Hello,
This my first posting at Sideshow Freaks. I am a huge Alien Fan and really like this forum with it's discussions.
I just read the last pages in this thread and I want to add a short information about the question, why the Xenomorph in Alien:Isolation has those strange looking legs.
It was in an interview with one of the CA designer but sadly I do not have the link at hand.
He said, one big problem was to fit the tall Xenomorph into the narrow and flat/low designed corridors and chambers at Sevastopol. Fully erected the original Alien design would break through the ceiling in more then 50% of the environment and so normaly would need to crawl for moving forward.
By inserting an additional "ankle-joint", they enabled the animators to level/adjust the height of the Alien in relation to the environment. So the legs fold in but the upper torso remains erected when needed.
The two images on page 678 explain it well. The upper image shows the Alien with legs in "crouched" mode while moving through a standard room.
On the second image, outtaken from the scripted final scene of San Cristobal, it is more elevated as the reception-hall has a very high ceiling.