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X-rays identify a 240-million-year-old mystery fossil
An ichthyosaur fossil found in Svalbard is finally revealing its secrets 15 years after it was discovered.
Scientists X-rayed the flattened remains to reveal which species of ancient marine reptile this previously unknown fossil belongs to.
Around 240 million years ago, the islands of Svalbard in the Arctic Circle lay beneath a warm, tropical ocean.
The remains of marine species that once roamed these seas during the Triassic Period can now be found preserved within the rocks of the archipelago.
One of these fossils was discovered in 2008, but millions of years of compression had jumbled up and flattened the remains. From some features that could be identified palaeontologists determined that it was a type of ichthyosaur, a now-extinct group of marine reptiles which dominated the oceans during the time of the dinosaurs.
But the remains were so distorted it was virtually impossible for researchers to determine the exact species it once belonged to.
In a new study published in the journal Plos One, scientists used X-ray techniques to reveal that the remains belonged to a species of small ichthyosaur called Phalarodon atavus.
Dr Aubrey Roberts, an associate scientist at the Museum and co-author of the study, says, ‘We were completely flabbergasted. We’ve had this CT machine and the fossils for years, and we just haven’t put them in the scanner because they’re flat and we thought it’s probably not going to show us much.’
‘But the results are amazing and have actually revealed so much about this specimen.’
With the help of X-rays and CT scans, the researchers could make out the features of the ichthyosaur fossil. Image © Aubrey Roberts
How did the team discover the species of this ichthyosaur?
The specimen was found on Edgeøya, or Edge Island, in a geological layer on Svalbard where dozens of ichthyosaur specimens have been found before.
Despite the poor condition of the remains, researchers could identify some features, such as the small skull, teeth and vertebral column.
Based on these components, as well as its size and the location of where it was discovered, the researchers believed that it was likely a species of small-bodied ichthyosaur that is part of a group called the mixosaurids.
While X-ray techniques can be effective in investigating well-preserved fossil remains, the results depend on how fossils are preserved. In the case of the mystery fossils from Svalbard, scientists from the University of Oslo accidentally discovered that a lot of information could be gained from these remains despite their poor condition.
The researchers were actually CT-scanning rocks collected from the same location to get a closer look at some invertebrate fossils embedded in the material, but noticed something surprising with the flecks of bone preserved within.
‘There were some ichthyosaur bones which happened to be in one of these sections of rock that were being scanned and, to our surprise, it came up with amazing contrast,’ says Aubrey. ‘We were completely mind blown by this because fossils don’t usually contrast that well, so I suggested we scan this ichthyosaur to see what happens.’
‘And so we put the skull in the CT scanner and were completely amazed.’
The specimen was spread across multiple tall blocks of rock, which were difficult to fit into the scanner. So they called on a colleague in the nearby Museum of Cultural History to borrow a large X-ray machine, which they usually use to scan big artefacts such as Viking ships.
‘We scanned some of our specimens in the X-ray machine, and they came out beautifully. It was like a work of art.’
The ichthyosaur fossil skull. A. Photograph (visual observation). B. Radiograph. C. Computed Tomography scan. Image © Engelschiøn et al. Plos One, CC-BY 4.0
Why did the X-rays come out so well?
When you go for an X-ray at the hospital, the machine passes a type of radiation through your body. The energy is absorbed at different rates by different body parts depending on the object’s density. A detector on the other side then picks up the X-rays that have passed through and turns them into an image.
Dense parts of the body, such as bones, show clear white on the image as the X-rays find it difficult to pass through them. In contrast, softer parts such as internal organs appear dark because the X-rays pass through more easily.
As fossil skeletons no longer have the robust bone structure they once did and the minerals have been replaced with rock, they don’t often show up in clear contrast on X-rays. But in the case of the Svalbard fossil, the bones have been completely replaced by barite, a mineral that consists of barium sulphate.
Coincidently, barium sulphate is often used in medicine to help doctors examine parts of the body, such as the oesophagus, stomach and intestine, that don’t normally appear on X-rays or CT scans. Patients will consume a solution containing barium sulphate and the organs will show up in clear contrast.
Palaeontologists are now pushing this method forward as a potential method to gather more data from flattened specimens.
‘Following on from this project, we want to X-ray and CT scan other fossils from different locations which also have this compression to see if we can get similar results to what we found from Svalbard,’ says Aubrey.
‘It will be interesting to see if we come up with similar results for other places, or it could be that different minerals cause a different type of contrast. We’re stepping into unknown territory here.’
‘Using this method, we can actually get a lot of information from these specimens, which is really important for flattened samples from places like Lyme Regis. Perhaps we can reveal more of their secrets using these x-rays.’
