The Wallace Line splits Asian and Australian faunas across a narrow sea gap
Between Bali and Lombok — and along a deeper trench to the north — Alfred Russel Wallace mapped an abrupt change from Asian mammals and birds to marsupials and cockatoos typical of Australasia.
Deep water persisted through ice-age sea-level drops that joined other islands into land bridges, so many species never crossed. The line is a living record of plate tectonics meeting dispersal limits.
Biogeography can be sharper than a coastline suggests. A few dozen kilometers of uncrossable sea have kept two evolutionary worlds side by side for millions of years.
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