For more than a century, paleontologists had to break open fossils to analyze internal anatomy, often destroying their prized specimens. In recent decades, scientists have turned toward nondestructive techniques like CT scanning to create three-dimensional renderings of fossils. Because Oda’s bones were stamped into the rock, Ms. Engelschion and her colleagues opted to go for a more traditional approach by shooting X-rays through the fossil to render two-dimensional images.

Fitting Oda, which is preserved with its spine curled, its tail bent and its flipper and rib bones strewn about, into an X-ray machine proved daunting.

“We do not have any machine that can make radiographs of large specimens, but luckily our colleagues at the Cultural History Museum did, as archaeologists use this technique much more often,” Ms. Engelschion said.

In the initial scans, Oda’s fossilized bones leaped off the X-rays. This contrast was a result in part of the fact that the material inside the animal’s bones had been entirely replaced by barite, a sulfate mineral that is used today as a radiographic contrast agent for medical exams.

“The ichthyosaur’s bones were no longer bones, which caused them to light up,” Ms. Engelschion said.