Science

Ankylosaurs fought each other as much as T. rex

Ankylosaurs fought each other as much as T. rex

Zuul crurivastator in battle. Credit: Illustrated by Henry Sharp. © Henry Sharp

Zool shows that ankylosaurs may also have used their tails for social dominance.

Scientists have discovered new evidence of how armored dinosaurs used their iconic tails. The extraordinary Ankylosaurus fossil The blood curdling roar has spikes on its flanks that were broken and regrown while the dinosaur was alive – injuries that scientists believe were caused by a blow from another of Zuul massive tail club. This suggests that ankylosaurs had complex behaviours, possibly fighting for social and territorial dominance, or even engaging in a ‘rutting season’ for mates.

The research, conducted by scientists from the Royal Ontario Museum (ROM), the Royal BC Museum and the North Carolina Museum of Natural Sciences, was published Dec. 7 in the journal Biology Letters.

Zuul crurivastator Skull

Zuul crurivastator skull. Credit: © Royal Ontario Museum

The 76-million-year-old plant-eating dinosaur is part of the Royal Ontario Museum’s vertebrate fossil collection and is named after the fictional monster “Zull” from the 1984 film. Ghostbusters. The skull and tail were initially freed from the surrounding rock, but the body was still encased in 35,000 pounds of sandstone. After years of work, it was revealed that the body retained most of the skin and bony armor across the back and flanks, providing a remarkable insight into what the dinosaur looked like in life.

of Zuul the body was covered with bony plates of various shapes and sizes, and those along its sides were particularly large and spiked. Interestingly, the scientists noticed that a number of spines near the thighs on both sides of the body were missing their tips and the bone and horn had grown into a blunter shape. The pattern of these injuries is more consistent with them being the result of some form of ritualized combat or skirmish with their tails, and probably not caused by an attacking predator like a tyrannosaurus due to where they are located on the body.

Photo and illustration of Zuul crurivastator

Photo and illustration of Zuul crurivastator with injured spikes marked in red. Credit: Daniel Dufault, © Royal Ontario Museum

“I’ve been interested in how ankylosaurs used their tail clubs for years, and this is a really exciting new piece of the puzzle,” says lead author Dr. Victoria Arbor, curator of paleontology at the Royal BC Museum and former NSERC postdoctoral fellow at the Royal Ontario Museum. “We know that ankylosaurs could use their tails to deliver very strong blows to an opponent, but most people thought they used their tails to fight predators. Instead, ankylosaurs like Zool they may have quarreled with each other.

Zool injured and healed Spike

A bruised and healed spike on Zool’s left side. Credit: © Royal Ontario Museum

of Zuul the tail is about three meters (10 ft) long with sharp spikes running down its sides. The back half of the tail was hard and the tip was encased in huge bony patches, creating a formidable weapon similar to a blacksmith’s hammer. The blood curdling roar means “Zuul, the destroyer of shins,” a nod to the idea that tail clubs were used to break the legs of bipedal tyrannosaurs. The new research doesn’t disprove the idea that tails could be used for self-defense against predators, but it does show that tails could also function for intraspecific fighting, a factor that more likely led to their evolution. Today, specialized animal weapons such as deer antlers or antelope horns have generally evolved to be used primarily for fighting members of the same species during fights for mates or territory.

Wounded and healed Zool Spike

A bruised and healed spike on Zuul’s right side. Credit: © Royal Ontario Museum

Years ago, Arber proposed the idea that ankylosaurs might have butted each other in the flanks, and that broken and healed ribs might provide evidence to support that idea. But ankylosaur skeletons are extremely rare, making it difficult to test this hypothesis. The fully preserved back and tail of Zoolincluding skin, allows an unusual insight into the lives of these amazing armored dinosaurs.

“The fact that the skin and armor are preserved in place is like a snapshot of how Zool watched when it was alive. And the injuries Zool maintained throughout its life tell us about how it may have behaved and interacted with other animals in its ancient environment,” said Dr. David Evans, Temerty Chair and Curator of Vertebrate Paleontology at the Royal Ontario Museum.

Undamaged Zuul flank spike

Undamaged flank spike from Zuul. Credit: © Royal Ontario Museum

The remarkable skeleton of Zool was discovered in the Judith River Formation in northern Montana and was acquired by the ROM through the generous support of the Louise Hawley Stone Charitable Trust.

Reference: “Paleopathological evidence for intraspecific combat in ankylosaurid dinosaurs” by Victoria M. Arbor, Lindsey E. Zano, and David S. Evans, 7 Dec. 2022. Biology Letters.
DOI: 10.1098/rsbl.2022.0404

Funding for this project was also provided by the Natural Sciences and Engineering Research Council, L’Oreal-UNESCO for Women in Science, Alberta Innovates and the Dinosaur Research Institute.



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