We have concrete prof that earth is somewhat round and solid but some people still believe that there is a micro sun inside, and will fight you if say otherwise.
With these extinct or close to extinction species happens the same
Wait, isn't the Earth's core molten and hot? Or do people believe the Earth is hollow and has a small star inside?
I'm shocked that anyone actually believes this in modern days, but it's a fun thing to fantasize about.
There is a fictional series about hollow earth called Pellucidar by Edgar Rice Burroughs that I enjoyed immensely. A fun read, not unlike Tarzan.
There is even a paper that states it is crystallizing at a rate of about 1 mm/year, and this process contributes some of the heat. [1] I have been trying to dig back to the data on this in the past, but haven't found anything but the claim itself.
[1] http://www.nature.com/ngeo/journal/v4/n4/abs/ngeo1083.html