Wallace Line connected islands on the west (Sumatra, Java, etc.) with the Asian continent and with similar wildlife, and islands on the east such as New Guinea were connected to Australia and were characterised by the presence of marsupials. Wallace used his extensive travel in the region to propose a line to the east of Bali since "all the islands eastward of Borneo and Java formed part of an Australian or Pacific Continent, from which they were separated." The name 'Wallace's Line' was first used by Thomas Huxley in an 1868 paper to the Zoological Society of London, but showed the line
Sundaland Russel Wallace as the eastern boundary of the range of Asia's land mammal fauna, and thus the boundary of the Indomalaya and Australasia ecozones. The islands east of the Wallace line are known as Wallacea, a separate biogeographical region that is considered part of Australasia. The Wallace Line corresponds to a deep-water channel that has never been crossed by any land bridges. The northern border of Sundaland is more difficult to define in bathymetric terms; a phytogeographic transition at approximately 9ºN is considered to be the northern boundary. Greater portions of Sundaland were most recently exposed during the last glacial