This is the skull of their last female elephant Samorn who died at Monarto Zoo in 1994.
EDIT: Actually her whole skeleton is on display at Adelaide Museum, so this can't be her. No idea which elephant this is but it might be one of the ones that died in the 1930s or 1950s.
Did this building hold rhinos as well at one time? Adelaide had the last Javan rhino known to have been in captivity, which died in 1907. Incidentally, where did that specimen end up - anyone know?