Where Australia Collides with Asiaand it is only the deep Lombok Strait which separates these main islands from the
smaller islands to the east. The Lombok Strait represents the boundary between the
fauna of Asia and that of Australasia, a boundary which Thomas Huxley later named
the Wallace Line. We only have to look at a seafloor map now to realize that this line
represents the edge of the Asian continental shelf.
On the Asian side of the Wallace Line are the Asian elephant, the rare Javanese
rhinoceros, Sumatran tigers, Borneo leopards, the orangutans of Sumatra and Borneo,
and numerous birds that are specific to Asia. On the Australasian side are the white
cockatoos and other birds specific to Australia such as the megapodes or scrub turkeys
which build large mounds in which they incubate their eggs, the marsupials such as the
possum-like cuscus, the tree kangaroos, and the spectacular birds of paradise found
in Papua and the Moluccas (Maluku). It is no surprise that no megapodes exist west
of Lombok as they had evolved on a continent that was mostly devoid of mammalian
carnivores. How long could a ground-living bird survive on a forest floor occupied by
tigers or leopards?
Land exposed during the lowering of sea levels during the ice ages allowed
Australian flora and fauna to be distributed across the eastern Indonesian islands
except as far as the deep Lombok Strait and its extension north between Borneo
Map showing the Wallace Line and some of his travels around the Indonesian archipelago, Ian Burnet137