I don't see any reason why a question based on a movie couldn't be on topic. In fact, I'm fairly certain that we have plenty of those, if for no other reason then because someone saw something they liked in a movie (or novel, or other work), want something similar in their own world, and want to better understand either how it could have come to be or the consequences of the element involved. (Not to mention that answers quite often draw on existing fictional works.)
However, the question must still stand on its own. We discussed this in the context of answers in Are answers solely referencing novels/movies/etc. okay?; I feel the points made in the accepted answer to that one apply potentially equally to questions as well.
A question that simply states "how could a creature like X in movie Y evolve naturally?" should probably be closed as "unclear what you are asking" because without watching the movie and analyzing it, it really is. Without the additional reference material or knowledge, it is impossible to know what the OP wants. The question doesn't stand on its own, hence it is unclear. Compare also Should a question that is meaningless without viewing an external link be closed? and Something in my web site or project doesn't work. Can I just paste a link to it? on Meta Stack Overflow.
A question that states "in the movie Y, there is a creature X with traits A, B and C. what would be the prerequisites for these traits to evolve naturally in our world?", where the traits are adequately described in the question itself, is likely just fine. There is also a reference for those who are curious and want to learn more, or see more exactly what you have in mind, but the necessary information is in the question itself so the reference is nice but not mandatory in order to produce an answer.
Of course, all other points to consider about whether a question is a good fit (such as broadness, general on-topic considerations, and so on) remain the same.
Also, please for the love of all things holy, give the question a good title. "Anatomically correct X" is, I think, a horrible question title. "How could a creature with traits A and B evolve in an Earth-like setting?" would be a much better starting point for a question title, because it actually sets the context of reading the question.