Mammals remained at low diversity for the first 160 Myr or so of their existence, during the Mesozoic, but they underwent a major radiation in the Palaeocene and early Eocene (see pp. 333-4). Indeed, those 10Myr or so are often regarded as the best example of a rapid evolutionary radiation, during which 20 or more new lineages arose. Since the Eocene, the rate of mammalian diversification has slowed; no major new body plans have arisen in the last 50Myr (Figure 10.47). The relative fates of the mammalian orders show changes, with great diversification of the rodents, insectivores, bats and artiodactyls, and apparent declines of the xe-narthrans, whales, perissodactyls and proboscideans.
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