Highball apparently didn't know this.
I knew it, I thought my original response was more than adequate. My mistake.
The fact that the common ancestor is no longer around doesn't mean it didn't exist. It also doesn't matter *why* the common ancestor is no longer around, except as an intellectual exercise.
For my own part, I think that the common ancestor probably died out because it was not as well adapted to changes in its environment as both man and apes. Is that sufficient for you, or would you rather make another snarky comment?