How do we know that mammals lived alongside the dinosaurs? What proves that whales evolved from four-legged land animals and are related to hippos? Did hunting by humans or climate change cause the extinction of mammoths? How far back would we need to go to see that horses were once almost identical to tapirs and rhinos? Donald R. Prothero takes readers on a journey through the history of mammals, opening a window onto the worlds of some of the most incredible and peculiar animals that ever lived. He tells the dramatic stories of fossil findings and the paleontologists who unraveled them, showing how scientific ingenuity advanced our knowledge of both ancient and present-day mammals. Alongside iconic animals like mastodons, dire wolves, and sabertoothed cats, Prothero introduces readers to a vast range of little-known prehistoric creatures. Some resemble their living relatives, but with a twist: short-necked giraffes, camels without humps, rhinos without horns, bear-sized beavers. Others are like nothing alive today, such as chalicotheres, which look like a cross between a horse and gorilla but with claws, and uintatheres, which one scientist compared to "giant horned bunnies." Lively and informative, The Story of the Mammals in 25 Discoveries highlights the wonder, beauty, and strangeness of the creatures that have shared our world.