Figure 20.7   A classic example of a radiation, the pattern of diversifi cation of the placental mammals after the Cretaceous- Tertiary mass extinction. Mammals originated in the Triassic, and diversifi ed at a modest rate during the Jurassic and Cretaceous. Modern placental superorders originated in the Late Cretaceous, and the orders began to diversify. Only after the dinosaurs had died out did the placental mammals really diversify and become abundant worldwide. (From Benton 2005.)

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