Hi, Bud.  I'm not a professional, but I'll tell you what I know and have experienced on this subject.  Usually, anger is a cover-up for fear because fear can make us feel weak, while anger feels powerful.  I'm not sure what you mean by its developmental stage, but I've found this to be the case.  Of course, there are times when we do get rightfully angry and it's pure anger, but there's that other kind that's rooted in fear.  My dad has been angry all his life and yet, I can see a little boy in there who is afraid.  He was in World War II, so some of it could be untreated PTSD because he was shot, but he also suffered as a child from beatings.

Well, that's maybe way more of an answer than you wanted, but hope that helps, hope it makes sense.