Prospective versus Retrospective
views of taxon emergence
Clade B arises from Clade A
at time T1 as a single new species. The clade
subsequently
undergoes extensive speciation as part of an adaptive radiation,
resulting
in a diversity of species with distinctive morphology at time T2
(the present). Given
a recognition of this history and the present diversity of species in
clade
B, a present-day taxonomist would probably classify
all of the B clade as a separate major taxon. However, a
taxonomist living at time T1 would not recongize the single ancestral
species of the B clade
as a distinct taxon.
