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

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

Zuul crurivastator in Battle

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

Zuul shows that ankylosaurs may also have used their tail clubs for social dominance.

Scientists have found new evidence for how armored dinosaurs used their iconic tail maces. The exceptional fossil of the ankylosaurus The bloodcurdling roar has spikes along its flanks that broke and healed back when the dinosaur was alive – injuries the scientists believe were caused by an attack by another Zuuls huge tail club. This suggests that ankylosaurs exhibited complex behaviors, possibly fighting for social and territorial dominance or even engaged in a “matting season” for mates.

The research, by scientists from the Royal Ontario Museum (ROM), Royal BC Museum and 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

Part of the Royal Ontario Museum’s collection of vertebrate fossils, the 76-million-year-old herbivorous dinosaur was named after the fictional monster “Zuul” from the 1984 film Ghostbusters. Initially, the skull and tail were freed from the surrounding rock, but the body was still encased in 35,000 pounds of sandstone. After years of work, the body was found to have retained most of the skin and bony armor all over its back and flanks, providing a remarkable picture of what the dinosaur looked like in life.

Zuuls body was covered with bony plates of various shapes and sizes and those along the sides were particularly large and prickly. Interestingly, the scientists noticed that a number of spines near the hips on both sides of the body are missing their tips and that the bone and horny sheath have healed into a blunt shape. The pattern of these injuries is more consistent with the result of some form of ritual combat or jousting with their tail clubs, and was probably not caused by an attacking predator such as a tyrannosaur due to its location on the body.

Zuul crurivastator photo and illustration

Zuul crurivastator photo and illustration with injured spikes highlighted in red. Credits: Danielle Dufault, © Royal Ontario Museum

“I’ve been interested for years in how ankylosaurs used their tail clubs and this is a really exciting new piece of the puzzle,” said lead author Dr. Victoria Arbour, 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 tail clubs to deliver very powerful blows to an opponent, but most people thought they used their tail clubs to fight off predators. Instead, ankylosaurs love it Zuul may have fought each other.

Zuul injured and healed Spike

Wounded and healed peak to the left of Zuul. Credit: © Royal Ontario Museum

Zuuls tail is about three meters (10 feet) long with sharp spines running down the sides. The back half of the tail was stiff and the tip was sheathed in huge bony blobs, creating a formidable sledgehammer-like weapon. The bloodcurdling roar means ‘Zul, the destroyer of shins’, a nod to the idea that tail maces were used to smash the legs of bipedal tyrannosaurs. The new research doesn’t refute the idea that tail maces could be used for self-defense against predators, but shows that tail maces would also have functioned for intra-species combat — a factor that more likely drove their evolution. Today, specialized animal weapons such as the antlers of deer or the horns of antelopes have mostly evolved to be used primarily for fighting members of the same species during fights for mates or territory.

Wounded and healed Zuul Spike

Wounded and healed peak to the right of Zuul. Credit: © Royal Ontario Museum

Years ago, Arbor had suggested that ankylosaurs clubbed each other in the flanks, and that broken and healed ribs might support this idea. But ankylosaurus skeletons are extremely rare, making it difficult to test this hypothesis. The fully preserved back and tail of Zuulincluding skin, provided an unusual glimpse into the lives of these incredible armored dinosaurs.

“The fact that the skin and armor are kept in place is like a snapshot of how Zuul looked when it was alive. And the injuries Zuul that it survived during its lifetime tell us how it may have behaved and how it interacted with other animals in its ancient environment,” says Dr. David Evans, chairman of Temerty and curator of vertebrate palaeontology at the Royal Ontario Museum.

Undamaged Zuul Flank Spike

Zuul’s undamaged flank spike. Credit: © Royal Ontario Museum

The remarkable skeleton of Zuul was found in the Judith River Formation of northern Montana and 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. Arbour, Lindsay E. Zanno, and David C. Evans, December 7, 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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