One of the most often sighted cryptids and or sea monsters is the sea serpent, sailors, for centuries, gace reports of giant sea monsters that were large enough to endanger their ships and other wise scare the bejesus out of otherwise brave men. Some of the examples were the giant squids, now days we know that giant squids exist, maybe not as big as reported but still big enough to be monsters. Sea Serpent sightings are now days thought to be the result of Oarfish being mistaken for Sea Serpents but there are sea serpents alive today, real snakes that live in the sea, one of which is reputed to grow to 9 feet long. But has there ever been a real giant sea serpent like the one of legend?
Yes! Yes around 50 million years ago there is thought to have been a sea snake that could have been as long as 40 feet or more! Palaeophis colossaeus was this snake! From the description
With all the "cryptid" enthusiasm for Megalodon I am quite surprised this snake isn't being blamed for sea serpent sightings, possibly it's relatively new discovery or maybe it is still to obscure, for whatever reason it remains true that giant sea serpents once existed... and old time sailors reported seeing them. I doubt there was any real connection but it remains an interesting coincidence.
Now, if we can just find one washed up on shore 😁