Idaho State University researchers said fossils of the 270 million-year-old fish known as Helicoprion have long mystified scientists because, for the most part, the only remains of the fish are its teeth.
The rest of the fish's skeletal system was made of cartilage, which doesn't preserve well, they said.
Up to now it has been difficult to explain how the teeth -- looking something like a circular saw blade -- were positioned in the ancient animal, long assumed to be an early species of 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," Idaho State geoscience Professor Leif Tapanila said.
Tapanila and his colleagues said virtual reconstructions of the Helicoprion's jaws clear up the biggest mystery surrounding these teeth.
"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."
The location within the jaw likely created a rolling-back and slicing movement, the researchers said, and Helicoprion likely ate soft-tissued prey such as squid, rather that hunting creatures with hard shells.