Australia is a land like no other, with about one million different native species. More than 80 per cent of the country’s flowering plants, mammals, reptiles and frogs are unique to Australia, along with most of its freshwater fish and almost half of its birds.

Australia’s marine environment is home to 4000 fish species, 1700 coral species, 50 types of marine mammal and a wide range of seabirds. Most marine species found in southern Australian waters occur nowhere else.

Australia’s geographic isolation has meant that much of its flora and fauna is very different from species in other parts of the world. Most are found nowhere else. However, some closely related species are found on the continents which once made up the ancient southern supercontinent Gondwana.

Covered in rainforest and ferns 300 million years ago, Gondwana included South America, Africa, India and Antarctica. Most of Australia’s flora and fauna have their origins in Gondwana, which broke up about 140 million years ago.

Australia separated from Antarctica 50 million years ago. As it drifted away from the southern polar region, its climate became warmer and drier and new species of plants and animals evolved and came to dominate the landscape.

From dfat.gov.au

Australia’s Flora and Fauna and Charles Darwin

Observations of Australia’s unique fauna and flora, combined with considerations of the continent’s geographical isolation, contributed toward Charles Darwin (1809–1882) developing his theory of evolution by natural selection.

Charles Darwin’s theory was that species change over time, or evolve, in response to their environment. This theory transformed the way people understood the living world, and provided a logical, unifying explanation for the diversity of life. Darwin’s theory of evolution changed the face of science and natural history forever.

While Darwin never saw a kangaroo in Australia, despite riding a horse from Sydney to Bathurst, he did see many other species. Darwin made some very astute observations about Australian animals, especially the platypus. At the time, the platypus was regarded as a curious creature, and it baffled the scientific world. Darwin was the first British scientist to see a platypus in its natural environment, at a creek near Bathurst, in 1836.

For over forty years after his visit, Darwin used and relied upon collections of specimens from Australia that related directly to his ‘theoretical concerns at any given time and his recognition of the peculiar status of the continent’.

From australia.gov.au.