For example, did you know that you don't even need a rust monster? According to Pliny the Elder, some kinda=s of mice were known to gnaw on iron and even gold!
|And the blood of the pelican's breast resurrects her dead offspring|
For that matter, we need not stop with characteristics of specific animals. We can build whole ecologies from outdated theories of the generation of life. One of my favorite disproved theories is spontaneous generation. This theory refers to how life might spontaneously birth itself from dead or inanimate objects. For example, without understanding the relation of flies to maggots, it was really easy to observe how maggots seem to sprout from rancid meat without any sort of outside cause.
Taken further, spontaneous generation could have profound implications for the "living dungeon", a dungeon that lives and breathes of its own (mysterious and seemingly incomprehensible) accord. You know the one, that weird link to the mythic underworld that mutates and evolves given enough time to sit alone. How does it get its monsters? Well now we have an answer!