Figure 1.

Logarithmic plots (both scales logarithmic) of the size distribution of genera, assuming only cataclysmic extinctions. The top row corresponds to n₀ = 1 and the bottom row to n₀ = 5. The three columns (from left to right) correspond to τ = 2,4 and 10. In all cases λ = 1 and γ = 0.1. For the sake of display the points of the probability mass function have been joined by lines:- dotted for derived genera; dot-dash for the pioneering genus and solid for the mixed distribution of all genera. The distribution of the pioneering genus (dot-dash) does not appear in the lower right-hand panel because the pmf assumes values less than 0.0001 for all sizes up to 100. In consequence the mixed distribution (solid line) is overlaid on that of derived genera (dotted line). Similarly in the upper right-hand panel the dotted and solid lines are overlaid.