Britannica Educational Publishing 
Cenozoic Era [PDF ebook] 

Its constant evolution over the millennia since its inception has made the Earth a dynamic entity, subject to numerous climactic and environmental forces that are forever changing this planet. In its most recent stage, the planet has seen an incredible diversification in plant and animal life, with the most prominent development of the Cenozoic era being the emergence of mammals. This book examines our most immediate ancestors and the geologic, geographic, and environmental factors that helped make their primacy inevitable.