0:00:08.086,0:00:11.916
There are few places on Earth [br]less hospitable to life

0:00:11.916,0:00:14.787
than the bone-dry Sahara Desert.

0:00:14.787,0:00:17.547
Yet it wasn't always this way.

0:00:17.547,0:00:22.117
100 million years ago, during a period[br]known as the Mid-Cretaceous,

0:00:22.117,0:00:25.536
a gargantuan river system flowed[br]across the region

0:00:25.536,0:00:28.647
from modern day Egypt to Morocco.

0:00:28.647,0:00:32.317
The whole world at that time[br]would look rather different to us.

0:00:32.317,0:00:35.618
The continents had yet to assume[br]their current positions.

0:00:35.618,0:00:37.628
Extreme temperatures were common

0:00:37.628,0:00:41.297
and fierce storms made life unpredictable.

0:00:41.297,0:00:43.799
Dinosaurs flourished on land,

0:00:43.799,0:00:45.907
pterosaurs roamed the skies,

0:00:45.907,0:00:51.368
and giant marine reptiles and sharks[br]swam in warm seas.

0:00:51.368,0:00:56.458
Small mammals, our ancestors,[br]lived quite literally in the shadow

0:00:56.458,0:00:59.948
of these extraordinary creatures.

0:00:59.948,0:01:02.169
In this world of huge predators,

0:01:02.169,0:01:03.803
the River of Giants,

0:01:03.803,0:01:07.758
which is what some call this region[br]of what is now northern Africa,

0:01:07.758,0:01:10.809
stood out as particularly dangerous.

0:01:10.809,0:01:14.748
In most ecosystems, it's lonely at[br]the top of the food chain.

0:01:14.748,0:01:18.438
There usually isn't enough prey[br]to sustain many predators.

0:01:18.438,0:01:23.920
Yet an incredible variety of aquatic[br]prey species in the river-based ecosystem

0:01:23.920,0:01:30.599
may have allowed a large and diverse[br]population of apex predators to coexist.

0:01:30.599,0:01:34.079
We know this thanks to a wealth of fossils[br]we found in an area

0:01:34.079,0:01:36.429
called the Kem Kem Beds.

0:01:36.429,0:01:39.919
Many of the predators we've discovered[br]had head and body shapes

0:01:39.919,0:01:44.270
that made them uniquely adapted[br]to hunt the different types and sizes

0:01:44.270,0:01:46.791
of aquatic prey.

0:01:46.791,0:01:49.950
This allowed many Kem Kem predators to[br]take full advantage

0:01:49.950,0:01:55.489
of the one abundant food source[br]in this environment: fish.

0:01:55.489,0:01:58.462
This also allowed them [br]to avoid direct competition

0:01:58.462,0:02:03.110
with the predators going after[br]land-loving animals.

0:02:03.110,0:02:08.098
Prey species in the river system had to[br]contend with attacks from all sides,

0:02:08.098,0:02:10.431
including from above.

0:02:10.431,0:02:13.052
Flying reptiles dominated the skies.

0:02:13.052,0:02:17.232
Alanqa Saharica had a wingspan of[br]up to nine meters,

0:02:17.232,0:02:20.709
and long slender jaws that helped it[br]snatch fish

0:02:20.709,0:02:24.661
and small terrestrial animals.

0:02:24.661,0:02:27.950
At least seven different types [br]of crocodile-like predators

0:02:27.950,0:02:29.851
patrolled the waterways,

0:02:29.851,0:02:33.411
including the roughly [br]ten-meter-long Elosuchus.

0:02:33.411,0:02:38.982
And multiple species of T-rex-sized[br]carnivorous dinosaurs called theropods,

0:02:38.982,0:02:41.882
lived side by side.

0:02:41.882,0:02:45.661
In the River of Giants,[br]Spinosaurus was king.

0:02:45.661,0:02:49.542
This 15-meter-long dinosaur was even[br]longer than T-rex,

0:02:49.542,0:02:51.732
with short muscular hind legs,

0:02:51.732,0:02:53.132
a flexible tail,

0:02:53.132,0:02:54.992
and broad feet.

0:02:54.992,0:02:59.612
It's two-meter-high sail warned[br]other creatures of its fearsome size

0:02:59.612,0:03:03.012
and may have also been [br]used to attract mates.

0:03:03.012,0:03:07.912
Spinosaurus' long slender jaws were spiked[br]with conical teeth,

0:03:07.912,0:03:13.793
perfect for swiftly clamping down[br]on slippery aquatic prey.

0:03:13.793,0:03:16.870
This apex predator, [br]as well as its ecosystem,

0:03:16.870,0:03:21.710
is unparalleled in the history[br]of life on Earth.

0:03:21.710,0:03:25.337
All that's left of these [br]fearsome predators are fossils.

0:03:25.337,0:03:28.852
About 93 million years ago, [br]sea levels rose,

0:03:28.852,0:03:32.663
submerging the Kem Kem region[br]in a shallow sea.

0:03:32.663,0:03:34.543
Tens of millions of years later,

0:03:34.543,0:03:36.023
an asteroid impact,

0:03:36.023,0:03:37.744
volcanic eruptions,

0:03:37.744,0:03:40.303
and associated changes in climate

0:03:40.303,0:03:45.983
wiped out the dinosaurs, pterosaurs, and[br]many other groups of animals and plants,

0:03:45.983,0:03:49.192
including their unique ecoysystems.

0:03:49.192,0:03:53.455
That mass extinction paved the way[br]for the rise of new kinds of birds,

0:03:53.455,0:03:54.824
larger mammals,

0:03:54.824,0:03:57.015
and eventually us.