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Phylogenetic evidence suggested that the Queensland Euastacus diversified through ‘simultaneous vicariance’, where the range of a widespread ancestral Euastacus receded to tops of mountains with the Pliocene warming of the continent and subsequent isolation lead to speciation. Implicit in the simultaneous vicariance hypothesis are three postulates on ancestral history: (1) warm temperatures were effective barriers to ancestral gene flow; (2) the ancestral Euastacus had an extensive contiguous distribution; and (3) there was a single vicariant event associated with Pliocene warming. It is argued that if there was interspecific diversification due to simultaneous vicariance then, within extant species, there are three predictions on current population structure. First, lowland areas, even those connected by streams, would be barriers to contemporary dispersal. Second, there would be contemporary dispersal between catchments covered by mesic rainforests. Third, there would have been recent Pleistocene intraspecific vicariant events. The population structure of E. robertsi, E. fleckeri, E. hystricosus and E. sulcatus was investigated with mtDNA and allozymes and it was found that the intraspecific data were consistent with these predictions. Furthermore, the Euastacus underwent limited range expansions during the cooler Pleistocene glacial cycles, and it is hypothesised that during cooler glacial periods, lowlands were still effective barriers to dispersal because of increased Pleistocene aridity. Keywords: dispersal, freshwater crayfish, gene flow, population structure