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Vast size of prehistoric megalodon shark, which had a fin as long as a human, revealed for the first time

(CNN) The true size of a gigantic prehistoric megalodon shark that ruled the oceans millions of years ago has been revealed for the first time -- and it had teeth as big as hands, and a fin as tall as a human adult.

Researchers at the University of Bristol, in southwestern England, and at the Swansea University, in south Wales, used mathematical calculations to work out the size of the megalodon shark from rare fossil remains of its teeth.

The findings were published Thursday in the journal Scientific Reports.

Researchers told CNN that the giant shark species would have grown up to 18 meters (59 feet) in length and weighed about 48 tons, which is larger than any other shark known to have existed and more than twice the size of a great white shark.

With teeth as big as human hands, it would have had a bite force of more than 10 tons, dwarfing that of a great white shark's bite force of two tons, researchers said.

Its tail would have been as long as 3.85 meters (12.6 feet) and its fin would have stood at 1.62 meters in length (5.3 feet) -- the height of a human adult.

Measuring an estimated 1.6 meters (5.3 feet), the megalodon's fin was as tall as an adult human.

The team was able to estimate its size by comparing its teeth with that of modern shark species, which, they said, grow into adults in proportion unlike humans who are born with shorter limbs and a larger head.

This means they can estimate the shark's growth curve, based on that of modern species.

Jack Cooper, who has just completed the MSc in Palaeobiology at the University of Bristol's School of Earth Sciences and led the study, told CNN the shark -- which lived from 23 million to about three million years ago -- would have fed on small whales and pinnipeds -- which are marine mammals that today include seals, walrus and sea lions.

"There have been some fossils found with large serrated bite marks on them that would incriminate megalodon as the attacker," Cooper told CNN.

"I have always been mad about sharks. As an undergraduate, I have worked and dived with Great Whites in South Africa -- protected by a steel cage of course," he added in a statement. "It's that sense of danger, but also that sharks are such beautiful and well adapted animals, that makes them so attractive to study.

"Megalodon was actually the very animal that inspired me to pursue palaeontology in the first place at just six years old, so I was over the moon to get a chance to study it."