Tertiary Evolution of the Australian Flora in the Light of Latitudinal Movements of the Continent

Abstract

Australia has drifted 150 of latitude northwards since breaking away from Antarctica in mid-Eocene times (45 million years BP). Evidence for the climate at that time indicates warm, wet conditions favouring sub-tropical rain forest. Maps are presented of Australia's likely climatic zonation in midEocene, Oligocene and Miocene times, at respectively 45, 30 and 15 million years BP; these show the probable extent of a dry non-seasonal climate in northwest Australia as early as the Eocene. By the Oligocene, desert conditions were established in the north and northwest, with the first Mediterranean climatic zone appearing, also in northwest Australia. By the Miocene, desert extended to almost its present limits, and the Mediterranean zone had moved southward to become more extensive than at present. Accordingly the evolution of desert xerophytes in Australia probably dates back to the Eocene, and of Mediterranean-type xerophytes to the Oligocene.