The recent discovery of the 168 million-year-old Bashanosaurus in China, an ancient species of Stegosaur, marks the oldest find in Asia and possibly the world

Bashanosaurus is thought to have lived about 168m years ago, according to study of fossils found in China

A dinosaur that sported spine-like plates along its back is one of the earliest stegosaurs yet discovered, fossil hunters have revealed, and they say the find could shed light on the evolution of some of the most famous dinosaurs to roam Earth.

The stegosaur, which has been named Bashanosaurus primitivus in a nod to the ancient name of the region in China in which it was found in 2016 and its position on the stegosaur family tree, is thought to have lived about 168m years ago.

The discovery makes the animal an early cousin of stegosaurus, which lived about 150m years ago and had a stocky build, spiked tail and huge kite-shaped plates down its back.

Dr Susannah Maidment, of the Natural History Museum in London and a co-author of the study, said Bashanosaurus would have looked rather different. “It has this bizarre mix of features that we commonly see in quite primitive armoured dinosaurs,” she said.

“Bashanosaurus doesn’t have these great big flashy, massive giant plates – very, very thin plates – that stegosaurus has, it has much smaller plates, and they’re quite spine-like really.

“Maybe Bashanosaurus’s armour was actually more useful as body armour – it could have used it to defend itself – whereas stegosaurus’s armour [was]… probably for display.”

The new specimen was found to differ from other stegosaurs in a number of features, including having thicker plates that curve outwards at their base. It is thought Bashanosaurus measured about 2.8 metres in length – a relatively small size, although the team note it is not clear if the fossils are from an adult or juvenile.

Maidment said that while it could often be difficult to work out when such creatures lived, as fossils cannot be dated directly, the team was able to pin down the age of the stegosaur as volcanic minerals were found above and below the fossilised remains. The upshot was that Bashanosaurus could be dated to the Middle Jurassic, and it appears to be the oldest stegosaur yet found in Asia.

Maidment said the latest discovery, which is published in the Journal of Vertebrate Paleontology, shed new light on how species of stegosaurus evolved.

“They must have lost a lot of armour on their back. They developed these big plates and spines, and lots of other niche features of their anatomy changed as well,” she said. “The more we find these very early stegosaurs, that fills in the gap in our understanding.”

Maidment said the discovery of Bashanosaurus, and other early stegosaurs in Africa, Argentina and Asia, also provided insights into the origins of such creatures. “They’re already worldwide, and they’re already quite diverse, by this relatively early point in the Middle Jurassic,” she said. “That really indicates to us that they must have evolved right back into the early Jurassic.”

While the study suggests Bashanosaurus supports the idea stegosaurs may first have emerged in Asia, Maidment said the jury was still out, noting it was necessary to further investigate rocks from around the world.

Prof Steve Brusatte, of the University of Edinburgh, who was not involved in the work, said Bashanosaurus gave a glimpse of the earliest evolution of the stegosaurs.

“It tells us that the big stegosaurs evolved from older, smaller ancestors with a more generalised body plan, with less gaudy plates and spikes,” he said. “These stegosaurs go all the way back to the Middle Jurassic, around 170m years ago, and were part of a wave of worldwide dinosaur diversification at that time, as the supercontinent of Pangea was breaking apart.”

Michael Benton, a professor of vertebrate palaeontology at the University of Bristol, described the find as a great new discovery, adding that the specimen was quite complete.

New species of stegosaur is oldest discovered | EurekAlert!

“The new find pushes the age [of stegosaurs] back a little, and reflects a time of rapid evolution among dinosaurs following the end-Triassic mass extinction event 201m years ago,” he said, adding the first armoured dinosaurs emerged soon after that crisis, and included Scelidosaurus from the Lower Jurassic of Lyme Regis – a creature that came before the subsequent split of armoured dinosaurs into ankylosaurs and stegosaurs. “Tracking the steps in this process is important and the new fossil helps plug a gap,” he said.

Sia

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