The most recent 65 million years of the history of life on Earth is known as the Cenozoic Era, or the Age of Mammals. Although mammals had evolved during the early part of the Mesozoic Era (the Age of Dinosaurs), they thrived during the Cenozoic, when the absence of dinosaurs made it possible for a great diversity of species to emerge.

The last two million years of earth history are the Pleistocene Epoch, or the Ice Age. At least four times during this epoch, ice sheets advanced and retreated over much of the northern hemisphere. The fluctuating climatic conditions strongly affected plant and animal evolution and distribution.

The fantastic creatures that have evolved during this era are featured in the Hall of Fossil Mammals. Displayed in the hall are fossil representatives of Cenozoic plants, fish, and mammals. The exhibits are arranged chronologically according to their appearance in the fossil record. Actual skeletons and lifelike models illustrate the various life forms that flourished two million years ago. Other exhibits demonstrate anatomical changes, such as the evolution of two families that were originally North American natives: the camel and the horse. Visitors can see the evolution of the horse from a small cat-sized animal to the present day animal. The hall also discovers early ancestors of the llama, rhino, and dog.