Scientist Solve Spiral-toothed Fossil Mystery

Fossil evidence has allowed scientists to reconstruct the Helicoprion, the ancient spiral-toothed fish.

Scientists were able to answer questions like how that ancient beast of the seas looked like, how it ate, and even the more puzzling mysteries surrounding the Helicoprion: whether the unique saw-like spirals were located inside or outside the fish’s mouth.

All this was possible using CT scans that allowed the researchers to build a computer model of the fish.

The model also shows that the fish was more closely related to modern chimaeras, or ratfish, than sharks.

Conducted by scientists at Idaho State University, the findings of the study were published in the Royal Society journal Biology Letters.

The university's Museum of Natural History has the largest public collection of fossilized Helicoprion in the world.

The fish lived 270 million years ago but because they were largely formed from cartilage, which does not preserve well, their fossil record comprises unusual spiral structures.

Referred to as "whorls", these features have been compared to spiraling saw blades and have puzzled the scientific community for over a century.

Early theories suggested that they were actually used for defense and were located on the fish's upper or lower jaws, or even the dorsal fin.

In order to solve the mystery, Dr Leif Tapanila and colleagues investigated the most complete fossil in the collection.

The fossil, discovered in Idaho, has a whorl measuring 23cm with 117 individual teeth. Unlike other specimens, the fossil also includes impressions of the cartilage structures.

The team used a high-powered CT scan, which uses X-rays to create a detailed computer image, in order to fully analyse what was inside the rock.

"When we got the images back, we could easily see that we had the upper and lower jaw of the animals, as well as the spiral of teeth," said Dr Tapanila.