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9 Prehistoric Monsters Guaranteed to Haunt Your Dreams

Take a look at nine of the most alarming prehistoric monsters that have ever swum, crawled and slithered around our planet.


You think you've got problems? Life today is a walk in the park compared with prehistoric Earth's relentless survival free-for-all where we'd have been first on the menu. Just take a look at those fossil records and tell us they're not the stuff of nightmares. The oxygen-rich atmosphere and over-abundant food supply of the planet's early years unleashed an evolutionary arms race on land and sea that led to some of the largest — and scariest — beasts that have ever swum, crawled and slithered. We took a look at nine of history's most alarming prehistoric monsters.

1. Megalodon

(Carcharocles megalodon)

Here's a guy who's pretty much all mouth. The giant shark megalodon is by far the biggest vertebrate aquatic predator ever discovered by paleontologists.

Its name means "great tooth" and that's no overstatement. The megalodon's multiple rows of 276 teeth — which could be up to 7 inches long — were set in a jaw 6.5 feet across. This mighty maw could exert up to 41,000 pounds of bite — making it more than a match for those delicious giant turtles, porpoises and sea cows it enjoyed having round for dinner.

Looking a little like an oversized great white — at around 60 feet, these prehistoric monsters were three times the size of their younger cousins — and way more aggressive, the megalodon lived in the seas around Europe, Africa, Australia and the Americas in the Cenozoic Era between 16 million and 2.6 million years ago.

2. Basilosaurus

(Basilosaurus cetoides)

Illustration by Pavel Riha

Despite its name, basilosaurus, or "king lizard," was actually a whale that lived during the Eocene epoch until around 34 million years ago. When its fossilized bones were first found in the United States, their shape and distribution led scientists to think they had found a giant reptile of some kind and it was named accordingly.

This shouldn't be too surprising as it is believed the basilosaurus was shaped like, and indeed moved like, a giant eel — a 60-foot eel, that is, with long, powerful back legs and a jaw that could snap through its victims with 3,600 pounds of biting force.

These prehistoric monsters hunted fish and sharks in the shallow seas — which covered what is now Alabama, the only location in which they've ever been found — and became that state's official fossil in 1984.

3. Elasmosaurus

(Elasmosauridae)

The elasmosaurus, or "ribbon lizard" — a 46-foot, 2-ton reptile from the Cretaceous period (about 80 million years ago) — liked to stick its neck out. So much so, in fact, that more than half its total length was taken up by collar.

The elasmosaurus had 71 cervical vertebrae — a huge number of neck bones — which allowed it to feed by both stealth and speed. Instead of being a fast swimmer, the prehistoric predator would creep up on shoals of fish and then suddenly dart its head into the crowd to snatch a few hapless souls away.

These unlucky fish would be impaled on teeth that were long and spiny to prevent escape but which were no good for chewing. This suggests the elasmosaurus swallowed its prey whole. Well, if you're not going the whole way, why go at all?

4. Titanoboa

(Titanoboa cerrejonensis)

Another primordial hunter that liked skewering its victims was the carnivorous titanoboa — a monstrous snake with needle-like teeth that could pierce flesh and so hold its unfortunate prey in place. Up to 50 feet long and 3 feet wide, the fearsome creature could then wrap itself around its prey before squeezing it to death.

Far larger than modern constrictors, these prehistoric monsters were almost certainly the largest and most dangerous things slithering through the rain forest river systems of what is now the Colombian jungle 60 million years ago.

Though it could also lurk in the trees, the huge serpent hit its deadly stride with its agility in the water and woe betide any large fish, turtle or even crocodile that got in its way.

5. Onchopristis

(Gigantichthys numidus)

Onchopristis was a pretty awesome-looking beast. At over 26 feet long, it would be scary enough but, armed with an 8-foot snout "saw," lined with barbed teeth, it looks positively terrifying.

Yet this fearsome beast from the Cretaceous period (which ended 65 million years ago) actually used its mighty weapon for nothing more than digging out and capturing crustaceans from the river and sea bed. Not so good news if you happen to be a prehistoric crab, maybe, but less alarming for any time-traveling paleontologists out there.

With a population spread all across the globe, from north Africa to New Zealand, it is thought these prehistoric monsters lived communally in schools and, like modern-day salmon, followed their senses back home to lay their eggs.

6. Sarcosuchus

(Sarcosuchus imperator)

Sarcosuchus imperator means "flesh crocodile emperor," and there's little doubt these prehistoric monsters were every bit as horrifying as that fantastical name suggests.

At around 40 feet long and weighing 10 tons, there probably weren't a large number of challengers to the imperial crown worn by this mighty beast on the banks of Africa and South America 110 million years ago.

Like modern-day crocodiles, the muscles used to open its jaws were probably fairly weak — it is thought, however, that this supercroc's bite force may have been as much as 17,500 pounds. That's pretty much lights out if you happen to be any large, lobe-finned fish, turtle or rival dinosaur that happens to be passing.

7. Giant Sea Scorpion

(Jaekelopterus rhenaniae)

Illustration by Jaime Chirinos/SPL

If you have any kind of phobia about insects, you might want to look away now. At 8 feet in length and with elongated, jointed arms ending in giant, spiked claws, the giant sea scorpion is enough to make anyone lose a little sleep.

Jaekelopterus menaced the waters that covered what is now Germany around 390 million years ago and is thought to have been keen on snapping up fish and crustaceans and anything else soft and fleshy that came to … er, claw. It may, however, also have been cannibalistic, making a meal of even its nearest and dearest.

Should you find yourself in the Devonian Era, however, you should be safe. Paleobiologists think these prehistoric monsters had such flimsy legs that they would have been incapable of leaving the water. That just leaves the 6-foot millipedes and the dragonflies the size of seabirds for you to worry about.

8. Cameroceras

(Cameroceras)

Cameroceras (or "chambered horn") was a cephalopod that lived in the Ordovician period around 470 million years ago. Related to squid and octopuses, this ancient kraken consisted of a huge spiral cone — possibly around 18 feet long — with protruding tentacles that could reach out and seize fish, crustaceans and other shellfish.

Though soft tissue doesn't leave anything in the fossil record for us to study, by comparing the Cameroceras to modern cephalopods like cuttlefish, scientists can build up what they think is a fairly accurate picture of the half-billion-year-old beast.

It's thought the tentacles would drag unfortunates toward a hard "beak" made of keratin that could easily snap bone, shell and tendon in two. It's also possible that, like related modern-day sea creatures, Cameroceras had a "toothed tongue," a barbed appendage that could be used to drag out and devour the soft tissue from inside a shell.

9. Stupendemys

(Stupendemys geographicus and Stupendemys souzai)

Prehistoric Earth wasn't a complete nightmare, though. After all — everyone loves a turtle — even with a carapace 11 feet across and a neck so long it has to fold it sideways to fit into the shell.

Stupendemys is pretty lovable even if it's still a teensy bit scary. This freshwater beast was massive — so massive, in fact, scientists think it was probably too heavy to do much hunting and would have more likely grazed on underwater plants in the inland seas, rivers and freshwater swamps of South America in the late Miocene, around 5 million years ago. (S. geographicus hung out in Venezuela, whereas its close relative, S. souzai lived in Brazil.)

It is thought the turtle developed its titanic proportions as a response to the giant crocodiles and other hella-hungry threats that shared its habitat. Stupendemys means "astonishing turtle," and we certainly think any easy going vegetarian surviving that kind of world has to be something pretty special.

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