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Bizarre, dog-sized dinosaur species discovered in Chile had a unique slashing tail

The new species, called stegosour, has something never seen before on any animal: seven pairs of ‘blades’ laid out sideways like a slicing weapon.

People in Santiago, Chile, take pictures of models of a Stegouros elengassen, a new species of non-avian dinosaur the remains of which were discovered intact in Patagonia.
People in Santiago, Chile, take pictures of models of a Stegouros elengassen, a new species of non-avian dinosaur the remains of which were discovered intact in Patagonia.
Martin Bernetti / Getty Images

Fossils found in Chile are from a strange-looking, dog-sized dinosaur species that had a unique slashing tail weapon, scientists reported in a new study in the journal Nature.

Unlike dinosaurs that had spiked tails they could use as stabbing weapons or tails with clubs, this new species has something never seen before on any animal: seven pairs of “blades” laid out sideways like a slicing weapon used by ancient Aztec warriors, said Alex Vargas, the lead author of the study.

“It’s a really unusual weapon,” said Vargas, a University of Chile paleontologist. “Books on prehistoric animals for kids need to update and put this weird tail in there. ... It just looks crazy.”

The plant-eating critter had a combination of traits from different species that initially sent paleontologists down the wrong path. The back end, including its tail weapon, seemed similar to a stegosaurus, so the researchers named it stegouros elengassen.

This illustration by Mauricio Alvarez shows a Stegouros. Fossils found in Chile are from the bizarre, dog-sized dinosaur species that had a unique slashing tail weapon.
This illustration by Mauricio Alvarez shows a Stegouros. Fossils found in Chile are from the bizarre, dog-sized dinosaur species that had a unique slashing tail weapon.
Mauricio Alvarez via AP

After Vargas and his team examined the pieces of skull and did five DNA analyses, they concluded it was only distantly related to the stegosaurus, though the steouros name stuck.

Instead, it was a rare southern hemisphere member of the tank-like ankylosaur family of dinosaurs.

Vargas called it “the lost family branch of the ankylosaur.”

The fossil was dated to about 72 million to 75 million years ago.

It appears to be an adult, based on the way bones are fused, Vargas said.

It was found with its front end flat on its belly and the back end angled down to a lower level, almost as if caught in quicksand, Vargas said.

From its bird-like snout to the tip of its tail, stegouros stretched about six feet, but its height would come up only to the thighs of humans, Vargas said.

The tail was probably for defense against large predators, which also were likely to have been put off by the armor-like bones jutting out that made stegouros “chewy,” Vargas said.

Not only is this “a really bizarre tail,” but it is from far southern Chile, “a region that hasn’t yielded these types of animals before,” said Kristi Curry Rogers, a biologist at Macalester College in St. Paul, Minn., who wasn’t part of the study.

“We’re just scratching the surface when it comes to a comprehensive understanding of dinosaur diversity,” Rogers said. “Stegourus reminds us that, if we look in the right places at the right times, there is so much more still to discover.”

This illustration by Luis Perez Lopez shows a Stegouros.
This illustration by Luis Perez Lopez shows a Stegouros.
Luis Perez Lopez via AP