I believe I have a theory that might be valid. If you look in the Bible, in Genesis, when the tower of Babel was being built. The Good Book says that Nimrod was trying to build a tower to "shoot an arrow into God's eye." Now, back in that time, technology consisted of your basic Bronze Age stuff, so how were a primitive people supposed to build a tower to heaven if they could barely make bronze? Aliens aka "fallen angels," the "sons of God" mentioned in Gen 6.
It has been proven that "sightings" have been happening throughout recorded history, and also that people had visitations from "gods." Well, there is proof that some ancient tribes would alter the skulls of their infants to look like these "gods" (like the "gods" that helped Nimrod with the tower) by banding their heads so their skulls would grow in oblong shapes. My theory is simply that this is one of those skulls.