The angels and the greek gods
When dinasours were alive
No, many other organisms came before megalodon.
God created them and let them roam the earth
Satan is the only name. People on earth have given demons many names for these "demonic like" people or souls which roam the earth. Satan is the one and only demon, people choose to do "demonic" things to be like Satan or choose their destiny with an Angel stricken from the Heavens by the Lord God.
People turn into ghosts, because they do not belive that they are dead, so they still roam Earth
Paleozonic era
No. But they make good fun for storytellers.
It is very unlikely.
160 million years
No it is not
Not sure. More specifics?
I think it's a dinosaur.