Xenomorphs WERE SJ's = Evolution/Mutation

Unless the REAL SJ's we've been speculating on are actually a different being althogether, and the species we've been shown hints of in the trailer are what the Xeno-morphs use to be before the human intervention we'll see in Prometheus. . . Just thought I'd throw the idea out there that we'll be shown a completley new and unknown alien in the movie, so what we think are SJ's are infact a pre-Alien version of Xeno's.