Elongated skulls are common in ancient times, who were the people trying to immitate? It's weird to think how humans came up with this technique unless it was in honor of a god or king they wanted to look like. Serpent burial mounds in the US by Indians is interesting. When I was exploring the museum at Moundsville WV, it was said to be some 3000 years old and the Indians used it as a burial ground. The interesting thing that I learned from an archeologist on site was that it was built over a burial site even much older. That burial site had one body the original "king" with a deformed enlarged skull and the DNA was not the same as any of the others buried at the site.
You can reason all the skulls are clues to finding these much older and different race that existed and the other people who considered them gods kings or whatever.
Ultimately DNA studies will uncover who they were or more properly who they weren't really related to.
Who ever the "original large skulled people" were they sure left a mark on many cultures across the entire globe.
It's relevent to the ancient alien concept although I'd speculate they are probably decent of something not homo sapien but still not really alien, just a past more advanced culture that disappeared. I don't rule out that some cultures may have even been exposed to real other worldly travellers that had "stations" here and there. It would take a long time if ever to discover where they really originated even if you had proof of a totally different intelligent species and artifacts.