Ankylosaurs fought each other as much as they fought against T. rex.

Scientists from the Royal Ontario Museum (ROM), the Royal BC Museum and the North Carolina Museum of Natural Sciences have found new evidence for how armored dinosaurs used their iconic tail sticks.

The exceptional fossil of the Ankylosaur Zuul crurivastator has spikes on its flanks that broke off and healed again while the dinosaur was alive—injuries that scientists think were caused by the impact of another Zuul’s gigantic tailbone. This suggests that ankylosaurs had complex behaviors, possibly fighting for social and territorial dominance or even going into “resentment” for mates. The research was published in the journal Biology Letters.

Part of the Royal Ontario Museum’s vertebrate fossil collection, the 76-million-year-old plant-eating dinosaur is named after the fictional monster “Zuul” from the 1984 movie “Ghostbusters.” Originally the skull and tail were recovered from the surrounding rock, but the body was still covered with 35,000 pounds of sandstone. After years of study, it turned out that the body retained most of its skin and bone armor on all its back and flanks, providing a remarkable view of what the dinosaur looked like in life.

Zuul’s body was covered with bony plates of different shapes and sizes, and those next to him were particularly large and spiny. Interestingly, the scientists noticed that the ends of a set of nails near the hips on both sides of the body were missing, and the bone and horny sheath had healed to a more blunt shape. The pattern of these injuries was more consistent with being the result of some form of ritualized fighting or jousting with tail sticks, and were not caused by an attacking predator, such as a tyrannosaur, likely due to their location on the body.

D., Curator of Paleontology at the Royal BC Museum and former NSERC postdoctoral fellow, lead author Dr. “I’ve been interested in how ankylosaurs used their tail sticks for years, and this is a really exciting new piece of the puzzle,” says Victoria Arbour. Royal Ontario Museum.

“We know that ankylosaurs could use their tails to deliver very powerful blows to an opponent, but most people thought they used their tails to fight predators. Instead, ankylosaurs like Zuul may have been fighting each other.”

Zuul’s tail was about three meters (10 feet) long and had sharp spikes on its sides. The rear half of the tail was hard, and the tip was covered with huge bony spots that formed a formidable sledgehammer-like weapon.

Zuul crurivastator means “Zuul, the destroyer of shanks”, a reference to the idea that tail sticks were used to break the legs of bipedal tyrannosaurs. The new research doesn’t disprove the idea that tail sticks could be used for self-defense against predators, but it does show that tail sticks may have also functioned for interspecies combat—a factor that more likely drove their evolution. Today, special animal weapons such as antlers or antelope horns have been developed, often for use in fighting members of the same species in battles for mates or territory.

Years ago, Arbor had put forward the idea that ankylosaurs might have struck each other on the side with clubs, and that broken and healed ribs might provide evidence to support this idea. But ankylosaur skeletons are extremely rare, making this hypothesis difficult to test. Zuul’s fully preserved back and tail, including the skin, provided an unusual insight into the lives of these incredibly armored dinosaurs.

“The preservation of the skin and armor in place is like a snapshot of what Zuul looked like when he was alive. And Zuul’s wounds throughout his life tell us how he may have behaved and interacted with other animals in his former environment. Temerty Head and Vertebrate at the Royal Ontario Museum. Dr. David Evans, Curator of Paleontology.

Zuul’s remarkable skeleton was found in northern Montana’s Judith River Formation.