Monster From A Lost World?
People supposedly fear the unknowable and things they don’t comprehend. This is absolutely true because we have a strong propensity to reject unfamiliar things, especially those that we are unable to comprehend. It could be that we perceive threats to our existence, security, or even safety from those things we cannot fully comprehend.
The earth’s oceans are not 100% discovered yet, so unknown creatures washing up the beach can be considered a possibility. In Egypt, one creature brought fear to the people around because a mummified monster-looking sea creature got washed up along the beach. Turns out, it was just a mummified moray eel. Although, it really does look terrifying.