This monster marine killing machine was so big it would make today's great white shark look positively friendly by comparison.
Scientists can only guess the size of the extinct "megatooth" shark from fossilised teeth, one of which has been found by a team of New Zealand and Australianscientists aboard an NZ research ship near Norfolk Island.
The team were trawling the seabed from the RV Tangaroa, a National Institute of Water and Atmospheric Research vessel, as part of an expedition exploring the volcanic Norfolk Ridge, an undersea range extending from the top of the North Island to New Caledonia.
The tooth was found about 1km below the surface.
"They are usually only found by luck when scientific sampling equipment is in the right place, which is what happened off the coast of Norfolk Island," said Dr Alan Williams, of Australia's Commonwealth Scientific and Industrial Research Organisation.
The megatooth, Carcharodon megalodon, lived millions of years ago - scientists cannot decide whether that is 4 million or 25 million.
Its fossilised teeth suggest it grew to between 13m and 17m - about three times the size of a great white.
The dorsal fin alone would have been about 1.6m tall. Reconstructions show the shark could have swallowed a rhinoceros whole.
Scientists are divided over whether megatooth was a cousin of the great white or an evolutionary dead-end. Some scientists have even speculated that the giant shark still roams the oceans, gobbling up whales, sharks and dolphins.
"There is always debate about fossil sharks," said Ministry of Fisheries scientist Dr Malcolm Francis.
"It's difficult to sort out how they relate to our living ones.
"But it grew up to about 16m - that's enough to contemplate."
Teeth from the shark have been found in mainly warm waters off the coast of Europe, the United States, South America, Africa and Asia.
Why they became extinct is a mystery.
Some scientists have suggested megatooth lost an important food source when the great whales migrated to polar regions, while others think the big shark went the way of the dinosaurs for similar reasons - climate change or a cataclysmic meteor strike.
Either way, Dr Francis, for one, does not mourn its demise.
"Certainly not. I'm a diver and I wouldn't like to see one."
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