Fossil Shark Similar to Ratfish

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Artwork by Ray Troll, 2013

Dr. Dominique A. Didier, biology, has been working with colleagues on describing a fascinating fossil shark. This fish is called Helicoprion, and it is also known as a “whorl tooth shark” because it has a single blade of teeth (like a circular saw) in its mouth.  People have wondered about this unusual shark for over 100 years.

“Our research gives evidence of how the shark used its teeth—and what’s even more exciting is that it seems like this shark might be more close to the ratfish, also known as chimaeras, that I study more than the more conventional sharks,” said Didier.

Researchers at Idaho State University led by Dr. Leif Tapanila published new findings concerning the appearance and evolutionary history of the long-extinct 25-foot predator in Biology Letters on Feb. 27.

Didier’s work on the Helicoprion was supported by her National Science Foundation (NSF) grant, which is part of a $2.8 million Tree of Life Grant.

“Past models placed the spiral of teeth in many different places on the body, from the tail, to the dorsal fin and most recently in the throat,” said Tapanila.  “There has been a lot of debate about how many spirals might have been in one animal.”

Tapanila and his team, including Didier, conducted CT scans of newly discovered fossils of the Paleozoic fish found in Idaho and were able to show “with great confidence” that “one spiral of teeth filled the lower jaw.” The Idaho Museum of Natural History commissioned a 13-foot model of Helicoprion based on the team’s scans.

Helicoprion’s anatomy has been debated in part because the species’ cartilaginous skeletons didn’t form fossils the way bones do. The uncertainty has led some to believe that Helicoprion was a kind of ancient shark. But new research suggests it was more closely related to the ratfish (or chimaeras), modern-day shark-relatives that make their home in deep waters of all the world’s oceans.

Didier has been fascinated with ratfish since completing her senior thesis in college, and she is the world’s expert on ratfish diversity and evolution.

The Idaho Museum of Natural History in Pocatello is planning a major exhibit on Helicoprion, featuring the artwork of Ray Troll, Gary Staab’s sculpture and many fossils. It opens on June 22.

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