Drifting Continents

As long ago as the middle of the eighteenth century, it became apparent to some palaeontologists that there were sometimes striking similarities in the types of fossils found in rocks of the same age in widely separated continents. These similarities could not be satisfactorily explained by the migration of plants and animals across vast expanses of ocean. With the development of the theory of plate tectonics in the 1960s which led to the widespread acceptance of continental drift, the similarities in the plants and animals of different continents could be readily explained by the drifting apart of land masses that formerly lay together. Deep in the mountain forests east of Melbourne there are plants and animals which hark back to this ancient connection, the Living Relics, and there are others which mark Australia's more recent separateness, the New Flora and Fauna.

150 million years ago Artist - Karina H McInnes Source - Museum Victoria

Amongst scientists there is widespread acceptance that South America, Africa, Arabia, Madagascar, India, Antarctica, Australia and New Zealand were once joined together in a supercontinent known as Gondwana.

The Southern Beech tree (genus Nothofagus) evolved about 80 million years ago in the cool, temperate climate of southern Gondwana. The super-continent of Gondwana had already begun to break up by this time, but South America, Antarctica, Australia and New Zealand were still connected. Nothofagus spread to all these regions (shown in dark green).

70 million years ago Artist - Karina H McInnes Source - Museum Victoria

40 million years ago Artist - Karina H McInnes Source - Museum Victoria

Nothofagus was dominant in many parts of south-eastern Australia in the cool, moist climate of 40 million years ago. At about this time, the last links between Tasmania and Antarctica were broken, and Australia drifted north. Antarctica became colder and its forests died out.

By 20 million years ago, south eastern Australia was becoming drier as the continent floated north into drier latitudes. Bushfires became more frequent. Fire-adapted Eucalyptus forests (light green) were evolving and beginning to replace Nothofagus forests (dark green) in many areas.

20 million years ago Artist - Karina H McInnes Source - Museum Victoria

Today Artist - Karina H McInnes Source - Museum Victoria

In more recent times, grasslands and Eucalyptus forests (light green) have become the norm in Australia, and Nothofagus forests (dark green) are now restricted to isolated pockets of the Eastern Highlands of Victoria, NSW and south-east Queensland and the Central Highlands of Tasmania. They are also still found in Papua New Guinea, New Zealand, southern South America and New Caledonia.