10. Shastasaurus
This creature is probably the one that closest resembles Dolphins. It was known to reach more than 65 feet in length but although it was massive, it wasn’t particularly dangerous and mostly preyed on smaller fish.

9. Dakosaurus
This one originates from the Jurassic period and closest resembles crocodiles of today. IT would reach around 16 feet in length and they were very dangerous thanks to the sharpness of their teeth.


8. Thalassomedon
This massive prehistoric creature could reach over 40 feet in length. With its incredibly long neck and flippers, it could move around the bottom of the ocean with ease. It went extinct when even larger predators appeared.
7. Nothosaurus
This one is said to have lived during the Triassic period. Its length would not reach more than 13 feet but it’s aggressiveness was phenomenal. The smaller body allowed them to sneak up on their targets.
6. Tylosaurus
This incredibly terrifying creature was the king of the ocean for several hundred years. Its size could easily reach 50 feet length. A very dangerous carnivorous creature.


5. Thalattoarchon Saurophagis
Alive during the Triassic period, it is said to have been 30 feet long, and is said to have survived one of the biggest mass extinctions of species in our world.
4. Tanystropheus
Another creature from the Triassic period but this time no exclusive marine. This one could actually go on land even though it spent most of its time in sea. Thanks to the gigantic length of its neck it could reach more than 20 feet away from it.
3. Liopleurodon
Here is another terrific creature from the Jurassic period. Although its total length was a little about 20 feet long, some say just its jaw was over 10 feet long.

2. Mosasaurus
This one is known as the most dangerous and horrific creature to have lived in the Cretaceous period. Reaching over 50 feet in length and with a set of hundreds of sharp teeth, it’s no surprise this creature was the terror of the ocean at the time, able to rip through anything.
1. Megalodon
The king of the sea, the most dangerous and incredible sea creature of all time and also the largest shark to have ever existed. It lived in the Cenozoic era. It is said to have been over 65 feet long and it was the apex predator of the ocean at the time.

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