Comparisons of the the late Miocene Alcoota Local Fauna and the middle Miocene Bullock Creek Local Fauna reveal fundamental similarities in faunal composition and in the structure of the terrestrial component of their respective communities. The Bullock Creek palaeocommunity contains an abundance of aquatic and stream-bank species. Few aquatic species are present in the Alcoota palaeocommunity. The taxonomic succession is predominantly at the level of generic rank. The temporal succession by closely related ecomorphic species suggests continued integrity of the basic community structure. The Alcoota LF expresses an increase in species diversity and an increase in the body sizes of diprotodontids and macropodids that occurred during the approximately three million year long interval between the two local faunas. Biological, taphonomic and geological data indicate that both communities were intermittently subject to environmental stresses due to periods of low precipitation and high evaporation. The Bullock Creek Local Fauna shows evidence of seasonal aridity. The Alcoota Local Fauna shows evidence of one or more event-based mass mortalities due to regional drought.