From the Daily Mail:
The bizarre fish Helicoprion, an early ancestor of sharks, had a conveyor belt of jagged teeth that spiralled out of its lower jaw and ripped prey to shreds.
Using state of the art scanners to create 3-D virtual reconstructions of its jaws, researchers have now discovered what the ancient beast would have looked like as it homed in on marine animals.
Located at the back, the teeth were 'saw-like' with the jaw creating a rolling back and slicing mechanism.
Professor Leif Tapanila, of Idaho State University, said: 'We were able to answer where the set of teeth fit in the animal.
'They fit in the back of the mouth, right next to the back joint of the jaw.
'We were able to refute it might have been located at the front of the jaw.'
The creature, unlike any shark alive today, grew up to twenty-five feet in length and weighed almost half a ton (71 stone), making it the biggest fish in the sea.