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You only wish you could be this fabulous millions of years after you die. Precious stones recovered from the opal fields of Australia have turned out not just to be opalised fossils – but the opalised fossils of a dinosaur previously unknown to palaeontology.
It’s called Weewarrasaurus pobeni – named for the Wee Warra opal field near the small country town of Lightning Ridge, where it was found, and opal buyer Mike Poben, who donated the specimens to science.
This creature lived nearly 100 million years ago in the Cretaceous, when what is currently the Lightning Ridge desert was still a lush, green space.
It’s also the first new dinosaur species to be named in the Australian state of New South Wales in nearly a century.
The only fragment of Weewarrasaurus that was recovered was its lower jaw, but with teeth intact – and that’s been able to reveal a lot. For a start, it wasn’t a big dinosaur, only about the size of a medium-sized dog.
Based on its teeth and the shape of its jaw, palaeontologist Phil Bell from the University of New England in Australia determined that it was a small species of ornithopod, a group of bipedal grazing herbivores that includes Iguanodon and Parasaurolophus.
Lightning Ridge is one of Australia’s fossil hotspots. It was once a rich floodplain on the edge of a giant inland sea called the Eromanga Sea that spread across the Australian continent.
The once abundant prehistoric life that filled the area would often be preserved in the mud, which over thousands and millions of years would turn to sandstone.
This is a process that can be seen around the world. But in Australia, something else happened.
When the inland sea started disappearing 100 million years ago, acidity in the drying sandstone increased. This, in turn, released silica from the rock, which collected in hollows and pockets – such as those left behind by decayed bones, for instance.
As acidity levels then decreased, these silica pockets hardened into opal, resulting in perfect shimmering rainbow moulds of ancient remains. Nowhere in the world did this opalisation occur so abundantly as Lightning Ridge.
And this is what was found by Poben, who came across the two pieces of the opalised jawbone in a bag of rough opals he bought from miners, as John Pickrell reports for National Geographic.
So, Poben brought his find to Bell.
“I remember Mike showing me the specimen and my jaw dropped. I had to try hard to contain my excitement, it was so beautiful,” Bell said.
But it’s not just beautiful. In their paper, Bell and his colleagues note that, while Australia only seems to have been home to one or two large ornithopods, Muttaburrasaurus and one that is currently in the process of being studied, it seems to have been much richer in the smaller varieties.
Based on fossils found at Lightning Ridge, there were perhaps small ornithopod species thriving on the lush vegetation, and another four species in the southeastern state of Victoria. Only one small species has been found in the northeastern state of Queensland.
This is very different from America, where smaller herbivores would have had to compete for food with giants such as Triceratops and Alamosaurus.
So fossils like Weewarrasaurus are much more than just a pretty face – they can help us better understand how dinosaur biodiversity differed around the world, and piece together how that diversity may have come about.
Bell and his team are currently working hard to describe more opalised fossils – a tricky task, since they are usually found broken as part of mining spoils.
The team’s paper has been published in the journal PeerJ.