Novelization gives clues to Xenomorph origins.

That is the plausible idea I was hoping for.  I wish they could have made that clear in the film tho.  I am of the belief the Deacon (mural) is what they knew and had created on some level.  He at most tweaked and re-created something that had been documented and laid out within their written works.

For me it was made somewhat obvious from the scene with David and Daniels in the room with the scrolls. Who is to say David wrote all those scrolls, maybe he was just adding his findings to scrolls that were already there? It wouldn't make any sense for David to be the "inventor" of the eggs with all the evidence that the alien species was in existence way before David. It is completely possible that David could recreate and/or manipulate the already existing "formula".

To bad Ridley says David actually create it because "i found that much more interesting ". :(

That defiantly makes more since with the mural from Prometheus but I think it's very clear David will make the biomechanical features to the Xenomorphs later.

Now since Ridley is basically in control of the franchise now what he says goes. He says "Let change it to David creating the Xenomorphs" then that's what will happen.

Still have wiggle room there, kept referring to it and him - could just be the current and later incarnations or evolutions of the creatures.  As scattered as his interviews have been, they were also carefully worded so that if backlash hit key points, basically everything could be tuned around it in the future.

I'm curious as to whether Alan Dean Foster added this without Ridley's knowledge as his own interpretation. He may have just assumed it was the case. On the other hand, Foster was perhaps shown an uncut version of the film that included David saying this.

I agree, the point is he didnt invent the xenomporph, his goal was to create life...be a creator.

As Holloway stated in Prometheus "That there is nothing special about the creation of life. Right? Anybody can do it. All you need is a dash of DNA and half a brain"

this essentially what David has done