"Contrary to popular belief, the sailors of Columbus's day did not think they would sail right off the edge of the earth. They were, however, apprehensive about what they would find in their travels. Mistakes about marine life have ranged from inaccurate assumptions about the behavior of known species to fanciful depictions of animals that 'might' exist...."
These days, we know that monsters like the kraken (that's not what's pictured there, by the way - the kraken was big) don't really exist.
Or, maybe, that such creatures don't like the sound of propellers, or experience long dormant periods. I know enough about the history of science and philosophy to be a trifle dubious about our current working hypotheses being the final word.
- "Once it Was Believed, Now We Know"
Brian's Attic (2003)