Michael Denton on the Fossil RecordEvolution: A Theory in Crisis (Bethesda, Maryland, Adler & Adler, Pub.: April 1986), p.162.
It is still, as it was in Darwin’s day, overwhelmingly true that the first representatives of all the major classes of organisms known to biology are already highly characteristic of their class when they make their initial appearance in the fossil record. This phenomenon is particularly obvious in the case of the invertebrate fossil record. At its first appearance in the ancient paleozoic seas, invertebrate life was already divided into practically all the major groups with which we are familiar today.