I think it was late in the scriptwriting when they made Cera into a girl based on Spielberg's suggestion, if it was him who made it, I don't recall correctly.
As for the eyelashes they are pretty inconsistent with those since as I recall in some movies Litttlefoot's looks so long that if you turn the sound off he could be a girl. To bad they were not more consistent. That could have been one easy way for the audience to tell the difference in the genders. Though Dinos would not have eyelashes for real, it would make it easier to tell the difference if say only females had eyelashes. That's what I would have done. Having the males brighter colored like birds and females more drab is a thing most folks would likely miss since I'd guess most folks, and kids, don't really notice that.
I'd guess Mo's main diet would be fish since I'd guess the type of creature he's based on ate fish, though I"m no expert in that era. Though from what I heard Petrie's type should be eating fish also, but they have him as a plant eater.
As for Dinah and Dina they vanished into limbo like ever other character who usually appears in just 1 movie or maybe gets 1 episode appearance. You can make up your own story as to what happened to them. And oddly enough, I think they are in one of the games on the 4th movie dvd, playing in the mists.