Frogs have no inherent meaning, but a justification for being may or may not arise during the duration of their existence.
It means that you've either left your door open or there is a large gap under it. Frogs prefer cool damp conditions and it probably entered your house because the gap under your door looked like a...
I have read that frogs are symbols of both fertility and good luck in Japanese culture.
Pre-columbian means before Christopher Columbus arrived. Explorations came after.
Native people in North and South America before Coloumbus arrived there.