Hell Creek, 66 million years ago. You are Mesodma — a mouse-sized multituberculate mammal, one of the most common mammals on this warm, humid floodplain in what will become Montana and the Dakotas. Flowering plants, palms and bald-cypress swamps stretch toward the shrinking inland sea, and every large animal here is one museums still display today. Scan the codes hidden along the trail: record the animals, answer the exhibit questions, survive the predators — then face the King.