Yes, I've seen it before. Is it an alien? Well, technically yes. The skull is from Mexico and resides in the US. boooooo, bad pun.
Anyway, it's an interesting skull. I recall the dna donors are human and undetermined. Alien? Who knows. I assume it's a genetic deformity, but we don't see similar deformities now. If it was 100% human, wouldn't that be easy to prove? If so, why hasn't it been proven?
There are a lot of interesting anomalies out there that are unexplained and point to things that were not possible during our known technological abilities during the time. While a bit outlandish at points, the show Ancient Aliens on History Channel is great. Most of it is unexplainable through modern science. Here are a couple of examples:
Japanese lost city off the coast:
http://news.nationalgeographic.com/news/2007/09/070919-sunken-city.html
Pumapunku
http://en.wikipedia.org/wiki/Pumapunku
Egyptian pyramids, mass sightings over LA, Phoenix, etc....
I find it amusing how many people are quick to dismiss alien life (outside of this planet), but are anxious to go to church every Sunday. Not knocking anyone's faith, but it *is* interesting.