New research indicates that the tail clubs of huge armored dinosaurs known as ankylosaurs may have evolved to hit each other rather than deter hungry predators. This is a complete change from what was previously believed.
Prior to today’s article in Biology Letters, most scientists viewed the dinosaur’s tail club, a substantial bony protrusion made up of two oval-shaped knobs, primarily as a defense against predation. The team behind the new document argues that this is not necessarily the case. To make their case, they focus on years of ankylosaur research, analysis of the fossil record, and data from an exceptionally well-preserved specimen named Zuul Cruvivastat.
The name Zuul, in fact, embraces this previous idea. While “Zuul” refers to the creature in the original ghost huntersthe two Latin words that make up its species name are raw (tibia or hock) and vassator (destructive). Hence, the shin destroyer: a direct reference to where the dinosaur club may have hit the approaching tyrannosaurs or other theropods.
But this name was given when only its skull and tail had been extracted from the rock where the fossil was locked. After years of skilled work by fossil preparators at the Royal Ontario Museum, Zuul’s entire back and sides are exposed, offering important clues as to what his tail club might be targeting.
The lead author, Dr. Victoria Arbour, is currently curator of paleontology at the Royal British Columbia Museum, but is a former NSERC postdoctoral fellow at the Royal Ontario Museum in Toronto. It’s been Zuul’s home since 2016, two years after his initial discovery in Montana. She spent years studying ankylosaurs, a type of dinosaur that appears in the fossil record from the Jurassic to the late Cretaceous. Some species of ankylosaurs have tail clubs, while others, known as nodosaurs, do not. This difference raises questions about the use of these structures.
“I think a natural follow-up question to, ‘Could they use their cue clubs as a weapon?’ is “Who are they using this weapon against? ‘” Arbor explained. “And that’s when I really started thinking about it.
In 2009, she authored a paper suggesting that ankylosaurs might use their tail clubs for intraspecific combat – fights with other ankylosaurs. This work has focused on the potential impact of tail clubs when used as a weapon, especially since clubs come in many different shapes and sizes, and in some species were not even present until recently. until the animal matures. By measuring the available fossil-tailed clubs and estimating the force of the blows they could produce, she discovered that the smaller clubs (about 200 millimeters or half a foot) were too small to be used as defense against predators. .
She recommended further research, noting that if ankylosaurs used them for intraspecific combat, one would expect to see wounds along the flanks of adults, since an ankylosaur tail can only swing so far.
It’s one thing to have an idea about an extinct animal, but it’s another thing to have proof. Ankylosaurus fossils are rare in general; dinosaurs with tissue preservation that would have been damaged in these fights are much rarer. It’s amazing, then, that Arbor was able to test his ideas through an animal with its entire back – most of its skin and everything – intact.
“I floated the idea that we would expect to see some damage on the flanks, just based on how they might line up against each other,” Arbor told Ars. “And then a decade and a bit later, we get this amazing Zuul skeleton with damage where we thought we could see it. And that was pretty exciting!
Zuul’s back and sides are covered with various spikes and bony structures called osteoderms. Just as Arbor predicted, there is evidence of broken and injured osteoderms on both sides of the flanks, some of which appear to have healed.
“We also did a kind of baseline statistics to show that injuries are not randomly distributed across the body,” she continued. “They’re really limited to the sides in the areas around the hips. This is not due to chance alone. It seems more likely to be [the result of] repeated behavior.
There are only a handful of well-preserved ankylosaurs, including at least one nodosaur named Borealopelta in the Royal Tyrrell Museum. The authors note that there are no comparable injuries on known nodosaurs, a pertinent point. As mentioned earlier, nodosaurs do not have a tail club 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 were found on Zuul’s body.