On our very own, familiar Earth, there are places that never see the light. There are strange creatures wholly unlike us, with different ways of existence and wildly different bodies. On our own planet, there is deep, dark mystery.

Mankind has explored and knows more of the reaches of outer space than it does of the dark depths of Planet Earth. The sea mystifies us and lures us in, it makes us want to go to unseen lands and write tales of adventure and danger. When you think of it, though, the norm is ocean life, not life on dry land: marine organisms make up 50 to 80 percent of the total on the planet. And, of that enormous oceanic living space, we have only explored a meager 10 percent.

This fact gets magnified when you realize that the Earth is, actually, 4.543 billion years old. Imagine everything we do not know about the landscapes and the creatures that have inhabited it before us! Innumerable plants and animals have lived and died in the long history of the oceans and we are only now beginning to find out what they were like.

Among the too diminutive to be noticeable and the probably unremarkable, there were also strange and terrifying creatures. Scientists have found fossils of a time when, if a mariner had been able to roam the seas at will, he would have really written on his map: “Here there be monsters”. Read on to find out more about the weirdest of these prehistoric sea creatures!

The 7 Weirdest Prehistoric Sea Monsters

#7 – The Giant Stingray

Straight from the Jurassic period (approximately 100 million years ago), we get the giant stingray. This cartilaginous fish is a distant cousin of sharks. Its flat, flying-carpet-like body is tipped by a tail and 10-inches-long poisoned spike that serves as its defense. They can reach a width of 17 feet!

Plot twist: stingrays are still alive and going strong! Remember Steve Irwin (R.I.P.)? The giant stingray might not look as stereotypically scary as other creatures further down this list, but you really, really do not want to mess around with them.

While they will not try to make you their next meal () and only attack when threatened, they are still extremely dangerous. For example, they can plunge their tail spike— neurotoxins included— through a human limb or torso. Sadly, like many other stingrays, it is endangered today.

#6 – The Kronosaurus

A beast whose name means “lizard of Kronos” has to be a badass, doesn’t it? The Kronosaurus swam in the seas of the Cretaceous period— from 145 million years ago to 99 million years ago.

This sea monster could grow to measure up to 33 feet and weighed around 9 tons. Impressive, right? What’s more: as demonstrated by fossil findings, its head alone could reach 9 feet long. On the bright side, its 11-inches teeth were not especially sharp— just, you know, regular 11-inches teeth.

Do you want to know what made the Kronosaurus even scarier? Scientists think that it terrorized all the seas in the world.

#5 – The Liopleurodon

The Liopleurodon belongs to the same family of sea dinosaurs as the Kronosaur: the Pliosaurs. These are characterized by a relatively enormous head and teeth, a stout neck, and wide turtle-like fins.

This sea reptile could reach, it is thought, 30 feet long, and weighed around 10 tons. Despite its ridiculously big size, it was fast, especially in short distances. This was the apex predator of the Jurassic period (166 million years ago to 139 million years ago) and ate just about anything. Unlike the Kronosaurus, these one’s teeth were actually pretty sharp.

#4 – The Dunkleosteus

Imagine a cross between an old, benign sea turtle and a T-rex. Done? There you have the dunkleosteus. This creature lived in the Late Devonian period, 358 to 382 million years ago. That is before the dinosaurs!

The dunkleosteus belongs to a family of armored fish— yes, you read that right— measured up to 20 feet, and weighed more than one ton. What is it that makes it so terrifying? If you don’t consider a giant, carnivorous armored fish absolutely ghastly, maybe you will now: the dunkleosteus’ ridged mouth opened so fast that it sucked its prey in and crushed it. The fish version of a vicious black hole.

#3 – Livyatan Melvillei

Named after a Biblical monster of doom and the terrifying Moby Dick of Melville’s novel, this guy was a heavyweight. It lived from 9.9 to 8.9 million years ago and has been called a hyper-predatory whale. Basically, a whale that preys on other predators (including other whales).

In case that was not savage enough for you: the livyatan melvillei’s teeth are the longest, biggest teeth ever recorded that were actually used for eating. Each tooth could reach a whopping 1.18 feet long! And, like present-day— tamer— whales, the livyatan had an inbuilt sonar system that it used to locate its unfortunate prey.

#2 – The Jaekelopterus Rhenaniae

A scorpion is usually a nasty, unwelcome, and even feared visitor. What about an armored sea scorpion that measured more than 8 feet (bigger than a man)? Yes, it also had teethed claws and a possibly venom-loaded tail.

This ungodly abomination prowled the ocean until the Permian extinction event, which happened 250 million years ago. The Jaekelopterus rhenaniae was the biggest recorded bug to ever live! Its measly heir is the— fortunately, much less intimidating— horseshoe crab.

#1 – The Megalodon

Sharks, though controversial and sometimes bloody creatures, are pretty cool. They also make very profitable movie and TV stars. It’s doubtful, however, that anyone could have filmed the Megalodon and lived to tell the story.

This ancient ancestor of modern-day sharks was, sometimes, 60 feet long (bigger than a school bus) and weighed 70 tons (about 10 elephants). Its name, quite fittingly, means “big tooth”, and it probably looked like a much bigger, much scarier white shark. One of the youngest monsters on this list, it went extinct only 1.5 million years ago— when humans already walked the earth. That must have been a terrifying time!

Final Thoughts

Fortunately, humans did not live early enough to share a beach or sailing day with most of these insane creatures. On the other hand, it is a little sad that we will never be able to witness their magnificence and power. But— you know— if you find yourself flung back in time by some sort of freak time-machine accident, don’t go for a swim.

Bonus – Does the Megladon Still Exist