‘Destroyer of shins’ Ankylosaurids such as Zuul are best known for their tails, which by 100 million to 90 million years ago had evolved into stiff sledgehammers each capped with a bony knob that in some later species grew to two feet wide. Zuul’s formidably spiky tail, seen here, stretched nearly seven feet long and may have helped it fend off tyrannosaurs such as Gorgosaurus or other members of its own species. To honor Zuul’s weaponized posterior, Evans and his colleague Victoria Arbour gave the dinosaur the species name crurivastator—Latin for “destroyer of shins.”