Everyone knows Ankylosaurus. It’s the epitome of the titular group of highly-armored herbivores to which it belonged, and there’s even a case to be made that it’s the best dinosaur. The living tank’s tail club certainly plays into that. It’s difficult to look at that knob of bone and not imagine it smacking into the leg of an attacking tyrannosaur or battering the side of another ankylosaur in a territorial dispute. But how did this famous piece of the dinosaur armament evolve?

North Carolina Museum of Natural Sciences paleontologist Victoria Arbour has quickly become one of the world’s foremost experts on ankylosaurs. In the past she’s helped sort out the number of ankylosaur species and