There are few places on Earth less hospitable to life than the bone-dry Sahara Desert.
地球上很少有能比极其干燥的撒哈拉沙漠还不适合生物生存的地方。
Yet it wasn't always this way. 100 million years ago, during a period known as the Mid-Cretaceous,
但它本来并不是这样的。1亿年前的白垩纪中期，
a gargantuan river system flowed across the region from modern day Egypt to Morocco.
有一个庞大的河流体系流经这个区域，从现代埃及延伸至摩洛哥。
The whole world at that time would look rather different to us.
那时的世界面貌跟我们如今所看到的截然不同。
The continents had yet to assume their current positions.
各大洲还没有呈现出现时的地理位置。
Extreme temperatures were common and fierce storms made life unpredictable.
极端温度的出现是很常见的事情，还有猛烈的暴风雨让生存变得不可预测。
Dinosaurs flourished on land, pterosaurs roamed the skies, and giant marine reptiles and sharks swam in warm seas.
恐龙在陆地上繁衍不息，翼龙漫游在天空中，大型海洋爬行动物和鲨鱼在温暖的大海中畅游。
Small mammals, our ancestors, lived quite literally in the shadow of these extraordinary creatures.
我们的祖先即小型的哺乳动物生活在这些非凡生物的阴影里。
In this world of huge predators, the River of Giants,
这个大型捕食者的世界，还有巨人之河，
which is what some call this region of what is now northern Africa, stood out as particularly dangerous.
有人说这里就是现在的北非地区，因极其危险而引人关注。
In most ecosystems, it's lonely at the top of the food chain.
在绝大多数生态系统中，位于食物链顶端的生物是孤寂的。
There usually isn't enough prey to sustain many predators.
通常没有足够的猎物能够供养那么多捕食者。
Yet an incredible variety of aquatic prey species in the river-based ecosystem
然而，在以河流为基础的生态系统中有各种各样的水生猎物，
may have allowed a large and diverse population of apex predators to coexist.
得以让数量庞大、品种多样而且处于食物链顶端的捕食者共存。
We know this thanks to a wealth of fossils we found in an area called the Kem Kem Beds.
多亏了我们在某个区域里发现的大量化石，我们才知道了这一切，这个区域名字叫卡玛卡玛地层。
Many of the predators we've discovered had head and body shapes
我们所发现的许多捕食者都具有头部和身体形态，
that made them uniquely adapted to hunt the different types and sizes of aquatic prey.
这使它们能特异性适应于不同类型和大小的水生生物的猎捕。

This allowed many Kem Kem predators to take full advantage of the one abundant food source in this environment: fish.
这让卡玛卡玛捕食者能充分利用在这个环境里一种充足的食物来源：鱼。
This also allowed them to avoid direct competition with the predators going after land-loving animals.
这得以让它们避免直接的竞争，不用跟其他捕食者一起追逐陆地动物。
Prey species in the river system had to contend with attacks from all sides, including from above.
河流体系中的猎物需要应对来自四面八方的攻击，包括天上飞的捕食者的攻击。
Flying reptiles dominated the skies.
飞行类爬行动物在天空中占支配地位。
Alanqa Saharica had a wingspan of up to nine meters,
萨哈瑞卡翼龙的翅膀展开后可达九米，
and long slender jaws that helped it snatch fish and small terrestrial animals.
还有它细长的下颚能够协助它捕捉鱼类和小型的陆生生物。
At least seven different types of crocodile-like predators patrolled the waterways, including the roughly ten-meter-long Elosuchus.
至少有七种不同类型的鳄鱼类捕食者在水域中巡视，其中包括了身长大概10米的埃罗鳄。
And multiple species of T-rex-sized carnivorous dinosaurs called theropods, lived side by side.
还有一类被统称为是兽脚亚目恐龙的有着霸龙王体型的肉食性恐龙，它们和平共存着。
In the River of Giants, Spinosaurus was king.
在巨人之河中，棘龙是国王。
This 15-meter-long dinosaur was even longer than T-rex, with short muscular hind legs, a flexible tail, and broad feet.
这种恐龙身长15米，比霸王龙还要长，它有强壮的短小后腿，一条灵活自如的尾巴和宽大的脚。
It's two-meter-high sail warned other creatures of its fearsome size and may have also been used to attract mates.
它两米高的帆翼让其他生物惧怕于它的体型，或许还被用来吸引雌性恐龙。
Spinosaurus' long slender jaws were spiked with conical teeth, perfect for swiftly clamping down on slippery aquatic prey.
棘龙细长的下颚中长满了锥形牙齿，能快速地将表面光滑的水生猎物完美制服。
This apex predator, as well as its ecosystem, is unparalleled in the history of life on Earth.
这种位于食物链顶端的捕食者，还有它赖以生存的生态系统，在地球的生命史上是前所未有的。
All that's left of these fearsome predators are fossils.
但这些可怕的捕食者最后剩下的只有化石。
About 93 million years ago, sea levels rose, submerging the Kem Kem region in a shallow sea.
大约在9300万年前，海平面上升，将卡玛卡玛地区淹没成一片浅海。
Tens of millions of years later, an asteroid impact, volcanic eruptions, and associated changes in climate
数千万年后，小行星撞击，火山爆发，气候随之改变，
wiped out the dinosaurs, pterosaurs, and many other groups of animals and plants, including their unique ecoysystems.
恐龙、翼龙还有许多动植物都因而灭绝，这其中包括了它们独一无二的生态系统。
That mass extinction paved the way for the rise of new kinds of birds, larger mammals, and eventually us.
这种大规模的灭绝为新物种，如鸟类，还有大型哺乳动物的诞生创造了条件，最终人类得以诞生。