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Evolution of Australian Biota. Drifting continents. Plate tectonics and continental drift explains how mineral and fossil fuels originated and where they might be found. Alfred Weger in 1912 proposed continental drift.
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Drifting continents Plate tectonics and continental drift explains how mineral and fossil fuels originated and where they might be found. Alfred Weger in 1912 proposed continental drift. Single landmass called Pangea which split into smaller landmasses. They drifted to separate places around the world. Harry Hess in the 1960’s proposed that landmasses are carried on crustal plates of Earth’s surface on the semi-molten interior. This movement is believed to have caused the uplift of Indian plate in Asia to form the Himalayas.
The island continentAustralia Australia an island continent * 5.6 million square kilometres * Surrounded by ocean. There is evidence that it was originally part of an ancient super-continent, Pangea. Australia became a separate continent about 45 million years ago.
About 160 million years ago Pangea split into two large continents Laurasia to the north and Gondwana to the south. Laurasia consisted of today’s North America, Europe and Asia except India. Gondwana comprised of the current South America, Africa, Madagascar, India, Antarctica, Australia and New Zealand. The separation was not complete as individual countries until 45 million years ago. Australia is still drifting north at the rate of 6cm each year.
Geological evidence. Geologists have found around continental margins have matched perfectly in many places. Mid-ocean ridges, where the mantle is welling up indicate that the further away from the ridge the older the rock. Showing that this has been happening for many years.
Biological evidence. The fossil record and present day distribution of plants and animals provide biological evidence that Australia was once part of Gondwana.
Biological evidence. Fossil evidence: Glossopteris and Gangamopteris are fossil plants found in rocks of the same age in Africa, Australia, South America, Antarctica and New Zealand.
Marsupial mammals are widespread in Australia. They also have a long fossil record on the continent. Only one marsupial, the opossum, is still found in North and South America, but fossil records show marsupials were present on all continents.
Present-day organisms • Nothofagus, The southern beech trees, are found in forests in Australia, New Guinea, New Zealand and South America. Fossils also found in Antarctica.
Present-day organisms • Many groups of animals have close relatives in the same countries. They include parrots, flightless birds, marsupial mammals, chelid turtles, some geckoes, earthworms etc.
These biological examples when considered together with geological evidence, help support the theory that land masses in southern hemisphere, were once connected. • The long isolation of the Australian continent has produced a large number of plants and animals that are endemic (unique to a region) to Australia. • In Australia 85% of flowering plants, 82% of land mammals, • 89% of reptile species and 93% of frog species are endemic.
The fossil record shows a decline in size since late Pleistocene. Both the eastern grey kangaroo (Macropus giganteus) and red kangaroo (Macropus rufus) can be considered megafauna survivors, but they are up to 30% smaller than they were thousands of years ago.
Australia’s megafauna • Megafauna are large animals. Today there are only a few types elephants and whales. • There are two main theories for the extinction of megafauna. • One: climate change, at the end of the ice age. Australia went from cold and dry to warm and dry and water became scarce. • Two: human expansion, megafauna slow and therefore vulnerable to hunting. • Australia probably both factors involved. • Today many smaller relatives of Australia’s megafauna survive.
Living Fossils • Plants: Plum pines, celery pines, huon pine, kauri pine, primitive cycads and Wollemi pine.
Living Fossils • Animals: Velvet worms, Queensland lungfish, two species of crocodiles and monotremes. Australia’s animals and plants (many unique) with early origins are often referred to as our ‘biological ark’ an important heritage to us and significant to anyone who studies the evolution of life on Earth.
