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10 Terrifying Giant Prehistoric Sea Monsters

Some of the largest and most dangerous creatures this world has ever seen, lived on Earth millions of years ago. Here are ten of the biggest and most fearsome sea monsters that roam the oceans:


10: Mosasaurus, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


Fossil evidence suggests that Mosasaurus could reach 50 feet (15 meters) in length, making it one of the largest marine predators of the Cretaceous period. Mosasaur's head was like that of a crocodile, lined with hundreds of sharp teeth that could kill even the most heavily armored of enemies.


9: Megalodon, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


One of the largest predators in the history of the seas and one of the largest sharks ever recorded, Megalodon was just as terrifying as its appearance.


Megalodon roamed the depths during the Cenozoic Era, 28 - 1.5 million years ago, and was a much larger version of the great white shark, a predator at the top of today's oceans. But while our white greats reach a maximum length of 20 feet (6 metres), megalodon can reach up to 65 feet (20 metres) - longer than a school bus!


8: Tylosaurus, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


Tylosaurus was a type of Mosasaur. It was enormous, reaching over 50 feet (15 meters) in length.


The tylosaurus was a carnivore with a very diverse diet. Stomach remains show signs of fish, sharks, smaller mosasaurs, plesiosaurs, and even some flightless birds. They lived during the late Cretaceous period in the seas that covered North America, where they sat firmly at the top of the marine food chain for several million years.


7: Thalattoarchon Saurophagis,  Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters



T. saurophagis was only recently discovered and is about the size of a school bus measuring nearly 30 feet (9 meters) in length. It is one of the early species of ichthyosaurs that lived during the Triassic period, 244 million years ago. Since they survived shortly after the Permian Extinction (the largest mass extinction on Earth, when 95% of marine life is believed to have been wiped out), their discovery gives scientists new insights into the ecosystem's rapid recovery.




6: Liopleurodon,  Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters



Liopleurodon was a marine reptile that measured more than 20 (6 meters) in length. It mostly lived in the seas that covered Europe during the Jurassic period, and was one of the best predators around. Its jaws alone are believed to be over 10 feet long - roughly the distance from floor to ceiling.


With teeth this big, it's easy to see why Liopleurodon dominates the food chain.


5: Dakosaurus, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


First discovered in Germany, the dcoosaurus, with its strange body, was a still fishy reptile, one of the most important predators of the sea during the Jurassic period.


Fossil remains are found across a very wide distribution, and they appear everywhere from England to Russia to Argentina. Although it is most commonly compared to modern crocodiles, the dinosaur can reach 16 feet (5 meters) in length. Its unique teeth have led scientists to consider it a major predator in the Reign of Terror.



4: Thalassomedon, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters




Thalassomedone was a type of Pliosaur whose name is translated from Greek as "lord of the sea" — and for good reason. They were huge predators, reaching lengths of up to 40 feet (12 m).


Its fins were nearly 7 feet (2 meters) long, allowing it to swim into the depths with deadly efficiency. His reign as a predator continued through the late Cretaceous period, finally ending when the sea saw new and larger predators such as the Mosasaur.


3: Chastasaurus,  Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


Ichthyosaurs were marine predators that looked like modern dolphins and could reach gigantic size during the Triassic period more than 200 million years ago.


Shastasaurus, the largest marine reptile ever found, was a diverse group of ichthyosaurs that could grow to more than 65 feet (20 meters) long, much taller than most other predators. But one of the largest creatures that swam in the sea was not a fearsome predator; Shastasaurus was a specialized suction feeder, eating mainly fish.


2: Helicoprion, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters



Who wouldn't fear the nightmarish jaw of a helikoprion, a large, 270-million-year-old cartilaginous fish with an elaborate spiral of teeth set in the middle of its mouth? First discovered in 1899, this sea monster shares a common ancestor with sharks, though scientists aren't sure how and why its jaws formed as they are.


Recent studies revealed that Helicoprion had a partially hidden tooth factory that began near the area where the upper and lower jaw meet, and ran over the mouth where the tongue would be if it had one, and then into the cartilage supported by the lower jaw. The recovered teeth helped determine that these creatures were at least 25 feet (about 8 meters) long.


1: Nothosaurus, Giant Sea Monsters

10 Terrifying Giant Prehistoric Sea Monsters


Nothosaurus, which was only about 13 feet (4 meters) long, was an aggressive hunter. They were armed with a mouth full of sharp teeth pointing outward, suggesting a diet of squid and fish. Nothosaurus is thought to have been an ambush predator, using the reptile's elegant shape to sneak up on prey and take it by surprise.


Nothosaurs are thought to have been related to pliosaurs, another group of deep-sea predators. Fossil evidence indicates that they lived during the Triassic period more than 200 million years ago.

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