I'm going to warn you...women on this BMB are not fans of guessing gender (because people post this question about 5 times a day). So, you will get a lot of snarky/sarcastic responses. It's not personal...I promise.
My guess:
It's a baby raptor. Congrats!
Seriously though, this is nothing personal against you op, but there's absolutely no way to tell gender this early, regardless of the theory, best bet is a 50/50 guess. Giving joking made up responses is our way of drawing you into the fun. Feel lucky you got this instead of flamed. :x
I would try to help you but unfortunately I don't know anything about any of the theories. All the u/s always look the same to me. Your baby looks cute though like it's trying to do the back stroke!!!!! Maybe I should try to guess athletic skills instead of sex!
Re: Skull theory?