Team up with Ackerley the Acanthostega to travel back 66 million years to the Tertiary and Quaternary periods of prehistoric Earth, when mammals came to dominate the planet. Many of them are now extinct--but not the most powerful of all: humans!

Discover the facts, fossils, and fun science of behind the intriguing mammals of this time period, including killer pigs, the largest land mammal ever, and the earliest humans. The fourth part of the exciting story of life on Earth unfolds through amazing lifelike illustrations and fascinating diagrams, all narrated by a friendly prehistoric guide.