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. 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.