[CRICKETS] [BING] [TIGER ROARING] [MUSIC PLAYING] [WATER RUSHING] NEIL SHUBIN: Our
planet is teeming with many kinds of animal life,
including groups with defining structures, such as the
four legs of land animals, the feathered wings of birds,
and the dexterous hands of primates. Understanding the origins
of these structures and of the groups that
possess them has long been a central quest of biology. Charles Darwin asserted
that each kind of animal must have evolved from
pre-existing, earlier kinds of animals that
lacked those structures. He boldly predicted that buried
in the crust of the earth were animals that connected
one major group to another. Such transitional
fossils would be intermediate in form between
earlier and later groups. What made Darwin's
prediction so bold was at the time he stated
it in The Origin of Species, no such fossils had been found. His critics immediately
latched onto the admission that transitional
animals are somehow missing from the fossil record. Over the decades, it's become
a standard talking point for those who have
closed their mind to the science of evolution. SPEAKER 1: There you go. NEIL SHUBIN: Yeah,
this is the stuff. Right, so this was the-- But, in fact, since
Darwin, paleontologists have unearthed hundreds
of transitional creatures that have enabled
us to reconstruct the origins of many groups. And even so, searching
for such fossils remains a challenging adventure,
and finding the right one can change the way we think
about the origins of living creatures. [THEME MUSIC] For me, paleontology
has always been about filling the gaps
in the story of life. And for a long time,
one of the biggest ones was understanding the
origin of animal limbs, with fingers and toes. [MUSIC PLAYING] Paired limbs are a
feature of many animals, but there's little
at first glance that suggests the limbs of
different species are related. On frogs, they're springy. On elephants, not so much. They're feathered on
eagles, not on bats. But inside the limbs of
mammals, amphibians, reptiles, and birds, one finds
a common architecture. Here's a dog. Dogs run and jump. What do you have? One bone, two bones, little
bones, and then the digits-- the equivalents of
the fingers or toes. And, of course, here's a bird. It flies. Its limb has been
modified into a wing. And it has one bone, two bones,
lots of bones, and then digits. The amazing fact is
every four-limbed animal walking the earth today has
this fundamental pattern. One bone, two, bones,
little bones, fingers. That pattern
suggests a connection between these very
different groups of animals. And it's not the only
feature they share. They also all have a backbone. They're vertebrates. The history of vertebrates
has been captured in rock we can accurately date. Fossils reveal when each
of these groups of animals first emerged. The youngest group is the birds. Go further back in
time, and you'll find the first mammals, and
then the first reptiles, and the first amphibians. And then you get to
370 million years ago. Suddenly, there are no
four-limbed creatures, or tetrapods,
anywhere to be found. Where the first pods
came from has always been one of the great
mysteries of biology. I mean, it's not like there
weren't animals or vertebrates around 400 million years ago. There were, but
they were all fish. Did four-legged
animals come from fish? Fish might seem
unlikely candidates to be the earliest ancestors
of frogs, horses, and humans. They don't even have limbs. They have fins. Despite their different
external appearances, there are revealing
similarities. First, fish and tetrapods
are vertebrates. And early in life,
when they are embryos, they look remarkably similar. Finally, DNA analysis shows
that fish are tetrapods' closest relatives. All of this suggests
four-legged animals did indeed come from fish. But how did a fish
with fins give rise to tetrapods with four legs? As a young scientist,
I wanted to find fossils that could help
answer that question. I knew it wasn't
going to be easy. The world's a big place,
the earth is a giant planet, and fossils are very small. So how do you find those things? Well, there's a
checklist we run through. We look for places
in the world that have rocks of the right age. You know, if you're interested
in the origin of dinosaurs, there's one age of
rock to look at. If you're interested in
the origin of land living creatures, there's
another age of rocks. Then you look for
places in the world that have rocks of the right type. The kinds of rocks that
are likely to hold fossils. A lot of things have to
come together for an animal to be fossilized. For starters, it has to be
in the right kind of setting where sediments form. And soon after it
dies, it has to be buried before its remains are
ravaged by decay, weather, or scavengers. The dirt and mud burying it
has to harden sufficiently to protect what's left
for thousands, or more likely millions, of years. After which,
something, say erosion, has to bring the embedded
remains to the surface. And then someone who
cares about such things, like me or my longtime
colleague, Ted Daeschler, has to wander by and find it. The fossils I
wanted to find would have been alive in
the Devonian era, between 365 and 385
million years ago. But where could we find
the right kinds of rocks from that era? But you could still see
one of these ledges-- I remember sitting
in the office, and we were doing the sort
of usual banter one day about something geological. We had a college textbook. We were just thumbing
through the diagrams in the book and, boom,
there was this figure that changed our lives. I remember seeing that and
saying to myself, holy cow! This is what we're looking for. It was a map of
North America which highlighted three areas
of Devonian rock of just the right type to hold
fossil fish moving onto land. Two of those areas
had already been worked on, so we focused on
the third, the Canadian Arctic. My heart was racing when
I saw that because-- and I'm sure yours was too. I mean, no-- TED DAESCHLER: Yeah. NEIL SHUBIN: --paleontologist
had worked on that expressly looking for early tetrapods. Then you dug out
the aerial photos, and that's when I got
kind of terrified. I remember seeing this for
the first time thinking, you got to be kidding me. Yeah, look at all this snow. How do you work there? [MUSIC PLAYING] The Arctic presents
some unusual challenges. You're far from help
so you have to bring everything you'll need. And you have to move fast
because the season is short. And you don't want to be
there when the weather turns. So when the helicopter
drops you off in the Arctic for
the first time, you're standing here saying,
what am I doing here? You know, you're
thinking, oh, polar bears. That's the first
thing you look for. Is there anything
on the landscape? Everything white becomes a polar
bear when you're first here. The last thing on
your mind are fossils. [MUSIC PLAYING] It's hard to believe
when you look out across this frozen
terrain that, once, this was a warm, watery world,
swimming with life. There's this huge disconnect
between the present and the past. What we see today is a valley
with red and green rocks that are tilted, stacked
one on top of the other. But that's not how
it was in the past. These valleys have
been carved by glaciers that have moved back and forth,
and those red and green rocks actually at one point
extended across the valley. And they were straight,
they weren't tilted. Now, look inside the rocks. And what those rocks tell
us, that this valley, 375 million years ago,
was a giant flood plain. And that flood plain
was filled with rivers that swelled their banks
and sometimes shrunk, but in those conditions
formed swamps and streams of all different sizes. And inside those streams
was diverse life. Including, we suspected,
a fish with features that would ultimately enable
animals to walk on land. [MUSIC PLAYING] But even if it had
been there, could we find evidence of
it buried on one of the nameless hillsides
that had built up and eroded over the past 375 million years? So how do you find fossils? I pick up a lot of stuff, right? Sometimes it's just
a piece of rock. Sometimes it's bird poop. Sometimes it's a leaf. But, occasionally, you know,
it's a jaw with teeth in it. So what you begin
to learn is to tell the difference between white
which is not bone and white which is bone, teeth, or scale. Once you have that in
your mind, then you start to apply that search
image to other rocks. Here's another scale here. It stands out like a sore thumb. And then we go-- if you look around, right here. OK. So this is the
underside of a skull. So you never know where you're
going to hit it around here. You know, that's why
we keep on looking. [MUSIC PLAYING] But that first expedition
ended without finding what we had come for. And as our second trip drew to a
close, we were still searching. Then a bit before our scheduled
departure, we had a real scare. The team had separated. And the idea is everybody
needs to return back to camp by radio call. Hey, you guys see Jason? No, I didn't see Jason. Did you see Jason? I said, I asked
you the question. You didn't see Jason? And then all of a sudden,
it became where's Jason? This is our youngest member. We were looking out for him the
entire season, and no Jason. I mean, my heart was
really beginning to race. Then I hear footsteps
outside the tent. There's Jason. His eyes are like globes. And he's like, I found it! I mean, every pocket was
burgeoning with bones. He was like, I got these
bones-- he's laying them down on the table, one after another. It's daylight 24 hours a day,
so we ran down to Jason's site. As soon as we came to this
bluff here and looked down, we saw why Jason was so excited. Because beneath our feet
were fossil fish bones, fragments of fossil fish-- many
of them, thousands of them. It wasn't just one fish,
it was a whole aquarium. It was different species. It got better. Because as we
walked up the hill, and we followed that carpet of
fossil fragments, it stopped, meaning it likely
came from one layer. And if we had any luck at
all, we'd find that layer and see what's inside. Hard as we tried,
we couldn't discover what was buried in Jason's
hill before we had to leave. But we kept coming back
to it in following years to dig, chip, and search. The second week of
July in 2004, we're all working and
serious in this hole. You know, where my head is
right next to Farrish's feet, and Farrish's feet is
next to Steve Gatesy. And we're digging together
and Steve says, hey, guys, what's this? Ted and I go running over to
see what Steve was referring to, and what we saw was this v here. It was covered with rock. And as soon as we saw this v
and we saw these teeth under it, it became very clear that
this little v we're seeing is the tip of a snout,
and that this was a snout of a flat-headed fish. And it was sticking
out of the rock. So if we had any
luck whatsoever, the rest of the creature
would be encased in the rock. And here it is. What's really wonderful
about this specimen is that we have pretty
much the whole thing, and the whole thing
is put together. That is, the head is
connected to the body and the body is
connected to the fins, so we know that this fin
comes from this body. And when we put it
all together, we see this creature is
about four feet long. And some of the biggest
were about nine feet long. What's really amazing is that
this is an animal that Darwin would have predicted. A real mix of
characteristics-- a combination of fish-like and
tetrapod-like features. Like a fish, it has
scales in its back and it also has
fins with fin rays. But like a tetrapod, it has
a flat head with eyes on top. And when we look inside
the body, what we see are these huge
interlocking ribs that suggested that it had lungs. When you put the body
and the head together, you see it had a neck, where
the head can move independently of the body. What that means is this
animal could use the neck to peer outside the water,
find prey, and avoid predators. So we have many bones
of these animals, including this one, which is
a hip bone of these creatures. And what it reveals is that the
hind fins were already evolving into legs while these
animals were living in water. I get really excited when I see
the front fins of tiktaalik. Here's one from one of
the larger specimens. And what you see is
the shoulder, but also some of the fin bones inside. What you see is a version of
the one bone, two bone pattern that's inside our own arms. You have one bone, two bones. You even have a
version of a wrist. [MUSIC PLAYING] And once those fins
were strong enough to lift its body
out of the water, a whole new frontier opened. Over millions of years, the
two pairs of fins and fish like tiktaalik would
lead to the two pairs of limbs in every tetrapod. So what does this all mean? What it means is that
our arms and legs are derived from the paired
fins of our fishy ancestors. So how fast did this
transition happen? Well, we know the tiktaalik
didn't exist in a vacuum. There are other creatures,
other transitional fossils, that are more
fish-like and others that are more tetrapod-like,
and these creatures existed for over
15 million years. So what this means is that
this great transition from fish to tetrapod didn't
happen in a single step, but happened
gradually over time. The discovery of
tiktaalik made headlines because it is one of the
earliest in a series of fossils that illuminate the
transition from water to land. And that's just one key
transition that fossils have shed light on. One of the very first
was the evolution of birds from
feathered dinosaurs. That's now one of the best
documented transitions in the story of life. SPEAKER 1: Well, this is skull. NEIL SHUBIN: What
it and other well studied examples tell us is
that what at first seemed to be huge leaps
are almost always products of a series of
smaller evolutionary steps. That's true for when our fish
ancestors first came to land, when dinosaurs took to
the air and when we first stood upright. [MUSIC PLAYING] Fish, and an ancestor who
lived 3.2 million years ago. SPEAKER 2: She's beautiful. [MUSIC PLAYING]
