Students of paleontology have long known that prehistory is a strange and scary place. But it’s a place that is safely gone. Giant insects, gargantuan dinosaurs, monsterous fliers–all locked safely behind a tomb of rock, barred from rising and devouring mankind. If mankind had lived with such creatures, who knows what horrid scars it would have on our collective psyche? Luckily, humanity was spared the worst of it.

Right?

Well, as it happens, not so much. As humanity spread across the globe, they found plenty of things terrifying enough to brand themselves into cultural nightmares. In honor of Halloween, we’re counting down the five most horrifying creatures that mankind met in its march across the world. Creatures like…

5: The Mega Shark

Humanity has always been afraid of the ocean. Legend after legend has told of cruel monsters waiting just outside the breakers, ready to tear and devour any who are foolish enough to brave the waters. I’m not saying that Carcharodon megalodon caused it. But it damn well helped.

A denizen of warm waters, much like its relatives the Great White and the Mako, Megalodon was a truly epic beast: a 60 foot long shark, able to devour just about anything that crossed its path. Whales of all sizes, dolphins, sea turtles, and dugongs all were on the menu. And it’s not entirely impossible that the menu included humans. Megalodon’s known range is quite large, though it had shrunk some what by the time Homo Sapiens arrived. Still, the warm waters of the Indian and Pacific likely provided a last haven to these massive beasts, and humans have been tooling around those shores for quite a while. It was not a long interaction, as the Megalodon  was already on its way out when humans appeared. Still, the creature has left some mark on human conscious: Megalodon is nearly as famous as T.rex in popular culture.

4: The Scimitar Cat

Ice Age Europe was a cruel place. Freezing cold and half covered in glaciers, it provided a special challenge to humans. Unlike other continents, it did not host extravagant monsters, making due with the usual ice age suspects: mammoth, cave bear, wooly rhino, dire wolf. All of them terrifying, given the right circumstances. But the scimitar cat, Homotherium, was in a league of its own.

With a hyena like form and teeth adapted for slashing rather then stabbing (the major disadvantage Saber Tooth Cats faced was long, fragile teeth) Homotherium was just the right size to take down a human being. Long front legs and a cheetah like nose and eyes made it a truly formidable predator, able to move fast, take in air efficiently and see very, very well. Moreover, it was perfectly placed to scare the bejesus out of people: Homotherium finally went extinct sometime around 9,000 B.C.E. For those of you that are up on your history, that’s right at the crux of the Neolithic, when most of the mega fauna in Europe and America were long extinct. But in the dark forests and caves of Europe, the scimitar cat lurked as one last, deadly reminder of the ice age.

3: Haast’s Eagle

The Maori people arrived on the shores of New Zealand to find a world populated by birds like the Moa, all of them docile and unready for the scourge of human hunting. All except one. With a shrill scream and a gust of air, horrible death fell from above at 30 pounds and 50 miles an hour. Harpagornis, the Haast’s eagle, welcomed the Maori to New Zealand.

With a wingspan of 10 feet, Haast’s Eagle was the largest of the true raptors, outstripping even the largest vultures. While Golden Eagles approach that wing size, they are 40 % smaller. And Golden Eagles have killed people. With relatively short wings and a long tail, Haast’s eagle was fast and maneuverable in the scrub forests, preying on the giant moa and other flightless birds. Being struck by one was the equivalent of receiving a clawed cinder block to the head from 82 feet up. And as Moa began to be hunted to extinction, humanity was almost certainly next on the menu. But Haast’s eagle was never common, and when the Maori finally grew tired of having clawed cinderblocks dropped on their head, they drove it to extinction in 1400 C.E.

2: The Short Faced Bear

In North America humanity was spreading with, if not speed, then at least some alacrity. The mega fauna were dying off, thanks in part to hunting, and the forests were beginning to look a bit safer. But if you’ve made it this far, you can probably guess this was not the case. Neither eagles or sabertooths awaited the newly arrived native Americans. Instead, it was bears; grizzlies and black bears and polar bears. Any one of these animals was more then capable of killing a man in an extraordinarily messy fashion; but the Short Faced Bear raised it to a high art.

Five feet tall at the shoulder, 11 feet when standing upright, the Short Faced Bear was well adapted for death dealing. Massive jaws, long canines, and a bulk of up to 1,800 pounds were combined with long limbs to make it the most powerful land predator in America. Given that modern bears show no special running adaptations and still can barrel along at speeds faster then a man can run, the Short Faced Bear was probably extremely fast, possibly able to reach speeds of 40 miles per hour. That, combined with the natural toughness of bears, likely made it a prime killer of mastodon… and humans as well.

1: The Dust Dragon

Australia. The continent already holds its fair share of bowel churningly terrifying creatures. But when the Aborigines landed on Australia’s shores, they found a land populated with creatures stranger then anything anywhere else in the world. Marsupial lions, giant wombats, and short faced kangaroos roamed the grasslands. Ok, they thought, we can handle this. Then they met Megalania.

Imagine a Komodo dragon nearly 26 feet long and up to 4,300 pounds, it’s jaws loaded with ripping teeth and septic venom. While rare, it was able to sustain high levels of activity for a longer amount of time. That combined with it’s size and probable love of ambush attacks, made it a creature to be feared. To put it in context; a seven foot Komodo monitor is more then capable of taking down a human. A 26 foot predator is capable of taking down a lot of them. And Komodo monitors are tough, able to take wounds most animals would die from. Scale that up, and you have juggernaut predator, the apex monster of the dream time. Megalania likely went extinct 39,000 years ago, leaving plenty of time to sear itself into Aboriginal mythology.

We’re luckier then we know to live in a time without megafauna. But we can still remember, on dark nights, the terror that our ancestors must have felt when they made their way through a world full of monsters.