The creature, Tyrannoneustes lythrodectikos or Tyrant swimmer is believed to have terrorised the warm Jurassic seas around the British coastline around 165 million years ago.
The new research makes it one of the world's oldest known 'super-predators' - carnivores that can feed on prey as large, or larger, than themselves, the 'Daily Mail' reported.
The beast was a marine crocodile measuring up to 30ft long that looked part shark and part sinister dolphin.
Its partial skeleton, including a jawbone and teeth, has been stored by the Hunterian Museum at the University of Glasgow ever since it was discovered by an amateur palaeontologist in a clay pit near Peterborough in the early twentieth century.
Its significance was overlooked for years until a team of experts led by the University of Edinburgh examined the creature and identified it as a possible 'missing link' between a group of ancient marine crocodiles and modern-day killer whales.
"It is satisfying to be able to classify a specimen that has been unexamined for more than 100 years, and doubly so to find that this discovery improves our understanding of the evolution of marine reptiles," Dr Mark Young, of the University of Edinburgh's school of geosciences, who led the study, said.
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He said that at the time the creature lived much of Europe was covered by a shallow sea, creating a chain of differently sized islands. Tyrannoneustes lived in this shallow sea, along with numerous other marine reptiles, including pliosaurs, plesiosaurs and ichthyosaurs.
"Giant pliosaurs were even larger than the Tyrant Swimmer, so they might have feasted on the formidable species," Young said.
"As its name suggests, however, Tyrant Swimmer would have been swift in the water, so it likely could have out-swam possible predators and used the swimming prowess to capture its own prey," Young added.
He indicated that Tyrant Swimmer most likely evolved into an even more stealthy marine predator with very large and numerous teeth and a mouth that could open extremely wide.
"Little research has been done on this specimen since it was first listed in 1919. It is comforting to know that new species can still be found in museums as new research is carried out on old collections," Dr Neil Clark, palaeontology curator at The Hunterian, said.
The discovery was published in the Journal of Systematic Paleontology.