You can see why people thought there were sea monsters. Because basically, there are: giant squid, sharks, etc. But the most terrifying of sea creatures lived along with the dinosaurs. If you time traveled back to those days, you'd be better off fighting the giant land creatures because, frankly, the sea dinosaurs were even more deadly.
Take this recent fossil discovery. It's of a 50 ft long marine reptile from the Jurassic era, with a bite force of 33,000 lbs per square inch. So it could crush anything it wanted.
"'With a skull that's more than 10 feet long you'd expect the bite to be powerful but this is off the scale,' said Joern Hurum, an associate professor of vertebrate paleontology at the Natural History Museum of Oslo University. 'This one is more like it could crush a Hummer.'"
Well that's one way to take out gas-guzzling vehicles.
Plus, the creature's name so far? Predator X. Just wait until this one gets made into its own direct-to-video release. (You've got competition now, Megalodon!)
The fossil was discovered on the Norwegian Arctic archipelago of Svalbard. For all the book nerds out there, Svalbard is where the armored bears live. Only an armored bear could take on Predator X!