Unraveling the Mysteries of Oda the Ichthyosaur

Paleontologists used X-rays to identify the 240-million-year-old creature’s flattened and fossilized remains

Skeleton encased in rocks
Paleontologists discovered Oda's remarkably intact fossilized skeleton in Svalbard in 2008. Engelschiøn et al. PLOS ONE, CC-BY 4.0

Today, polar bears and reindeer roam the islands of Svalbard, a Norwegian-governed archipelago north of the Arctic Circle. But 240 million years ago, during the middle Triassic Period, the landscape was underwater and teeming with marine reptiles—like Oda the ichthyosaur.

Paleontologists discovered Oda’s fossilized skeleton encased in shale on Edgeøya, or Edge Island, in Svalbard in 2008. But they had a big problem: The creature’s bones had been jumbled up and flattened during millions of years of compression, which made it impossible to determine the species. They could tell Oda was an ichthyosaur—a now-extinct, air-breathing aquatic reptile that looks like a blend of a crocodile and a dolphin—but they couldn’t get more specific than that.

Now, in a new paper published Wednesday in the journal Plos One, scientists with the University of Oslo’s Natural History Museum describe how they used X-rays to produce a two-dimensional view of Oda and learn more about the specimen.

They now suspect Oda is a Phalarodon atavus, a type of small, dolphin-like ichthyosaur. Paleontologists have previously discovered P. atavus remains in China and Europe, so the discovery in Svalbard adds another pin to the map of the creature’s former range.

Landscape of rocky cliff
A view of Edgeøya, or Edge Island, in Svalbard Sofie Bernhardsen, CC-BY 4.0

Oda was a perfect contender for X-rays, because over time, barite had completely replaced the creature’s bones. Doctors regularly use barite, a sulfate mineral, as a contrast medium when taking X-rays of their patients. As such, Oda’s bones glowed “bright as day” in the X-ray machine, says Neil Kelley, a paleontologist at Vanderbilt University who was not involved in the study, to the New York Times’ Jack Tamisiea.

“I’m very jealous—that’s exactly the result that you want when you put something in an X-ray,” he tells the Times.

This radiance allowed researchers to see previously hidden and overlooked details. For instance, the X-rays revealed that Oda’s skull was longer than they’d previously assumed. The technique also showed vertebrae and limb bones they hadn’t been able to see before. But Oda’s teeth were the key to deciphering its identity—some had grooves that paleontologists recognized from other P. atavus fossils.

The non-destructive method also meant scientists could keep the ichthyosaur fossil intact, while still gleaning important insights.

After solving the mystery of Oda, researchers can now apply their X-ray learnings to other fossils in Svalbard and beyond. They don’t fully understand why or how barite replaced the creature’s bones, but they suspect it has something to do with ancient volcanic activity. They now know that fossils discovered in Svalbard—and places with similar conditions—may be good contenders for X-ray analysis.

Researchers previously discovered the oldest-known ichthyosaur in Svalbard, so the area seems ripe for further study.

“The rocks from Svalbard are full of flattened marine reptiles,” the study’s co-authors say in a statement. “Our discovery of the exceptional X-ray contrast means that we can learn much more about these ancient predators than we previously thought.”

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