I seem to recall the "fallen tree" in the 80s at least (I'll have to look at old slides to remmeber if it was the same) and colobus and guenon were there at least from my first visit in 1986. I remember when aardwolf was in the colobus exhibit as well
The zoo used to be full of cool little surprises like that. I can recall there being dik-dik in the moat in front of the hippos at the elephant house.