Several years ago, we realized that the most prominent ideas that had been ex pressed about the origin and early evolution of the Metazoa seemed to have been developed chiefly by zoologists using evidence from modern species without reference to the fossil record. Paleontologists had, in fact, put forth their own ideas but the zoological and the paleontological evidence were about the problem, seldom considered together, especially by zoologists. We believed that the paleon tological documentation of the first Metazoa was too scattered, too obscure to Western readers, and much of it too recent to have been readily available to our colleagues in zoology. Whether or 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.

Abstract: The Middle Member of the Poleta Formation (Cambrian, Stage 3) Esmeralda County, Nevada, was deposited in shallow marine, siliciclastic-dominated settings during a transgressive to highstand cycle in western Laurentia. Carbon isotopic stratigraphy suggests correlation with the Cambrian Arthropod Radiation isotopic Excursion (CARE). The Middle Member of the Poleta Formation includes at least three less than 1 m-thick and discontinuous horizons of exceptional fossil preservation termed the Indian Springs Lagerstatte. Most fossils were collected from the horizons of exceptional preservation and mostly consist of biomineralizing animals such as trilobites, helicoplacoids, hyolithids, and inarticulate brachiopods. Examples of preserved nonbiomineralized animals and anatomy include mantle setae in brachiopods, demosponges, hyolithid gut tracts, trilobite appendages, and body fragments of nonbiomineralizing arthropods. Exceptional fossil preservation was facilitated through preference of durophageous carnivores, obrution deposition, and favorable geochemical conditions during fossil diagenesis after burial.

First published in 1992, The Proterozoic Biosphere was the first major study of the paleobiology of the Proterozoic Earth.