Tyrannosaurus rex...
Big.
Nasty.
A killer dinosaur.
Even its name means the king of the tyrant lizards.
The most famous prehistoric carnivore
that ever roamed Earth,
surely looked like the ruler of all reptiles.
As tall as a two-story building and as long as a school bus,
with scaly skin
and a huge jaw packed with razor-sharp teeth.
In popular culture,
tyrannosaurus rex has often been portrayed
as a freakishly oversized lizard,
but is this image a big mistake?
New evidence is revealing that T. rex is not what we thought.
Is the king of the dinosaurs having an identity crisis?
Could Tyrannosaurus rex actually have been...
(Tyrannosaurus roars)
(Chicken clucking)
A chicken?
(♪♪♪)
1902, the badlands of Hell Creek, Montana,
one of the world's most famous paleontologists
was on a mission to find evidence
of prehistoric creatures.
And this was a region rich in fossils
from the late Cretaceous period.
Barnum Brown was known by the nickname "Mr. Bones."
He'd been digging for three years there,
when he unearthed just 11% of a creature
that had never been seen before.
In 1908, he discovered half of the giant
that would be named "the king",
tyrannosaurus rex.
Although Mr. Bones found less than half of a skeleton,
those bones painted a picture of a towering lizard-like beast.
>> It was just totally terrifying to the public
to think of something that looked like a giant reptile,
45 to 50-feet long, a skull, 6-feet long,
full of amazing gigantic teeth.
>> Barnum's discovery put tyrannosaurus rex
at the top of the prehistoric food chain.
It was king of the carnivores, roaming parts of North America
for several million years
during the late Cretaceous period
until it disappeared forever 65 million years ago.
For the past 113 years, paleontologists have tried
to piece together more clues
to build a picture of this unusual creature.
Scientists had to study fossils and skin impressions
from similar dinosaurs
to put the pieces of the puzzle together.
The name dinosaur means, "fearfully great lizard"
and this new discovery was one huge dinosaur.
>> I think T. rex is fascinating to the public
for a number of reasons.
I mean, its size is truly incredible.
It is a gigantic meat-eating animal.
It could swallow a human in one bite.
Of course, its look,
I mean, it has this, sort of, primeval reptilian look,
at least in popular lore.
>> While tyrannosaurus rex ruled the land,
birds ruled the skies.
But not any bird that we're used to seeing today.
In 1861, 41 years before the discovery of T. rex,
an ancient bird was accidentally unearthed
from a limestone quarry in Southern Germany.
It was the size of a raven.
It had feathers, broad wings, and was probably able to fly.
Its name was archaeopteryx
and it lived around 151 million years ago,
long before T. rex even walked the earth.
>> At first sight, the most striking feature of the animal
is the faint but clear impressions
of feathers along the arms and along the tail.
And at that time,
the only known animals to possess feathers were birds.
And in the eyes of the scientists of the time,
that classified this animal as a bird right away.
>> But aside from its feathers,
this strange bird had teeth and a bony tail
just like a dinosaur.
>> If we look closer at the skeleton,
we reveal some ancient characters of reptiles
and some characters that are only found in dinosaurs.
And archaeopteryx really represents
an amazing transitional form
in the evolution of reptiles and dinosaurs to birds.
A long bony tail is something you see in dinosaurs,
as well as other reptiles,
but it's not something that we see in modern birds.
If we look to the skull of archaeopteryx
and into the jaws,
we see a number of fine
but distinctive teeth lining both the upper and lower jaws.
Again, birds do not have teeth.
They have beaks.
The wings are magnificent with asymmetrical feathers,
which suggest that they had a flight function
just like a modern bird feather.
But, at the ends of the arms,
three-fingered hands that are tipped in claws
and this is something
that you only see in meat-eating dinosaurs.
>> Paleontologists scratched their heads
at this Frankenstein hybrid.
Was this a bird or a dinosaur?
But a scientist named Thomas Henry Huxley
knew exactly what he was looking at.
He was a big supporter
of Charles Darwin's theory of evolution.
And when he looked at archaeopteryx, he saw a link.
In 1868, he published a paper that ruffled a lot of feathers
when he proposed a connection
between modern birds and ancient dinosaurs.
>> Thomas Henry Huxley,
the prominent evolutionary biologist of the day,
known to many as Darwin's bulldog,
was the first champion of the idea
that birds were, in fact, descendants of dinosaurs
and could be considered living dinosaurs.
This idea was very controversial at the time
and many scientists didn't accept the evidence.
>> The theory of evolution was not even 10 years old
and skeptical scientists couldn't believe
that giant meat-eating dinosaurs
could have transformed into creatures as benign as birds
over millions of years.
So for a century, the debate about dinosaurs
evolving into modern-day birds was buried.
T. rex remained in the eyes of the world,
a terrifying lizard.
Then in the 1960s, John Ostrom,
one of the world's most-respected paleontologists
would revive the dino-debate.
>> In the summer of 1964,
John Ostrum mounted an expedition
to the Cloverly Formation,
a set of rock exposed in southern Montana
to collect dinosaurs from early Cretaceous age.
He discovered the bones of a group of raptor dinosaurs,
which he went on to name "deinonychus"
or "terrible claw."
The remains were of a remarkably agile,
perhaps even warm-blooded predator.
And this ran counter to all of the entrenched ideas
about dinosaurs at the time.
(♪♪♪)
>> This was a theropod,
the same group of dinosaurs as T. rex,
but had a large brain, while T. rex's was small.
The finding was a game-changer.
>> The pictures of dinosaurs at the time
was one of overgrown lizards, slow, dim-witted, cold-blooded.
Ostrum's find of deinonychus
completely changed that perception.
To find a small, agile, intelligent,
and potentially warm-blooded raptorial dinosaur
was something that really revolutionized
the scientific community.
>> A few years after digging out deinonychus,
T. rex's smaller relative,
John Ostrum examined the fossil remains
of archaeopteryx,
the ancient bird found 100 years earlier.
As he studied the unusual bird,
he noticed more and more similarities
between it and deinonychus,
and the dino-debate was reignited.
Was archaeopteryx the missing link in the 100-year-old theory
that dinosaurs evolved into today's birds?
>> One of the similarities,
and one that John Ostrum was particularly interested in,
was the structure of the wrist.
These dinosaurs have a reduced number of wrist bones
and their anatomy shows
that these dinosaurs could only fold their arms
in one particular way
and that way is exactly like the way a bird folds its wings.
We see more evidence of a close relationship
between dinosaurs and birds in the anatomy of the vertebrae
or the spinal column.
If you look closely along the sides of the vertebrae,
you'll see holes
and these are the hallmarks of where air sacs have invaded
the spinal column.
And these air sacs are
the signature of an avian-style respiratory system.
>> These physical links raise the possibility that theropods,
the bipedal meat-eating family of dinosaurs
that includes tyrannosaurus, evolved into modern-day birds.
Scientists found that T. rex and other theropod dinosaurs
shared part of their anatomy with birds.
But tyrannosaurus rex was missing one bone
that was unique to only birds, the furcula.
Otherwise known as the prize
after polishing off a turkey dinner, the wish bone.
In the last century,
more and more tyrannosaurus rex bones
have been dug out of the earth, but without a wishbone.
With no complete T. rex skeleton,
paleontologists would never know if this giant lizard
was really related to birds.
But in 1990, paleontologists found
the most complete set of T. rex bones ever found.
With over 90% of its skeleton found,
they could finally get closer to finding out
what T. rex anatomy shared with creatures that fly.
>> Tyrannosaurus rex may not look very bird-like
and it's certainly not as closely related to birds
as the raptor dinosaurs.
But T. rex in fact shares a large number of similarities
with birds, including hollow bones.
And with the discovery
of the most complete tyrannosaurus rex, Sue, in 1990,
scientists even recovered the first wishbone
for tyrannosaurus rex,
which provides direct evidence for a link
between large carnivorous dinosaurs like T. rex
and modern-day birds.
>> And it's not just the furcula, spinal air sacs,
and hollow bones these creatures share.
Birds and theropods dinosaurs, like T. rex,
may also have borrowed the same book on parenting.
>> The similarities between birds and theropod dinosaurs
are not just limited to their skeletal characteristics.
We also have remarkable evidence of a link
between birds and meat-eating dinosaurs
in their reproductive characteristics.
This is an Oviraptor egg,
and you can see that the egg itself is oblong.
It's not symmetrically round.
And this is a characteristic of all modern-bird eggs
and it's a characteristic of the eggs
we crack to make breakfast in the morning.
And that oblong shape of the egg is a feature
that birds inherited from theropod dinosaurs.
It's not just the shape of the eggs,
but also how the mothers interacted
with the nests themselves
that demonstrate that link between birds and dinosaurs.
There's been some truly amazing fossils found that show
that Oviraptor dinosaurs and raptor dinosaurs,
not only laid oblong eggs like birds,
but that they actually sat on top of the nest
and incubated the nest with their feathered-bodies
just like a bird.
So that iconic image of a mother hen
sitting on top of her nest of eggs
is actually an inherited behavior
from its dinosaur forebears and another connection between
theropod dinosaurs and living birds.
>> But T. rex weighed as much as three elephants.
>> Because of the immense size of a mother T. rex,
in excess of 6 tonnes,
it's very unlikely it would have been able to sit
on top of its nest of eggs.
>> Tyrannosaurus rex may not have perched in a nest,
but members of the theropod family did,
further establishing the link between theropods and birds.
Scientists were also getting a better understanding
about what the T. rex really was by digging into its bones,
not digging them out.
There have been great advances in science.
Collecting and analyzing genetic material
was getting more and more advanced.
And like collecting DNA from a crime scene,
this new branch of molecular paleontology
could be used to solve other mysteries,
thousands, even millions of years old.
>> When we think of new dinosaur discoveries,
our tendency is to think of crews unearthing new fossils
in the badlands under a hot midday sun.
But with respect to T. rex,
some of the most exciting discoveries about its biology
have been made right here in the lab
and are only visible under the microscope.
>> In 2001,
paleontologist Mary Schweitzer was given
a piece of a very well-preserved T. rex bone.
She put a section of the 68 million-year-old bone
under the microscope
and she was shocked to see something inside the bone.
T. rex bones are hollow, but this one wasn't.
Mary found tissue called the medullary bone,
that is usually found in pregnant female birds.
But now, here it was inside a tyrannosaurus rex fossil.
>> Here's an example of medullary bone
in the thigh bone of a egg-laying kiwi.
Here we have cut the bone in half
and where the shaft is typically hollow,
you can actually see that there is some tissue
in the middle of the bone cavity.
When we make a thin section of this
and put it under the microscope, it looks like this.
This is the outer cortex of the bone, which is normal,
but this is the medullary bone tissue
and this is unique to birds
that are in their egg-laying cycle
and it only occurs in females.
So it was really big advance
in terms of studying dinosaur biology.
>> Finding of the gender of a T. rex
had never been done before.
Now there was evidence
that this old T. rex was more of a queen than a king.
And Mary Schweitzer went one step further
with the fossilized bone.
>> Now when we think of fossil bones,
we typically think of the mineral component of the bone,
that all the soft tissues have degraded
and they are not anywhere to be found within the fossils.
So she demineralized a sample of this T. rex bone.
She was left with networks of soft tissue
with what appeared to be cells inside.
No one expected any soft tissue to be preserved
in a 68 million-year-old tyrannosaurus rex bone.
She added to the experiment.
She analyzed the composition of that soft tissue
and what she found was truly remarkable
that some original collagen was still preserved
in a T. rex bone.
>> This T. rex may have been dead for 68 million years,
but under magnification,
those cells were revealing new secrets.
>> This was then sequenced using a special sequencer
and her team was able to identify
the amino acid sequence of the proteins
in that collagen.
And when that was compared to the collagen
in a number of different animal groups,
it was found to most closely resemble that of chicken.
>> Tyrannosaurus rex, the king of all lizards
is distantly related to a chicken.
Could the beast that terrorized the Earth for millions of years,
now be something that everyone eats for dinner?
Paleontologists have found striking similarities
between certain groups of dinosaurs and modern birds,
from hollow bones to wishbones.
T. rex and the humble chicken may share common genes,
but packaging was still a crucial piece of the puzzle.
Chickens have feathers, and that's what makes a bird,
well, a bird!
And no one has ever found a tyrannosaurus rex
with feathers, at least not in North America.
In the early 20th century,
the vast desert landscape of Mongolia was a no man's land.
But it was here that Roy Chapman Andrews discovered
the first dinosaur nests and other dinosaur fossils
in Asia.
This opened up a new frontier for dinosaur hunters,
looking to find even stranger creatures
to show the world.
Since then,
a Chinese paleontologist named Xu Xing
has uncovered more important finds in this area
than any other paleontologist on the planet.
>> Xu Xing is one of the world's leading paleontologists.
He works at the Institute of Vertebrate Paleontology
and Paleoanthropology in Beijing
and he's one of the most prolific namers of dinosaurs
out there.
He's actually named more dinosaurs
than just about anybody on the planet.
>> And among those finds,
Xu Xing unearthed one of the most important fossils
to help solve the mystery.
A smaller gentler version of T. rex named Dilong
that had feathers.
>> Dilong was one of our first good pictures
of a very early tyrannosaur,
and a very early member of that lineage
that included tyrannosaurus rex.
But it was really special for what was preserved
that's not typically preserved with the dinosaur skeleton.
We're used to the preservation of bones
and seeing skeletons like this in the museum.
But the Dilong specimen that was found
showed the unmistakable impressions
of proto-feathers, a kind of dino fuzz.
>> But Dilong was only the size of a dog,
so would have needed some kind of coat to stay warm.
T. rex was 10 times the size of Dilong.
If it had feathers, it would have overheated.
>> Dilong would have been likely completely covered
in these filamentous proto-feathers
that would have insulated the animal
and allowed it to regulate its body heat.
Small mammals, of course, are covered in hair.
But the largest mammals like rhinos and elephants,
in fact, have lost most of their hair
and this is at least in part to help them to dissipate heat
because of the problems of overheating at large size.
>> Dilong shows us that
some type of feather-covered small tyrannosaurs,
but not those the size of tyrannosaurus rex,
existed.
But in 2012,
Xu Xing made another remarkable find in Chinese Mongolia
that would trump his discovery of Dilong.
Meet Yutyrannus,
tyrannosaurus rex's closest relative.
It's not quite as big as its cousin,
but Yutyrannus was covered in feathers.
This made it even more possible to believe
that a beast as large as tyrannosaurus rex
could have sported plumage.
>> It's another primitive member of the tyrannosaur lineage
that includes T. rex.
But Yutyrannus measured over 30-feet in length.
And it showed that even large tyrannosaurs
could have sported a dino-fuzz type covering
of filamentous proto-feathers
and this suggests to us that T. rex itself
was likely covered in fuzzy proto-feathers.
>> Over the last 100 years,
what we've learned about tyrannosaurus rex
has been changing.
The scary giant lizard we've all grown up with
is most likely related to something else.
Birds.
They share the same bones, behavior, and genetics.
What we're missing are just a few more feathers.
>> I think it's just a matter of time
until we find a T. rex skeleton
that was preserved in the right conditions
that will reveal whether or not T. rex had a scaly skin
or whether it did indeed have a external covering
of filamentous proto-feathers or dino fuzz.
>> But until a feathered-T. rex is found,
there are still gaps in the family tree.
And science has not completely solved the mystery
of whether this is T. rex's closest living cousin.
(Tyrannosaurus roars)
(♪♪♪)