Wallace Line by the Sahul Shelf to New Guinea. The biogeographic boundary known as Lydekker's Line, which separates the eastern edge of Wallacea from the Australian region, has a similar origin to the Wallace line. During ice age glacial advances, when the , both Asia and Australia were united with what are now islands on their respective continental shelves as continuous land masses, but the deep water between those two large continental shelf areas was, for over 50 million years, a barrier that kept the flora and fauna of Australia separated from those of Asia. Wallacea consists of islands that were not
Blakiston's Line Blakiston's Line, there are very many that can be found at either side of the line, in part because of human involvement. Examples of the latter are the Japanese Shorthorn, a breed of small Japanese beef cattle that is distributed in northern Honshu and also in Hokkaido, and the Japanese weasel, which was introduced to Hokkaido by human intervention. It has also been studied whether or not this biogeographic boundary applies to far smaller organisms like soil microbes. Apart from Blakiston's Line, other faunal boundary lines have been proposed for Japan, like Watase’s line (Tokara Straits): for mammals, reptiles, amphibians