If the Sarcophogi are already ruptured that would suggest that some form of chest-burster has already wiped out at least some of the Derelict's original crew. That would jive with the Alien glimpsed in the mural. Both are strong hints of a version of the creature that exists already and I guess would already have some importance. To someone. I guess the bio-mechanised killers mentioned in the synopsis. But are these the Jockeys, engineers or something else?
Or, is the big blue guy one of our crew infected with that nano-bio-tech goop that David is looking at.
Is the mural part of the Derelict, or the Temple?