I don't know that I go along with the idea (though it's interesting) because there's a whalloping huge number of insects with the same body design... 3 parts, wings dividing the abdomen. In Africa, there are a number of species that look just like this. It was, as was said, the aspect of rebirth/birth from the ball of dung that was important.

The human skull had no such connection in any text that I know of. The sun was not born from a human skull, and more importantly, Re-as-Khepera has a head shaped like a scarab... not a skull.