This book is a unique compendium and synthesis of the cumulative knowledge of more than 100 years of discovery and study of North American tertiary mammals. The potentially most valuable contribution of this book is the detailed information of the distribution in time and space of each species at fossil localities, recorded in a uniform scheme, so that each chapter provides the same level of information. Thirty six chapters are devoted to a particular family or order, written by leading North American authorities, including discussion of anatomical features, systematics, and paleobiology. Three introductory chapters summarize information on the geological time scale, Tertiary vegetation, and Pleistocene events, and four summary chapters integrate systematic and biogeographic information for higher taxa. This book will serve as a unique data base for continuing studies in faunal diversification and change, and for questions such as how changing biogeography and climates influenced the evolution of mammalian communities. It will be an invaluable addition to the libraries of paleontologists and zoologists.