The terrifying 12-tonne dinosaur that ruled the seas 150 million years ago named after Kevan the cafe owner who discovered it Kevan Sheehan discovered the fossils of the pre-historic marine reptile pliosaurus - believed to be most powerful creature ever The 68-year-old painstakingly unearthed it from the beach over five years Reptile believed to have weighed 12 tonnes, could have swallowed a great white shark whole and had a bite powerful enough to rip a car in half British experts claim fossil is one of the best preserved and most significant discoveries British scientists have identified a new species of a pre-historic marine reptile which they believe was the most powerful creature on Earth. The four-flippered pliosaurus would have weighed 12 tonnes, could have swallowed a great white shark whole and had a bite powerful enough to rip a car in half. Experts have hailed the fossil find as one of the most significant in the world and one of the most complete and best preserved skulls ever uncovered. The sea monster has been named Pliosaurus kevani after Kevan Sheehan, the retired café owner who spent five years painstakingly unearthing it. The sea monster has been named Pliosaurus kevani after Kevan Sheehan, the retired café owner who spent five years painstakingly unearthing it Dr Richard Forrest assembling the giant skull. Experts have hailed the fossil find as one of the most significant in the world and one of the most complete and best preserved skulls ever uncovered Mr Sheehan, a retired cafe owner from Osmington, near Weymouth, Dorset, spent five years unearthing the pliosaurus on a beach on Britain's World Heritage Jurassic Coast. He said: "I found three pieces of the pliosaurus by complete luck. I stumbled across them thinking they were fossilised wood and only picked them up because I thought they had a nice grain. Although a handful of pliosaurus specimens have been found before, Sheehan's beast has been declared as a new species that was bigger and stronger than its cousins. Scientists have officially named it the 68-year-old's honour after publishing it in the online science journal Plos One. Experts pieced the 25 parts together to form an 8.5ft long jaw of a 60ft long pliosaurus that existed 150 million years ago. The skull measures 19.95cm along the dorsal midline of the cranium and with a length of 20.45cm. Pliosaurids were ocean predators, some of which achieved giant sizes over 12 metres long. They spanned 110 million years and occupied the upper tiers of marine ecosystems from the Middle Jurassic until the early Late Cretaceous. British scientists have identified a new species of a huge pre-historic sea monster. It is believed to have been the most powerful creature on earth Dr Roger Benson, from the University of Oxford's earth science department, has been involved in researching Pliosaurus kevani. "This discovery is very significant for British palaeontology," he said. Several other pliosaurs have been found since the 1820s but they are fragmentary compared to this one. This fossil was much larger and stronger teeth that other pliosaurs. They also grew upwards and outwards compared to other pliosaurs teeth that went straight up. Mr Shhehan said: 'I stumbled across the remains thinking they were fossilised wood and only picked them up because I thought they had a nice grain' Dr Richard Forrest assembles the giant skull measuring 19.9 5cm along the cranium and with a length of 20.45cm (left) Kevan Sheehan with the pliosaur on display at Dorset County Museum, Dorchester (right) Richard Edmonds, the earth science manager for the Jurassic Coast World Heritage Site, said: "What is so significant about this fossil is that, aside from being so big and spectacular, it is the missing link in studies on the genus Pliosaurus." It has helped scientists understand what happened to these creatures over seven million years and also puts them into an evolutionary context. The enormous fossil is on display at the Dorset County Museum in Dorchester after the county council paid Sheehan £10,000 for it.