What did horses look like millions of years ago? How big were mammoths and mastodons? This book gives readers an in-depth look into the world of prehistoric mammals by investigating the remains they left behind. Readers will study colorful images of mammal fossils to learn about the size and shape of each animal, but also the behavior and lifestyle they may have lived. The text is paired with a fact-file design, complete with sidebars and diagrams, to give readers a well-rounded and exciting reading experience. Readers will learn to think like a paleontologist as they uncover these amazing mammal fossils!