  Cretaceous-Cenozoic history of angiosperms led to the a certain character of
the distribution of taxa of different levels (the number of species and genera
in families, species/genera ratio in families, the number of species in the
genera). In most cases, these distributions are satisfactorily described by a
power law (Pareto distribution). In logarithmic coordinates power function is a
straight line. Empirical curves repeat this line is good enough, but on the
right side of the graph (at low volumes taxa), there is a marked deviation of
theoretical from the empirical curves. This suggests that the small volumes of
taxa should be greater for full compliance with the theoretical curves.
Modeling ratios among genera and species in families showed that only in the
case of dynamic extinction factor observed satisfactory agreement between
observed and calculated the number of species in a wide range of iterations.
This suggested that there was a differential extinction of species during the
evolution of angiosperms. This implies that the rate of extinction had to be
minimal in genera with a large number of species. On the contrary, extinction
rates may be increased by orders of magnitude with a decrease in the number of
species. As a result, large genera became getting bigger and small genera
become less. The species frequencies of distribution in the genera varied
according to a power law. The initial divergence of taxa volume, which led to
their further division into large and small, could be caused by the emergence
and expansion of herbs with their functional and adaptive capabilities.
