Image caption The ancient squid hunted using its two long tentacles

The ancestors of modern squid may have existed half a billion years ago - a lot earlier than previously thought.

In a new study, Canadian researchers identified a previously unclassifiable fossil that was long believed to belong perhaps to the shrimp family.

They called it Nectocaris pteryx - a small soft-bodied cephalopod with two tentacles rather than the eight or 10 seen in today's octopuses.

The new survey's results were presented in the journal Nature.

The findings make the ancestors of modern squid and octopuses at least 30 million years older.

Evolutionary biologist Martin Smith, the main author of the study, told PA news agency that the findings bring cephalopods much closer to the first appearance of complex animals.

"We go from very simple pre-Cambrian life-forms to something as complex as a cephalopod in the geological blink of an eye, which illustrates just how quickly evolution can produce complexity," said Mr Smith.

The authors described Nectocaris as a kite-shaped creature that was flattened from top to bottom. They say it was between two and five cm long and had large, stalked eyes.

The tiny animal is believed to have been a carnivore that hunted for prey with two long grasping tentacles. It used a nozzle-like funnel under its eyes that could "swivel like a pivoted cannon" to jet itself around the ocean - just like modern squids and octopuses.

'Unclassified' creature

Image caption Nectocaris was a small, kite-shaped creature

The fossil isn't a new find - it was discovered decades ago in the Burgess Shale deposits atop a mountain in Yoho National Park in British Columbia, Canada.

The Burgess Shale Formation is one of the world's most famous fossil fields.

Scientists tried to describe the fossil for the first time in 1976 - but back then, they just weren't sure where it belonged on the evolutionary tree.

They dubbed it "unclassified". According to Jean-Bernard Caron, Mr Smith's co-author, researchers originally thought the mystery creature could have been a relative of anything from a lobster to a fish.

But after Mr Smith, a University of Toronto PhD student, decided to re-examine the fossil together with 91 new specimens collected in recent years, scientists were finally able to give the animal its proper place in history.