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There are few places on Earth less hospitable to life
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than the bone-dry Sahara Desert.
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Yet it wasn't always this way.
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100 million years ago, during a period known as the Mid-Cretaceous,
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a gargantuan river system flowed across the region
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from modern day Egypt to Morocco.
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The whole world at that time would look rather different to us.
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The continents had yet to assume their current positions.
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Extreme temperatures were common
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and fierce storms made life unpredictable.
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Dinosaurs flourished on land,
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pterosaurs roamed the skies,
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and giant marine reptiles and sharks swam in warm seas.
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Small mammals, our ancestors, lived quite literally in the shadow
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of these extraordinary creatures.
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In this world of huge predators,
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the River of Giants,
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which is what some call this region of what is now northern Africa,
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stood out as particularly dangerous.
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In most ecosystems, it's lonely at the top of the food chain.
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There usually isn't enough prey to sustain many predators.
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Yet an incredible variety of aquatic prey species in the river-based ecosystem
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may have allowed a large and diverse population of apex predators to coexist.
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We know this thanks to a wealth of fossils we found in an area
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called the Kem Kem Beds.
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Many of the predators we've discovered had head and body shapes
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that made them uniquely adapted to hunt the different types and sizes
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of aquatic prey.
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This allowed many Kem Kem predators to take full advantage
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of the one abundant food source in this environment: fish.
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This also allowed them to avoid direct competition
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with the predators going after land-loving animals.
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Prey species in the river system had to contend with attacks from all sides,
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including from above.
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Flying reptiles dominated the skies.
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Alanqa Saharica had a wingspan of up to nine meters,
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and long slender jaws that helped it snatch fish
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and small terrestrial animals.
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At least seven different types of crocodile-like predators
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patrolled the waterways,
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including the roughly ten-meter-long Elosuchus.
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And multiple species of T-rex-sized carnivorous dinosaurs called theropods,
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lived side by side.
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In the River of Giants, Spinosaurus was king.
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This 15-meter-long dinosaur was even longer than T-rex,
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with short muscular hind legs,
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a flexible tail,
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and broad feet.
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It's two-meter-high sail warned other creatures of its fearsome size
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and may have also been used to attract mates.
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Spinosaurus' long slender jaws were spiked with conical teeth,
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perfect for swiftly clamping down on slippery aquatic prey.
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This apex predator, as well as its ecosystem,
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is unparalleled in the history of life on Earth.
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All that's left of these fearsome predators are fossils.
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About 93 million years ago, sea levels rose,
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submerging the Kem Kem region in a shallow sea.
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Tens of millions of years later,
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an asteroid impact,
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volcanic eruptions,
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and associated changes in climate
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wiped out the dinosaurs, pterosaurs, and many other groups of animals and plants,
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including their unique ecoysystems.
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That mass extinction paved the way for the rise of new kinds of birds,
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larger mammals,
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and eventually us.
