Researchers solve mysteries of ancient spiral toothed ‘shark’

27 February 2013

Researchers have solved part of the mystery surrounding large spiral fossils of a fish’s teeth, it is revealed in Biology Letters today.

Scientists at Idaho State University used CT scans of newly discovered specimens to make three dimensional virtual reconstructions of the jaws of the ancient fish Helicoprion.

The fossils of this 270-million-year-old fish have long mystified scientists due in most part to the remains of the fish being its teeth. This is because its skeleton system was made of cartilage, which doesn’t preserve well. No one could determine how these teeth – that look similar to a spiral saw blade – fit into a prehistoric fish with a poor fossil record, long assumed to be a species of a shark.

“New CT scans of a unique specimen from Idaho show the spiral of teeth within the jaws of the animal, giving new information on what the animal looked like, how it ate,” said Leif Tapanila, principal investigator of the study.

“We were able to answer where the set of teeth fit in the animal,” Tapanila said. “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; “The main thing it has in common with sharks is the structure of its teeth, everything else is Holocephalan (like a ratfish)”, Tapanila.

Based on the three dimensional virtual reconstruction of the Helicoprian’s jaw, Idaho Museum of Natural History is creating a full-bodied reconstruction of a modest-sized, 13-foot long Helicoprion. Larger specimens are thought to have grown as long as 25 feet.