not that was entirely true, we thought that a single volume reviewing the fossil record of the earliest Metazoa would be useful to many in both paleontology and zoology, especially since so much new informa­ tion has been developed in the last few years. Some of this information has been summarized in general articles recently, but an overview of most of the field does not exist. We therefore organized this book in five parts so that the evidence could be placed in perspective and summarized and inferences made from it. Part I intro­ duces the previous hypotheses that have been proposed for the origin and early radiation of Metazoa. Part II consists of two summary chapters that set the sedi­ mentological, geochemical, and biological background to the known radiations of Metazoa.