The enclosures for lions today have been round for many many years and they can be seen on the map as far back as the 1940's, the orignal walls have not changed to much and infact the placement of species in the two pits is exactly the same. (I'm working on a paper on the history of Taronga at the moment in case your wondering). In the areas where the sun bears now live, (the 1996 lion caves exhibit), was originally a dual wire enclosure on level, that housed panthers and a jaguar, they then were modified to become one wired and one pit, the pit was home to jaguars and ran down from next to the lion pit to the level of the current viewing, and the other stayed a wire enclosure for tigers, all this time lions were also kept in what was to become the current bear canyon, after much modification of course. Sun bears have been seen at the zoo for many many years dating back to the old bear pits, the old sun bear exhibit (ran till late 90's) is an original pit and is currently being modified to house red pandas.