While exploring an Arctic mountaintop in 2008, paleontologists unearthed a tiny skeleton resembling a coiled sea serpent, pressed into a slab of 240-million-year-old rock. The remarkably complete skeleton, nicknamed Oda, was deposited in the collection of the Natural History Museum of the University of Oslo.
It was clear that Oda was an ichthyosaur, but no one could tell if it was a known genus of marine reptiles, resembling a hodgepodge of crocodile and dolphin. While most of his skeleton remained, centuries beneath a muddy seabed had squeezed Oda into a two-dimensional jumble of bones.
To identify the reptile, paleontologists put the baffled patient under an X-ray machine to piece together the petrified puzzle. This is according to an article published in the magazine on Wednesday PLoS Onethe researchers described the anatomical details they gleaned from the ghostly glow of Oda’s bone X-rays.
“The contrast of these bones is clear,” said Neil Kelley, a paleontologist at Vanderbilt University who studies marine reptiles and was not involved in the new study. “I’m very jealous — that’s exactly the result you want when you put something in an X-ray.”
The findings, he added, show the technique’s potential to add new dimensions to mysteries in the fossil record that have been smoothed over by the passage of time.
The enigmatic skeleton was discovered on a windswept plateau on Edgeoya Island in Svalbard, an Arctic archipelago north of Norway that is home to reindeer and polar bears. But during the mid-Triassic period, the area was a deep-sea plateau off the northern coast of the supercontinent Pangea and a haven for marine reptiles.
Victoria Sjoholt Engelschion, a doctoral researcher at the Natural History Museum in Oslo, came across bits of bluish ichthyosaur bones when she made computed tomography scans of clumps of fossilized clams from the area. A colleague recommended scanning Oda for clues.
For more than a century, paleontologists had to crack open fossils to analyze internal anatomy, often destroying their prized specimens. In recent decades, scientists have turned to nondestructive techniques such as CT scanning to create three-dimensional representations of fossils. Because Oda’s bones were pounded into the rock, Ms. Engelschion and her colleagues took a more traditional approach, shooting X-rays through the fossil to create two-dimensional images.
Oda, who is preserved with his spine curled, his tail arched and his fins and ribs scattered all over, fitting into an X-ray machine proved to be a daunting task.
“We don’t have a device that can take X-rays of large specimens, but fortunately our colleagues at the Cultural History Museum did, as archaeologists use this technique much more often,” said Ms. Engelschion.
In the first scans, Oda’s fossilized bones popped out of the X-rays. This contrast was, in part, the result of the material in the animal’s bones being completely replaced by barite, a sulfate mineral used today as a radiographic contrast agent for medical examinations.
“The bones of the ichthyosaur weren’t bones anymore, so they lit up,” said Ms. Engelschion.
Because the barite gave the ichthyosaur bones a bright glow, the team was able to spot anatomical features that had been overlooked or hidden. They found that the animal’s alligator-like skull was significantly longer than previously thought. They also located previously unseen bones and vertebrae of limbs.
“This study illustrates the importance of using some of the more ‘tried’ techniques that can still reveal new data,” said Dean Lomax, a palaeontologist at the University of Manchester in England who specializes in ichthyosaurs and was not involved in the new study.
The crucial clue was in the creature’s teeth. The X-rays revealed that Oda’s larger teeth had grooves reminiscent of teeth found in the jaws of Phalarodon atavus, a small and slender ichthyosaur found in mainland Europe and China. According to Ms. Engelschion, finding this ichthyosaur on Svalbard sheds light on how widespread and successful the species was during its heyday.
Dr. Kelley added that finding Oda’s rightful place in the fossil record helped give context to the emergence of ichthyosaurs, which would dominate marine ecosystems for 150 million years. He said he thought re-examining other marine reptile fossils under X-rays might reveal hidden clues about how these reptiles evolved.