Thirty Million Years of Mammals: The Oligocene Fossil Beds

About thirty-three to twenty-three million years ago, what is now the Badlands looked nothing like what you see today. This was a subtropical savanna, wetter than the modern plains, with rivers draining east from the young Rocky Mountains and depositing thick layers of sediment across a broad lowland. The animals living here would be unrecognizable.

There were creatures called Titanotheres, animals the size of rhinoceroses with paired bone horns above their noses, that were browsers, among the last of their kind, since titanotheres died out around the start of this era. There were small three-toed horses no bigger than a large dog, ancestors of the modern horse, called Mesohippus. There were catlike predators called nimravids that had no living descendants.

And there were Oreodonts, pig-like animals that lived in dense herds and have no close modern relatives. The Badlands fossil record for this Oligocene epoch is considered one of the richest in the world. The fossils are exposed because the same ongoing erosion that shapes the badlands formations also brings buried bones to the surface.

Rain eats the sediment around a fossil, leaving it sitting on a pedestal of remaining rock or scattered on the slope below. Visitors who hike the backcountry sometimes spot fossilized bone without any special equipment. The park asks that anything found be left in place and reported to rangers, since in-place fossils retain scientific context that removed specimens lose.

The fossil preparation lab at the Ben Reifel Visitor Center lets visitors watch scientists clean and prepare specimens found in the field.