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.