A 30 million-year-old dog fossil has been discovered in America. The fossil was hidden in a museum collection for years but has now been identified as one of the most complete ancient dog fossils found in North America. The fossil belonged to Mesocyon coryphaeus, a dog species that lived before the Miocene epoch. This discovery can help us learn more about how ancient dogs lived and evolved over millions of years. The fossil includes most of the dog's body, missing only the tail, hands, and feet. Dogs are thought to have first arrived in North America around 40 million years ago. Mesocyon coryphaeus lived around 10 million years later, during a time when thick forests were becoming more open. This ancient dog species had shorter and stronger bones than modern dogs, making it better suited for climbing. The fossil also shows that the dog had a large thumb, which suggests it may have walked on its heels and moved differently than modern dogs.