Fig 2. Croizat's 1961 (in Principia Botanica) hypothesis of the composite geological nature of the Americas based on his strictly biogeographic analyses. Western North and South America are postulated to have drifted from the west as a consequence of the opening or widening of the Pacific Ocean, while Eastern North and South America drifted from the east as the Alatantic Ocean opened. These continental fragments then fused to form one modern geography: North and South America. Wallace's Nearctic (North America) and Neotropical (Central and South America) regions are thus not natural biogeographic or geologic taxa. In the last five years some geologists and other scientists have begun to accept this novel concept which originates in Croizat's panbiogeographic synthesis.