In 1981 University of Nebraska paleontologists came upon an unexpected concentration of carnivore dens at Agate Fossil Beds National Monument in north?west Nebraska. The discovery of bones of Miocene beardogs, mustelids, and canids in their burrows was an exceptional event. Survey and excavation (1981?1990) established that six species of carnivores had, over time, occupied the dens with traces of their prey: juvenile and adult oreodonts, camels, and a neonatal rhinoceros. At least nine individuals of the wolf-like beardog Daphoenodon superbus, the most common carnivore, were identified. The carnivores found together in the dens represent a moment in time?the oldest carnivore den community yet discovered with remains of predators, their prey, and their ecology in evidence. Dated at 22 to 23 Ma (million years), the den complex provided scientists with the oldest documented evidence of carnivore denning behavior.