Some dinosaurs are better at hiding than others. There’s no single reason for their edge. Some were rare. Others too small to gain much notice from the paleontologists who were set on finding large, imposing specimens for museum centerpieces. Still more became preserved in slices of rock that haven’t gained the attention of the most famed quarries. Whatever the reasons, though, a big, heavily-armored dinosaur was able to escape the notice of paleontologists despite over a century of Jurassic exploration.

North America’s Morrison Formation is a fossiliferous wonderland. Spectacular bonebeds dot its reach from Canada to Mexico, and it was one of the focal points for the great Bone Wars between O.C. Marsh and E.D. Cope in