Right, John Carpenter's The Thing being contained in that etcetera. I listed most of those in my far too long voicemail.
I think that of the suggestions, Night of the Living Dead would be the likeliest entry, because it would top a list factoring in both earliest with most currently influential or guiding. It doesn't feel like a 51 year old movie, because it's too modern to have come only a year after Dr. Dolittle and King Kong Escapes, but in fact, Night of the Living Dead is closer in time to Freaks and Frankenstein than it is to us. For that matter, Nosferatu and Dr. Caligari are closer cousins than we are. Its line in the sand is a deep one, and that's an area that gets escalated above many other criteria on lists of this sort.