The Most Horrifying Sea Monsters To Ever Terrorize The Ocean

The ocean is massive - and the creatures lurking beneath its surface can grow to sizes that would be impossible on land. Whales are the largest living creatures in the sea, but these gentle giants were preceded by some of the scariest sea monsters of all time. The fossil record is full of scary sea animals that would make Jaws look like a little guppy in comparison - so many that it’s a miracle that none of them are alive today (maybe). 

Giant fish, sharks, and reptiles dominated the oceans for millions of years, becoming the apex predators of one of the craziest and most diverse environments on our planet. Sea scorpions the size of crocodiles swam in the same waters as massive armored fish who could bite a great white in half. The oldest sea creatures were more terrifying than anything cartographers ever doodled onto their maps. These are some of the deadliest creatures of all time, the ones who epitomize the phrase “there’s always a bigger fish.”


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    Dunkleosteus, An Armored Death Machine

    This ancient fish lived 400 million years ago, but its bite has stood the test of time. Scientists believe the Dunkleosteus had the strongest bite of any fish ever discovered - one that could be compared to the bite of a Tyrannosaurus rex. Scientists have crunched the numbers and determined that, just at the tip of its fang, this fish’s bite could measure at 8,000 pounds per square inch. They were absolute apex predators, preying on sharks and basically anything it could catch (everything). Dunkleosteus was also 33 feet long from tooth to tail and covered in thick armor-like plating, making it one of the ocean’s first giant predators.

  • Megalodon, The Whale-Sized Shark
    Photo: Mary Parrish, Smithsonian / Wikimedia Commons / Public Domain

    Measuring at more than 50 feet long, the megalodon was the largest known shark of all time. Their jaws alone were large enough for a full-grown person to walk through with ease, and they used those jaws to hunt whales. To put it in perspective, researcher Peter Klimey with the University of California at Davis said, "A great white is about the size of the clasper, or penis, of a male megalodon.”

    Scientists believe that megalodons hunted whales by first ripping off their tails and fins - immobilizing their prey so they could more easily feast. It is also believed that the extinction of these giant sharks is what allowed whales to reach the enormous sizes that they are known for today. Researchers confirmed that the last megalodon died only 2.6 million years ago, right around the same time the evolution of the first humans began to take place.

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    Helicoprion, The Spiral-Mouthed Killer

    Terrorizing the seas nearly 300 million years ago, the Helicoprion was a bizarre species of shark that sported one of the craziest sets of teeth in natural history. This unusual feature has been the subject of widespread debate in the scientific community for a century, and it’s easy to see why. The only fossils that have been found of this animal contain sets of spiraled teeth, and scientists are still trying to figure out just how they would have possibly fit into the shark’s mouth.

    What they do know is that, like many modern sharks, the Helicoprion most likely had to replace their teeth pretty regularly. And although many illustrations show the Helicoprion with a buzz-saw mouth, some scientists believe that the tooth-spiral may have actually been located inside the shark’s throat. Others claim it was more like a ratfish than a shark, with its teeth positioned at the rear of its jaw.

  • Liopleurodon, A Reptilien Behemoth
    Photo: Bogdanov / Wikimedia Commons / CC BY 2.5

    The Liopleurodon was a giant marine reptile and one of the fiercest predators of the Jurassic period. These massive sea monsters could grow up to 30 feet in length (although some fossils suggest even larger sizes) and had sizeable teeth that would have made a quick meal out of most marine life.

    Despite its size, scientists estimate this reptile probably swam surprisingly fast, and like many sharks, Liopleurodon had an excellent sense of smell, which it used to locate prey. While this all may sound intimidating, chances are Liopleurodon was not even the largest animal in its class; that title most likely goes to Kronosaurus.