Bizarre spiral-toothed shark not actually a shark

By Celeste Tholen Rosenlof | Posted - Feb 28th, 2013 @ 8:29am

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POCATELLO, Ida. — An extinct fish with a spiral tooth structure rolled its lower jaw and sliced its food with razor-sharp teeth like a saw, researchers say.

A team of Idaho State University researchers — led by Leif Tapanila, and associate professor of geosciences and research curator at the school's museum of natural history — made several discoveries about the helicoprion, a 270 million-year-old fish fossil.

The fish has long been a mystery to research due to its cartilage skeleton structure. The only clues the fish left behind was its teeth, which preserved the spiral pattern of what ISU researchers say was the lower jaw.

Further, their evidence shows that the fish, previously believed to be a shark, has more similarities to a ratfish.

The researchers base their claims on evidence gathered from CAT scans and 3-D virtual reconstructions of jaws that belong to the museum. ISU Museum of Natural History has one of the largest public collections of helicoprion fossils in the world, according to the university.

By studying the scans and reconstructions, Tapanila and his team came to the conclusion that the teeth were located in the back of the lower jaw, and that the teeth and jaw moved like a saw: the jaw would have rolled back and the teeth would have sliced the fish's prey.

Previous studies claimed the teeth were in the front of the lower jaw.

Tapanila said the teeth structure resemble a shark's but everything else about the fish resembles a ratfish. The ratfish is a holocephalan and, like a shark, has a cartilage skeleton.

The researchers are currently working to reconstruct a full-bodied helicoprion model based on their findings. The model will be 13 feet long, a modest-sized helicoprion. The fish could have grown up to 25 feet long, they said.

The model will go on display alongside illustrations of the fish this summer in the museum's helicoprion exhibit.


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