# Welcome to the Age of Mammals

Large rhino-like brontotheres roam a semitropical forest. Dog-sized, three-toed horses dart between the trees. The cat-like nimravid and bear dogs stalk their prey. The climate cools and forests alter to dryer grasslands. Saber tooth cats and camels get replaced by mountain lions and deer. Paleontologists learn more about the ancient animals and environment with every new fossil they discover. Read More