For you who doesn't know yet https://www.atlasobscura.com/articles/the-hollow-earth-is-filled-with-giants-germans-and-a-little-sun
So it's a fact that many mammals that lived during dinosaurs period survived the theory of asteroid crash, impact and climate change. That, because of a single fact. They could dig caves.
Caves.
The main theory of Inner Earth is that around the round there are many Caves that leads to inner earth. One of them being on the North Pole. Funny fact, if you try to reach the center of the North Pole, google map has it censored so we can't see what is in there.
