xenos exist before prometheus

I have been thinking. Not sure if this has already been covered, but we see the xeno mural, the SJ piled up with holes in them. So what if the xenos have already been established and have already been brought into existence and the chest bursters harvested? what if the black goo is from the xenomorphs. But they dont quite look like the aliens we recognise as human dna hasnt been added? the cobrahugger is a form of facehugger which may be result of SJ contamination but couldnt yet infect a human. yet the squid from shaw is the result of human infestation which goes on to infest the SJ. The speed of contagion and evolution is pretty scary at the rate it develops. For example: Xeno goo> holloway > xeno infected seed > shaw > xeno hybrid > SJ > Xeno human sj combo! A new breed of evolved alien with sj and human dna