Graphic image of the prehistoric mammal, Propalaeotherium, one of the earliest horses.

Graphic image of the largest land mammal ever identified, Paraceratherium.

Read about the Didelphodon, a marsupial from the Mesozoic era and Cretaceous period. Learn what fossils have taught us about their habitat, diet, and senses, and view an animated image showing how this mammal may have moved.

Illustration of the prehistoric mammal, the giant ground sloth.

Illustration of two bear dogs fighting with each other.