I've heard this "Theory" that when you die you become an animal known as animalization.In that case has my father become an animal?
Yes he is an alligator
Only if your father is dead, and the theory is correct. I very much doubt the latter.
Is that some sort of native American belief?
I believe so.. Start calling him, if that thing turn around that's your father lol
That is also known as reincarnation. I don't personally believe in that.