Biogeographical zone of islands between Southeast Asia Sunda shelf and the Sahul shelf - an area separating Australia from Southeast Asia for 70 million years. It marks the division between two major faunal groups: oriental animals (elephants, tigers, and apes) and the animals of Australia (kangaroos, wombats, and monotremes). Dates of first human settlement are uncertain; the first settlers of Australia prior to 30,000 years ago had to cross sea gaps of up to 70 km in this zone. The water formed a barrier to the spread of animals and humans into Australia and New Guinea. It is named after the British naturalist A.R. Wallace, who first recognized its significance.