Mystery of Ancient Sea Predator's Spiral-Toothed Jaw Solved

A new study sheds light on the mysterious spiral-toothed jaw of an ancient sea creature - Helicoprion.

Helicoprion was a predator fish that became extinct 225 million years ago. The marine animal had cartilage rather than calcified bones, just like modern-day sharks. Cartilage doesn't preserve well and so the only remains of the prehistoric fish in the fossil record are their bizarre spiral-teeth, which look similar to a spiral saw blade.

Earlier, researchers have attempted to reconstruct how Helicoprion would have looked like. Some have claimed that the teeth might have been located at the front of the jaw. They have also debated whether Helicoprion was a species of shark or related to the ancient group of cartilaginous fish, the chimaera, reports LiveScience.

Now, a team of researchers from Idaho State University have found new information about the marine animal's physical appearance and what it ate, using computed tomography (CT) scans of the specimens of a 270-million-year-old fish.

Using CT scans, the research team made 3-D virtual reconstructions of the jaws, giving a more detailed look at the spiral teeth. They were able to determine where the set of teeth fit in the marine predator. "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," Leif Tapanila, principal investigator of the study from Idaho State University, said in a statement.

The teeth were "saw-like", located in the back of the jaw. While feeding on prey, the jaw would have created a rolling-back and slicing mechanism, said the researchers. The fish would have eaten soft-tissued prey such as squids rather than eating animals with hard shells, they said.

The research team also found what the animal looked like. Unlike earlier presumptions that Helicoprion was a species of a shark, this new study has revealed that the ancient fish is more closely related to ratfish. "t was always assumed that the Helicoprion was a shark, but it is more closely related to ratfish, a Holocephalan," Tapanila said. "The main thing it has in common with sharks is the structure of its teeth, everything else is Holocephalan."

Based on this 3-D virtual reconstruction of the Helicoprian's jaw, researchers can also infer other characteristics of the fish. Using this information, the team is making a full-bodied reconstruction of a modest-sized, 13-foot long Helicoprion, which probably grew as long as 25 feet.

The findings of the study are published in the journal Biology Letters.