The seventy-fifth anniversary of the Journal of Paleontology presents a felicitous opportunity to review major changes in interpretation of mammalian phylogeny. Founding of the journal coincides with the nascence of the career of the most influential paleomammalogist of the past century, George Gaylord Simpson (1902–1984). It occurred at a time when now-archaic models for mammalian systematics and evolution, such as the aristogenesis of H. F. Osborn (1857–1935) and the typological concept of taxa, were prevalent (e.g., Simpson, 1945). These models were soon to give way to “new ways of going at things” (Laporte, 2000, p. 87); most significantly,...

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