During these times of quarantine, last month feels like 100 million years ago. But if you were to actually go back to that period of time and make your way to the western Sahara, you’d likely run into a whole new set of problems in the form of hordes of enormous predators, according to a new study.

Instead of a desert, the region was covered by a vast river system that flowed up through present-day Morocco and Algeria. Strangely, paleontologists have found very few fossils of the plant-eating dinosaurs that roamed much of the world at the time. Rather, many of the fossils they have identified belonged to flesh-eating dinosaurs, flying reptiles called pterosaurs, and ancestors of modern crocodiles.

“It was arguably the most dangerous place in the history of planet Earth because it was home to so many different kinds of predators in all shapes and sizes,” says Nizar Ibrahim, a paleontologist at the University of Detroit Mercy. “This river of giants is unlike any ecosystem today, and in fact it’s also pretty unique compared to other dinosaur age ecosystems.”

Ibrahim and his colleagues have taken a sweeping look at the denizens and geology of this ecosystem, the remnants of which are preserved in the rock formations in eastern Morocco known as the Kem Kem Group or Kem Kem beds. Their report, published on April 21 in the journal ZooKeys, is based on the team’s findings from two decades of expeditions to the area and visits to fossil collections in museums around the world.

“This work represents the first detailed synthesis of all previous works on the geology and the paleontology of the Kem Kem Beds, and the first attempt to reconstruct the environmental conditions in this zone of North Africa between 100 and 95 million years ago,” Andrea Cau, an independent researcher who has collaborated with museums and universities in Italy, the United Kingdom, and elsewhere, told Popular Science in an email.

While some of the paleontological findings are still preliminary and will need to be confirmed with more detailed studies, the report could provide a valuable resource for paleontologists on future expeditions in the area, said Cau, who has studied the Kem Kem Group and other ancient ecosystems in northern Africa.

The area dubbed the Kem Kem Group consists of layers of sedimentary rock exposed on a long, winding escarpment near the border between Morocco and Algeria. The fossils found here are a motley bunch.

“You get very small things—tiny little amphibians and delicate plants—all the way up to massive dinosaurs,” Ibrahim says. A few of these fossils represent herbivorous dinosaurs such as the long-necked sauropods. But these creatures don’t seem to be nearly as common as their carnivorous kin, a pattern that paleontologists have noted in sites across northern Africa since the 1930s.

These fearsome beasts included at least four large predatory dinosaurs. One belonged to a group called abelisaurids; its short snout and relatively small teeth suggest it may have been a scavenger. Paleontologists have also unearthed fossils from a Spinosaurus with a narrow snout and teeth specialized for puncturing and snaring fish, a fleet-footed raptor around 26 feet long, and a massive hunter with serrated teeth that resembled steak knives known as Carcharodontosaurus saharicus that was nearly the size of T-rex. Meanwhile, pterosaurs with wingspans between 13 and 20 feet soared overhead and sharks and crocodile-like creatures the length of a school bus prowled the waters.

“If you were to visit this place as a human being, there really are many different ways to die,” Ibrahim says. “You wouldn’t be safe anywhere.”

By examining the broad assortment of fossils from this harrowing environment, Ibrahim says, he and his team hoped to better understand how the “incredible abundance” of predators coexisted and what they dined on. The researchers observed that the skulls belonging to carnivores from the Kem Kem Group varied quite a bit, suggesting they were specialized to feed on different kinds of prey. This might have allowed the predators to stay out of each other’s way and avoid having to compete for the same meals. In many cases, these meals would have been seafood. Fish appear to have been the most plentiful food source at the time, with some of these swimmers reaching the size of SUVs.

In today’s landscapes, top predators such as wolves and lions are well outnumbered by their herbivorous prey. However, even during the mid-Cretaceous Period when northern Africa was covered by vast river systems, ecosystems dominated by so many bulky predators would have been rare. “In some ways it’s more similar to what you might see in marine ecosystems, where predators are actually more common,” Ibrahim says.

The landscape these animals lived in was filled with meandering rivers, lakes, and mudflats. This suggests that the region couldn’t support enough vegetation for long enough periods of time to feed large numbers of plant-eating dinosaurs, Ibrahim says.

However, there may be other reasons why paleontologists have found so few remnants of large herbivores in this area. Most of the sauropod fossils from this region are single bones or isolated fragments rather than more complete skeletons, which makes it hard to determine which species they belonged to, Philip Mannion, a paleontologist at University College London who was not involved in the research, said in an email. Sauropods also tend to have similar-looking teeth, and the vertebrae that would be more revealing are often fragile and less likely to be preserved.

“We can’t ultimately be sure that [the fossils] don’t reflect a greater diversity,” he said. It’s also possible that these plant-eating dinosaurs primarily lived and died in other nearby habitats and only rarely ventured into the areas that happened to be preserved in the Kem Kem Group.

For Ibrahim, the Kem Kem Group is a reminder that the ecosystems of the past could be governed by very different rules from those we see today. This isn’t surprising, he says, given that more than 99 percent of all organisms that ever existed died out before the little slice of time we call the present.

“The Sahara is a breathtaking place as it is, but when you’re out there in this dry and inhospitable place and you pick up giant fish scales and crocodile teeth, that really gives you a sense of what we call deep time,” he says. “That’s when you really understand how much our planet has and can change over time.”