 In each burial event layer the commonest species generally has several times as many individuals as the second most common, and accounts for 15 % to 30 % of individual fossil animals. The more common a species is in one layer, the greater the number of other layers it appears in. These "recurrent" species account for 88 % of the individual specimens, but only 27 % of the number of species. This suggests that the majority of species were in existence for much shorter periods than the "recurrent" ones. Species that cover shorter periods of time occur mainly in the higher, younger layers. The GPB shows an overall trend of increasing diversity as time progresses.
