Rates of evolution - How do we measure large changes?
The taxonomic rate of evolution
Another method of measuring large evolutionary changes is by the taxonomic rate.
A taxonomic rate of evolution offers an abstract measure of how rapidly change is taking place in a group of species. If there were two separate evolutionary lineages and in the same time interval a taxonomist divided one lineage into two species and the other into three, it would suggest that the latter lineage had evolved at a higher rate. The measurement is not based on a single character but on several characters.
Taxonomic rates can be expressed in two main ways. One is the number of species, or genera (or whatever taxon) per million years. The table gives some examples from two taxa: horses and lungfish.
Table: taxonomic rates of evolution in horses and lungfish.