00:22:47,140 --> 00:22:52,380
But palaeontologist Per Ahlberg and
his team aren't looking for bodies,

293
00:22:52,380 --> 00:22:55,780
they're looking for the
marks the bodies left behind.

294
00:23:02,140 --> 00:23:04,940
393 million years ago,

295
00:23:04,940 --> 00:23:07,700
this was the soft muddy floor

296
00:23:07,700 --> 00:23:09,820
of a tropical lagoon.

297
00:23:09,820 --> 00:23:12,580
You can still see mud cracks
here from an episode

298
00:23:12,580 --> 00:23:15,700
when the lagoon dried out
and the mud all flaked up.

299
00:23:17,980 --> 00:23:21,420
Over millions of years, the mud
solidified into layers of rock,

300
00:23:21,420 --> 00:23:24,940
which were then tilted by
movements in the Earth's crust.

301
00:23:28,100 --> 00:23:32,180
By carefully exposing each layer,
Per and his team have been

302
00:23:32,180 --> 00:23:35,780
able to uncover
a series of intriguing tracks.

303
00:23:37,460 --> 00:23:39,340
There are three big dimples
in the rock.

304
00:23:39,340 --> 00:23:44,420
There's one here,
one here and one down by my feet.

305
00:23:50,220 --> 00:23:52,060
These are not erosional hollows,

306
00:23:52,060 --> 00:23:54,700
it's not like rock has been scooped
away, something's been

307
00:23:54,700 --> 00:23:57,660
pressed into the surface of the mud
while it was still soft.

308
00:23:57,660 --> 00:24:00,100
You can see that from the internal
texture here,

309
00:24:00,100 --> 00:24:04,940
but also from the fact that you've
got a slightly raised rim

310
00:24:04,940 --> 00:24:07,740
round the edge where the
mud has been displaced.

311
00:24:07,740 --> 00:24:11,860
So a large heavy animal, presumably
a vertebrate of some sort,

312
00:24:11,860 --> 00:24:14,620
pushed an appendage into the mud
here,

313
00:24:14,620 --> 00:24:17,340
once, twice, three times
in succession.

314
00:24:19,620 --> 00:24:22,260
The marks suggest a creature
floating

315
00:24:22,260 --> 00:24:24,620
and pushing itself
around in the shallows.

316
00:24:29,860 --> 00:24:33,100
But Per and his team have found
a more detailed set of prints

317
00:24:33,100 --> 00:24:36,340
that show an animal doing
something even more radical.

318
00:24:39,180 --> 00:24:42,380
This is one of the most important
specimens from the entire site,

319
00:24:42,380 --> 00:24:45,340
and the reason for that is the
pattern that these prints make.

320
00:24:45,340 --> 00:24:47,940
You can see, easily I think,
that they make pairs,

321
00:24:47,940 --> 00:24:51,460
one in front of another, in this kind
of diagonal arrangement.

322
00:24:51,460 --> 00:24:53,860
In order to be able to produce this,

323
00:24:53,860 --> 00:24:56,860
you need to have limbs that stick
out to the side

324
00:24:56,860 --> 00:25:00,260
and which can be swung forwards
and backwards rather freely

325
00:25:00,260 --> 00:25:02,420
while you're flexing your body from
side to side.

326
00:25:02,420 --> 00:25:04,620
Then, you can generate
this kind of pattern.

327
00:25:04,620 --> 00:25:08,460
A fish crawling trace would not
look like this.

328
00:25:10,900 --> 00:25:14,540
Another extraordinary slab
has even preserved the imprint

329
00:25:14,540 --> 00:25:17,580
of what Per believes is a
fully-formed foot

330
00:25:17,580 --> 00:25:18,780
complete with toes.

331
00:25:22,660 --> 00:25:26,180
So, how did the vertebrates
make this astonishing transition

332
00:25:26,180 --> 00:25:31,620
from fish swimming to animals
with four legs walking on land?

333
00:25:34,620 --> 00:25:36,900
In search of clues,
I'm heading to London

334
00:25:36,900 --> 00:25:40,140
and the Natural History Museum,
home to the largest

335
00:25:40,140 --> 00:25:43,300
collection of plant
and animal specimens in the world.

336
00:25:47,140 --> 00:25:50,300
I'm here to see the remains
of an ancient creature,

337
00:25:50,300 --> 00:25:54,100
once hailed as a missing link
that would answer such questions.

338
00:25:57,820 --> 00:26:01,860
This is a type of bony fish
called a Coelacanth.

339
00:26:01,860 --> 00:26:05,100
Its fossilized skeletons have been
found in rocks even older

340
00:26:05,100 --> 00:26:06,340
than those in Poland.

341
00:26:09,820 --> 00:26:14,860
Its fins have an intriguing feature
not seen in other kinds of fish.

342
00:26:14,860 --> 00:26:19,140
Their base is a rounded
fleshy stump that looks

343
00:26:19,140 --> 00:26:22,140
tantalizingly
like the beginnings of a leg.

344
00:26:24,220 --> 00:26:26,860
So scientists thought
that this might well be

345
00:26:26,860 --> 00:26:30,220
the ancestor of all land-living
vertebrates.

346
00:26:31,740 --> 00:26:33,220
And then, a sensation.

347
00:26:34,580 --> 00:26:39,540
A living coelacanth was hauled up
from the depths of the Indian Ocean

348
00:26:39,540 --> 00:26:42,860
and the museum has acquired several
of them.

349
00:26:45,340 --> 00:26:49,420
Here is the body of a baby
coelacanth.

350
00:26:49,420 --> 00:26:52,740
The coelacanth female retains
the egg in her body

351
00:26:52,740 --> 00:26:54,700
until it's fully developed.

352
00:26:54,700 --> 00:26:56,580
There's its yolk sack,

353
00:26:56,580 --> 00:26:57,980
and here's its fin,

354
00:26:57,980 --> 00:27:03,420
and you can see this fleshy base to
it here and then its fin rays.

355
00:27:03,420 --> 00:27:08,300
The question is, was that strong
enough to enable a fish like this

356
00:27:08,300 --> 00:27:12,340
to haul itself out of the water
and up onto land?

357
00:27:17,860 --> 00:27:19,900
Now, living coelacanths have been

358
00:27:19,900 --> 00:27:21,740
filmed in the depths of the sea.

359
00:27:24,740 --> 00:27:26,740
Its fleshy, muscular fins

360
00:27:26,740 --> 00:27:28,500
do certainly help it to

361
00:27:28,500 --> 00:27:30,820
manoeuvre its five-foot-long body.

362
00:27:33,620 --> 00:27:38,340
There is even the hint of a walking
pattern,

363
00:27:38,340 --> 00:27:42,420
but detailed analysis has revealed
that their fins

364
00:27:42,420 --> 00:27:45,260
are still a long way
from being legs.

365
00:27:49,340 --> 00:27:53,060
The ancient coelacanth marked
a crucial early stage in that

366
00:27:53,060 --> 00:27:57,260
transition, but some characteristics
ruled it out as a direct

367
00:27:57,260 --> 00:27:59,260
ancestor of the land vertebrates.

368
00:28:03,820 --> 00:28:08,780
All land-living backboned animals
have limbs which have a basic

369
00:28:08,780 --> 00:28:11,220
similar bone structure.

370
00:28:11,220 --> 00:28:14,820
There is one bone at the top,

371
00:28:14,820 --> 00:28:17,540
then there are two bones

372
00:28:17,540 --> 00:28:20,780
and a group of bones,
followed with digits.

373
00:28:22,500 --> 00:28:26,700
And the coelacanths
didn't have that structure.

374
00:28:26,700 --> 00:28:31,460
And then, recently, another
fossil discovery was made.

375
00:28:35,780 --> 00:28:38,820
Ellesmere Island lies in the icy
waters

376
00:28:38,820 --> 00:28:41,700
between northern Canada
and Greenland.

377
00:28:45,500 --> 00:28:49,860
A team of American palaeontologists,
who shot this footage,

378
00:28:49,860 --> 00:28:53,300
believed that the rocks here were
deposited in the right

379
00:28:53,300 --> 00:28:56,420
sort of environment
for the vertebrates move to land.

380
00:28:58,980 --> 00:29:01,300
We learned about a sequence of rocks

381
00:29:01,300 --> 00:29:04,060
that formed in ancient stream
systems.

382
00:29:04,060 --> 00:29:08,340
Our hypothesis was that it was in
those sorts of environments,

383
00:29:08,340 --> 00:29:12,580
where limbs were being
favoured over fins.

384
00:29:18,700 --> 00:29:23,140
The arrival of plants on land
had stimulated a surge in life

385
00:29:23,140 --> 00:29:25,620
in and around fresh water swamps

386
00:29:25,620 --> 00:29:29,540
and this created new opportunities
for the fish that lived here.

387
00:29:33,340 --> 00:29:36,580
One of the nitches that was being
developed at the time,

388
00:29:36,580 --> 00:29:39,620
was for shallow-water predators.

389
00:29:39,620 --> 00:29:43,860
You know, which fish could find
other fish that were living

390
00:29:43,860 --> 00:29:47,740
in the shallows, the swamps,
the productive eco systems

391
00:29:47,740 --> 00:29:51,180
that were just starting to appear on
Earth at that time?

392
00:29:53,220 --> 00:29:57,100
Ted Daeschler and his colleagues
believed that limb-like fins

393
00:29:57,100 --> 00:30:00,540
could have helped a fish to
hunt in this kind of environment.

394
00:30:04,420 --> 00:30:07,220
And then, on the slopes
of a barren valley,

395
00:30:07,220 --> 00:30:09,460
they made a thrilling discovery.

396
00:30:14,940 --> 00:30:18,340
This was the fossil that got us
really excited.

397
00:30:18,340 --> 00:30:21,380
We couldn't have dreamed
actually that we would find

398
00:30:21,380 --> 00:30:23,660
something as
well preserved as this one.

399
00:30:23,660 --> 00:30:25,300
It's about the front

400
00:30:25,300 --> 00:30:27,540
two-thirds or half of the body,

401
00:30:27,540 --> 00:30:28,580
as you can see,

402
00:30:28,580 --> 00:30:30,340
a very complete skull,

403
00:30:30,340 --> 00:30:32,620
and a large piece of the body,

404
00:30:32,620 --> 00:30:34,820
including parts of the fin.

405
00:30:37,300 --> 00:30:40,340
The team found features that
matched the profile

406
00:30:40,340 --> 00:30:42,220
of a shallow-water predator.

407
00:30:44,020 --> 00:30:47,420
Eyes placed on the top
of a flattened head...

408
00:30:49,260 --> 00:30:51,700
..and ranks of sharp teeth.

409
00:30:54,780 --> 00:30:57,940
They gave it a local Inuit name -

410
00:30:57,940 --> 00:30:59,340
Tiktaalik.

411
00:31:02,900 --> 00:31:06,340
We can now work out from its
bones how Tiktaalik

412
00:31:06,340 --> 00:31:08,820
moved around in those swamps
and shallows.

413
00:31:21,380 --> 00:31:25,100
In deep water, it must have swum
like any other fish.

414
00:31:30,380 --> 00:31:34,540
But further examination of its bones
showed that it could also

415
00:31:34,540 --> 00:31:37,260
move its body in a far
more radical way.

416
00:31:39,660 --> 00:31:42,060
One of the really amazing aspects

417
00:31:42,060 --> 00:31:44,180
of Tiktaalik that we've noticed

418
00:31:44,180 --> 00:31:46,980
is this evolution of the neck.

419
00:31:46,980 --> 00:31:50,380
There was not a rigid
connection between the skull

420
00:31:50,380 --> 00:31:51,900
and the rest of the body.

421
00:31:51,900 --> 00:31:54,620
Tiktaalik is the first vertebrate

422
00:31:54,620 --> 00:31:58,780
we see that has freed up the neck.
And when you think about it,

423
00:31:58,780 --> 00:32:02,220
all limbed animals, including
ourselves, would not be able

424
00:32:02,220 --> 00:32:06,500
to move our head independently
of our shoulders if it were not

425
00:32:06,500 --> 00:32:11,540
for these innovations that were
occurring in a form like Tiktaalik.

426
00:32:11,540 --> 00:32:16,900
A flexible neck allowed Tiktaalik
to point its jaws at its prey

427
00:32:16,900 --> 00:32:19,860
when space was too cramped to
manoeuvre its whole body.

428
00:32:21,700 --> 00:32:24,340
But it was the fins
that provided the team

429
00:32:24,340 --> 00:32:26,460
with the most exciting evidence.

430
00:32:30,980 --> 00:32:35,100
Behind the spiny rays,
there were lobe-like stumps,

431
00:32:35,100 --> 00:32:37,620
like those of the coelacanth.

432
00:32:37,620 --> 00:32:41,620
But Tiktaalik's bones revealed
a pattern that was much

433
00:32:41,620 --> 00:32:45,060
closer to the
basic structure of limbs.

434
00:32:46,940 --> 00:32:49,820
We learned a lot

435
00:32:49,820 --> 00:32:51,980
about the fin of Tiktaalik

436
00:32:51,980 --> 00:32:53,420
from this specimen.

437
00:32:53,420 --> 00:32:57,340
Now, this is a cast of all
the different bones that we found

438
00:32:57,340 --> 00:33:02,100
in association,
including the shoulder girdle here.

439
00:33:02,100 --> 00:33:04,780
But that is the complete fin skeleton

440
00:33:04,780 --> 00:33:06,620
from the front fin so...

441
00:33:06,620 --> 00:33:12,060
I'm a lobe-fin fish, here is
my front fin, we call it a limb now,

442
00:33:12,060 --> 00:33:15,220
but here is Tiktaalik's front fin.

443
00:33:15,220 --> 00:33:17,980
We've got a shoulder joint

444
00:33:17,980 --> 00:33:20,580
and it's very important that
there's a shoulder joint

445
00:33:20,580 --> 00:33:23,020
which is oriented a little bit
laterally,

446
00:33:23,020 --> 00:33:25,300
a little bit down in Tiktaalik.

447
00:33:25,300 --> 00:33:28,340
Very different from an animal that's
just swimming with its fin

448
00:33:28,340 --> 00:33:32,940
and paddling along, this fin seemed
to be oriented beneath the body.

449
00:33:32,940 --> 00:33:34,860
So this is the humerus.

450
00:33:34,860 --> 00:33:39,060
We all have a humerus, that's the
first bone in the front appendage.

451
00:33:39,060 --> 00:33:42,300
We have an ulna and a radius.

452
00:33:42,300 --> 00:33:44,740
So you and I, all limbed animals,

453
00:33:44,740 --> 00:33:46,500
have an ulna and radius.

454
00:33:46,500 --> 00:33:47,980
We have some wrist bones

455
00:33:47,980 --> 00:33:50,060
and we actually then have something

456
00:33:50,060 --> 00:33:52,100
which, like a wrist, could

457
00:33:52,100 --> 00:33:55,420
bend together and allow this fin

458
00:33:55,420 --> 00:33:57,780
to sit down and to contact

459
00:33:57,780 --> 00:34:00,820
a surface with a surface area.

460
00:34:00,820 --> 00:34:03,900
And so, when
we see all of these features,

461
00:34:03,900 --> 00:34:07,580
we see a structure
which is very much like our limbs.

462
00:34:07,580 --> 00:34:12,180
So here is a fish using
its fin in a very limb-like way.

463
00:34:14,620 --> 00:34:18,500
Tiktaalik's heavy-duty fin still
helped it to swim.

464
00:34:21,540 --> 00:34:23,500
But if it hit the shallows,

465
00:34:23,500 --> 00:34:25,860
the bones and joints would help to

466
00:34:25,860 --> 00:34:28,380
push itself up and punt around.

467
00:34:32,540 --> 00:34:36,140
But this new limb didn't just help
mobility in the water.

468
00:34:43,220 --> 00:34:46,740
It became the driving force
behind one of the most spectacular

469
00:34:46,740 --> 00:34:49,340
events in evolutionary history...

470
00:34:51,940 --> 00:34:55,940
..the arrival of the first
vertebrate animals on land.

471
00:35:25,380 --> 00:35:27,980
Over time, creatures evolved

472
00:35:27,980 --> 00:35:30,980
that spent most of their time
out of water.

473
00:35:33,020 --> 00:35:36,300
They formed a new group
we call amphibians.

474
00:35:36,300 --> 00:35:40,780
And to survive on land,
they had to solve a new challenge.

475
00:35:40,780 --> 00:35:43,820
They had to be
able to extract oxygen

476
00:35:43,820 --> 00:35:47,140
not from water, like their fish
ancestors, but from the air.

477
00:35:48,900 --> 00:35:52,780
Fish use gills to absorb
oxygen into the body.

478
00:35:56,700 --> 00:36:00,420
In air, gills quickly dry out
and stop working.

479
00:36:05,340 --> 00:36:09,180
China is the home of a rare
and fascinating creature

480
00:36:09,180 --> 00:36:13,020
that can show us how the ancient
amphibians overcame this problem.

481
00:36:17,740 --> 00:36:23,220
Today, the biggest amphibian
alive is this creature -

482
00:36:23,220 --> 00:36:26,060
the Chinese giant salamander.

483
00:36:27,100 --> 00:36:34,260
It breathes partly through its skin
which has these long flaps on it,

484
00:36:34,260 --> 00:36:37,540
and that absorbs oxygen
from the water...

485
00:36:39,620 --> 00:36:42,620
..but it also breathes air.

486
00:36:46,580 --> 00:36:53,860
It's going to come up, and as it
does, it snatches a gulp of air,

487
00:36:53,860 --> 00:36:55,340
blows a few bubbles...

488
00:36:59,740 --> 00:37:01,180
..and sinks down again.

489
00:37:04,860 --> 00:37:09,620
Its jaw acts as a pump,
forcing air down into the body.

490
00:37:11,180 --> 00:37:15,020
Here, oxygen is absorbed
into the bloodstream

491
00:37:15,020 --> 00:37:19,540
from two inflatable
sacks with permeable walls - lungs.

492
00:37:22,420 --> 00:37:26,580
Because they're enclosed inside the
body, they don't dry out.

493
00:37:28,460 --> 00:37:32,260
The lungs it uses are just
simple pouches

494
00:37:32,260 --> 00:37:34,740
coming from the back of the throat.

495
00:37:34,740 --> 00:37:39,820
But nonetheless, they were the first
kind of lungs that animals had.

496
00:37:39,820 --> 00:37:44,140
The forerunners of the air-breathing
organs that all of us

497
00:37:44,140 --> 00:37:46,900
land-living vertebrates now have.

498
00:38:00,300 --> 00:38:01,700
From their origins,

499
00:38:01,700 --> 00:38:03,980
around 365 million years ago,

500
00:38:03,980 --> 00:38:07,300
the amphibians took on many
different forms.

501
00:38:09,860 --> 00:38:14,100
Over 7,000 species now live
in a variety of habitats

502
00:38:14,100 --> 00:38:16,460
on land and in water.

503
00:38:23,220 --> 00:38:24,620
They include salamanders...

504
00:38:27,380 --> 00:38:28,500
..frogs...

505
00:38:32,420 --> 00:38:34,020
..and newts.

506
00:38:37,060 --> 00:38:40,540
But two things tie
the amphibians to water.

507
00:38:40,540 --> 00:38:44,900
First - their skins are moist
and if they dry out, they die.

508
00:38:44,900 --> 00:38:49,700
And secondly - their eggs,
like this frogspawn,

509
00:38:49,700 --> 00:38:52,340
are covered in nothing
more than jelly.

510
00:38:52,340 --> 00:38:55,420
And they have to be laid in water
or at the very least,

511
00:38:55,420 --> 00:38:57,420
in moist conditions.

512
00:38:57,420 --> 00:39:01,060
And until the vertebrates could
solve those two problems,

513
00:39:01,060 --> 00:39:05,300
they would not be able to colonise
the dry parts of the land.

514
00:39:12,460 --> 00:39:15,500
Then, a group of pioneers appeared

515
00:39:15,500 --> 00:39:18,700
with an amazing new feature
to their bodies.

516
00:39:20,540 --> 00:39:23,460
We can find
the evidence for this next step

517
00:39:23,460 --> 00:39:26,820
by looking at animals that
can survive far from water today.

518
00:39:33,180 --> 00:39:35,540
This little creature is a lizard.

519
00:39:35,540 --> 00:39:38,820
They call it in these parts
a tree dragon.

520
00:39:38,820 --> 00:39:43,340
And its body is very much the same
shape as an amphibian.

521
00:39:43,340 --> 00:39:47,980
Long body with a backbone
and two pairs of limbs.

522
00:39:47,980 --> 00:39:49,860
But there's one crucial difference

523
00:39:49,860 --> 00:39:52,620
between an animal like this
and an amphibian.

524
00:39:52,620 --> 00:39:55,540
Its skin is not moist, it's dry.

525
00:39:57,900 --> 00:40:01,500
We can see what has changed
by putting the two types of skin

526
00:40:01,500 --> 00:40:03,460
under the microscope.

527
00:40:05,420 --> 00:40:07,060
The skin of an amphibian

528
00:40:07,060 --> 00:40:08,860
is smooth with living cells

529
00:40:08,860 --> 00:40:10,700
visible on the surface.

530
00:40:12,700 --> 00:40:15,380
A lizard's skin is much rougher

531
00:40:15,380 --> 00:40:18,060
because it contains large
amounts of keratin -

532
00:40:18,060 --> 00:40:22,060
a protein similar to that from which
our own fingernails are formed.

533
00:40:25,100 --> 00:40:29,980
Keratin-filled cells dry out
and layer up to form scales.

534
00:40:34,980 --> 00:40:39,340
This creates a barrier,
sealing water inside the body.

535
00:40:41,620 --> 00:40:46,100
We humans have inherited this
keratin barrier in our skin,

536
00:40:46,100 --> 00:40:50,260
allowing us to maintain up
to 70% of our bodies as water.

537
00:40:55,420 --> 00:40:59,060
Animals with this body plan
became a huge success.

538
00:40:59,060 --> 00:41:03,220
They evolved into a great
number of species big and small.

539
00:41:03,220 --> 00:41:05,340
We call them reptiles.

540
00:41:08,500 --> 00:41:12,460
But the reptiles still had
to overcome a second challenge -

541
00:41:12,460 --> 00:41:15,300
how to lay their eggs out of water.

542
00:41:22,540 --> 00:41:26,500
I have come to Lufeng, in southern
China, to see evidence

543
00:41:26,500 --> 00:41:31,340
gathered by local scientists
of the ingenious solution.

544
00:41:31,340 --> 00:41:32,980
Thank you very much.

545
00:41:36,900 --> 00:41:39,860
These eggs were laid by a reptile,

546
00:41:39,860 --> 00:41:42,260
and as you might imagine,

547
00:41:42,260 --> 00:41:44,780
a pretty big one at that.

548
00:41:44,780 --> 00:41:49,020
The first reptilian eggs almost
certainly had a leathery covering,

549
00:41:49,020 --> 00:41:52,500
rather like those
a turtle lays today.

550
00:41:52,500 --> 00:41:58,580
But these eggs are different,
they have a hard covering - a shell.

551
00:41:58,580 --> 00:42:00,980
And you can see where the weight

552
00:42:00,980 --> 00:42:02,820
of the sand that eventually

553
00:42:02,820 --> 00:42:04,780
covered them and fossilized them

554
00:42:04,780 --> 00:42:07,220
bore down upon them,
they crushed that shell,

555
00:42:07,220 --> 00:42:10,340
but the pieces are still in place.

556
00:42:11,860 --> 00:42:14,140
From examining modern reptile eggs,

557
00:42:14,140 --> 00:42:18,500
we know that this shell must have
been made of hard calcium carbonate

558
00:42:18,500 --> 00:42:21,700
and it must have supported
an inner fibrous membrane.

559
00:42:23,180 --> 00:42:26,420
Together, they made the
egg water-tight.

560
00:42:26,420 --> 00:42:30,660
And that meant that the animals that
laid them no longer had to

561
00:42:30,660 --> 00:42:35,420
go back to the water to lay their
eggs, as all amphibians had to do.

562
00:42:35,420 --> 00:42:41,300
Instead, they could go to the
driest part of the land and breed

563
00:42:41,300 --> 00:42:44,020
and nest and lay their eggs.

564
00:42:44,020 --> 00:42:47,300
So all the dry
land was open to them.

565
00:42:51,140 --> 00:42:56,100
The amphibians had spearheaded
the move to land.

566
00:42:56,100 --> 00:42:58,620
Now, their descendants,
the reptiles,

567
00:42:58,620 --> 00:43:00,940
were able to establish themselves

568
00:43:00,940 --> 00:43:02,780
in its driest parts.

569
00:43:09,020 --> 00:43:12,900
Over 9,500 species
now inhabit our planet.

570
00:43:19,420 --> 00:43:22,460
But the limbs that helped
the vertebrates

571
00:43:22,460 --> 00:43:25,740
emerge from the water
began to present problems

572
00:43:25,740 --> 00:43:29,420
when it came to
walking efficiently on dry land.

573
00:43:29,420 --> 00:43:31,860
Because they projected sideways,

574
00:43:31,860 --> 00:43:35,660
it took a lot of effort to
hold their bodies off the ground.

575
00:43:38,100 --> 00:43:41,220
Then, around 230 million years ago,

576
00:43:41,220 --> 00:43:45,460
one set of reptiles developed
an amazing solution.

577
00:43:47,300 --> 00:43:51,060
These eggs were laid by an animal
belonging to the most

578
00:43:51,060 --> 00:43:54,140
successful of all reptile groups,

579
00:43:54,140 --> 00:43:58,700
a group that dominated the world
for 100 million years -

580
00:43:58,700 --> 00:44:00,660
the dinosaurs.

581
00:44:20,780 --> 00:44:24,660
More than 150 different
species of dinosaur have been

582
00:44:24,660 --> 00:44:28,900
found in the rocks of China alone,
and over 1,000 worldwide.

583
00:44:37,300 --> 00:44:40,940
And they too depended on
a crucial advance.

584
00:44:40,940 --> 00:44:45,060
A radical modification of the bone
that connects the leg to the body -

585
00:44:45,060 --> 00:44:46,540
the hip.

586
00:44:51,780 --> 00:44:55,900
This is Lufengosaurus,
a plant-eater.

587
00:44:57,620 --> 00:45:02,060
The early reptiles had legs which
splayed out from either side

588
00:45:02,060 --> 00:45:05,660
of the body and left the body
very close to the ground.

589
00:45:05,660 --> 00:45:09,020
But a change in the shape
of the hips of the dinosaurs

590
00:45:09,020 --> 00:45:12,780
enabled them to bring their hind
legs underneath the body

591
00:45:12,780 --> 00:45:17,060
and so, lift them up and give them
greater freedom of movement.

592
00:45:17,060 --> 00:45:20,260
And some of them,
including Lufengosaurus,

593
00:45:20,260 --> 00:45:24,300
were able to support the entire
weight of the body on the hind legs.

594
00:45:29,660 --> 00:45:34,300
This new hip, along with sturdier
leg joints, allowed the dinosaurs

595
00:45:34,300 --> 00:45:36,100
to take longer strides...

596
00:45:40,260 --> 00:45:42,460
..and support heavier bodies.

597
00:45:44,260 --> 00:45:48,900
They became the largest animals
that have ever lived on land.

598
00:45:50,140 --> 00:45:54,540
But this new way of walking was also
the first step on the road to

599
00:45:54,540 --> 00:45:57,700
an even more
radical evolutionary advance.

600
00:45:59,700 --> 00:46:05,180
It was from this group of two-legged
dinosaurs that there came a truly

601
00:46:05,180 --> 00:46:09,980
astonishing development that we are
only just beginning to understand,

602
00:46:09,980 --> 00:46:13,500
and that was to lift the vertebrates
to a completely new level.

603
00:46:16,580 --> 00:46:22,220
The backboned animals had colonized
the seas and invaded the land.

604
00:46:22,220 --> 00:46:26,780
But there was one final habitat
to explore - the skies.

605
00:46:29,420 --> 00:46:33,180
Another extraordinary Chinese
fossil bed is providing the missing

606
00:46:33,180 --> 00:46:39,100
evidence for one of the great
mysteries in evolutionary science -

607
00:46:39,100 --> 00:46:42,740
the intriguing
link between dinosaurs and birds.

608
00:46:48,700 --> 00:46:54,580
I'm heading for Liaoning province
to fulfil a long-held dream

609
00:46:54,580 --> 00:46:58,220
and see the site of these
discoveries for myself.

610
00:47:01,860 --> 00:47:06,260
These rocks are
about 125 million years old.

611
00:47:06,260 --> 00:47:09,980
At that time,
this part of China was tropical

612
00:47:09,980 --> 00:47:13,820
and the land was covered with
a lot of freshwater lakes.

613
00:47:13,820 --> 00:47:17,260
And in those lakes
was washed sediment

614
00:47:17,260 --> 00:47:19,940
which formed these bands here.

615
00:47:19,940 --> 00:47:24,340
But every now and again,
the sediment changes colour.

616
00:47:24,340 --> 00:47:29,700
And that is ash that was spewed
out from a nearby volcano

617
00:47:29,700 --> 00:47:32,500
so that about that level there,

618
00:47:32,500 --> 00:47:36,180
there were a lot of skeletons
waiting to be discovered.

619
00:47:36,180 --> 00:47:41,460
And when they were discovered,
they revealed some sensational facts

620
00:47:41,460 --> 00:47:45,380
about dinosaurs, the most
sensational for a very long time.

621
00:47:47,980 --> 00:47:49,660
This fossil was one of

622
00:47:49,660 --> 00:47:52,140
the most remarkable to emerge.

623
00:47:52,140 --> 00:47:53,980
A two-legged dinosaur

624
00:47:53,980 --> 00:47:55,860
about the size of a cat.

625
00:47:55,860 --> 00:47:59,220
It's been named Sinosauropteryx.

626
00:48:01,060 --> 00:48:04,140
Its discovery revealed an
intriguing feature

627
00:48:04,140 --> 00:48:06,620
never seen before on a dinosaur.

628
00:48:08,100 --> 00:48:10,540
Up its tail and down its back,

629
00:48:10,540 --> 00:48:13,300
a covering of what looks like fur.

630
00:48:16,380 --> 00:48:21,380
Fresh finds have revealed that
a wide range of two-legged dinosaurs

631
00:48:21,380 --> 00:48:25,260
had skin covered by very
similar hair-like filaments.

632
00:48:27,340 --> 00:48:28,580
But what were they for?

633
00:48:31,620 --> 00:48:35,020
In Beijing, there are the
crucial specimens

634
00:48:35,020 --> 00:48:37,380
that answered those questions.

635
00:48:40,580 --> 00:48:44,220
This is one of the world's leading
institutions in the study

636
00:48:44,220 --> 00:48:46,180
of dinosaur evolution.

637
00:48:49,300 --> 00:48:53,580
Professor Xu Xing and his colleagues
have been analysing another

638
00:48:53,580 --> 00:48:56,540
larger specimen of Sinosauropteryx.

639
00:49:00,260 --> 00:49:02,940
It too retains traces,

640
00:49:02,940 --> 00:49:05,580
just fragments of
the mysterious filaments.

641
00:49:08,820 --> 00:49:15,300
If you look near the tail,
the dark things there near the tail,

642
00:49:15,300 --> 00:49:17,740
they are single filaments,
just like our hair,

643
00:49:17,740 --> 00:49:19,340
which are very, very simple.

644
00:49:20,700 --> 00:49:24,060
Xu Xing has been puzzling
over their function.

645
00:49:24,060 --> 00:49:28,260
Together, these filaments create
a covering like fur,

646
00:49:28,260 --> 00:49:30,700
so the most likely answer
is that they served

647
00:49:30,700 --> 00:49:33,700
to keep these dinosaurs warm.

648
00:49:33,700 --> 00:49:38,020
But detailed examination has
suggested an additional

649
00:49:38,020 --> 00:49:39,740
and very different function.

650
00:49:42,100 --> 00:49:45,780
Experts at the institute have
taken minute samples

651
00:49:45,780 --> 00:49:49,020
and examined them
under powerful magnification.

652
00:49:50,220 --> 00:49:53,260
They contain intriguing structures.

653
00:49:54,460 --> 00:49:57,300
Some are lozenge-shaped,

654
00:49:57,300 --> 00:50:00,540
some spherical.

655
00:50:00,540 --> 00:50:04,660
Investigators identified them
as melanosomes -

656
00:50:04,660 --> 00:50:09,100
microscopic capsules that
contain pigment.

657
00:50:09,100 --> 00:50:13,860
They would have given the filaments
on Sinosauropteryx's tail colour.

658
00:50:15,220 --> 00:50:18,460
Based on our analysis,
you see stripes.

659
00:50:18,460 --> 00:50:23,940
One like white, brown, white, brown.
Really?

660
00:50:23,940 --> 00:50:28,620
Yes, definitely. It's a beautiful
pattern. Of course you can't see all,

661
00:50:28,620 --> 00:50:32,100
that's maybe for display
or communication or...

662
00:50:32,100 --> 00:50:34,100
Do we know how it held its tail?

663
00:50:34,100 --> 00:50:37,580
Uh, tails definitely can
move in different directions.

664
00:50:37,580 --> 00:50:40,820
In most cases,
I would guess is up or horizontal.

665
00:50:40,820 --> 00:50:44,580
So it's like a ring-tailed lemur
waving its tail around as a display.

666
00:50:46,460 --> 00:50:48,100
Dinosaurs may have used

667
00:50:48,100 --> 00:50:50,860
these coloured furry bands to signal

668
00:50:50,860 --> 00:50:52,580
to other members of the species

669
00:50:52,580 --> 00:50:55,460
or to act as camouflage.

670
00:50:55,460 --> 00:50:58,860
But then came a discovery that
suggested another far more

671
00:50:58,860 --> 00:51:00,900
significant function.

672
00:51:04,180 --> 00:51:08,300
I've been granted privileged
access to the underground vaults

673
00:51:08,300 --> 00:51:12,100
of the Beijing Museum of Natural
History, to look at one of the most

674
00:51:12,100 --> 00:51:16,340
important creatures yet to be found
in the fossil beds of Liaoning.

675
00:51:47,980 --> 00:51:53,940
This is Anchiornis, a creature
that's clearly a dinosaur.

676
00:51:53,940 --> 00:51:58,620
It's got powerful legs here ending
with toes with sharp claws

677
00:51:58,620 --> 00:52:01,460
on them, and its head,

678
00:52:01,460 --> 00:52:04,100
which has been detached, lies here

679
00:52:04,100 --> 00:52:08,220
upside down but you can see the jaw,

680
00:52:08,220 --> 00:52:09,700
which has teeth in them.

681
00:52:11,980 --> 00:52:16,620
But what is spectacular about
this particular specimen

682
00:52:16,620 --> 00:52:20,980
is the perfection of the
preservation of these structures.

683
00:52:20,980 --> 00:52:24,580
They show that the simple filaments
have developed into something

684
00:52:24,580 --> 00:52:26,220
far more complex.

685
00:52:27,700 --> 00:52:30,420
The central stalk has tiny strands

686
00:52:30,420 --> 00:52:32,700
branching out on either side.

687
00:52:32,700 --> 00:52:35,700
The filaments have become feathers.

688
00:52:38,420 --> 00:52:44,500
Analysis of them has shown that
the crest here on the head

689
00:52:44,500 --> 00:52:46,700
was a rufous red colour

690
00:52:46,700 --> 00:52:48,980
and the body feathers

691
00:52:48,980 --> 00:52:51,460
were striped black and white.

692
00:52:55,300 --> 00:52:57,900
There are feathers all
down the legs.

693
00:53:01,780 --> 00:53:06,420
And looking at the density of them
on the forearms here,

694
00:53:06,420 --> 00:53:09,700
it does look very like a wing.

695
00:53:09,700 --> 00:53:11,300
So the question is,

696
00:53:11,300 --> 00:53:14,820
could this animal fly?

697
00:53:14,820 --> 00:53:21,060
Could this be the moment
when a dinosaur became a bird?

698
00:53:26,900 --> 00:53:31,860
A clue to the answer could come from
the environment in which it lived.

699
00:53:31,860 --> 00:53:36,900
At this time, this area of northern
China was covered in lush forests.

700
00:53:39,700 --> 00:53:42,980
Animals that could climb trees
would be able to collect food

701
00:53:42,980 --> 00:53:45,020
that was not available
on the ground.

702
00:53:46,740 --> 00:53:50,100
They could also find safety
from ground-living predators.

703
00:53:52,660 --> 00:53:57,220
Xu Xing and his colleagues see
evidence that Anchiornis adapted

704
00:53:57,220 --> 00:54:01,900
to a tree-living way of life, by
putting its feathers to a new use.

705
00:54:03,940 --> 00:54:08,820
Anchiornis has some features
suggesting a tree-living lifestyle.

706
00:54:08,820 --> 00:54:12,860
For example, you look at
the Anchiornis' toe,

707
00:54:12,860 --> 00:54:15,780
they have very curved claws.

708
00:54:15,780 --> 00:54:19,580
And also, they have
big feathers attached to their feet.

709
00:54:19,580 --> 00:54:23,860
If Anchiornis is a tree-living
animal, then I have good reason

710
00:54:23,860 --> 00:54:27,500
to believe that flight started
from tree down.

711
00:54:27,500 --> 00:54:32,980
Which means that the birds' ancestor
can take advantage of gravity

712
00:54:32,980 --> 00:54:35,620
and then start
their journey to the sky.

713
00:54:38,380 --> 00:54:40,820
Because Anchiornis lived high up,

714
00:54:40,820 --> 00:54:43,300
it could use its feathers to glide.

715
00:54:59,780 --> 00:55:03,860
It must have needed all the feathers
growing along its front limbs,

716
00:55:03,860 --> 00:55:08,340
hind limbs and tail to create
a large enough surface to catch

717
00:55:08,340 --> 00:55:10,740
the air and slow its descent.

718
00:55:22,140 --> 00:55:28,220
It wasn't capable of flapping flight
but, at 160 million years old,

719
00:55:28,220 --> 00:55:32,900
it's now the earliest creature we
know to have used feathers to fly.

720
00:55:40,140 --> 00:55:42,860
The gliding dinosaurs would
eventually give rise to

721
00:55:42,860 --> 00:55:45,060
a whole new group
of vertebrates...

722
00:55:46,700 --> 00:55:48,060
..the birds.

723
00:55:53,420 --> 00:55:56,820
Over 9,000 species
crowd our skies today.

724
00:56:00,540 --> 00:56:04,500
An astonishing evolutionary journey
had enabled the vertebrates

725
00:56:04,500 --> 00:56:07,620
to dominate every
corner of the planet.

726
00:56:11,740 --> 00:56:15,940
It was a journey that began
in the Cambrian seas

727
00:56:15,940 --> 00:56:18,380
over 500 million years ago,

728
00:56:18,380 --> 00:56:20,420
and that led to the development of

729
00:56:20,420 --> 00:56:25,060
a set of body parts that we
ourselves would ultimately inherit.

730
00:56:27,140 --> 00:56:30,380
Jaws and a bony skeleton
from the early fish...

731
00:56:35,100 --> 00:56:37,860
..limbs and lungs from
the amphibians...

732
00:56:40,460 --> 00:56:43,780
..water-tight skin
from the reptiles.

733
00:56:46,060 --> 00:56:48,900
By the time the birds
appeared on the planet,

734
00:56:48,900 --> 00:56:53,700
the early pioneers of another major
vertebrate group had also evolved.

735
00:56:56,460 --> 00:57:00,580
At first, they were tiny but
they were destined eventually to

736
00:57:00,580 --> 00:57:02,900
dominate the Earth -

737
00:57:02,900 --> 00:57:04,700
they were the mammals.

738
00:57:07,580 --> 00:57:11,620
Most, I dare say,
were little better than snack food

739
00:57:11,620 --> 00:57:15,060
for the dinosaurs,
but all that was about to change.

740
00:57:20,660 --> 00:57:23,140
A devastating meteor strike,

741
00:57:23,140 --> 00:57:26,380
that many believe triggered
a mass extinction.

742
00:57:30,020 --> 00:57:32,660
We don't know exactly what happened,

743
00:57:32,660 --> 00:57:37,620
but certainly, 65 million years ago,
all the dinosaurs disappeared.

744
00:57:39,100 --> 00:57:42,900
But some of the
birds and mammals survived

745
00:57:42,900 --> 00:57:47,820
and with the bigger dinosaurs gone,
the world was up for grabs.

746
00:57:54,300 --> 00:58:00,060
Next time, I'll be investigating the
extraordinary rise of the mammals

747
00:58:00,060 --> 00:58:04,860
to discover how they developed a
remarkable set of new bodily

748
00:58:04,860 --> 00:58:09,180
features to become the most complex
and successful vertebrates yet.

749
00:58:11,500 --> 00:58:13,980
Powerful senses,

750
00:58:13,980 --> 00:58:17,100
a radical new way
of producing their young,

751
00:58:17,100 --> 00:58:19,660
and monstrous bodies.

752
00:58:21,420 --> 00:58:24,540
We will also see how
we humans finally

753
00:58:24,540 --> 00:58:26,700
arrived on the tree of life

754
00:58:26,700 --> 00:58:30,820
with hugely advanced brains that
would allow us to out-compete

755
00:58:30,820 --> 00:58:33,540
all other species on the planet.

756
00:59:12,860 --> 00:59:15,480
Of all the animals that
live on our planet,

757
00:59:15,480 --> 00:59:18,320
one extraordinary group dominates.

758
00:59:20,160 --> 00:59:22,800
It has produced the largest...

759
00:59:22,800 --> 00:59:24,080
The blue whale!

760
00:59:25,440 --> 00:59:27,480
..the fastest,

761
00:59:27,480 --> 00:59:31,720
the most intelligent creatures
that have ever lived.

762
00:59:31,720 --> 00:59:33,680
They're known as the vertebrates.

763
00:59:35,800 --> 00:59:39,040
And they all share one vital
feature - a backbone.

764
00:59:41,880 --> 00:59:45,600
I'm travelling back in time
to look for the key advances

765
00:59:45,600 --> 00:59:47,680
that drove their remarkable success.

766
00:59:50,240 --> 00:59:54,920
So far, I have seen the vertebrates
grow from tiny origins

767
00:59:54,920 --> 00:59:57,320
to dominate the oceans,

768
00:59:57,320 --> 00:59:58,760
colonise the land...

769
01:00:00,640 --> 01:00:02,480
..and take to the skies.

770
01:00:04,440 --> 01:00:08,080
In this programme, I'm going to
track the rise of a whole new branch

771
01:00:08,080 --> 01:00:10,040
of vertebrate life.

772
01:00:10,040 --> 01:00:13,160
The most complex animals yet
to appear on Earth.

773
01:00:14,240 --> 01:00:17,240
They started as a group
of tiny little creatures

774
01:00:17,240 --> 01:00:19,760
scarcely bigger
than my little finger.

775
01:00:19,760 --> 01:00:21,400
Nocturnal animals.

776
01:00:21,400 --> 01:00:24,960
But they were to develop
into some of the biggest creatures

777
01:00:24,960 --> 01:00:27,320
the planet has ever seen.

778
01:00:27,320 --> 01:00:30,880
It's a group that also contains us.

779
01:00:30,880 --> 01:00:34,200
This is the story of the mammals.

780
01:00:37,120 --> 01:00:41,200
I want to investigate how the
mammals acquired a new set of key

781
01:00:41,200 --> 01:00:46,240
features that allowed them to thrive
in every corner of our planet.

782
01:00:46,240 --> 01:00:50,040
Features we also have inherited.

783
01:00:51,000 --> 01:00:54,720
We'll find the evidence in a series
of thrilling fossil discoveries

784
01:00:54,720 --> 01:00:56,680
and in living animals.

785
01:00:58,520 --> 01:01:01,080
With the latest scientific analysis,

786
01:01:01,080 --> 01:01:04,960
we'll be able to bring our ancient
ancestors back to life.

787
01:01:27,720 --> 01:01:32,600
Today, animals with backbones
dominate our planet

788
01:01:32,600 --> 01:01:36,640
on land, in the air and at sea.

789
01:01:36,640 --> 01:01:42,040
But how did that evolutionary
takeover come about?

790
01:01:42,040 --> 01:01:44,880
There've been
lots of gaps in the story.

791
01:01:44,880 --> 01:01:46,600
But in recent decades,

792
01:01:46,600 --> 01:01:51,080
exciting new discoveries
have been made here in China,

793
01:01:51,080 --> 01:01:53,120
and I'm here to look at them.

794
01:01:56,560 --> 01:02:00,600
The rocks of China are yielding up
the elusive missing links

795
01:02:00,600 --> 01:02:02,080
in the vertebrate story.

796
01:02:04,160 --> 01:02:07,320
Ancient creatures
preserved as fossils.

797
01:02:09,560 --> 01:02:13,240
To find new evidence from the very
start of the mammals' story,

798
01:02:13,240 --> 01:02:16,320
I'm travelling
to the south of China,

799
01:02:16,320 --> 01:02:18,480
and the province of Yunnan.

800
01:02:29,480 --> 01:02:32,720
Fossils found here can reveal
the kind of world

801
01:02:32,720 --> 01:02:36,080
those first mammals encountered,
and the kind of animals

802
01:02:36,080 --> 01:02:40,240
they had to compete with
to gain a foothold and survive.

803
01:02:42,920 --> 01:02:47,520
This area of southern China
is known as the Lufeng Basin,

804
01:02:47,520 --> 01:02:52,320
and 180 million years ago,
it was a vast natural hollow

805
01:02:52,320 --> 01:02:56,280
into which waters from all
the surrounding hills flowed.

806
01:02:56,280 --> 01:03:00,640
And with those streams came
sediment, which is now this,

807
01:03:00,640 --> 01:03:04,440
and they also brought the bodies
of the animals that lived

808
01:03:04,440 --> 01:03:08,040
in those hills,
including creatures like this one -

809
01:03:08,040 --> 01:03:09,560
a dinosaur.

810
01:03:15,560 --> 01:03:20,480
Excavators have uncovered
hundreds of specimens like this one

811
01:03:20,480 --> 01:03:22,240
in the surrounding countryside.

812
01:03:28,000 --> 01:03:31,800
The local museum is crowded
with one of the largest collections

813
01:03:31,800 --> 01:03:34,440
of complete dinosaur skeletons
in the world.

814
01:03:44,680 --> 01:03:47,080
But a unique discovery here

815
01:03:47,080 --> 01:03:49,960
has revealed
some of the earliest evidence

816
01:03:49,960 --> 01:03:53,960
for the origins of the animal group
that would eventually succeed them.

817
01:03:57,160 --> 01:04:00,880
At the same time the dinosaurs
were roaming in this area,

818
01:04:00,880 --> 01:04:05,400
there was another very different
creature evolving in their shadow.

819
01:04:05,400 --> 01:04:08,400
One that was on a much,
much smaller scale.

820
01:04:11,880 --> 01:04:16,320
Palaeontologist Wang Tao has spent
his life exploring these hills.

821
01:04:18,720 --> 01:04:23,200
He's used to finding
the remains of large dinosaurs.

822
01:04:23,200 --> 01:04:26,680
But on this hilltop site,
he and his colleagues discovered

823
01:04:26,680 --> 01:04:30,320
something that didn't match
the usual profile.

824
01:04:32,160 --> 01:04:37,440
TRANSLATION: I came to collect
fossils with my colleagues

825
01:04:37,440 --> 01:04:38,680
in this area here.

826
01:04:40,280 --> 01:04:42,720
At the time, it was not like this.

827
01:04:42,720 --> 01:04:45,480
There were no crops growing here.

828
01:04:45,480 --> 01:04:49,000
After looking around,
we followed this little slope.

829
01:04:49,000 --> 01:04:54,480
And finally we found a small fossil
about two centimetres long.

830
01:04:56,360 --> 01:04:58,920
We thought it might be
something special,

831
01:04:58,920 --> 01:05:02,440
so we sent it to the lab
in Beijing to clean it up.

832
01:05:06,880 --> 01:05:12,200
I have travelled north to Beijing to
see Wang Tao's discovery for myself.

833
01:05:12,200 --> 01:05:16,440
It's now stored in one of
the world's leading institutes

834
01:05:16,440 --> 01:05:18,240
for the study of fossils.

835
01:05:23,720 --> 01:05:25,600
And this is it.

836
01:05:25,600 --> 01:05:30,040
And what seems extraordinary,
near miraculous to me,

837
01:05:30,040 --> 01:05:34,720
is that anybody should notice that
a tiny, tiny little thing like this

838
01:05:34,720 --> 01:05:36,880
is actually a fossil.

839
01:05:36,880 --> 01:05:38,960
But a fossil it is.

840
01:05:38,960 --> 01:05:41,400
It's the head of the tiny animal.

841
01:05:41,400 --> 01:05:43,840
There's the tip of its nose.

842
01:05:43,840 --> 01:05:46,120
That's the back of its neck.

843
01:05:46,120 --> 01:05:50,360
And you can also see
it's got an eye socket.

844
01:05:50,360 --> 01:05:53,440
It's called Hadrocodium.

845
01:05:53,440 --> 01:05:55,600
If I turn it upside down

846
01:05:55,600 --> 01:05:58,280
you can see the bottom of its jaw.

847
01:05:59,680 --> 01:06:05,080
It might be the skull
of a really minute little reptile.

848
01:06:05,080 --> 01:06:06,760
But it's not.

849
01:06:06,760 --> 01:06:12,080
Because reptiles have simple
cone-shaped teeth,

850
01:06:12,080 --> 01:06:15,240
and this one has a tooth
that is rather different.

851
01:06:15,240 --> 01:06:20,120
That has the shape of a little
insect-eating mammal's tooth.

852
01:06:21,440 --> 01:06:26,720
So, this is one of the earliest
mammal fossils we know of.

853
01:06:26,720 --> 01:06:32,560
And to that extent, it's the
ancestor of all mammals alive today,

854
01:06:32,560 --> 01:06:34,240
including ourselves.

855
01:06:37,680 --> 01:06:42,000
As such, Hadrocodium holds a key
position in the evolutionary story

856
01:06:42,000 --> 01:06:44,800
of the backboned animals,
the vertebrates.

857
01:06:46,600 --> 01:06:49,640
The first creature
with the beginnings of a backbone

858
01:06:49,640 --> 01:06:52,720
lived over 500 million years ago.

859
01:06:53,960 --> 01:06:55,800
Then fish,

860
01:06:55,800 --> 01:06:57,080
amphibians

861
01:06:57,080 --> 01:06:59,000
and reptiles evolved.

862
01:07:00,560 --> 01:07:04,640
It's from the reptile line
that the first mammals emerge.

863
01:07:06,280 --> 01:07:11,600
The Hadrocodium fossil dates
to 195 million years ago.

864
01:07:13,160 --> 01:07:16,960
These simple origins led to
the vast diversity of mammals

865
01:07:16,960 --> 01:07:18,640
we see around us today.

866
01:07:20,920 --> 01:07:25,400
Over 5,700 living species
have adapted to survive

867
01:07:25,400 --> 01:07:27,360
in every corner of the planet.

868
01:07:30,280 --> 01:07:34,960
We humans dominate and are the most
numerous of the large mammals.

869
01:07:39,160 --> 01:07:42,440
This astonishing journey
was built on a series

870
01:07:42,440 --> 01:07:47,080
of key evolutionary advances
that began in very early forms

871
01:07:47,080 --> 01:07:48,560
like Hadrocodium.

872
01:07:54,080 --> 01:07:58,120
We only have its skull, but we can
work out from modern mammals

873
01:07:58,120 --> 01:08:00,360
what the rest of its skeleton
was like.

874
01:08:19,000 --> 01:08:22,880
So, how did this minute animal
gain a foothold

875
01:08:22,880 --> 01:08:24,520
in the age of the dinosaurs?

876
01:08:33,440 --> 01:08:36,520
Kunming city in southern China.

877
01:08:38,560 --> 01:08:40,760
I've come to this late-night market

878
01:08:40,760 --> 01:08:45,440
to observe one of the first crucial
steps in the mammals' story.

879
01:08:48,240 --> 01:08:51,160
The development
of an amazing feature

880
01:08:51,160 --> 01:08:53,960
that gave them a key advantage.

881
01:08:53,960 --> 01:08:55,600
But only after dark.

882
01:08:59,840 --> 01:09:02,520
The mammals found a niche
for themselves

883
01:09:02,520 --> 01:09:05,360
not so much in space
as in time - at night,

884
01:09:05,360 --> 01:09:08,800
when the reptiles are not active.

885
01:09:09,760 --> 01:09:11,640
A simple experiment with two pets

886
01:09:11,640 --> 01:09:14,080
that happened to be for sale
in the market tonight

887
01:09:14,080 --> 01:09:16,320
can demonstrate why this is so.

888
01:09:17,960 --> 01:09:20,280
This is a thermal camera,

889
01:09:20,280 --> 01:09:25,680
and it will show a cold body
as a black or very dark.

890
01:09:25,680 --> 01:09:29,360
So, this lizard which is on the
table is cold-blooded,

891
01:09:29,360 --> 01:09:33,400
and it appears to be very much
the same temperature as the table.

892
01:09:34,520 --> 01:09:40,360
Reptiles get much of their energy
directly from the sun as warmth.

893
01:09:40,360 --> 01:09:43,000
But there is no sun at night.

894
01:09:43,000 --> 01:09:46,360
As a consequence, it's scarcely got
the energy to move.

895
01:09:46,360 --> 01:09:48,920
This puppy, on the other hand,

896
01:09:48,920 --> 01:09:51,120
is very active.

897
01:09:51,120 --> 01:09:53,720
And when you look at him
with the camera,

898
01:09:53,720 --> 01:09:57,880
you can see that
his body is very warm indeed.

899
01:09:57,880 --> 01:09:59,480
And you mustn't eat the lizard!

900
01:10:01,800 --> 01:10:04,960
The mammals, very early
in their history, developed

901
01:10:04,960 --> 01:10:10,040
the remarkable ability to generate
heat within their bodies.

902
01:10:10,040 --> 01:10:12,000
They became warm-blooded,

903
01:10:12,000 --> 01:10:15,320
and they achieved this
by driving their metabolism

904
01:10:15,320 --> 01:10:17,480
at a much higher rate.

905
01:10:17,480 --> 01:10:21,920
But to do that, you need extra fuel,
extra food.

906
01:10:23,760 --> 01:10:28,440
A reptile like a lizard can go
for many days without eating.

907
01:10:28,440 --> 01:10:33,520
But if a mammal is denied its food
for several days, it will die.

908
01:10:33,520 --> 01:10:36,680
So, in order to keep
their fuel bills down,

909
01:10:36,680 --> 01:10:41,080
the mammals used a technique
familiar to any householder -

910
01:10:41,080 --> 01:10:42,920
insulation.

911
01:10:42,920 --> 01:10:45,960
They coated their bodies,
as this puppy has,

912
01:10:45,960 --> 01:10:47,520
with fur.

913
01:10:53,640 --> 01:10:56,240
With warm blood
and a covering of hair,

914
01:10:56,240 --> 01:11:00,640
Hadrocodium was free to hunt for
insects in the cool of the night.

915
01:11:03,160 --> 01:11:05,600
But now came a new challenge -

916
01:11:05,600 --> 01:11:08,840
to find its way around
in pitch darkness.

917
01:11:15,560 --> 01:11:19,800
Detailed analysis of Hadrocodium's
skull is revealing remarkable

918
01:11:19,800 --> 01:11:23,880
new evidence of a set of ingenious
solutions to this problem.

919
01:11:25,080 --> 01:11:29,400
The clues are tiny and invisible
to outside scrutiny.

920
01:11:31,600 --> 01:11:35,680
But professor Zhe-Xi Luo,
an expert on early mammals,

921
01:11:35,680 --> 01:11:40,520
is using a micro CT scanner to
unlock the skull's inner secrets.

922
01:11:41,760 --> 01:11:44,600
X-rays penetrate the rock

923
01:11:44,600 --> 01:11:47,240
and pick out
detailed fossil structures within.

924
01:11:48,440 --> 01:11:52,520
A computer then builds
a 3D model of the bones,

925
01:11:52,520 --> 01:11:55,840
and, in particular, the cavity
that once held the brain.

926
01:11:59,560 --> 01:12:02,880
Professor Luo is able to identify
an area that is clearly

927
01:12:02,880 --> 01:12:05,920
much larger than its equivalent
in a reptile.

928
01:12:07,400 --> 01:12:11,040
If you look at the CT scan here,

929
01:12:11,040 --> 01:12:16,400
you can tell that, despite a tiny
little skull, the brain is enormous.

930
01:12:18,120 --> 01:12:22,480
But one of the most striking features
of this particular fossil

931
01:12:22,480 --> 01:12:27,240
is that it has very large
olfactory bulbs.

932
01:12:28,480 --> 01:12:31,120
When you say olfactory bulbs,

933
01:12:31,120 --> 01:12:34,880
those are the part of the brain
that detects smell. Correct.

934
01:12:34,880 --> 01:12:41,480
This mammal must have had
very refined sensory detection

935
01:12:41,480 --> 01:12:47,120
of all kinds of smell, allowing it to
be active in the dark of the night.

936
01:12:50,040 --> 01:12:55,480
This powerful sense of smell would
have helped Hadrocodium pick out

937
01:12:55,480 --> 01:12:58,320
the scent of the worms
and insects it fed on.

938
01:13:01,800 --> 01:13:06,240
The scanners have also revealed
a radical advance in a second sense

939
01:13:06,240 --> 01:13:07,920
that's vital in the dark.

940
01:13:07,920 --> 01:13:09,480
Hearing.

941
01:13:10,560 --> 01:13:15,800
The tell-tale clue lies,
surprisingly, in Hadrocodium's jaw.

942
01:13:15,800 --> 01:13:18,280
One very interesting feature

943
01:13:18,280 --> 01:13:22,080
that's so unique about
this fossil mammal is...

944
01:13:22,080 --> 01:13:25,960
very flat jaw.

945
01:13:25,960 --> 01:13:31,240
The surface on the inside of the jaw
is perfectly flat.

946
01:13:31,240 --> 01:13:34,080
In the primitive,

947
01:13:34,080 --> 01:13:38,120
pre-mammalian forms,
there are big grooves.

948
01:13:41,000 --> 01:13:45,160
Grooves like these indicate
the presence of two key bones

949
01:13:45,160 --> 01:13:47,880
that are attached
to the jaw of a reptile.

950
01:13:49,320 --> 01:13:52,240
Seen here in green and red.

951
01:13:52,240 --> 01:13:56,640
A third bone, coloured blue,
transmits sound waves in its ear.

952
01:13:58,040 --> 01:14:02,880
In a mammal there has been a truly
amazing evolutionary development.

953
01:14:02,880 --> 01:14:06,800
The two jawbones have shifted
to form, with the third...

954
01:14:08,200 --> 01:14:09,440
..the middle ear.

955
01:14:11,440 --> 01:14:13,480
This three-bone arrangement

956
01:14:13,480 --> 01:14:15,960
opens up a range
of higher-pitched frequencies

957
01:14:15,960 --> 01:14:17,960
that a reptile cannot hear.

958
01:14:21,840 --> 01:14:26,040
It's the system
we have inherited inside our ears.

959
01:14:27,120 --> 01:14:33,600
So, in Hadrocodium,
we get the earliest indication

960
01:14:33,600 --> 01:14:39,080
that the three ear bones
so important for our hearing

961
01:14:39,080 --> 01:14:42,520
have already originated
with this fossil.

962
01:14:47,000 --> 01:14:52,080
Now ears could pick up the faintest
rustle in the undergrowth

963
01:14:52,080 --> 01:14:56,120
and guide Hadrocodium
to any insects moving nearby.

964
01:14:59,000 --> 01:15:02,400
Professor Luo's analysis
has also identified

965
01:15:02,400 --> 01:15:06,480
a spectacular advance
in a third key sense.

966
01:15:06,480 --> 01:15:10,040
It also has very large areas

967
01:15:10,040 --> 01:15:12,840
responsible for skin touch.

968
01:15:12,840 --> 01:15:16,280
For touch? That's right.
Mammals have hairs.

969
01:15:16,280 --> 01:15:19,760
One of the most important functions
of the hair is actually

970
01:15:19,760 --> 01:15:22,000
to give us the sensory touch,

971
01:15:22,000 --> 01:15:25,560
and this animal has
already developed that.

972
01:15:28,560 --> 01:15:33,320
The use of hairs as touch sensors
is perhaps most obvious from the way

973
01:15:33,320 --> 01:15:35,360
modern mammals use their whiskers.

974
01:15:37,440 --> 01:15:41,640
This brown rat relies on them
for finding its way around at night,

975
01:15:41,640 --> 01:15:43,040
or underground.

976
01:15:44,680 --> 01:15:48,560
At the base of each of those
long hairs on its nose,

977
01:15:48,560 --> 01:15:50,440
there is a nerve receptor.

978
01:15:51,600 --> 01:15:53,640
And whenever the hair is touched,

979
01:15:53,640 --> 01:15:56,680
a message is sent
up to the rat's brain.

980
01:15:58,480 --> 01:16:00,400
It's not just the whiskers, though.

981
01:16:00,400 --> 01:16:04,520
Hairs all over its body are wired up
to its nervous system.

982
01:16:05,800 --> 01:16:08,080
This creates a sensory bubble,

983
01:16:08,080 --> 01:16:12,680
allowing the rat to map the world
around it just by using its hairs.

984
01:16:16,360 --> 01:16:18,680
195 million years ago,

985
01:16:18,680 --> 01:16:22,400
the hairs on Hadrocodium must have
been wired up in the same way.

986
01:16:29,400 --> 01:16:33,040
This remarkable little creature
now had a whole array

987
01:16:33,040 --> 01:16:37,280
of new powers with which to meet
the challenges of the night.

988
01:16:46,040 --> 01:16:49,080
A heightening of the senses
powered by a growing brain

989
01:16:49,080 --> 01:16:52,200
had enabled the early mammals
to survive in the shadow

990
01:16:52,200 --> 01:16:57,000
of the dinosaurs. And then, they
also developed a radical new way

991
01:16:57,000 --> 01:16:59,040
of nourishing their young.

992
01:17:02,720 --> 01:17:05,720
We can look for clues
to this next crucial step

993
01:17:05,720 --> 01:17:09,200
in our evolutionary story
in Australia.

994
01:17:09,200 --> 01:17:10,600
Not in fossils,

995
01:17:10,600 --> 01:17:14,280
but in the bodies of two highly
unusual creatures that live here.

996
01:17:23,480 --> 01:17:26,080
The first is the platypus,

997
01:17:26,080 --> 01:17:29,680
which uses its rubbery beak
like a radar transmitter

998
01:17:29,680 --> 01:17:32,360
to hunt for shrimp
or molluscs underwater.

999
01:17:36,400 --> 01:17:39,040
And the second is the echidna,

1000
01:17:39,040 --> 01:17:42,080
which forages
for ants and termites on land.

1001
01:17:44,160 --> 01:17:47,600
The platypus and echidna
are the only two survivors

1002
01:17:47,600 --> 01:17:50,440
of a group of mammals
called the "monotremes".

1003
01:17:55,280 --> 01:17:57,520
Trace their genetic line back,

1004
01:17:57,520 --> 01:17:59,920
and we discover
they split from all other mammals

1005
01:17:59,920 --> 01:18:02,240
around 200 million years ago.

1006
01:18:05,160 --> 01:18:08,400
Because they retain traits
from that distant time,

1007
01:18:08,400 --> 01:18:11,760
they give us a remarkable insight
into very early mammals

1008
01:18:11,760 --> 01:18:13,280
like Hadrocodium.

1009
01:18:18,920 --> 01:18:22,520
The most extraordinary feature
of all is one that no other

1010
01:18:22,520 --> 01:18:24,360
modern mammal has retained.

1011
01:18:27,200 --> 01:18:28,720
They lay eggs.

1012
01:18:30,200 --> 01:18:32,840
This echidna egg is tiny,

1013
01:18:32,840 --> 01:18:35,120
only about the size of a marble.

1014
01:18:36,200 --> 01:18:40,400
The hatching process itself has only
rarely been captured on film.

1015
01:18:50,360 --> 01:18:53,920
These are newly-hatched
platypus young,

1016
01:18:53,920 --> 01:18:56,040
filmed in their mother's burrow.

1017
01:18:58,080 --> 01:19:00,680
They're only about the size
of jelly beans.

1018
01:19:02,360 --> 01:19:05,360
The early mammals must have
laid eggs in the same way,

1019
01:19:05,360 --> 01:19:08,880
and they inherited this trait
from their reptile ancestors.

1020
01:19:13,720 --> 01:19:17,200
This is a view inside a reptile egg.

1021
01:19:17,200 --> 01:19:21,400
The embryo feeds on a supply
of highly nutritious yolk.

1022
01:19:25,080 --> 01:19:27,240
By the time reptiles hatch,

1023
01:19:27,240 --> 01:19:30,760
they're sufficiently well-developed
to go looking for their own food.

1024
01:19:34,240 --> 01:19:37,480
But the platypus and echidna
are very different.

1025
01:19:37,480 --> 01:19:41,000
Their smaller eggs contain
only a small amount of yolk,

1026
01:19:41,000 --> 01:19:44,360
so their young hatch
in a far less-developed state.

1027
01:19:45,680 --> 01:19:49,480
They need a lot more nourishment if
they're going to grow and survive.

1028
01:19:53,160 --> 01:19:55,960
But at Healesville Sanctuary
near Melbourne,

1029
01:19:55,960 --> 01:19:59,760
we can find delightful evidence
that platypus young do develop

1030
01:19:59,760 --> 01:20:03,520
with great success without having
to leave their mother's burrow.

1031
01:20:06,200 --> 01:20:08,360
Four months after it hatched,

1032
01:20:08,360 --> 01:20:11,280
a youngster is emerging
for the first time.

1033
01:20:13,840 --> 01:20:18,080
It has grown from a tiny hatchling
to near adult size.

1034
01:20:20,520 --> 01:20:23,800
And that is thanks to an amazing
form of nourishment

1035
01:20:23,800 --> 01:20:27,040
that is a defining feature
of all mammals.

1036
01:20:28,640 --> 01:20:29,800
Milk.

1037
01:20:31,120 --> 01:20:35,800
This rich mixture of proteins,
fats, carbohydrates and minerals

1038
01:20:35,800 --> 01:20:39,000
oozes from the bellies
of female platypus and echidna

1039
01:20:39,000 --> 01:20:40,560
rather like sweat,

1040
01:20:40,560 --> 01:20:44,080
and provides their young
with everything they need to grow.

1041
01:20:46,960 --> 01:20:50,000
It's likely that early mammals
like Hadrocodium

1042
01:20:50,000 --> 01:20:52,440
nourished their young
in the same way.

1043
01:20:52,440 --> 01:20:55,720
First with a reduced amount of yolk,
and then with milk.

1044
01:20:57,720 --> 01:21:01,760
So, what could explain
this hugely significant step?

1045
01:21:05,720 --> 01:21:09,040
New genetic analysis
is providing the answer.

1046
01:21:10,520 --> 01:21:14,160
Dr Henrik Kaessmann has been using
the platypus to investigate

1047
01:21:14,160 --> 01:21:16,600
the DNA of the early mammals.

1048
01:21:17,840 --> 01:21:20,880
The platypus is really
an amazing creature.

1049
01:21:20,880 --> 01:21:25,280
It's really this crossover
of a mammal and a reptile, right.

1050
01:21:26,520 --> 01:21:30,720
And so it has a key position
in the evolutionary analysis

1051
01:21:30,720 --> 01:21:31,960
of all mammals.

1052
01:21:33,360 --> 01:21:36,480
First, he looked
at the reduction in egg yolk.

1053
01:21:38,160 --> 01:21:41,200
Reptiles have at least
three genes that together

1054
01:21:41,200 --> 01:21:43,200
manufacture their large yolk.

1055
01:21:44,400 --> 01:21:47,480
Dr Kaessmann has found that
the platypus DNA

1056
01:21:47,480 --> 01:21:51,840
records a dramatic change
taking place in the early mammals.

1057
01:21:51,840 --> 01:21:55,960
We found only one egg yolk gene
in the platypus genome

1058
01:21:55,960 --> 01:22:00,680
that really was functional and
was producing the egg yolk protein.

1059
01:22:00,680 --> 01:22:04,960
Presumably the fact that
there was only one gene

1060
01:22:04,960 --> 01:22:07,160
which was producing yolk
accounts for the fact

1061
01:22:07,160 --> 01:22:09,080
that the platypus egg is so small?

1062
01:22:09,080 --> 01:22:11,040
Exactly.

1063
01:22:11,040 --> 01:22:15,720
The early mammals must have started
to switch off their yolk genes.

1064
01:22:15,720 --> 01:22:19,360
And Dr Kaessmann has made
a second key discovery.

1065
01:22:20,560 --> 01:22:24,440
The trigger for this shutdown
was the arrival of the genes

1066
01:22:24,440 --> 01:22:26,880
that produce milk.

1067
01:22:26,880 --> 01:22:29,520
So, you have the milk genes
appearing that then allow

1068
01:22:29,520 --> 01:22:32,560
for the subsequent loss
of the egg yolk genes.

1069
01:22:34,000 --> 01:22:37,440
The mammals began to favour milk
over egg yolk as a way

1070
01:22:37,440 --> 01:22:38,840
to nourish their young.

1071
01:22:40,280 --> 01:22:43,440
And that is because milk has
one key advantage.

1072
01:22:44,880 --> 01:22:49,640
It's on tap, and that means that
none of it need go to waste.

1073
01:22:49,640 --> 01:22:51,400
And there's no limit on how much

1074
01:22:51,400 --> 01:22:54,400
and for how long
a mother can feed her young.

1075
01:22:59,320 --> 01:23:01,720
Warm bodies, powerful senses,

1076
01:23:01,720 --> 01:23:05,680
and now, milk, had allowed
the early mammals like Hadrocodium

1077
01:23:05,680 --> 01:23:09,120
to gain a foothold
while the reptiles still ruled.

1078
01:23:13,040 --> 01:23:16,240
But combining egg-laying
with milk-feeding

1079
01:23:16,240 --> 01:23:18,480
brought a new challenge.

1080
01:23:18,480 --> 01:23:22,400
A mammal mother could not leave
the eggs to hatch by themselves

1081
01:23:22,400 --> 01:23:24,960
as most reptiles do today.

1082
01:23:24,960 --> 01:23:26,320
She had to stay with them.

1083
01:23:31,400 --> 01:23:33,920
Then came a truly
astonishing solution.

1084
01:23:36,600 --> 01:23:38,760
The egg, instead of being laid,

1085
01:23:38,760 --> 01:23:44,040
was retained inside the body
and started its development there,

1086
01:23:44,040 --> 01:23:47,120
so that the young was born alive.

1087
01:23:50,960 --> 01:23:52,560
Apart from the monotremes,

1088
01:23:52,560 --> 01:23:56,040
there are two other major groups
of modern mammals around today.

1089
01:23:57,000 --> 01:24:00,320
Marsupials and placentals.

1090
01:24:00,320 --> 01:24:02,560
It's thought that
they first appeared

1091
01:24:02,560 --> 01:24:05,200
around 160 million years ago.

1092
01:24:06,560 --> 01:24:09,480
Both give birth to live young.

1093
01:24:09,480 --> 01:24:12,480
But they do so
in two very different ways.

1094
01:24:15,920 --> 01:24:20,360
Spectacular fossil beds in the north
of China have, in recent years,

1095
01:24:20,360 --> 01:24:24,480
produced the earliest ancestors yet
found of these two groups.

1096
01:24:28,440 --> 01:24:31,160
This is Liaoning province.

1097
01:24:34,640 --> 01:24:37,280
125 million years ago,

1098
01:24:37,280 --> 01:24:40,280
volcanoes were erupting
in this region.

1099
01:24:45,480 --> 01:24:50,080
They left layer upon layer
of yellow ash in these rocks.

1100
01:24:56,520 --> 01:25:00,520
Excavations have revealed
the fossilised remains of animals

1101
01:25:00,520 --> 01:25:04,280
trapped in these layers and
preserved in extraordinary detail.

1102
01:25:05,800 --> 01:25:09,560
This is a fossil
that's been called Sinodelphys.

1103
01:25:10,600 --> 01:25:14,280
Its skeleton is very easily seen.

1104
01:25:14,280 --> 01:25:18,120
But around its skeleton
there are dark marks,

1105
01:25:18,120 --> 01:25:21,960
and close examination shows
that they are fur.

1106
01:25:21,960 --> 01:25:26,800
So, we can be pretty sure that
this is the fossil of a mammal.

1107
01:25:26,800 --> 01:25:30,080
But its skeleton,
and in particular, its teeth,

1108
01:25:30,080 --> 01:25:33,560
make it clear that
it was a marsupial.

1109
01:25:37,160 --> 01:25:41,000
Marsupials were once distributed
throughout the globe.

1110
01:25:42,280 --> 01:25:45,120
But most are found today
in Australia.

1111
01:25:46,360 --> 01:25:47,960
And they allow us to see

1112
01:25:47,960 --> 01:25:52,560
how their ancestors began to bring
their young into the world alive.

1113
01:25:57,160 --> 01:26:01,040
This is a sanctuary for breeding
endangered species of wallaby

1114
01:26:01,040 --> 01:26:03,280
through the use of foster mothers.

1115
01:26:08,680 --> 01:26:10,520
Running the conservation project

1116
01:26:10,520 --> 01:26:14,040
is Dr David Taggart
of the University of Adelaide.

1117
01:26:17,640 --> 01:26:21,680
Today, he and his team
are conducting a health check

1118
01:26:21,680 --> 01:26:24,720
on a newly arrived baby wallaby,
known as a "joey".

1119
01:26:28,240 --> 01:26:33,680
This joey looks like it's about
two grams, so about 16 days old.

1120
01:26:33,680 --> 01:26:36,720
So, 16 days ago,
this young would have been born.

1121
01:26:36,720 --> 01:26:39,360
All marsupial young are born
very immature,

1122
01:26:39,360 --> 01:26:42,400
so its ears are folded
and the eyes are closed.

1123
01:26:43,840 --> 01:26:47,080
Instead of being enclosed in an egg
when leaving its mother

1124
01:26:47,080 --> 01:26:50,200
like a baby echidna,
this joey emerged

1125
01:26:50,200 --> 01:26:54,800
directly from its mother's birth
canal just 30 days after conception.

1126
01:26:55,840 --> 01:26:58,040
Its front legs are more developed

1127
01:26:58,040 --> 01:27:01,480
and strong enough for it
to pull itself up through the fur

1128
01:27:01,480 --> 01:27:05,960
and wriggle inside a feature that
is unique to marsupials - a pouch.

1129
01:27:13,560 --> 01:27:17,240
Here, there's a highly developed
milk delivery system.

1130
01:27:20,440 --> 01:27:24,200
The milk is channelled through
long, fleshy tubes, teats.

1131
01:27:27,680 --> 01:27:29,720
A wallaby mother has four of them,

1132
01:27:29,720 --> 01:27:33,200
and can even feed young of different
ages at the same time.

1133
01:27:36,480 --> 01:27:39,160
She might have a young,
just newly born,

1134
01:27:39,160 --> 01:27:41,600
attached to one teat,
and she'll have a young

1135
01:27:41,600 --> 01:27:44,160
with its head in the pouch
feeding from another teat.

1136
01:27:44,160 --> 01:27:46,840
And those two teats
will be producing a milk

1137
01:27:46,840 --> 01:27:51,040
that is of different consistency.

1138
01:27:51,040 --> 01:27:54,120
So, one will be to nourish
a new-born young

1139
01:27:54,120 --> 01:27:57,400
and the other's to nourish a young
that's almost ready to wean.

1140
01:27:57,400 --> 01:27:58,800
It's a great system.

1141
01:28:00,800 --> 01:28:03,680
The long teats also give
the young a way to cling

1142
01:28:03,680 --> 01:28:05,680
onto their mother
as she moves around.

1143
01:28:10,320 --> 01:28:14,200
This opossum is a marsupial that
lives in South America

1144
01:28:14,200 --> 01:28:15,960
and it has no pouch.

1145
01:28:17,480 --> 01:28:20,520
Its young seal their mouths
so tightly round the teats,

1146
01:28:20,520 --> 01:28:23,360
they stay firmly attached.

1147
01:28:23,360 --> 01:28:27,560
This may well be how the early
marsupials, like Sinodelphys,

1148
01:28:27,560 --> 01:28:29,200
carried their young around.

1149
01:28:31,320 --> 01:28:34,120
They were now no longer tied
to a nest or a burrow

1150
01:28:34,120 --> 01:28:35,520
like the egg-laying mammals.

1151
01:28:37,240 --> 01:28:40,000
But this method had
one obvious drawback.

1152
01:28:41,040 --> 01:28:43,000
Outside their mother's body,

1153
01:28:43,000 --> 01:28:48,200
the newborn young were vulnerable
to accident and exposed to disease.

1154
01:28:54,680 --> 01:28:58,280
In China, new evidence
is emerging for the pioneers

1155
01:28:58,280 --> 01:29:00,720
of an even more radical solution.

1156
01:29:02,160 --> 01:29:06,200
At the same time
as the marsupials appeared,

1157
01:29:06,200 --> 01:29:10,480
another branch developed
on the family tree of the mammals,

1158
01:29:10,480 --> 01:29:13,120
a branch that we belong to.

1159
01:29:13,120 --> 01:29:18,280
And it had way of nurturing
their young before birth.

1160
01:29:24,920 --> 01:29:29,000
I'm travelling to Beijing
and its museum of natural history,

1161
01:29:29,000 --> 01:29:32,440
to see remarkably early evidence
for this group.

1162
01:29:40,760 --> 01:29:42,240
This is it.

1163
01:29:45,280 --> 01:29:47,840
It's been called Juramaia,

1164
01:29:47,840 --> 01:29:50,920
which means "Jurassic mother".

1165
01:29:52,040 --> 01:29:55,200
Its bones,
and in particular, its teeth,

1166
01:29:55,200 --> 01:29:59,040
identify it as a member of the
mammal group to which we belong.

1167
01:30:00,280 --> 01:30:03,480
But the key thing
about it is its date.

1168
01:30:03,480 --> 01:30:07,560
It's Jurassic -
160 million years old.

1169
01:30:08,680 --> 01:30:12,760
And this makes Juramaia
the earliest creature we know of

1170
01:30:12,760 --> 01:30:16,480
that could have nurtured its young
in a revolutionary new way.

1171
01:30:22,920 --> 01:30:27,840
Juramaia lived and hunted in a world
still dominated by the dinosaurs.

1172
01:30:33,960 --> 01:30:36,880
But it may have had
a powerful advantage -

1173
01:30:36,880 --> 01:30:39,880
the ability for a mother
to carry her young,

1174
01:30:39,880 --> 01:30:42,480
not outside her body
like the marsupials...

1175
01:30:44,520 --> 01:30:46,920
..but inside, in a womb.

1176
01:30:51,360 --> 01:30:55,120
To understand how Juramaia could
have achieved this, we can look at

1177
01:30:55,120 --> 01:30:58,560
one of its living descendants, the
one that carries its young inside

1178
01:30:58,560 --> 01:31:02,120
for the longest period
of all mammals, the elephant.

1179
01:31:03,840 --> 01:31:05,840
This is Dokkoon.

1180
01:31:07,000 --> 01:31:10,520
She is part of a breeding programme
at Melbourne Zoo in Australia,

1181
01:31:10,520 --> 01:31:11,960
and she is pregnant.

1182
01:31:13,800 --> 01:31:17,440
Dr Thomas Hildebrandt,
one of the world's leading experts

1183
01:31:17,440 --> 01:31:21,680
in mammal birth, is monitoring
progress with an ultrasound scanner.

1184
01:31:22,960 --> 01:31:26,520
We study the longest pregnancy
on the planet,

1185
01:31:26,520 --> 01:31:29,080
which the elephant
has with 22 months.

1186
01:31:29,080 --> 01:31:30,840
And so ultrasound allows us

1187
01:31:30,840 --> 01:31:33,440
non-invasively to see
all the differences

1188
01:31:33,440 --> 01:31:35,520
during the foetal development,

1189
01:31:35,520 --> 01:31:39,160
which is quite exciting
and was never done before.

1190
01:31:41,800 --> 01:31:44,640
More detailed 3D scans give us

1191
01:31:44,640 --> 01:31:48,160
a spectacular view inside her womb.

1192
01:31:48,160 --> 01:31:50,480
Even at an early stage
of development,

1193
01:31:50,480 --> 01:31:52,800
the baby's trunk is visible
and moving.

1194
01:31:54,400 --> 01:31:58,320
But we can also see the presence
of a remarkable organ

1195
01:31:58,320 --> 01:32:03,160
that evolved to make it possible to
feed a developing baby before birth.

1196
01:32:04,680 --> 01:32:05,960
The placenta.

1197
01:32:10,800 --> 01:32:14,520
This baby elephant was born
in the zoo just three weeks ago

1198
01:32:14,520 --> 01:32:18,160
and its placenta has been saved
for analysis.

1199
01:32:23,840 --> 01:32:27,400
Here we have the elephant placenta
of the baby which is running

1200
01:32:27,400 --> 01:32:29,080
outside the yard.

1201
01:32:29,080 --> 01:32:32,080
These blood vessels form
the umbilical cord,

1202
01:32:32,080 --> 01:32:35,320
allowing to move all
the nutrients to the baby

1203
01:32:35,320 --> 01:32:37,680
and take all the waste material away.

1204
01:32:39,280 --> 01:32:42,960
On the underside is a ring
of sponge-like tissue

1205
01:32:42,960 --> 01:32:46,000
that attaches to the lining
of the mother's womb

1206
01:32:46,000 --> 01:32:50,240
and allows nutriment
to flow in and waste to flow out.

1207
01:32:52,520 --> 01:32:55,760
But it also operates
as a life-saving barrier.

1208
01:32:56,880 --> 01:33:00,200
Because half of the unborn baby's
genes are from its father,

1209
01:33:00,200 --> 01:33:04,240
it was under threat in the womb
from its mother's immune system.

1210
01:33:04,240 --> 01:33:09,000
The baby is foreign materials
and alien to the mother,

1211
01:33:09,000 --> 01:33:15,240
and would be rejected if there's not
this very specific system engaged

1212
01:33:15,240 --> 01:33:19,200
which protects the baby against
the maternal immune system.

1213
01:33:20,520 --> 01:33:23,760
Because the tissues of the placenta
are composed of cells

1214
01:33:23,760 --> 01:33:28,080
from both mother and baby, and
the two blood supplies never mix,

1215
01:33:28,080 --> 01:33:30,280
the baby is protected.

1216
01:33:31,440 --> 01:33:34,520
This allows it
to remain inside the womb

1217
01:33:34,520 --> 01:33:37,120
until it's ready to survive
in the outside world.

1218
01:33:39,160 --> 01:33:42,960
Mammals equipped with this miracle
of evolutionary engineering

1219
01:33:42,960 --> 01:33:45,080
are known as "placentals".

1220
01:33:48,520 --> 01:33:52,600
It's likely that their earliest
ancestors, like Juramaia,

1221
01:33:52,600 --> 01:33:55,520
were the first to rear their young
inside their bodies

1222
01:33:55,520 --> 01:33:58,080
160 million years ago.

1223
01:34:00,880 --> 01:34:04,560
By now, the mammals had acquired
all the key characteristics

1224
01:34:04,560 --> 01:34:06,520
that define them as a group.

1225
01:34:06,520 --> 01:34:08,040
Hairy bodies,

1226
01:34:08,040 --> 01:34:09,880
milk

1227
01:34:09,880 --> 01:34:11,720
and live birth.

1228
01:34:11,720 --> 01:34:14,840
And this combination would
eventually provide them

1229
01:34:14,840 --> 01:34:19,040
with the platform for an astonishing
explosion in diversity.

1230
01:34:21,120 --> 01:34:24,480
For millions of years,
they remained the small,

1231
01:34:24,480 --> 01:34:27,320
shrew-like creatures
that we've encountered so far,

1232
01:34:27,320 --> 01:34:30,960
skittering about
around the feet of the dinosaurs.

1233
01:34:30,960 --> 01:34:34,240
But then came
a sudden global catastrophe

1234
01:34:34,240 --> 01:34:37,320
that threatened to bring
the whole history of the vertebrates

1235
01:34:37,320 --> 01:34:38,920
to a sudden end.

1236
01:34:46,040 --> 01:34:50,320
A meteor impact that sent
shock waves around the world,

1237
01:34:50,320 --> 01:34:53,920
and coincided with
the extinction of the dinosaurs.

1238
01:34:55,600 --> 01:34:59,640
We're still not exactly sure
WHY the dinosaurs disappeared,

1239
01:34:59,640 --> 01:35:03,200
but certainly 65 million years ago,

1240
01:35:03,200 --> 01:35:05,560
they disappear
from the fossil record.

1241
01:35:06,800 --> 01:35:09,800
But many other vertebrates survived,

1242
01:35:09,800 --> 01:35:13,880
and for them, the dominance
of the world was now up for grabs.

1243
01:35:17,320 --> 01:35:21,240
Scientists are unearthing
stunning evidence in Germany

1244
01:35:21,240 --> 01:35:24,040
for how the mammals seized
this opportunity.

1245
01:35:26,360 --> 01:35:30,440
This natural hollow
is known as the Messel Pit.

1246
01:35:32,360 --> 01:35:35,800
An entire community of animals
was entombed here

1247
01:35:35,800 --> 01:35:38,040
by an extraordinary freak of nature.

1248
01:35:40,360 --> 01:35:42,280
47 million years ago,

1249
01:35:42,280 --> 01:35:46,160
this was a lake fringed
by a subtropical rainforest.

1250
01:35:46,160 --> 01:35:48,560
But its waters held a dark secret.

1251
01:35:50,280 --> 01:35:53,680
The lake was in fact
a flooded volcanic crater.

1252
01:35:55,520 --> 01:35:58,960
It's thought that
lethal carbon dioxide gas

1253
01:35:58,960 --> 01:36:03,640
released from its depths
periodically bubbled to the surface,

1254
01:36:03,640 --> 01:36:07,680
killing the creatures that drank at
its shore or flew over its waters.

1255
01:36:10,360 --> 01:36:12,560
Their bodies drifted down
to the bottom

1256
01:36:12,560 --> 01:36:15,000
to be entombed
in the muddy sediment.

1257
01:36:19,520 --> 01:36:21,920
It's now one of the most remarkable

1258
01:36:21,920 --> 01:36:24,400
fossil excavation sites
in the world.

1259
01:36:30,880 --> 01:36:35,120
Painstaking work is uncovering
creatures sealed inside layers

1260
01:36:35,120 --> 01:36:36,920
of the ancient lake bed.

1261
01:36:40,440 --> 01:36:43,320
They're preserved
in extraordinary detail.

1262
01:36:51,720 --> 01:36:55,520
It's a unique snapshot of life
after the dinosaurs.

1263
01:36:57,880 --> 01:37:00,320
There are reptiles,
like lizards and snakes.

1264
01:37:04,000 --> 01:37:06,200
Here, too, are ancient birds,

1265
01:37:06,200 --> 01:37:09,240
the vertebrate group that evolved
from the dinosaurs.

1266
01:37:11,080 --> 01:37:14,720
But the biggest changes
are amongst the mammals.

1267
01:37:14,720 --> 01:37:16,960
They have started to specialise.

1268
01:37:18,920 --> 01:37:22,840
This, perhaps, is the least
specialised of them.

1269
01:37:22,840 --> 01:37:27,040
It's an insect-eater,
a creature like a large shrew,

1270
01:37:27,040 --> 01:37:30,240
and its teeth are still
relatively simple.

1271
01:37:31,400 --> 01:37:34,440
But then there are also animals
like this.

1272
01:37:38,280 --> 01:37:42,800
And this has very big,
gnawing front teeth.

1273
01:37:44,400 --> 01:37:48,160
This is an early rodent,
a creature like a rat.

1274
01:37:48,160 --> 01:37:49,960
And then bigger still...

1275
01:37:52,520 --> 01:37:53,920
..is this animal.

1276
01:37:56,000 --> 01:38:00,240
This has grinding molar teeth
at the back,

1277
01:38:00,240 --> 01:38:02,240
and long legs.

1278
01:38:02,240 --> 01:38:05,080
It's beginning to stand
up on its toes.

1279
01:38:06,920 --> 01:38:09,240
This is an early horse.

1280
01:38:09,240 --> 01:38:12,400
And perhaps the most specialised
and remarkable of all

1281
01:38:12,400 --> 01:38:14,840
at this still very early date

1282
01:38:14,840 --> 01:38:17,440
is this extraordinary specimen.

1283
01:38:18,800 --> 01:38:21,800
This, as you can see, is a bat.

1284
01:38:21,800 --> 01:38:25,400
And the preservation
is so remarkable

1285
01:38:25,400 --> 01:38:28,280
that the skin can be easily seen,

1286
01:38:28,280 --> 01:38:31,080
not only on its forelegs,

1287
01:38:31,080 --> 01:38:32,720
which turns them into wings,

1288
01:38:32,720 --> 01:38:37,520
but even you can see this large ear

1289
01:38:37,520 --> 01:38:39,440
on the side of its head,

1290
01:38:39,440 --> 01:38:43,480
which suggests that already
it was beginning to echo-locate,

1291
01:38:43,480 --> 01:38:47,160
to hear its own calls
so it navigates during flying.

1292
01:38:51,200 --> 01:38:54,280
The mammals were displaying
an extraordinary ability

1293
01:38:54,280 --> 01:38:59,320
to rapidly adapt their bodies to
fill the range of niches left vacant

1294
01:38:59,320 --> 01:39:01,360
by the death of the dinosaurs.

1295
01:39:03,000 --> 01:39:04,600
They had new opportunities,

1296
01:39:04,600 --> 01:39:07,280
but they also faced
a new evolutionary pressure.

1297
01:39:09,040 --> 01:39:10,560
Climate change.

1298
01:39:13,160 --> 01:39:16,200
Ten million years
of gradual global-warming

1299
01:39:16,200 --> 01:39:18,840
had triggered a surge in plant life.

1300
01:39:20,040 --> 01:39:24,160
The land became covered in forests
that grew ever denser and darker.

1301
01:39:26,320 --> 01:39:29,840
New mammals emerged
with new features that helped them

1302
01:39:29,840 --> 01:39:33,040
to thrive in this changed
environment.

1303
01:39:33,040 --> 01:39:36,840
Features that would have
huge significance for humans.

1304
01:39:38,600 --> 01:39:42,520
This is an early member
of the group of mammals

1305
01:39:42,520 --> 01:39:44,440
that was going to produce us.

1306
01:39:44,440 --> 01:39:46,880
This is an early primate.

1307
01:39:46,880 --> 01:39:51,120
And you can see that
on its front legs, its hands,

1308
01:39:51,120 --> 01:39:53,760
they have an opposable thumb,

1309
01:39:53,760 --> 01:39:55,200
so it could grasp.

1310
01:39:55,200 --> 01:39:59,480
And the same on the back legs -
the big toe is also opposable.

1311
01:40:00,600 --> 01:40:03,120
So, this animal was a climber.

1312
01:40:05,960 --> 01:40:09,440
The primates could now reach food
that was high up in trees.

1313
01:40:11,680 --> 01:40:14,720
And it's thought that it was
a new type of food that triggered

1314
01:40:14,720 --> 01:40:18,560
another astonishing advance
in their bodies.

1315
01:40:18,560 --> 01:40:21,200
A major improvement in sight.

1316
01:40:25,400 --> 01:40:29,520
Dr Sandra Engels
is part of a team investigating

1317
01:40:29,520 --> 01:40:33,240
the diet of the fossilised primate
from the Messel Pit.

1318
01:40:34,400 --> 01:40:38,640
Remarkably, she's able to examine
the preserved contents of its gut.

1319
01:40:40,920 --> 01:40:45,160
We have particles of the last meal
of this primate,

1320
01:40:45,160 --> 01:40:49,640
and we analysed it
with very high magnification

1321
01:40:49,640 --> 01:40:54,800
and we found
the oval outline of a seed

1322
01:40:54,800 --> 01:40:56,680
which is part of a fruit.

1323
01:40:56,680 --> 01:41:00,200
And because we found it
in the gut of this primate,

1324
01:41:00,200 --> 01:41:02,360
we know that it fed on fruit.

1325
01:41:02,360 --> 01:41:07,720
3D scans of its teeth make it clear
that fruit was a major part

1326
01:41:07,720 --> 01:41:12,040
of its diet. This animal was
a specialised fruit-eater.

1327
01:41:13,400 --> 01:41:16,520
If we take a closer look
to the shape of the teeth,

1328
01:41:16,520 --> 01:41:22,240
we have structures
as deep basins or rounder cusps

1329
01:41:22,240 --> 01:41:25,800
that are the right tools
to break up fruit.

1330
01:41:28,640 --> 01:41:32,720
47 million years ago,
large, fleshy fruit like this

1331
01:41:32,720 --> 01:41:35,960
had only recently been developed
by plants.

1332
01:41:35,960 --> 01:41:38,600
It was one of the ways
in which they had adapted

1333
01:41:38,600 --> 01:41:41,120
to the new dense forest
environments.

1334
01:41:42,640 --> 01:41:47,400
Many early plants relied on the wind
to distribute their seeds.

1335
01:41:47,400 --> 01:41:51,600
But in the forest, there is little
or no wind, so they had a problem.

1336
01:41:52,920 --> 01:41:56,960
They solved it
by recruiting the help of birds,

1337
01:41:56,960 --> 01:42:00,120
and they did that
by wrapping their seeds

1338
01:42:00,120 --> 01:42:03,480
in an edible, sweet flesh, fruit.

1339
01:42:05,040 --> 01:42:07,640
Birds carried the seeds
in their stomachs

1340
01:42:07,640 --> 01:42:11,080
and eventually deposited them
elsewhere in the forest.

1341
01:42:13,960 --> 01:42:18,400
The primates had clearly begun
to exploit this cosy arrangement,

1342
01:42:18,400 --> 01:42:22,480
but to take full advantage,
they needed to improve their vision.

1343
01:42:24,480 --> 01:42:26,520
During the age of the dinosaurs,

1344
01:42:26,520 --> 01:42:28,960
when the mammals were
largely nocturnal,

1345
01:42:28,960 --> 01:42:31,440
they had developed
better night vision,

1346
01:42:31,440 --> 01:42:34,440
but sacrificed a feature
not needed in the dark.

1347
01:42:34,440 --> 01:42:36,440
The ability to see colour.

1348
01:42:38,920 --> 01:42:44,240
Today, most mammals still see the
world largely in black and white.

1349
01:42:44,240 --> 01:42:47,440
But the reptiles
and their cousins, the birds,

1350
01:42:47,440 --> 01:42:49,840
retained excellent colour vision.

1351
01:42:52,920 --> 01:42:55,000
And the fruit-bearing plants

1352
01:42:55,000 --> 01:42:58,200
had evolved a signalling
arrangement to match.

1353
01:43:01,640 --> 01:43:04,080
There's no point in having
your seeds distributed

1354
01:43:04,080 --> 01:43:05,720
before they're fully formed.

1355
01:43:05,720 --> 01:43:08,800
So, the plants evolved
a colour-coding system

1356
01:43:08,800 --> 01:43:10,400
to show when that was.

1357
01:43:11,600 --> 01:43:15,960
This plant, for example,
here is a young fruit still growing.

1358
01:43:15,960 --> 01:43:20,520
Its flesh is hard and bitter,
and it's green.

1359
01:43:20,520 --> 01:43:23,560
But this fruit is fully formed.

1360
01:43:23,560 --> 01:43:27,040
Its flesh is good to eat, soft,

1361
01:43:27,040 --> 01:43:30,320
and the seed within is ready to go.

1362
01:43:30,320 --> 01:43:31,520
And it's red.

1363
01:43:33,160 --> 01:43:36,800
To spot a flash of red colour
in amongst the green foliage

1364
01:43:36,800 --> 01:43:39,240
is easy for a bird or a reptile.

1365
01:43:41,080 --> 01:43:44,120
But for a mammal,
with their night-time vision,

1366
01:43:44,120 --> 01:43:46,920
red and green
are indistinguishable.

1367
01:43:48,160 --> 01:43:50,000
Then, remarkably,

1368
01:43:50,000 --> 01:43:54,680
some of the primates managed
a feat no other mammal has achieved.

1369
01:43:55,920 --> 01:44:00,520
They put evolution into reverse
and re-acquired colour vision.

1370
01:44:02,800 --> 01:44:06,480
The common ancestor
of this monkey, and of me,

1371
01:44:06,480 --> 01:44:09,800
lived up in the trees
in the daylight.

1372
01:44:09,800 --> 01:44:15,400
And they quickly evolved
the ability to see colour,

1373
01:44:15,400 --> 01:44:18,440
and therefore, to know which was
ripe and which was unripe fruit,

1374
01:44:18,440 --> 01:44:21,280
and so take advantage of the system

1375
01:44:21,280 --> 01:44:23,760
that had already been worked out

1376
01:44:23,760 --> 01:44:26,400
between the birds and the plants.

1377
01:44:27,400 --> 01:44:30,240
Let's just see what
she thinks about that.

1378
01:44:31,600 --> 01:44:33,480
Which of those do you like?

1379
01:44:33,480 --> 01:44:34,680
There's it.

1380
01:44:40,200 --> 01:44:44,360
After the dinosaur extinctions
of 65 million years ago,

1381
01:44:44,360 --> 01:44:47,560
the mammals were using
their spectacular adaptability

1382
01:44:47,560 --> 01:44:51,040
to evolve and diversify
at an astonishing rate.

1383
01:44:54,400 --> 01:44:56,880
In the process,
they laid the foundations

1384
01:44:56,880 --> 01:44:59,720
for the major mammal groups
we see today.

1385
01:45:04,760 --> 01:45:10,440
But then, around 47 million years
ago, came a new set of problems.

1386
01:45:12,240 --> 01:45:15,000
The Earth's climate changed
yet again.

1387
01:45:15,000 --> 01:45:18,840
Many places became drier,
and where that happened,

1388
01:45:18,840 --> 01:45:21,000
the forest thinned out
and was replaced

1389
01:45:21,000 --> 01:45:24,080
by low, scattered bushes and grass.

1390
01:45:24,080 --> 01:45:28,720
And those new environments presented
new challenges to animals

1391
01:45:28,720 --> 01:45:32,320
and ushered in the age
of the mammal monsters.

1392
01:45:36,280 --> 01:45:39,680
Scientists are finding
stunning evidence of this change

1393
01:45:39,680 --> 01:45:42,720
in the Great Plains
of North America.

1394
01:45:48,840 --> 01:45:54,720
This dramatic country in South
Dakota is known as the Badlands.

1395
01:45:55,920 --> 01:46:00,320
Streams and rivers have eroded
the rocks into fantastic shapes.

1396
01:46:04,080 --> 01:46:06,120
But 40 million years ago,

1397
01:46:06,120 --> 01:46:10,200
these were layers of sediment laid
down across an open flood plain.

1398
01:46:14,440 --> 01:46:17,280
Palaeontologist Clint Boyd
is looking here

1399
01:46:17,280 --> 01:46:20,920
for the fossilised remains of
creatures from that ancient time.

1400
01:46:22,440 --> 01:46:25,800
And he's finding mammals
that are giants.

1401
01:46:28,600 --> 01:46:33,760
This is part of the bone we call
the femur or the upper-thigh bone,

1402
01:46:33,760 --> 01:46:37,360
and this round surface right here
is for the hip socket.

1403
01:46:37,360 --> 01:46:38,920
And so you can see it's very large.

1404
01:46:38,920 --> 01:46:41,520
We'd be talking about
a very large animal.

1405
01:46:41,520 --> 01:46:45,720
And not only do we have the
thigh bone but we've got ankle bones

1406
01:46:45,720 --> 01:46:48,760
spread out over here, and then
cascading down from that spot,

1407
01:46:48,760 --> 01:46:50,800
we've got some of the tail bones
coming down.

1408
01:46:50,800 --> 01:46:53,440
So, if we add all this up together,
based on the size,

1409
01:46:53,440 --> 01:46:55,720
we're looking at an animal
that's probably

1410
01:46:55,720 --> 01:46:57,480
about two metres tall at the hips.

1411
01:46:59,360 --> 01:47:03,360
The creature is
known as a Titanothere.

1412
01:47:03,360 --> 01:47:05,000
It was a herbivore.

1413
01:47:05,000 --> 01:47:08,480
It fed on the lush vegetation
that once covered this area

1414
01:47:08,480 --> 01:47:10,040
of the United States.

1415
01:47:13,560 --> 01:47:16,200
A range of different specimens
have been collected

1416
01:47:16,200 --> 01:47:19,000
at Denver Museum
of Nature and Science.

1417
01:47:20,240 --> 01:47:22,960
And they reveal that
the first Titanotheres

1418
01:47:22,960 --> 01:47:26,160
were built on a much smaller scale.

1419
01:47:26,160 --> 01:47:29,600
When Titanotheres first appear
on the scene, they look like this.

1420
01:47:29,600 --> 01:47:32,440
This is the lower jaw of one
of the first Titanotheres,

1421
01:47:32,440 --> 01:47:35,080
and it's one of these
sheep-sized animals.

1422
01:47:35,080 --> 01:47:36,920
In only five million years,

1423
01:47:36,920 --> 01:47:39,120
members of the group
go from sheep-sized...

1424
01:47:40,560 --> 01:47:43,000
..to about the size of a small horse.

1425
01:47:44,560 --> 01:47:48,160
Within only 15 million years
of their first appearance,

1426
01:47:48,160 --> 01:47:50,720
Titanotheres look like this.

1427
01:47:50,720 --> 01:47:54,160
Here you can see the skull
of one of these Titanotheres.

1428
01:47:57,000 --> 01:48:01,080
In evolutionary terms, the size
increase is astonishingly quick.

1429
01:48:02,480 --> 01:48:04,600
But what drove
this remarkable change?

1430
01:48:08,400 --> 01:48:11,240
Another fossil could provide
an explanation.

1431
01:48:11,240 --> 01:48:15,280
It dates back to the time of the
first and smallest Titanotheres,

1432
01:48:15,280 --> 01:48:17,680
but it's a very different type
of mammal.

1433
01:48:19,240 --> 01:48:22,400
This is the skull
of Malfelis Badwaterensis,

1434
01:48:22,400 --> 01:48:24,240
the "bad cat from Badwater".

1435
01:48:24,240 --> 01:48:26,320
This was the largest predator
at the time.

1436
01:48:26,320 --> 01:48:30,520
This is the skull. This large crest
is for large jaw muscles

1437
01:48:30,520 --> 01:48:34,400
which would've given a powerful
shearing bite that ran these

1438
01:48:34,400 --> 01:48:38,640
blade-like teeth, perfect
for chopping up a Titanothere.

1439
01:48:38,640 --> 01:48:41,680
And what's interesting
is that Malfelis was exactly

1440
01:48:41,680 --> 01:48:45,560
the same size as the top herbivores
of the time, like Titanotheres.

1441
01:48:50,000 --> 01:48:53,280
The earliest Titanotheres
could hide from these bad cats

1442
01:48:53,280 --> 01:48:56,200
in the dense forest environments.

1443
01:48:56,200 --> 01:48:59,160
But as those forests
began to thin out,

1444
01:48:59,160 --> 01:49:02,200
the Titanotheres were
more vulnerable to attack.

1445
01:49:02,200 --> 01:49:06,480
One way to improve their chances
was to grow bigger.

1446
01:49:07,760 --> 01:49:10,240
An herbivore is much more likely
to survive an encounter

1447
01:49:10,240 --> 01:49:12,160
with a predator if
it's a little bit larger.

1448
01:49:12,160 --> 01:49:13,960
And so there was a bit
of an arms race

1449
01:49:13,960 --> 01:49:15,840
between the predators and the prey.

1450
01:49:15,840 --> 01:49:19,680
And animals like Titanotheres were
able to escape this predator pressure

1451
01:49:19,680 --> 01:49:23,560
by becoming the super-sized giants
we see 35 million years ago.

1452
01:49:26,840 --> 01:49:31,000
Fossilised remains of Titanotheres
from the Badlands of South Dakota

1453
01:49:31,000 --> 01:49:33,200
and elsewhere across
the Great Plains

1454
01:49:33,200 --> 01:49:36,320
allow us to reconstruct
its rapid growth spurt.

1455
01:49:49,720 --> 01:49:51,160
From modest beginnings,

1456
01:49:51,160 --> 01:49:53,600
they increased their bulk
ten times over...

1457
01:49:54,800 --> 01:49:57,640
..till the largest stood
over eight feet tall.

1458
01:50:08,840 --> 01:50:12,280
On the open grasslands that
increasingly covered the Earth,

1459
01:50:12,280 --> 01:50:14,520
many other giant mammals emerged.

1460
01:50:15,760 --> 01:50:18,680
Together,
they're known as the "Megafauna".

1461
01:50:22,080 --> 01:50:25,080
This giant sloth
was found in California.

1462
01:50:33,840 --> 01:50:37,880
In China, I've come to see
the remains of mammoths.

1463
01:50:41,560 --> 01:50:45,520
And a remarkable creature
that was the largest land mammal

1464
01:50:45,520 --> 01:50:47,200
to walk this Earth.

1465
01:50:48,840 --> 01:50:53,160
This great beast is called
Paraceratherium.

1466
01:50:53,160 --> 01:50:58,600
It stood five metres tall
and nearly eight metres long.

1467
01:50:58,600 --> 01:51:01,040
Those furry little mammals

1468
01:51:01,040 --> 01:51:04,720
scampering about in the shadows
had produced descendants

1469
01:51:04,720 --> 01:51:07,920
that could stare
the biggest dinosaur in the eye.

1470
01:51:18,200 --> 01:51:22,400
Today, the elephant is one
of the few species of Megafauna

1471
01:51:22,400 --> 01:51:24,120
to have survived.

1472
01:51:26,040 --> 01:51:28,000
But those outsized versions

1473
01:51:28,000 --> 01:51:30,360
have otherwise disappeared
from the planet.

1474
01:51:32,720 --> 01:51:34,400
So, what happened to them?

1475
01:51:37,040 --> 01:51:41,400
Their eventual extinction
coincides with another key event

1476
01:51:41,400 --> 01:51:42,960
in the history of the Earth.

1477
01:51:49,440 --> 01:51:52,200
From around
two and a half million years ago,

1478
01:51:52,200 --> 01:51:55,680
ice sheets spread down
from the North and up from the South

1479
01:51:55,680 --> 01:51:58,320
to cover vast areas
of the continents.

1480
01:52:04,200 --> 01:52:07,480
But it was only when
the ice finally retreated,

1481
01:52:07,480 --> 01:52:11,320
just 10,000 years ago,
that the Megafauna vanished.

1482
01:52:12,720 --> 01:52:17,000
Some have blamed that on the rise
and falls of the temperature

1483
01:52:17,000 --> 01:52:19,640
as the Ice Age
finally came to a close.

1484
01:52:19,640 --> 01:52:23,560
But others have sought the culprit
amongst the mammals themselves.

1485
01:52:25,200 --> 01:52:27,880
A newly-evolved super predator.

1486
01:52:35,520 --> 01:52:39,120
To see some of the earliest evidence
for its arrival in China,

1487
01:52:39,120 --> 01:52:41,000
I've returned to Beijing.

1488
01:52:45,080 --> 01:52:48,880
These fossilised remains
belong to a primate.

1489
01:52:52,560 --> 01:52:56,520
It's been dated
to around 68,000 years ago.

1490
01:52:58,640 --> 01:53:02,400
This primate had
two new evolutionary features.

1491
01:53:02,400 --> 01:53:04,320
First, its pelvis.

1492
01:53:04,320 --> 01:53:06,480
An animal with a pelvis like this

1493
01:53:06,480 --> 01:53:08,880
would have been able
to walk upright.

1494
01:53:10,040 --> 01:53:11,840
Secondly, the skull.

1495
01:53:11,840 --> 01:53:15,080
Its brain case is enormous.

1496
01:53:15,080 --> 01:53:17,520
In proportion
to the size of its body,

1497
01:53:17,520 --> 01:53:20,920
it's six times
the average mammal size.

1498
01:53:20,920 --> 01:53:23,440
And that would have brought
great intelligence.

1499
01:53:25,280 --> 01:53:28,720
And this creature, of course,
was a human being.

1500
01:53:30,960 --> 01:53:35,000
The early humans put their new
intelligence to deadly use.

1501
01:53:37,120 --> 01:53:39,280
They worked out how to make weapons.

1502
01:53:41,280 --> 01:53:44,760
These stones, carefully chipped
to form sharp blades,

1503
01:53:44,760 --> 01:53:47,520
were found alongside human remains.

1504
01:53:49,200 --> 01:53:52,080
And they developed
new powers of communication

1505
01:53:52,080 --> 01:53:56,520
that enabled them to join forces
and hunt in teams.

1506
01:53:57,960 --> 01:54:01,000
This was a new kind of predator.

1507
01:54:01,000 --> 01:54:03,240
It first appeared in Africa

1508
01:54:03,240 --> 01:54:06,280
and then spread
to all the other continents,

1509
01:54:06,280 --> 01:54:09,160
and each time its appearance
in that continent

1510
01:54:09,160 --> 01:54:13,800
coincided more or less with
the disappearance of the Megafauna.

1511
01:54:13,800 --> 01:54:16,680
Which suggests,
at the very least,

1512
01:54:16,680 --> 01:54:20,240
that this creature had something
to do with that event.

1513
01:54:28,440 --> 01:54:30,520
To conclude my journey in China,

1514
01:54:30,520 --> 01:54:33,400
and find the last step
in our evolutionary story,

1515
01:54:33,400 --> 01:54:38,640
I'm back in Kunming city to visit
one of its busiest maternity wards.

1516
01:54:44,160 --> 01:54:48,160
An enlarged brain brought us
huge advantages,

1517
01:54:48,160 --> 01:54:53,200
but its size also presented
a basic design problem at birth.

1518
01:54:55,240 --> 01:54:57,720
The bony skull encasing the brain

1519
01:54:57,720 --> 01:55:00,920
still had to make it out
through the mother's birth canal.

1520
01:55:05,080 --> 01:55:08,640
A new addition to our species,
just 12 hours old,

1521
01:55:08,640 --> 01:55:10,680
can reveal how this is possible.

1522
01:55:14,720 --> 01:55:18,600
This little boy's name is Shao Bao.

1523
01:55:18,600 --> 01:55:21,240
It means "little treasure".

1524
01:55:21,240 --> 01:55:26,720
He was born because of
a special feature in his skull.

1525
01:55:26,720 --> 01:55:30,000
Mammal skulls are made up
of separate bones.

1526
01:55:30,000 --> 01:55:35,000
And in most species those are fused
together at the time of birth

1527
01:55:35,000 --> 01:55:40,120
to form a hard, bony box to protect
that most special organ, the brain.

1528
01:55:41,160 --> 01:55:45,600
But not so with Shao Bao
and other human beings.

1529
01:55:45,600 --> 01:55:47,640
They remain separate,

1530
01:55:47,640 --> 01:55:51,720
and that allowed his head
to slightly change shape

1531
01:55:51,720 --> 01:55:55,960
and squeeze through the aperture
of his mother's pelvis.

1532
01:55:59,640 --> 01:56:03,720
This also allows the brain
to continue to grow and develop

1533
01:56:03,720 --> 01:56:05,000
after birth.

1534
01:56:07,960 --> 01:56:10,560
In fact,
the plates won't start to fuse

1535
01:56:10,560 --> 01:56:13,280
until Shao Bao
is around two years old.

1536
01:56:16,880 --> 01:56:18,440
It's one of the most recent

1537
01:56:18,440 --> 01:56:21,600
in a long line of remarkable
evolutionary developments

1538
01:56:21,600 --> 01:56:25,120
that allowed the vertebrates,
animals with a backbone,

1539
01:56:25,120 --> 01:56:29,240
to create the dazzling diversity
we see around us today.

1540
01:56:31,720 --> 01:56:35,400
Shao Bao's ancestry,
like that of all of us,

1541
01:56:35,400 --> 01:56:39,000
stretches back
over 500 million years

1542
01:56:39,000 --> 01:56:43,480
to a tiny little wormlike creature
swimming in the bottom of the sea.

1543
01:56:46,960 --> 01:56:49,960
His backbone and jaw
came from the early fish.

1544
01:56:52,000 --> 01:56:54,600
His limbs and lungs from amphibians.

1545
01:56:56,520 --> 01:56:59,600
The reptiles gave him
his watertight skin.

1546
01:57:03,000 --> 01:57:06,440
Tiny nocturnal mammals donated
a bigger brain...

1547
01:57:07,680 --> 01:57:09,120
..sharper senses...

1548
01:57:10,880 --> 01:57:12,960
..and the manner
in which he was born.

1549
01:57:15,400 --> 01:57:19,880
His hands and colour vision
came from the fruit-eating primates.

1550
01:57:20,960 --> 01:57:25,760
And his larger brain and greater
intelligence, from the first humans.

1551
01:57:27,240 --> 01:57:31,360
So, all our features
of our body can be traced back

1552
01:57:31,360 --> 01:57:33,480
to our ancient ancestors,

1553
01:57:33,480 --> 01:57:36,920
and there's much more
we have yet to learn about them.

1554
01:57:38,320 --> 01:57:40,160
But one thing is certain -

1555
01:57:40,160 --> 01:57:43,800
the evolution of the vertebrates
has not yet come to an end.