Helicoprion was a puzzling looking animal, with teeth that look more like the blade of a table saw than anything we humans are familiar with. It swam the oceans about 270 million years ago. For a long time, scientists have debated whether or not the saw-like teeth were inside the fish's mouth, our lay outside. The fish had a cartilaginous skeleton, meaning it lacked solid bone, which tend not to preserve well as fossils. So, the existing fossil evidence could not settle the debate.
Until now. The researchers in this study, published in the journal Biology Letters, used CT scans to study the most complete fossil available at the university's Natural History Museum. From the resulting images, they were able to see the animal's upper and lower jaws. The toothy spiral connects to the lower jaw in the back of the mouth. When the mouth closed, the teeth would spin backward, both cutting into the meat and forcing it further back into the throat for swallowing. Based on the lack of wear and tear on extant fossil teeth, the researchers believe the animals fed on soft bodied animals, like squids.
The CT scans have been used to render an artist's impression of what Helicoprion looked like, which will be displayed in the Natural History Museum.