This book places into modern context the information by which North American mammalian paleontologists recognize, divide, calibrate, and discuss intervals of mammalian evolution known as North American Land Mammal Ages. It incorporates new information on the systematic biology of the fossil record and utilizes the many recent advances in geochronologic methods and their results. The book describes the increasingly highly resolved stratigraphy into which all available temporally significant data and applications are integrated. Extensive temporal coverage includes the Lancian part of the Late Cretaceous, and geographical coverage includes information from Mexico, an integral part of the North American fauna, past and present.

This book is designed as a source and reference for people interested in the history and fossil record of North American tertiary mammals. Each chapter covers a different family or order, and includes information on anatomical features, systematics, the distribution of the genera and species at different fossil localities, and a discussion of their paleobiology. Many of these groups have never been covered in this fashion before.

Imagine the blooming of the very first flower. Or a 3-ton sloth with massive claws standing as tall as a giraffe. And horses the size of small dogs that have toes instead of hooves. This is not a dream or vision of an artist or author. This is North America over 20 million years ago! Journey into the distant past with this book and witness the earliest events in North America; when mammals rose from the shadows of the extinct dinosaurs to fill the land, and the first flowers and grasslands bloomed.