system
Given the following post, respond as if you're commenting on Reddit:
human
[Godzilla] How does Shin Godzilla's biology differ from the older Godzilla and what was growing on the end of his tail?
gpt
Godzilla from the earlier movies was a mutated dinosaur or a prehistoric organism from when the earth was more radioactive. Because of this, his biology for the most part is comparable to non-mutant/regular living things. In Godzilla vs Mechagodzilla II (1993), a baby Godzilla is examined and revealed to have a secondary brain. In many movies, he has at least a skeleton. Other than that he has always at least been basically of normalish biology. An exception might be in GMK(2001), where he is a ghost/god of destruction. 

Shin Godzilla, however, is a mass of constantly mutating, rapidly evolving micro organisms. At the end, those things coming out of his tail were his next stage of evolution.