Well throughout the whole film you have this twisted family tree creating and mixing, David with the goo to Holloway to Shaw to trilobite to engineer to deacon. The point was that everybody had a hand in making that thing, and that there is human DNA in what we have come to know as the xenomorph. You don't need to see it doing anything else other than being born. It's an alien born from an engineer, just like the runner was an alien born from a dog, or Big Chap was an alien born from a human.
Fitting. Beautiful. Poetic. Even the screech was amazing. In fact, the last thing it felt was tacked on. It was building up to that the entire movie.
