Ancient predator had teeth like a circular saw

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Imagine swimming along minding your own business, and then coming face-to-face with a 7.6m/25' monster fish equipped with a set of teeth resembling a circular saw...

Researchers studying fossils of the 270-million-year-old Helicoprion, which until recently had been assumed to be a species of shark, have used CT scans which show the spiral of teeth within the animal's jaws.

The team from Idaho State University worked with the Idaho Museum of Natural History to produce the 3-D virtual reconstruction of Heliocprion's jaws.

Until now, fossils of the fish, which is thought may have reached an impressive 6-7.5m/20-25' in length and weighed nearly half a ton, had mystified scientists. For the most part, the only remains of the fish are its teeth because its skeletal system was made of cartilage, which doesn't preserve well. No one could determine how this highly unusual dentition – not unlike a circular saw blade in appearance – fit into a prehistoric fish with a poor fossil record.

"We were able to answer where the set of teeth fit in the animal," said Leif Tapanila, principal investigator of the study. "They fit in the back of the mouth, right next to the back joint of the jaw. We were able to refute that it might have been located at the front of the jaw."

Located in the back of the jaw, the teeth were "saw-like," with the jaw creating a rolling-back and slicing mechanism. The Helicoprion also likely ate soft-tissued prey such as squid, rather that hunting creatures with hard shells.

Another major find was that this famous fish, presumed to be a shark, is more closely related to ratfish. Both are fish with cartilage for a skeletal structure rather than bone, but they are classified differently.

"The main thing it has in common with sharks is the structure of its teeth, everything else is Holocephalan."

For more information see the paper published in Biology Letters: Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion, by Leif Tapanila, Jesse Pruitt, Alan Pradel, Cheryl D. Wilga, Jason B. Ramsay, Robert Schlader, and Dominique A. Didier.

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