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Relative frequency histograms illustrating the number of terminal Pleistocene genera in the (A) continental simulation and (B) biogeographic simulation. The black bar represents the empirical observation of 16 terminal Pleistocene genera. The biogeographic simulation recognizes seven physiographic zones (C): 1, Pacific Mountain System; 2, Intermontane Plateau; 3, Rocky Mountain System; 4, Interior Plains; 5, Interior Highlands; 6, Atlantic Plains; 7, Appalachian Highlands.
