I agree with what Takei said about the tongue, it looks like he's licking his teeth.
(One chin hook from below and the tongue gets cut off.)
I can't see what there is supposed(as you say) to be wrong with the ear or the fore-head. It looks true to the original to me, so if there is an error it must be in the reference already.

cool, the drawing is almost dead on to the original, and it's good that you put the reference in there too...will you be doing the rest of the series in the future?

Personally I think this is pretty cool, but one thing does bother me. The tongue seems to be sticking out towards the right of the creature's jaw instead of forward, unless it's supposed to be that way...