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Fauna of Australia
The fauna of Australia consists of a huge variety of animals; some 83% of mammals, 89% of reptiles, 24% of fish and insects and 93% of amphibians that inhabit the continent are endemic to Australia.〔Williams, J. et al. 2001. (''Biodiversity, Australia State of the Environment Report 2001'' (Theme Report) ), CSIRO Publishing on behalf of the Department of the Environment and Heritage, Canberra. ISBN 0-643-06749-3〕 This high level of endemism can be attributed to the continent's long geographic isolation, tectonic stability, and the effects of an unusual pattern of climate change on the soil and flora over geological time. A unique feature of Australia's fauna is the relative scarcity of native placental mammals. Consequently, the marsupials—a group of mammals that raise their young in a pouch, including the macropods, possums and dasyuromorphs—occupy many of the ecological niches placental animals occupy elsewhere in the world. Australia is home to two of the five known extant species of monotremes and has numerous venomous species, which include the platypus, spiders, scorpions, octopus, jellyfish, molluscs, stonefish, and stingrays. Uniquely, Australia has more venomous than non-venomous species of snakes.
The settlement of Australia by Indigenous Australians between 48,000 and 70,000 years ago 〔Josephine Flood (2004) Archaeology of the Dreamtime, J.B. Publishing, Marleston p. 283 ISBN 1-876622-50-4〕 (research in 2011 using DNA suggesting an arrival around 50,000 years ago), and by Europeans from 1788, has significantly affected the fauna. Hunting, the introduction of non-native species, and land-management practices involving the modification or destruction of habitats have led to numerous extinctions. Some examples include the paradise parrot, pig-footed bandicoot and the broad-faced potoroo. Unsustainable land use still threatens the survival of many species. To target threats to the survival of its fauna, Australia has passed wide-ranging federal and state legislation and established numerous protected areas.
==Origins==
(詳細はgeologic and climatic events helped to make Australia's fauna unique.〔Egerton, pp. 14, 20.〕 Australia was once part of the southern supercontinent Gondwana,〔Egerton, p. 20.〕 which also included South America, Africa, India and Antarctica. Gondwana began to break up 140 million years ago (MYA); 50 MYA Australia separated from Antarctica and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene era 5.3 MYA. The establishment and evolution of the present-day fauna was apparently shaped by the unique climate and the geology of the continent. As Australia drifted, it was, to some extent, isolated from the effects of global climate change. The unique fauna that originated in Gondwana, such as the marsupials, survived and adapted in Australia.
After the Miocene, fauna of Asian origin were able to establish themselves in Australia. The Wallace Line—the hypothetical line separating the zoogeographical regions of Asia and Australasia—marks the tectonic boundary between the Eurasian and Indo-Australian plates. This continental boundary prevented the formation of land bridges and resulted in a distinct zoological distribution, with limited overlap, of most Asian and Australian fauna, with the exception of birds. Following the emergence of the circumpolar current in the mid-Oligocene era (some 15 MYA), the Australian climate became increasingly arid, giving rise to a diverse group of arid-specialised organisms, just as the wet tropical and seasonally wet areas gave rise to their own uniquely adapted species.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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