Ankylosaurs used their sledgehammer tails to fight each other

Ankylosaurs used their sledgehammer tails to fight each other
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In addition to fending off predators like Tyrannosaurus rex, armored dinosaurs called ankylosaurs could use their sledgehammer-like tail clubs against each other in conflict.

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

Examination of the fossil revealed spikes on the dinosaur’s wings that broke and healed while the animal was still alive. Researchers believe the injuries were caused by another ankylosaur slamming its tail bar onto the dinosaur.

The study was published in the journal Tuesday Biology Letters.

Ankylosaurus sported bony plates of various sizes and shapes on its body; along the sides of its body, these plates moved like large spikes. Scientists also believe that ankylosaurs may have used their weapon-like tails to gain social dominance, establish territories, or fight for mates.

The way ankylosaurs used their tails to fight each other is similar to the way animals like deer and antelope use their horns and antlers to fight each other today.

The fossil is a member of a special species of ankylosaurus known by the taxonomic name, Zuul crurivastator. If the name sounds familiar, that’s because the researchers took the name Zuul from a monster in the 1984 film Ghostbusters.

The dinosaur’s full name means “Zuul, Destroyer of Legs,” because the ankylosaurus’ tail bar was thought to be the enemy of tyrannosaurs and other predators that walked upright on their hind legs.

The Ankylosaurus skull was one of the first parts of the fossil to be found.

These tails measure up to 10 feet (3 meters) long, with sharp spikes lining their sides. The tip of the tail was reinforced with bony structures, creating a club that could be swung with the power of a sledgehammer.

The skull and tail were the first fossil pieces to emerge from a 2017 excavation 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 the dinosaur’s back and flanks were left with remnants of skin and bony armor, giving it a very lifelike appearance.

This particular ankylosaurus appeared to be very run down by the end of its life, with spikes missing near its hips and sides. After receiving these injuries, the bone took on a more blunt shape.

Because of the location on the body, researchers do not believe the injuries were caused by a predator attack. Instead, the pattern appears to be the result of a powerful blow from another ankylosaur’s tail club.

A scarred spike can be seen on the right side of the fossil that has healed over time.

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

“We know that ankylosaurs could use tail clubs to deliver very powerful blows to an opponent, but most people thought they used tail clubs to fight off predators. Instead, ankylosaurs like Zuul may have fought each other.

Arbor hypothesized that ankylosaurs might have engaged in their behavior years ago, but needed fossil evidence of injuries—and ankylosaur fossils are rare.

The fossil includes the dinosaur's head, body and tail.

The exceptional Zuul crurivastator fossil helped fill this knowledge gap.

“Keeping the skin and armor in place is like a picture of what Zuul looked like when he was alive. And the injuries sustained by Zuul during its lifetime tell us how it behaved in its ancient environment and how it might have interacted with other animals,” said study co-author Dr. David Evans, Temerty Chair and Curator of Vertebrate Paleontology at the Royal Ontario Museum in Toronto.

The Zuul fossil is currently housed in the Vertebrate Fossil Collection of the Royal Ontario Museum.

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