A terrifying dinosaur with a bizarre but menacing armoured tail resembling a battle axe roamed the earth 75 million years ago, boffins have discovered.
Scientists analysing fossils found in Chile discovered the new species which measured around measured around 6.5 feet (two metres) long with a 'weaponised' tail unlike ones seen in any other creatures at the time.
The four-legged herbivore, named Stegouros elengassen, is thought to have used its tail as a form of defence to fend off other predatory dinosaurs by swinging it from side-to-side.
Researchers said the 'well preserved and mostly complete' fossils of the dinosaur were unearthed in the Magallanes province in Patagonia, Chile’s southernmost region.
In a study published in the journal Nature, scientists from the Universidad de Chile said the findings provide fresh insights into the origin and early evolution of armoured dinosaurs.
The scientists said the discovery highlights an 'arms race' that required dinosaurs to acquire new traits to survive.
Vertebrate palaeontologist Sergio Soto, lead author of the study, said: "For now, we can only imagine how might Stegouros have used this weapon – and tail-swinging side to side as self-defence mechanism is a good guess."
The newly discovered species had distinctive skull features similar to those seen in other ankylosaurs, whose tails had heavy clubs at the end.
But the rest of its skeleton was largely primitive, with some properties resembling stegosaurs, they said.
The study went on: “Stegouros shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters."
The dinosaur’s large tail weapon was composed of seven pairs of flattened, bony deposits fused together in a structure that resembled a frond across the outer part, they said.
The study continued: “Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: a flat, frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal [outer] half of the tail."
The researchers found it to be a “transitional ankylosaur” related to the Kunbarrasaurus from Australia and Antarctopelta from Antarctica.
They said armoured dinosaurs from Laurasia, the northern landmass of what was once the Pangaea supercontinent, are diverse and well studies.
But those from southern Gondwana, Pangaea's southern landmass, believed to be likely to include the earliest kinds of ankylosaur, are “rare and poorly understood".
Branches of the ankylosaur family tree may have existed in Laurasia and Gondwana after the final separation of these supercontinents in the late Jurassic period about 163 to 145 million years ago, the scientists said.
The earliest kinds of ankylosaurs may have lived in Gondwana and studying them may provide new clues to the origins and evolution of armoured dinosaurs, the scientists pointed out.
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