The terrifying 25 foot long prehistoric shark with a spiral of teeth that worked like a CHAINSAW Helicoprion had a conveyor belt of jagged teeth that spiralled out of its lower jaw and ripped prey to shreds Appearance had baffled scientists because no one could work out how the teeth fitted in its mouth A 25ft monster 'shark' with chainsaw teeth that roamed the prehistoric seas 270 million years ago has been revealed by scientists. 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. 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 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. The large 'spiral' fossils of teeth are all that remain from the hundred specimens found around the world as its skeleton was made of cartilage, just like its modern descendants, which does not preserve well. Professor Leif Tapanila, of Idaho State University, used state of the art scanners to create 3-D virtual reconstructions of its jaws Helicoprion's appearance has long mystified scientists because no one could work out how these teeth, which resemble a spiral saw blade, fit into it. Geoscientist Prof Tapanila said: 'New CT (computerised tomography) 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, and how it ate.' The findings, published in the Royal Society journal Biology Letters, are based on firm evidence fed into computers at his special virtualization laboratory. Another major breakthrough was the beast is more closely related to ratfish than sharks. Both species have cartilage, rather than bone, but are classified differently. The 3D models created by the team show how the 'spiral' teeth fitted in the head of the animal It was always assumed the Helicoprion was a shark, but it is more closely related to ratfish, a Holocephala. The main thing it has in common with sharks is the structure of its teeth, everything else is Holocephalan. Based on the information, the Idaho Museum of Natural History is creating a life size reconstruction of a modest thirteen foot long Helicoprion for an exhibition this summer, which will also include artwork by world renowned scientific illustrator Ray Troll. Rocks in southeastern Idaho have preserved the largest, most abundant and pristine specimens of Helicoprion many of which include the lower jaw cartilage, teeth and rare impressions of skin. Other remains have been found in Utah and Wyoming when these regions were covered in sea more than 250 million years ago. The researchers created several artist's impressions of the fish to try and work out what it looked like, before a 3D reconstruction revealed the truth (bottom)