Weird Nature
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The Most Horrifying Sea Monsters To Ever Terrorize The Ocean

Updated May 14, 2020 152.9k votes 33.5k voters 1.8m views11 items

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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    Jaekelopterus, A Sea Scorpion Bigger Than You

    Photo: ДиБгд / Wikimedia Commons / CC BY-SA 4.0

    Jaekelopterus reigned as an apex predator nearly 400 million years ago and was probably willing to eat anything smaller than itself - including members of its own species. These arthropods grew to over eight feet long and had huge, spiked claws that could ensnare fish with ease. Experts believe the Jaekelopterus ambushed prey with its claws before tearing the meal apart. Jaekelopterus is the largest discovered species of arthropod, a group that includes insects, arachnids, lobsters, and crabs.

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  • Photo: Jonagold2000 / Wikimedia Commons / CC-BY-SA 4.0

    The Mosasaurus became an international celebrity after its breakout performance in Jurassic World, and the real-life version is just as impressive. These giant reptiles could likely swallow most of their prey whole but preferred slicing meals into bite-sized morsels with their backward-bending teeth.

    Paleontologists have been studying these animals for years, and a recent discovery has shed new light on the early lives of mosasaurs. Researchers examined two baby mosasaurs and learned that they actually spent their early lives in the open ocean. This discovery has led some scientists to believe that mosasaurs gave birth to live young.

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    Livyatan Melvillei, The Whale That Ate Whales

    Photo: Apokryltaros / Wikimedia Commons / CC BY-SA 3.0

    Named after Herman Melville, the author of Moby Dick, Livyatan melvillei was a massive species of sperm whale that is believed to have preyed on primarily baleen whales. This creature lived only 12-13 million years ago, which is frighteningly recent when it comes to the span of geological time. And while it is estimated to have been about the size of a modern sperm whale, it had foot-long teeth that suggest its food of choice was quite a bit bigger than your average squid.

    Modern sperm whales hunt by using suction - basically sucking prey directly into their giant mouths. Livyatan, however, most likely hunted in a fashion similar to that of orca whales, biting and tearing at their prey. And, yes, a human being could easily fit inside of Livyatan's mouth, making the whale in Melville’s beloved novel seem a lot less fictional.

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    Plesiosaurs, Almost Too Strange To Believe

    Photo: FunkMonk / Wikimedia Commons / CC BY-SA 3.0

    Plesiosaurs are made up of more than one species and lived about 135 million years ago. These long-necked predators served as the main inspiration for the infamous Loch Ness monster, and their unique anatomy has placed it at the center of controversy in the scientific community. Mary Anning, the renowned paleontologist who first discovered these creatures, was actually accused of forgery when she first brought a Plesiosaurus fossil to her colleagues. Interestingly, their iconic long necks were actually not very flexible, making most depictions of them fairly inaccurate. 

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