Johnson says "Nobody is proposing that an ancestral rodent (or whatever)
became a whale or a bat in a single episode of speciation...." Please.
Johnson is a lawyer! Does he know the difference between a whale and a
rodent? Do you really expect him to? I think the emphasis ought (and quite
properly so) to be on the point he is attempting to make, and not on the
specific details of the paleontology. Lets argue about the point he is
making, and not about whether he did or did not grab the correct ancestor.
That borders on ad hominem argumentation. Now if he were a vertebrate
paleontologist, then we could (if we had the facts straight ourselves),
take him to task if he had made a mistake.
Where did Johnson get his impression? Perhaps from reading Steve Stanley:
"Let us suppose that we wish, hypothetically, to form a bat or a whale...
process of gradual transformation of established species. If an average
chronospecies lasts nearly a million years, or even longer, and we have at
our disposal only ten million years, then we have only ten or fifteen
chronospecies to align, end to end, to form a continuous lineage
our primitive little mammal with a bat or a whale. This is clearly
preposterous... A chain of ten or fifteen of these might move us from one
small rodent like form to a slightly different one, perhaps representing a
new genus, but not to a bat or a whale! "