The ferocious predatory dinosaurs of Cretaceous Sahara - Nizar Ibrahim

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In Cretaceous times (around 100 million years ago), North Africa was home to a huge river system and a bizarre menagerie of giant prehistoric predators -- including the Spinosaurus, a dinosaur even more fearsome than the Tyrannosaurus rex. Nizar Ibrahim uses paleontological and geological data to reconstruct this “River of Giants” in surprising detail.

Lesson by Nizar Ibrahim, animation by Silvia Prietov.

There are few places on Earth
less hospitable to life

than the bone-dry Sahara Desert.

Yet it wasn't always this way.

100 million years ago, during a period
known as the Mid-Cretaceous,

a gargantuan river system flowed
across the region

from modern day Egypt to Morocco.

The whole world at that time
would look rather different to us.

The continents had yet to assume
their current positions.

Extreme temperatures were common

and fierce storms made life unpredictable.

Dinosaurs flourished on land,

pterosaurs roamed the skies,

and giant marine reptiles and sharks
swam in warm seas.

Small mammals, our ancestors,
lived quite literally in the shadow

of these extraordinary creatures.

In this world of huge predators,

the River of Giants,

which is what some call this region
of what is now northern Africa,

stood out as particularly dangerous.

In most ecosystems, it's lonely at
the top of the food chain.

There usually isn't enough prey
to sustain many predators.

Yet an incredible variety of aquatic
prey species in the river-based ecosystem

may have allowed a large and diverse
population of apex predators to coexist.

We know this thanks to a wealth of fossils
we found in an area

called the Kem Kem Beds.

Many of the predators we've discovered
had head and body shapes

that made them uniquely adapted
to hunt the different types and sizes

of aquatic prey.

This allowed many Kem Kem predators to
take full advantage

of the one abundant food source
in this environment: fish.

This also allowed them
to avoid direct competition

with the predators going after
land-loving animals.

Prey species in the river system had to
contend with attacks from all sides,

including from above.

Flying reptiles dominated the skies.

Alanqa Saharica had a wingspan of
up to nine meters,

and long slender jaws that helped it
snatch fish

and small terrestrial animals.

At least seven different types
of crocodile-like predators

patrolled the waterways,

including the roughly
ten-meter-long Elosuchus.

And multiple species of T-rex-sized
carnivorous dinosaurs called theropods,

lived side by side.

In the River of Giants,
Spinosaurus was king.

This 15-meter-long dinosaur was even
longer than T-rex,

with short muscular hind legs,

a flexible tail,

and broad feet.

It's two-meter-high sail warned
other creatures of its fearsome size

and may have also been
used to attract mates.

Spinosaurus' long slender jaws were spiked
with conical teeth,

perfect for swiftly clamping down
on slippery aquatic prey.

This apex predator,
as well as its ecosystem,

is unparalleled in the history
of life on Earth.

All that's left of these
fearsome predators are fossils.

About 93 million years ago,
sea levels rose,

submerging the Kem Kem region
in a shallow sea.

Tens of millions of years later,

an asteroid impact,

volcanic eruptions,

and associated changes in climate

wiped out the dinosaurs, pterosaurs, and
many other groups of animals and plants,

including their unique ecoysystems.

That mass extinction paved the way
for the rise of new kinds of birds,

larger mammals,

and eventually us.