GREENBELT, Md. — Some 110 million years ago, in the swamp that would become the Washington suburbs, a hulking, armored nodosaur trudged along a riverbank, leaving a telltale print in the mud. Its offspring scrambled after it, slipping in the parent’s print. Other dinosaurs crowded the setting: A long-necked sauropod squelched through the muck, while several theropods — smaller cousins […]