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This Dino Species Has 'Something Never Seen Before'

Fossil of dog-sized stegouros shows it had a tail that could slash, slice like an ancient Aztec weapon
By Newser Editors and Wire Services
Posted Dec 2, 2021 11:30 AM CST
Updated Dec 5, 2021 11:40 AM CST
This Dino Species Has 'Something Never Seen Before'
This illustration shows a stegouros.   (Luis Perez Lopez via AP)

(Newser) – A fossil found in Chile is from a strange-looking dog-sized dinosaur species that had a unique slashing tail weapon, scientists reported Wednesday. Some dinosaurs had spiked tails they could use as stabbing weapons, and others had tails with clubs. The new species, described in a study in the journal Nature, has something never seen before on any animal: seven pairs of "blades" laid out sideways, like a slicing weapon used by ancient Aztec warriors, says lead author Alex Vargas. "It's a really unusual weapon," says Vargas, a University of Chile paleontologist, per the AP. "Books on prehistoric animals for kids need to update and put this weird tail in there. ... It just looks crazy."

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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. After Vargas and his team examined the pieces of skull and did five different DNA analyses, they concluded it was only distantly related to the stegosaurus. Instead, it was a rare Southern Hemisphere member of the tanklike ankylosaur family of dinosaurs. (The stegouros name stuck, though, and can be easily confused with the more well-known stegosaurus.)

Vargas calls it "the lost family branch of the ankylosaur." The fossil is from about 72 million to 75 million years ago and appears to be an adult based on the way bones are fused, Vargas says. It was found with its front end flat on its belly and the back end angled down to a lower level, almost as if it had been caught in quicksand, Vargas says. From its birdlike snout to its tail tip, the stegouros stretched about 6 feet but would have only come up to the thighs of humans, Vargas notes.

The tail was probably for defense against large predators, which were also likely turned off by armorlike 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," says Macalester College biologist Kristi Curry Rogers, who wasn't part of the study. "We're just scratching the surface when it comes to a comprehensive understanding of dinosaur diversity. Stegouros reminds us that if we look in the right places at the right times, there is so much more still to discover."

(Read more discoveries stories.)

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