Derek E.G. Briggs in American Scientist:
The recent surge in interest in the origins of multicellular animals (metazoans) is fueled by new evidence from three major sources: molecular sequencing, the study of evolutionary development and the discovery of exceptionally preserved fossils of Precambrian and Cambrian age, particularly from China. Genetic sequences provide a means of analyzing how the major animal groups are related and of estimating their time of origin (using the molecular clock)—a means that is independent of morphological data and the record of evolutionary events the fossils reveal. The study of developmental processes in an evolutionary framework (“evo-devo”) provides the link between genetics and morphology. These new approaches have prompted molecular biologists to join forces with paleontologists to focus on the sequence of events leading to the origin of body plans before and during the Cambrian Period (543 to 500 million years ago).
Few if any authors can embrace these fields with the experience and authority of James W. Valentine, professor emeritus of integrative biology at the University of California, Berkeley, who has been publishing novel and provocative ideas on the origin and nature of phyla for more than 30 years. His most recent book, On the Origin of Phyla, is an homage to the greatest biologist who ever lived by one of the greatest living paleobiologists.
More here.