Ankylosaurs used their mallet tails to fight each other.

Ankylosaurs used their mallet tails to fight each other.
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Armored dinosaurs called ankylosaurs might have wielded mallet-like tail clubs against each other in conflict, as well as warding off predators like Tyrannosaurus rex.

A well-preserved fossil of an ankylosaur, a plant-eating dinosaur that lived 76 million years ago, is changing the way scientists understand armored dinosaurs and how they used their tail clubs.

A study of the fossil revealed spikes on the dinosaur’s flanks that broke off and healed while the animal was still alive. The researchers believe the injuries were caused when another ankylosaur struck the dinosaur with its tail club.

The study published Tuesday in the journal biology lettering.

The ankylosaur sported bony plates of various sizes and shapes all over its body; along the sides of its body, these plates acted like large spikes. Scientists also believe that ankylosaurs could have used their weapon-like tails to assert social dominance, establish territory, or even while fighting in pairs.

An ankylosaur using its tail in combat with one another is similar to how animals like deer and antelope use their antlers and horns to fight each other today.

The fossil is of a member of a particular species of ankylosaur also known by its classification name, Zuul Crurivastator. If the name sounds familiar, it’s because the researchers borrowed the Zuul name from a monster in the 1984 movie “Ghostbusters.”

The dinosaur’s full name means “Zuul, the shin destroyer,” since the ankylosaur’s tail is believed to have been an enemy of tyrannosaurs and other predators that walked upright on their hind legs.

The ankylosaur skull was one of the first parts of the fossil to be recovered.

These tails were up to 10 feet (3 meters) long, with rows of sharp spikes on the sides. The tip of the tail was fortified with bone structures, creating a club that could be swung with the force of a sledgehammer.

The skull and tail were the first pieces of the fossil to emerge in 2017 from a dig site in the Judith River Formation in northern Montana, and paleontologists worked for years to free the rest of the fossil from 35,000 pounds of sandstone. The fossil was so well preserved that traces of skin and bone armor remain on the dinosaur’s back and flanks, giving it a very lifelike appearance.

This particular ankylosaur looked pretty battered at the end of its life, with spikes near its hips and on the sides without spikes. After sustaining these injuries, the bone healed in a much more forceful way.

Due to the location on the body, investigators do not believe the injuries were caused by a predator attack. Instead, the pattern looks like the result of taking a hard blow from another ankylosaur’s tail club.

On the right side of the fossil you can see an injured spike that healed over time.

“I’ve been interested in how ankylosaurs used their tail clubs for years and this is a really exciting new piece of the puzzle,” said study lead author Dr. Victoria Arbor, curator of paleontology at the Royal Columbia Museum. Union in Victoria, Canada, in a statement.

“We know that ankylosaurs could use their tail clubs to deliver very heavy blows to an opponent, but most people thought they were using their tail clubs to fight off predators. Instead, ankylosaurs like Zuul may have been fighting each other.”

Arbor hypothesized that ankylosaurs could have engaged in their behavior years ago, but fossil evidence of injury was needed, and ankylosaur fossils are rare.

The fossil includes the head, body, and tail of the dinosaur.

The rare Zuul crurivastator fossil helped fill that knowledge gap.

“The fact that the skin and armor are kept in place is like a snapshot of what Zuul looked like when he was alive. And the injuries Zuul suffered during his life tell us about how he may have behaved and interacted with other animals in their ancient environment,” said study co-author Dr. David Evans, Temerty chair and curator of vertebrate paleontology at the Royal Ontario Museum in Toronto, in a statement.

The Zuul fossil is currently held in the Royal Ontario Museum’s Vertebrate Fossils Collection.

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