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Piecing Together a Giant Otter’s Skull

How a fortuitous collaboration reconstructed a species

An artist depiction of Siamogale melilutra in prehistoric China.

The fossil was flattened like a prehistoric pancake. Excavated in Yunnan Province, southwestern China, it had been crushed from years of heavy sediments deposited above it. The broken 6.4-million-year-old otter skull needed to be put back together before it could make a splash in the science scene. Vertebrate Paleontology Curator Xiaoming Wang had a high-resolution CT scan of the smashed skull, which captured every detail inside and out, but combing through the data would take hundreds of hours. Wang needed the help of someone with expertise in medical imaging, ample free time, and a lot of patience. Where would you find such a person?

Sometimes they find you.

Stuart C. White, D.D.S., Ph.D., a retired professor from the UCLA School of Dentistry, had been volunteering at the Museum for a few months when he met Wang and learned of the digitized otter fossil in the queue for analysis.

“When I told him I had a background in radiology, he said, ‘I’ve got all this digitized fossil material, but we don’t know how to work it out and get images.’ So I said, ‘I don’t know anything about your fossils, but I do know how to get images.’"

The digitized smashed skull of giant otter Siamogale melilutra.

With powerful software, White got to work identifying every tiny bone fragment in 3-D space. Each one took hours of work, as he had to go through every slice in the CT scan, identifying the shapes of the approximately 200 broken pieces of bone.

And then it was time to reassemble the skull, like the world’s most complicated 3-D jigsaw puzzle. The software made it possible to move each defined piece in space, rotating it and dragging it around. With his background in human dental imaging and a crash course in mammalian anatomy, White made his best guesses and sent Wang his progress. The two collaborated for months, perfecting the 3-D puzzle of Siamogale melilutra’s reinflated head. In all, it took six months to put Humpty Dumpty back together again. White was thrilled to have the opportunity to, as he put it, “Let the big guy speak for itself.”

The reconstructed fossil tells the story of the largest species of otter known to science, about the size of a wolf. With its large and powerful jaws, it could have feasted on shellfish in the swamps of ancient China.

“It’s immensely satisfying to see a fossil specimen originally flattened like a pancake gradually taking shape and coming alive,” said Wang. “This is digital magic at its best.”

photo of taxidermy otters in the natural history museum's North American mammal hall
Though Siamogale melilutra is long extinct, visitors to the Museum can enjoy the river otter exhibit in the North American Mammal Hall. These otters live today in freshwater streams and lakes in northern and central California, where they eat fish, frogs, turtles, and crayfish.

 

 

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