.dropcap { color: #838078; float: left; font-size: 82px; line-height: 60px; padding: 5px 8px 0 0; } Kemmerer, Wyoming, is a sleepy little town with a main drag populated by quiet cafes and the JCPenney mother store. But there’s something that makes this place extraordinary, and it’s set in stone among the surrounding hills. The stacks of bare rock hemming Kemmerer host one of the most extraordinary graveyards in the world. Paleontologists know it as the “18-inch layer,” a roughly 50-million-year-old window into Eocene time, preserved in high-definition in a layer of sediment a foot and a half thick. Back in the Cenozoic Era, this piece of southwestern Wyoming was submerged by an enormous 40-mile-long lake. Fish, turtles, and alligators thrived in the water, while the surrounding subtropical forest hosted an array of other vertebrates—from ancient primates and horses, to early bats and birds. After they died, they were preserved in haunting detail in what...