"The earliest Cambrian, like Caesar's Gaul, is divided into three parts, called, from oldest to youngest Manakayan, Tommotian, and Atdabanian. (The names are all derived from Russian localities, where early Cambrian rocks are particularly well exposed.) The Manakayan contains many fossilized bits and pieces of cousins and precursors, but not the remains of major modern phyla. The Manakayan therefore pre-dates the Cambrian explosion. By the end of the Atdabanian, virtually all modern phyla had made their apperance. The Cambrian explosion therefore spans the Tommotian and Atdabanian stages.

My colleagues have dated the base of the Manakayan at 544 million years ago (with potential error of only a few hundred thousand years), and have determined that this initial stage lasted some 14 million years. The Tommotian began about 530 million years ago and--get this, for now the intellectual impact occurs--the subsequent Atdabanian stage ended only 5 to 6 (at the very most, 10) million years later. Thus the entire Cambrian explosion, previously allowed up to 30 or even 40 million years, must now fit into 5 to 10 (and almost surely nearer the lower limit), from the base of the Tommotian to the end of the Atdabanian. In other words, fast is much, much faster than we ever thought."

Dinosaur in a Haystack, p 97.

"One might argue, without great exaggeration, that 530 millions years of subsequent evolution has produced no more than a set of variations upon themes extablished during this initial explosion--though some of these little fillips, including human consciousness and insect flight, had quite an impact upon the history of life!"

Dinosaur in a Haystack, p 107.