Fossilised forms of a phallus-shaped invertebrate have shed light on a dramatic spurt in Earth's biodiversity that occurred half a billion years ago, Canadian scientists reported on Wednesday.

Remains of 10-centimetre (four-inch) worm-like creatures were found in shale beds in Yoho National Park in the Canadian Rocky Mountains.

The sediment dates back to the mid-Cambrian, a period when the number of species exploded and life forms became more complex.

The long-dead animal, named Spartobranchus tenuis, is an ancestor of the acorn worm, a marine animal that thrives in shallow mud and sand, according to the study, appearing in the journal Nature.

Identifying it means that a link in the marine ecosystem, a group of animals called enteropneusts, emerged 200 million years earlier than thought.

Enteropneusts feed by filtering small particles of food through gill slits.

If the fossil evidence is right, S. tenuis was so plentiful that its feeding may have helped store carbon -- a factor in the complex equations for global warming and ocean acidity -- on the ocean floor.

"It's possible Spartobranchus tenuis may have played an important role in moving carbon from the water column to the sediment in the early Burgess Shale environment," said University of Montreal biologist Chris Cameron.