This guide analyzes the changing geography, the arrival and departures of ecosystems and species, and the affect of climate on living things in the prehistoric seas of the eastern US. The author classifies all of the region's fossil-bearing formations and their contents within a logical, descriptive framework, allowing a determination of how community types were affected by geography and climate. This enables a study of life in the environmental and biotic contexts in which evolution, invasion, and extinction occur. The book is also an excellent field guide for fossil collectors, providing a detailed narrative for all species illustrated. Many organisms have never before been illustrated in a book on fossil shells.