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The Evolution of Australian Biota Essay

Question 1:

Wegener’s Theory:

During the 19th and early 20th Centuries, several geologists explored the idea that the continents may have and still are drifting across the Earth’s surface. This hypothesis of continental drift was largely developed by German astronomer and meteorologist, Alfred L. Wegener.

Wegener suggested that the Earths continents had at one time been joined in two super continents. In 1912 Wegener made the proposal that all the continents were previously one large continent, but then broke apart, and had drifted through the ocean floor to where they are now located. Apart from using the idea that continents fit together like a puzzle, Wegener also used fossil distribution, a similar sequence of rocks at numerous locations, and the apparent wandering of the Earth’s polar regions to support his idea. With the help of Alfred L. Wegener’s theory much of Australia’s geological history can be explained.

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The puzzle like shape of the continents was one of the first pieces of evidence Wegener noted when exploring his theory of continental drift. Many of today’s continents can be manoeuvred so they fit together into a large super continent.

Fossil evidence such as the distribution of animals, plants and fossils across the continents was used by Wegener to explain his theory. Wegener noted that certain plant and animal fossils of late Palaeozoic age found on several different continents were similar suggesting that they evolved together on a single large land mass. These fossils were also found on the coast of South America and Africa suggesting they had been joined together at these edges. Today similar species inhabit these once connected continents such as certain marsupial and monotreme species in Australia, Antarctica and South America.

Similar geological patterns were also noted among rocks in South America and Australia. These matching rock bands also supported his theory that the continents had been once connected.

Further evidence such as the lack of remains to support that the northern hemisphere was once covered in ice as the southern hemisphere once was also supports Wegener’s theory that the continents have moved. Lack of evidence to support that ice once covered the northern hemisphere suggests that the northern hemisphere was once at a more equatorial region 300 million years ago and experienced a more tropical climate. Evidence of tropical plant remains found in the form of coal also supports this. This is also supported by fossil remains found in the centre of Australia that suggest that the area was once lush tropical rainforest that supported many tropical species.

Question 2:

Australian Flora and Fauna:

Flora species: Proteaceae Grevillea

The Grevillea species from the Proteaceae family is an example of a species of flora that has evolved to suit its environment; the Australian bush. Particular evolutionary traits have arisen as a result of Australia’s isolation and increasing aridity.

Plants from the Proteaceae family exist in nearly all continents in the southern hemisphere and Australia has the greatest abundance of species. However when Australia separated from the great landmass ‘Gondwana’ about 100 million years ago, species of the Proteaceae family continued to evolve. As a result of its isolation the Grevillea species developed its own characteristics and features independent from other Proteaceae species in the southern hemisphere.

Different patterns of evolution can be seen even within Australia. Increasing aridity and a change in sea levels that occurred during the early Tertiary Period, between 12 and 5 million years ago, effectively divided Australia’s flora between east and west. Species that had been widespread across Australia became restricted to non-arid sections in the north, south, west and east. Thus these isolated plants evolved independently from each other, becoming distinct species. Further the gradual drying of the continent over the last few million years has reduced the habitats of certain Proteaceae species reducing the abundance of species in certain areas. The Grevillea demonstrates certain evolutionarily traits associated with these two factors, that is it has distinct features that are both different and similar to other Proteaceae species in Australia.

Figure A: Typical Proteaceae Grevillea

Fauna species: The Australian Red Kangaroo

The Australian Red Kangaroo is an example of an Australian species of fauna that has evolved over time to suit its environment. As the species has evolved certain characteristics have developed as a response to the animals arid and isolated environment.

The Australian Red Kangaroo came into existence around 25 million years ago, about 10 million years after Australia split from Antarctica, and preferred rainforest type environments. As a result of Australia’s split from Gondwana, about 100 million years ago and later Antarctica, the kangaroo evolved independently in an isolated environment, this is why kangaroo existence is solely limited to areas within Australia.

This original kangaroo was tree dwelling and much smaller that today’s kangaroos. These kangaroos had opposable digits to suit the trees in which they lived. As Australia became drier and woodlands slowly replaced rainforests around 15 million years ago, the kangaroo was forced to develop into a larger carnivorous animal living in open woodland environments.

About 5 to 2 million years ago, Australia’s arid areas increased, resulting in the extinction of some species of kangaroo that were unable to adapt to the climate change. Around 20,000 years ago today’s Red Kangaroo came into existence, with adaptations allowing it to live in Australia’s dry environment. These adaptation that’s have developed over that last 25 million years include that ability to have offspring when the environmental conditions are correct and very specialised methods of water balance.

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