(dinosaur growling)
A dinosaur with a giant sail on its back.
It's a Spinosaurus.
A 15 meter long huge carnivore.
It's wading out into the sea.
Some dinosaurs seem to have ventured into the water.
But maybe
they should have stayed on land.
Because at the time,
the sea was home to real monsters,
ones to terrify even dinosaurs.
The primeval ocean ruled by giant predators.
(calm music)
What dramatic life and death encounters unfolded
in the seas of the dinosaur age?
Discoveries by the world's top researchers
gave the first glimpse into the little-known domain
of life on prehistoric Earth.
These sea monsters belong to a different branch
of the evolutionary tree from dinosaurs.
They were marine reptiles.
Among them was Mosasaurus,
the apex predator of the ancient oceans.
As Tyrannosaurus rex ruled the land,
Mosasaurus ruled the sea.
How did it get to the top of the food chain
in the underwater world?
The ancestors of Mosasaurus were relatively small,
living in shadow of the dinosaurs.
But after tens of thousands of generations,
they turned the tables on the dinosaurs.
The stage for this drama is the Earth
of 66 million years ago,
the epoch when the dinosaurs were flourishing.
(dinosaurs roaring)
The vast blue ocean that lied beyond the familiar landscape
ruled by the dinosaurs
hides a dramatic world of colossal roaming reptiles.
(water splashing)
A giant ball composed of thousands of fish.
This potential feast draws all kinds of marine carnivores.
First to appear is a marine reptile
with a bizarre appearance, a species of Plesiosaur.
It's eight meters long.
It uses its amazingly long neck and sharp snaggle teeth
for snapping up fish.
Plesiosaurus flourished the longest
among marine reptiles in the Dinoworld seas.
Up from the depths swims the king of the fish,
the five meter long Xiphactinus.
It was among the largest predatory fish species
during the age of dinosaurs,
with a mouth big enough to gulp down a person in one bite.
It hunted prey in all types and sizes.
Long-necked Plesiosaurs
and giant Xiphactinus may have terrorized the oceans
but they were not the true rulers of the sea.
(dramatic music)
Tearing apart the Xiphactinus in one bite,
the giant Mosasaur makes its entrance.
13 meters in length, it's bigger than a large city bus.
This is the largest individual in this ocean.
She exerts her mighty predatory power over the ocean.
Other Mosasaurus gather around,
hoping to feast on the leftovers.
She slams her body fiercely into her rivals.
As a hunter of the seas, she is without rival.
A few days later, she floats at the surface.
With her head above the waves,
she seems to be scanning for prey.
(calm music)
(dinosaurs roaring)
It's a pair of Tyrannosauruses.
They have driven their prey into the surf
and are preparing to bring it down.
(dramatic music)
(water splashing)
(dinosaurs roaring)
The Mosasaur attacks one of the Tyrannosauruses.
The Tyrannosaurus isn't used to moving around in the surf.
Without firm footing,
it can't fully exert its own fearsome power.
The Mosasaur is powerful enough to deliver the killing blow,
even to a Tyrannosaurus.
A few years back, a Mosasaurus fossil was found in Japan.
In 2014, two high school students
in Kobe discovered it in the woods.
(calm music)
Here is the fossil they found.
At first, we didn't think
it was that important,
just a random shell fossil or something.
I realized these boys had made an amazing find.
Further study of the fossil determined
that it was part of a Mosasaurus jaw.
What's remarkable is the size.
When compared to other Mosasaurus fossils found
in other countries, this jaw fossil indicates
a head almost two meters long.
That means the whole body was 13 meters long.
It was among the largest Mosasaur ever found.
Mosasaurus is known for its bite force
comparable to a Tyrannosaurus.
With a jaw lined with razor sharp teeth,
it could prey on any creature living in the water.
That is proven by the contents of a fossil's stomach.
It contained fish, sharks, birds,
and even other Mosasaurs.
And the latest research indicates
that giant marine reptiles like Mosasaurus
would also attack dinosaurs.
This can be seen in this fossilized skull
of a Pliosaurus, an extinct marine reptile.
One of the most remarkable and extremely rare findings
with this skull is the association of these armor plates,
things called scute,
one which was preserved inside the roof of the mouth.
The triangular part is the dinosaur's scute.
Analysis revealed that this scute came
from the back of an armored dinosaur.
Researchers see this as evidence
that Mosasaurus and other marine reptiles
also ate land-dwelling dinosaurs.
It was feeding on a swimming dinosaur,
so this specimen shows a definite interaction
between predator and prey,
an interaction between a marine reptile
and a terrestrial dinosaur.
Recently, it's also become clear
that Mosasaurus was quite clever.
The clues are found in this museum.
The fossil is of an Ammonite,
a giant spiral-shelled mollusk.
This Ammonite's shell has multiple round holes in it.
Holes that line up perfectly with Mosasaurus teeth.
But how do holes in a shell give evidence
that Mosasaurus was smart?
Let's return to 66 million years ago.
(dinosaurs roaring)
Soaring through the skies of the Dinoworld are Pterosaurs,
large flying reptiles.
(water splashing)
The Mosasaur makes a sneak attack.
Like killer whales of today, Mosasaurus is thought
to have used stealthy ambush hunting tactics.
Here is a group of Ammonites.
They were another favorite food of Mosasaurus.
But Ammonite shells are very tough.
Even Mosasaurus can't just crack them open.
And despite their cumbersome appearance,
Ammonites are surprisingly nimble swimmers.
That's where the Mosasaurus' strategy comes in.
Because of their large shells,
Ammonites have a blind spot behind them.
Our Mosasaur sneaks up quietly from behind.
A plan of attack that proves ingenious.
She seizes the Ammonite in her jaws.
But soon, she lets it go.
Ammonites control their movements
by adjusting the pressure
inside the chambers in their shells
that give them buoyancy.
If the chambers are damaged, they just sink.
They can't nimbly move anymore.
The Mosasaur targets the weakness
by punching holes in the shell
to incapacitate their swift getaway movements.
Mosasaurus was a cunning hunter
that used clever strategies to stalk and kill its prey.
Power and strategies.
Mosasaurus had both,
and that enabled it to rule the seas.
Thousands of fossils found around the world so far
corroborate how Mosasaurus was thriving globally.
Takuya Konishi is a leading expert on Mosasaurs.
He says that the tremendous success
of these marine reptiles is exceptional
in the history of life on Earth.
(speaking in foreign language)
From the time the Mosasaurus first appeared,
in only about 10 million years,
they spread through the planet's oceans
and grew larger in size.
The speed of their rise stands out in the history
of life on our planet.
During the age of the dinosaurs,
Mosasaurus rose rapidly to dominance in the sea.
(calm music)
Even when she's sleeping,
other predators don't dare bother her.
But before the remarkable evolutionary rise,
they were just small creatures cowering
in the shadow of the dinosaurs.
About 300 million years ago,
the evolution of Mosasaurs and dinosaurs diverged
from their common ancestor, a primitive reptile.
The reptilian lineage separated into two large groups,
the lizard and snake branch and the crocodilians.
Mosasaurs evolved from the former,
while dinosaurs emerged from the latter.
The fates of the Mosasaur group
and dinosaurs were different.
By the time the first Mosasaurus species appeared on Earth,
dinosaurs had already evolved into large dominant creatures.
Meanwhile, what did our Protomosasaurus look like?
This is the coast of Africa 100 million years ago.
Protomosasaurus is not very big, less than a meter long.
It's living on land, not in the water.
(feet pattering)
(dinosaurs roaring)
The Protomosasaurus scampers around
at the feet of dinosaurs of enormous size.
It spots prey, a crayfish.
The ancient reptile gulps it down.
The Protomosasaurus belongs to the same reptilian group
as snakes that can open their mouths very wide.
It had the type of jaw that can stretch so much
it can even swallow large prey whole.
In this epoch, food was scarce on the seashore.
To survive the harsh environment,
the gaping mouth was quite helpful.
The scrawny Mosasaurus ancestor could quickly gobble up
any prey it could find.
A large predator, Abelisaurus, approaches.
(dinosaur roaring)
The Protomosasaurus flee in all directions,
looking for anywhere to escape.
(dinosaurs roaring)
(dramatic music)
(water splashing)
(dinosaur roaring)
To avoid ferocious predators,
Mosasaurus's ancestors, over hundreds of generations,
adapted to aquatic life.
Protomosasaurus mastered swimming.
(calm music)
In the ancient ocean, fish are abundant.
Unlike on land, ruled by the dinosaurs,
the sea offered plenty of food.
The wide opening mouth comes in quite handy
for chasing after fish.
The gaping mouth first evolved on land
to aid survival in a food scarce environment.
But by chance, it proved to be a mighty weapon in the sea.
And in this epoch, there were few carnivorous enemies
in the sea or rival predators competing for prey.
This environment ensured Protomosasaurus's survival.
Now we fast forward 30 million years
from the sea of 66 million years ago.
Our Mosasaur is chasing a school of fish.
From the timid lizard-like creature
who scuttled in the shadow of the dinosaurs,
the lineage has quickly grown
into this large dominant marine predator,
with the help of the gaping mouth that it continued.
Now Mosasaurus is the king of the primeval oceans.
It even preys on its ancient enemy.
(dinosaurs roaring)
The fully evolved Mosasaurus reigned supreme,
fearing nothing, not even the largest dinosaurs.
The massive mouth was one secret of its success
and now scientists have begun to identify another one.
Hideaki Kato of Shizuoka University does research
on the evolution of Mosasaurus
by studying the characteristics
of their living relatives, lizards.
(speaking in foreign language)
Lizards have a wide variety of shapes
and interesting behaviors.
They are showing us more and more
about the evolution of life.
Kato is on an expedition in Australia,
home to more than 1,000 species of lizards.
And some of these species exhibit a trait
that was critical to the flourishing of Mosasaurs.
Oh, there's something, right there.
Kato frantically grabs at the lizard
as it tries to escape.
There it is.
A Common Dwarf Skink.
It's a tiny lizard.
This one's full grown.
But I'm looking for something else.
Kato spots another lizard.
Gotcha.
Look, an Inland Bearded Dragon.
Look at those long toes and long limbs.
But once again,
it's not the lizard he's looking for.
There's one.
Look, look!
He finally found his target lizard.
He's fighting back hard.
Stronger than I expected.
The lizard Kato wanted, the Shingleback.
It's 30 centimeters long and armored in tough scales.
Isn't this species dangerous?
It has powerful jaws,
so if you get bit, it will do damage.
Modern Shinglebacks have one trait
that reveals the key to the success of Mosasaurs.
She's got one.
See, the belly's swollen, it's large?
Right here, there's a baby.
Probably just one.
She is pregnant.
Shinglebacks are one of the very few reptiles
that are viviparous, meaning they give birth to live young.
Most lizards don't give live birth,
but they lay eggs instead.
This rare footage shows
Shinglebacks delivering their young alive.
The trait of live birth may have evolved
in these lizards because it gave more chances
of survival of their offspring in harsh conditions.
Cold, hot, dry.
Ancestral Mosasaurs also lived in harsh conditions,
constantly threatened by powerful predators like dinosaurs,
which must have led them to acquire the ability
of live birth.
Evidence found in Europe shows
that live birth had already evolved
in early Mosasaur species.
This is a fossil of Carsosaurus marchesetti,
a primitive Mosasaur species,
soon after the lineage took to the sea.
Look closely at the stomach.
There's a slight indentation here.
This is actually the eye of a baby.
Analysis of the fossil revealed
that this ancestral Mosasaur had four babies in its belly.
Carsosaurus marchesetti was a very interesting animal
also because it was a viviparous animal.
So that's a lot, this animal to really cut every connection
with the earth and to start to move even to deep water
very, very outside the continents.
What happened when Mosasaurus evolved
to give live birth?
In the world where ancestral Mosasaurs lived,
this adaptation offered some survival advantages.
An ancient species of sea turtle has come ashore en masse.
Like Mosasaurus, their ancestors moved
from the land to the sea.
Although the turtles live at sea, they spawn on land.
They lay their eggs on sandy beaches.
(foot scraping)
Left on land, eggs are exposed to the dangers
of dinosaurs finding and eating them.
Not far away, the Protomosasaurus is also at the shoreline.
This one is pregnant.
Protomosasaurus has acquired the ability
to grow young within its body.
The newborns are very small.
(calm music)
Delivered underwater, they immediately head to the surface
to take their first breaths.
They're born tail first, so they can keep breathing
until the last possible moment.
The trait of live birth must have dramatically increased
the survival rate of young
and eliminated the need to return to shore to lay eggs.
It allowed Protomosasaurus to go out into the open sea.
Eventually, their offspring would occupy all the seas
across the planet.
The latest study reveals
that Mosasaurs may have further evolved pregnancy.
The discovery of this small fossil was published in 2018.
Based on bone characteristics,
it was determined to be part of the jawbone
from a baby growing inside its parent.
From the size of that jaw,
the baby Mosasaur is estimated to have been 2.2 meters long.
(speaking in foreign language)
We now know that Mosasaurus babies
were extremely large at birth.
In order to give birth to such a big baby,
the mother would have needed an organ like a placenta,
which could provide enough nutrition to the baby
to help it grow that large while inside the mother's body.
The process of Mosasaur evolution
may have brought forth an organ like a placenta,
which is also a hallmark of mammals.
The placenta is a special organ.
Animals that give birth do not always have one.
Through the placenta,
the baby inside the parent body could continuously receive
plenty of nourishment and thus grow very large.
In the case of Mosasaurus,
the gestation period continued for about one year
and the long pregnancy may have brought about a close bond
between mother and baby.
We can see that result in the Shingleback,
a modern lizard that also give birth to live young.
The Shingleback has a placenta
and the baby can grow
to 1/3 of its mother's size before birth.
The Shingleback is also extremely unusual among lizards,
as it takes good care of its young.
The mother licks her child.
And now, the child licks its mother.
(speaking in foreign language)
The mother uses a flick of her tongue
to the child to catch its scent
and confirms that it's her own offspring.
It is observed that the mother shows maternal affection
and after birth, the child will stay with its mother
for several months or even years.
Growing large babies inside the body
means they can only produce a small number of them.
And the mother tries to protect her few offspring
with the utmost care, creating a close bond
between mother and child.
This is an exceptional behavior
not found in any other lizard.
Luis Chiappe, a world renowned paleontologist,
has spent years researching the reproductive behaviors
of ancient species.
He believes that Mosasaurs and other marine reptiles
may have also nurtured a strong family bond.
We can infer that there was a strong bond
between mother and baby.
This bond most likely provided protection to the baby
but it also provided the opportunity to gain other skills,
such as for example learn how to hunt
or where to migrate and other skills
that would be critical for the baby's survival.
It was a very good strategy.
As a matter of fact,
it's a very good strategy for vertebrates in general.
66 million years ago.
The epic Mosasaurs were in their prime.
Our Mosasaurus' belly is swollen.
She has been pregnant for a year.
Her delivery date is coming soon.
(water splashing)
A few days later, on the night of a full moon,
a large group of Mosasaurus have gathered in the shallows.
More than 50 of them.
They are all pregnant females.
Fossil evidence strongly suggests
that they gathered to give birth to their young.
Our Mosasaur is among them.
It's obvious she's suffering labor pains.
Shinglebacks, a modern day lizard that give live birth,
are also known to have labor pains.
Delivering such big babies
may inevitably have involved a huge strain.
The Mosasaurus newborns are more than two meters long.
If the newborns don't get air to breathe right away,
they'll drown.
Perhaps mother can give them
a bit of help reaching the surface.
In another part of the ocean shallows, Plesiosaurs gather.
They also give live birth to large young.
In the age of dinosaurs,
these gigantic marine reptiles became viviparous
and made the seas their domain.
Mothers and babies have survived the strain of birth.
But now, a school of giant fish approaches.
They are Xiphactinus
and they aim to devour the Mosasaurus newborns.
Our mothers and babies try to escape the onslaught.
But one of them is lagging behind.
Mother comes to the rescue.
The Mosasaur mothers drive off the monster fish.
Live birth and the strong family bond.
By ensuring the survival
of their offspring quite effectively,
Mosasaurus could successfully thrive
in the seas of the dinosaur age.
(calm music)
The lineage of the ocean rulers continues.
On land, the feathered dinosaur Deinocheirus engages
in mating rituals to produce offspring.
And the highly intelligent Troodon raises the young
for the next generation.
They thrive protecting
and taking good care of their offspring,
and that ability allowed these lineages
to last for 150 million years.
Until suddenly interrupted by a huge asteroid
10 kilometers across, bearing down on Earth.
(calm music)
(asteroid crashes)
The impact led to 75%
of all species on Earth becoming extinct.
Despite their unprecedented success,
dinosaurs and marine reptiles suddenly disappeared
in the middle of their peak.
66 million years later, we are living on this planet
that was once home to the huge reptilians.
(speaking in foreign language)
I often think about the fact
that even though Mosasaurus was at the top
of the food chain, the ecosystem radically shifted,
they vanished in no time.
Right now, humanity is thriving to an amazing degree.
But what does the future hold?
Maybe the fate of Mosasaurus points to the answers.
In the Amazing Dinoworld,
the dramatic stories of life beyond our wildest imagination.
More stories are yet to be told by fossils.
Memories come to life
that are still waiting to be unearthed across the world.
(dramatic music)