Kahuna Burger said:
I am not of an adventuring class and am poorly traveled, but I know big jellyfish are probably poisoness, wolves can track me by scent, and a lot of things can see better in the dark than I can. I even know that bats have blindsight, some sea predators have a sort of electricity sense and snakes detect heat. and I'm, what, a low level commoner?
That is because of modern day technology. Things such as television, the invention of the airplane (broader ranges of trade), the printing press, and the world wide web make information available to millions and millions of people.
In the mid-evil time period that classic D&D is most often set... the only way you learned about something was: a) someone taught you their knowledge and/or experiences, b) you experienced it yourself, or c) you are lucky to find some written information.
Heck, the first scientific examination of a shark (other than to see what it ate) was not until 1919. Sailors have know of sharks for hundreds of centuries and it has not been until the last century that detailed knowledge of sharks and their behavior has been discovered (i.e. learned). Sailors used to think that sharks were from the devil himself, hungry to devour the souls of those that fall victim to it.