In general the late Middle and Upper Eocene floras mentioned above all show physiognomic signatures indicating warm, wet climates, whereas those known from the Oligocene-Miocene show much reduced, sclerophyllous signatures. Localities displaying these features include Kiandra in New South Wales as well as Berwick and Bacchus Marsh in Victoria (Figure 10.6).
Not only does the physiognomic signature change, but so does the taxonomic composition of the flora. As can be seen in Table 10.1, the domination by the Gondwanic Proteaceae, Lauraceae, and Gymnostoma evident in the Eocene floras has been lost by Oligocene time and is replaced by elements of the flora now found in different modern communities—namely, Eucalyptus, Acacia, and Epacridaceae. The Proteaceae and Casuarinaceae are still prevalent, but the Proteaceae is now dominated by Banksia and sclerophyllous forms, and Allocasuarina and Casuarina (sensu Johnson, 1982) have now replaced the more mesic Gymnostoma. All of the above changes are well documented in the pollen record, but frustratingly, very few occurrences of Eucalyptus and Acacia are known from the megafossil record. Thus, two distinct significant global climatic events (Figure 10.4) can be seen to be reflected in the Australian megafossil record and, when considered floristically, appear to have had a major effect on the vegetation development of the continent.