A SYSTEMATIC INCREASE IN ORIGINATION OF LONG-LIVED GENERA

One of the central questions of paleobiology has been why very little “progress” is documented in the fossil record. It has been argued that the normal processes of evolution, which might be expected to result in “progress”, are undone by other, higher “tier” processes such as mass extinctions. We show here that over the last 542 Myr, there has been a dramatic increase in the origination of long-lived genera during successive periods. This increase was broken only by the severe end-Permian mass extinction, and beginning in the Triassic the changes became more systematic and rapid. The emergence of genera with greater resistance to extinction might be viewed as a kind of progress. Nevertheless, it is largely consistent with population of the tail of an increasingly skewed distribution.