Recently, we noted new findings on the ways in which asexuality can lead to extinction. Even mass extinctions, however, have not been—as this recent story suggests—the “end of the world.” What often happens is that they open up niches for species that were there already or somewhere already, who just increase in numbers and range to fill the gap. These researchers argue that mammals arose at the end of the Permian, not in the Triassic, due to the departure of dominant land species:
However, new research suggests that this array of unique features arose gradually over a long span of time, and that the first mammals may have arisen as a result of the end-Permian mass extinction — which wiped out 90 per cent of marine organisms and 70 per cent of terrestrial species.
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The researchers concluded that cynodont diversity rose steadily during the recovery of life following the mass extinction, with their range of form rising rapidly at first before hitting a plateau. This suggests there is no particular difference in morphological diversity between the very first mammals and their immediate cynodont predecessors.
In short, they are not quite saying that mammals arose at the end of the Permian, but it sure sounds like it for all practical purposes. And if so, this is another one for the “earlier than thought” files.