New find suggests Ankylosaurus tail clubs were for hitting each other

New research indicates that the tail clubs of huge armored dinosaurs known as ankylosaurs may have evolved to strike each other rather than deter hungry predators. This is a complete change from what was previously believed.

Before the paper published today in Biology Letters, most scientists looked at the dinosaur’s tail club, a substantial bony protrusion composed of two oval-shaped knobs, primarily as a defense against predation. The team behind the new paper argues that this is not necessarily the case. To make their case, they draw on years of ankylosaur research, analysis of the fossil record, and data from an exceptionally well-preserved specimen called The roar that curdles blood.

The name Zuul, in fact, embraces this earlier idea. While “Zuul” refers to the creature in the original Ghostbustersthe two Latin words that make up its species name are raw (cinnamon or cane) i the answering machine (destroyer). Hence, the shin-buster: a direct reference to where the dinosaur’s club might have struck tyrannosaurs or other oncoming theropods.

But this name was given when only its skull and tail had been excavated from the rock where the fossil was found. After years of specialized work by fossil preparers at the Royal Ontario Museum, Zuul’s entire back and flanks are exposed, offering important clues as to what its tail club might be pointing at.

Target identification

The main author, Dra. Victoria Arbour, is currently the Curator of Paleontology at the Royal British Columbia Museum, but is a former NSERC Postdoctoral Fellow at the Royal Ontario Museum in Toronto. This has been Zuul’s home since 2016, two years after its initial discovery in Montana. He has spent years studying ankylosaurs, a type of dinosaur that appears in the fossil record from the Jurassic to the end of the Cretaceous. Some species of ankylosaurs have tail clubs, while others, known as nodosaurs, do not. This difference raises some questions about what these structures were used for.

“I think a natural follow-up question to, ‘Could they use their tail clubs as a weapon?’ it’s ‘Who are they using this weapon against?’” Arbour explained. “And that’s where I really started thinking about it.

In 2009, he wrote a paper this suggested that ankylosaurs might use their tail clubs for intraspecific combat—fights with other ankylosaurs. This work focused on the potential impact of tail sticks when used as a weapon, especially since sticks come in various shapes and sizes, and in some species, were not even present until the animal matured . By measuring the available fossil tail clubs and estimating the force of the blows they could produce, he found that the smallest clubs (about 200 millimeters or half a foot) were too small to be used as a defense against predators.

The roar that curdles bloodthe cinnamon

Royal Ontario Museum

He recommended further research, noting that if ankylosaurs used them for intraspecific combat, one might expect to see injuries to adult flanks, since an ankylosaur tail can only swing so far.

It’s one thing to have an idea about an extinct animal, but another to have evidence. Ankylosaur fossils are generally rare; dinosaurs with tissue preservation that would have been damaged in these fights are much rarer. So it’s surprising that Arbor was able to test his ideas on an animal with its entire back, most of its skin and all, intact.

“I came up with this idea that we expect to see damage on the flanks, just based on how they might line up against each other,” Arbour told Ars. “And a decade and a bit later, we have this amazing Zuul skeleton with damage right where we thought we’d see it. And that was really exciting!”

Damage assessment

Zuul’s back and flanks are covered in various spikes and bony structures called osteoderms. As Arbor predicted, there are signs of broken and injured osteoderms on both sides of the flanks, some of which appear to have healed.

“We also did some kind of basic statistics to show that lesions are not randomly distributed in the body,” he continued. “They are actually only restricted to the sides in the areas around the hips. This cannot be explained by chance alone. It seems more likely that [the result of] repeated behavior”.

There are only a handful of well-preserved ankylosaurs, including at least one named nodosaur From the boreal forest at the Royal Tyrrell Museum. The authors note that there is no comparable lesion in known nodosaurs, an important point. As mentioned above, nodosaurs do not have tail clubs and therefore could not have used them against each other.

Equally important, the damage is not accompanied by evidence of predation. No bite marks, puncture wounds, or tooth scratches are found anywhere on Zuul’s body.