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{\an8}Dinosaurs ruled the planet
for over 150 million years.

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They occupied almost every corner
of the globe

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and came in almost
every shape and size imaginable.

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Some were truly extraordinary.

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We now know that T. rex was
a powerful swimmer...

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Velociraptors were cunning,
feathered hunters,

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and that some dinosaurs had
the most bizarre behavior.

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But new discoveries
are being made almost every day

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that tell us more about life
on this planet 66 million years ago.

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This time on Prehistoric Planet,

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we reveal new animals

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and new insight
into their quest to find a partner,

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the challenges faced by raising a family,

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and their titanic battles.

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Journey to a time
when nature put on its greatest show.

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This is Prehistoric Planet 2.

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The ocean.

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The largest habitat
on the prehistoric planet...

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and home to one of the biggest predators
that has ever lived...

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a giant mosasaur.

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But not all mosasaurs are
ferocious 50-foot-long monsters.

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Taking refuge in the reef
is Phosphorosaurus.

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She too is a mosasaur.

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One of the smallest,
at less than ten feet long.

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She spends the daylight hours
hiding from danger.

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But once or twice an hour, she has to
dart to the surface to grab a breath.

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Like all of her kind,
she is air-breathing.

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She's dwarfed by the biggest mosasaurs.

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But she too is a deadly predator...

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and she doesn't always hide
in the shadows.

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When the time is right,
she becomes a hunter.

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And that time is when the sun sets.

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As darkness falls,
her underwater world transforms.

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Now, billions of creatures will begin
to rise from the depths

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to feed near the surface.

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The largest mass migration on Earth occurs
in almost total darkness

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and can only be seen
with special night-vision cameras.

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The most spectacular of these nighttime
visitors are a type of lantern fish.

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Their faint, eerie light is produced by
a chemical reaction inside their bodies.

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A flash of this bioluminescence
can be used to confuse predators.

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And when seen from below,
the glow enables them to blend with

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and hide against
the ocean's moonlit surface.

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But they can't hide from Phosphorosaurus.

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For her size,
her eyes are the largest of any mosasaur...

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allowing her to see through the illusion
and pick out her prey.

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By the time dawn arrives,

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the migrating shoal has sunk once more
to the depths.

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And Phosphorosaurus too must return
to her daytime hiding place.

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The biggest mosasaurs are back
on the prowl.

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She will have to wait till nightfall
before it's safe to hunt again.

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By day, the prehistoric ocean
provides opportunities

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for a very different type of hunter.

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In the warm,
shallow seas of North America,

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fish numbers can almost match
the nocturnal lantern fish shoal.

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And they are a magnet
for six-foot-long Hesperornis.

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Hesperornis may be unable to fly,
but it's superbly adapted for ocean life.

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Large, powerful feet propel it
with great agility.

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There's no escape for any unfortunate fish

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once it's caught by this beak
full of needle-sharp teeth.

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The Hesperornis don't have the shoal
to themselves for long.

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Xiphactinus, known as X-fish.

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The feeding opportunity soon attracts them
in large numbers.

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At over 17-feet long, they are one of
the largest and fastest fish in the ocean.

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With its huge mouth, Xiphactinus can
scoop up several fish at once

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and has even been known to swallow prey
half its size whole.

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At first, there is plenty for everyone.

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But as fish numbers dwindle,
the X-fish turn their attention elsewhere.

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Predator is about to become prey.

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The Hesperornis have only one option:
to swim for their lives.

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Xiphactinus is faster.

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Hesperornis is more agile.

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But in the eyes of an X-fish,
anything is on the menu...

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even their own kind.

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Within minutes,
the banquet is all but gone...

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and the predators move on.

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Danger in the ocean
doesn't only come from deadly hunters.

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It could come from the sea itself.

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Here, around the islands
of prehistoric Europe,

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it's the power of the tide
that creates challenges for life.

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Especially for the tiniest creatures.

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These are ammonite eggs.

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Thousands of them.

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They have been swept inshore...

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to rock pools.

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Here, they have the chance
to develop free from danger.

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The eggs are tiny,
only a fraction of an inch each.

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Now it's time for the young within
to break free.

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They move by jet propulsion.

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But mastering new swimming skills
is not easy.

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Until now,
these pools have provided a nursery.

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But as the tide retreats,
they become isolated.

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Others can make their escape.

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But for the helpless ammonites,

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their nursery can quickly become
a deadly trap.

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Under the midday sun,
the water in the pool starts to evaporate.

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If it dries out completely,
they will all die.

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But everything is not lost.

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Baby ammonites can do
something remarkable.

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Each makes its own bid for freedom,
forcing them together.

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The combined effort means
they effectively move as one.

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Each is carried along
on this tiny living tide,

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pushed over the bare rock by those behind...

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eventually escaping to deeper water.

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Now they wait for the rising tide.

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But not everyone escapes.

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Countless are left stranded...

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food for scavengers,
like these baby Pyroraptors.

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The rest are carried by powerful currents
many miles from land.

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Even as far as this,
the very heart of the Pacific Ocean.

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These enormous atolls
and the lagoons at their center

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provide the only shelter
for thousands of miles.

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In this rare place, Tuarangisaurus,
a kind of elasmosaur, finds safety.

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But outside these shallows,
it's a different story.

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Each day, the elasmosaurs must venture
into deeper water.

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Canyons in the atoll walls lead
from the shallows to rich feeding grounds.

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This deep water attracts
not just the hungry elasmosaurs

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but the predators that hunt them.

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The biggest in the ocean.

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50-foot-long Mosasaurus.

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Nutrients driven up from the ocean floor
ensure a plentiful supply of fish.

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Streamlined bodies
and four powerful flippers

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give elasmosaurs great maneuverability.

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But their daily feeding forays make
their movements predictable

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for an intelligent and patient hunter.

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Mosasaurus is an ambush predator.

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This enormous animal uses its huge tail
to accelerate with astonishing speed.

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This time, unlucky.

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In fact, most hunts fail.

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But with so many elasmosaurs living here,

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it's not long
before there is another opportunity.

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Camouflaged against the dark canyon floor,
the mosasaur can approach unseen...

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waiting for a young,
inexperienced individual.

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The ideal victim.

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Mosasaurus can strike their prey
with such force

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that the impact alone can kill.

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It's an attack so swift, the elasmosaur
almost certainly never saw it coming.

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Life in the ocean can be dangerous,
not only because of giants.

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Of the baby ammonites
that escaped the rock pools,

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less than one in a hundred has survived
several months at sea.

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But these few have been
particularly lucky.

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Ocean currents have carried them
to an ideal place to live:

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seagrass beds off the coast of Europe.

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Here, shoals of ammonites occur
in a surprising variety of sizes...

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and shapes.

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This strange,
six-foot-long giant is Baculites,

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which feeds near the seafloor.

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And almost matching it in size,

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Diplomoceras,
shaped like a giant paper clip.

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They all flourish here,
thanks to an abundance of food.

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Plankton. Small crustaceans.
Some even eat fish.

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These hatchlings are beginning to acquire

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the extraordinary shape they will have
when they are mature.

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The protruding spiral identifies them
as young Nostoceras.

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These are adult Nostoceras.

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They favor the seafloor in deeper waters.

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Ammonites have been thriving
in these prehistoric oceans

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for almost 400 million years.

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There are thousands of species.

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They are one of the most successful groups
of animals to have ever lived...

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flourishing in the warm, temperate seas
and even the coldest waters at the poles.

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Like here, in the frozen sea
around the Antarctic.

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After a winter of near-total darkness,
the low sun is beginning to melt the ice...

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making it accessible once more
for a giant seasonal visitor.

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Morturneria, a strange type of elasmosaur.

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They are warm-blooded,

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with a thick layer of blubber
which conserves the heat in their body.

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They're one of the world's most secretive
and elusive animals.

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This pod has migrated nearly 2,000 miles
from South America

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to arrive here in time for spring.

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It's the first time this year's calves
will have encountered sea ice.

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It can be dangerous
for an air-breathing reptile.

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They can only grab a breath of air
where there are gaps in the ice.

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Adults must navigate carefully
to find them,

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and the youngsters must stay close.

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These cold waters are an excellent habitat
for this giant's favorite food.

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Polar mud full of small creatures.

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There can be hundreds of tiny animals
in every square foot of seafloor.

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Separating what's edible
from the sticky mud is a challenge.

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But they have a neat solution.

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Scooping up a mouthful,
they partially close their jaws,

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creating a giant sieve
to filter out the food.

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These are the only animals
to have evolved teeth to feed in this way.

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The Morturneria will feed here all summer,

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until the water ices over again
in the polar winter.

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In warmer waters,
they will face other challenges.

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But the most resourceful animals
will always find opportunities

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in the vast oceans
of the prehistoric planet.

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The lands of the prehistoric planet
were ruled by the dinosaurs.

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But the seas were dominated
by a very different group of reptiles:

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the mosasaurs.

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And this is the skull of one of them.

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Mosasaurs were seagoing lizards.

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{\an8}Think of a giant, swimming,
whale-sized Komodo dragon.

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Tapered snout, rough skin,
four fins instead of normal limbs

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and a long tail that would look
a lot like a shark tail but upside down.

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That's basically a mosasaur.

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The largest was Mosasaurus hoffmanni.

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It was an ambush predator.

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But what was the secret of its success?

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{\an8}They can move from just still,
not moving at all

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{\an8}to incredible speeds
right before your eyes.

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In the modern world, we see
this ability in reptiles like crocodiles.

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Their muscles can deliver short bursts
of tremendous power.

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Mosasaurus, given that they're reptiles,
given that they're lizards,

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probably had similar capabilities
in their muscles.

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They also had another adaptation

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that could increase
the element of surprise.

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One of the tricky things about swimming is

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you need a special kind of dynamic
to get out of the gate quickly,

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to do the equivalent of a sprinter's start
from the blocks.

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00:32:28,323 --> 00:32:33,829
And one of the best ways of doing that is
to bend yourself into a C-shape

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and then push off of the water
with the side of your body.

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Fish today use this technique.

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Known as a C-start,

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{\an8}it allows them to accelerate from
a standstill to full speed in an instant.

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{\an8}Mosasaurs likely were able to do
something very similar,

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but of course at a much grander scale.

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So, exactly how fast could
a giant like Mosasaurus hoffmanni swim?

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To find out, the Prehistoric Planet team
commissioned a unique scientific study.

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Until recently,
no one had really attempted to estimate

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these kinds of performance values
in detail.

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Our work is one of the first attempts

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to really put numbers to the abilities
of these animals.

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And the results we got from that
are really pretty stunning.

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{\an8}The team ran the calculations four times

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{\an8}to ensure they were correct.

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{\an8}All four of the different trials
came to the same overall conclusion.

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These animals were able to generate
massive accelerations.

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This mosasaur, it could probably
clear 75% of its body length

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in one single second.

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That means, if that mosasaur is
17 meters away from you,

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in one second, it will be 75% closer.

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And in the second second,
it would have surpassed you

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and probably eaten you along the way.

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Being hit by a Mosasaurus would be

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a bit like being hit
by a full-size semitruck.

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Just the impact of the animal alone,
much less the bite that would follow,

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would kill a lot of its prey instantly.

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Mosasaurs could reach 30 miles an hour

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in as little as one second.

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This is what makes them, arguably,
the ultimate marine predator of all time.