Fossils found in Chile are 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, said lead author Alex Vargas.

Its 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.