
The Helicoprion was a bizarre creature that lived during the Carboniferous Period around 270 to 300 million years ago. It was believed to be part of the shark family. It had a very distinct and unusual feature in that fossils show that its lower jaw had a circular-saw like set of sharp serrated teeth.
There was much debate on how the creature would look like with this set of teeth. The first fossils discovered of the Helicoprion were very incomplete and didn't really indicate how the creature would really look like. Because of that, there were many theories on how this circular set of teeth fit in with the Helicoprion.
There were some that theorized that the teeth were attached and curled up to a tongue like organ that can extend out similar to an elephant's trunk. Other's believe that the teeth were situated inside the creature's mouth. Other's even suggested that the circular groupings were located on the tail of the Helicoprion.
Although some discovered fossils showed hints of cartilaginous tissue, none have included the braincase or postcranial parts of these fish.