I'm kinda worried about people talking about this thing as though it actually has an elephant trunk, and as though that isn't the most ridiculous thing that's ever been concieved by anyone, let alone an artist like Scott.
If any species in this film has an elephant trunk, how on Earth is anybody going to take this film seriously? A trunk? You literally have to be joking. Did anybody see the representation of the "elephant trunk" in the aliens comic, "The alien", by John Arcudi? (see Aliens Omnibus, vol 1, p 383). Have a look at that thing. That's awful. One of the worst creature designs I've ever seen. This simply can't work. I've seen so many 'Pilot species' artists renditions, and every one of them looks like a total joke, and doesn't make any sense - EXCEPT the ones you see in the original Giger design paintings, in which you see humanoids, wearing masks, with a very clear breathing apparatus, NOT a trunk. (Have a look: http://26.media.tumblr.com/tumblr_l5o9w6pWoh1qa1o5zo1_500.jpg
Noses don't have bones in them, they're soft flesh. If the creature had an elephant trunk, it wouldn't fossilize like that, unless it was made of solid bone, in which case, it wouldn't be able to move at all. How could a non-movable, bony elephant trunk possibly be an evolutionary advantage? It simply can't be, think about it.
I'm not at all convinced that the actual creature has a physical trunk attached to it, it doesn't make any sense whatsoever, from an artists prespective (ie, that this film should be taken seriously, and should be frightening at least to some degree) or even from a pseudo-scientific perspective.
You can actually see, if you look close enough at the images, that it has two layers - the bit with the trunk looks to me like a covering of some description. Look at the edge with the jaw, and then how the actual top bit is layered over. He's probably wearing breathing apparatus. That's how it looks to me.