India, April 10 -- A 300-million-year-old tentacled sea creature has lost its crown as the world's oldest octopus, after scientists found evidence that it's not an octopus at all.

Newly published research concludes that fossilized remains listed by Guinness World Records as the earliest known octopus belong instead to a relative of a nautilus, a cephalopod with both tentacles and a shell.

University of Reading zoologist Thomas Clements, the lead researcher behind the new findings, said the fossil, Pohlsepia mazonensis, has long been the subject of scientific debate.

"It's a very difficult fossil to interpret," he said. "To look at it, it kind of just looks like a white mush.

"If you look at it and you are a cephalopod researcher and y...