The discovery started as a building project. Laura and Bridger Hill were digging up their yard when something unexpected appeared. So, they got closer, using their fingers to brush away the dirt to see what they’d unearthed. It was a row of rib bones. Carefully, they exposed the rest of a nearly complete animal skeleton. Even then, they still didn’t realize its significance. And it was months before they showed it to experts, who told them it wasn’t just any animal.