'A terrifying sight:' ancient spiky headed worm discovered in fossils

In this illustration by Marianne Collins/Royal Ontario Museum shows a Capinatator praetermissus. (Marianne Collins/Royal Ontario Museum via AP)

Researchers at the Royal Ontario Museum and Yale University have discovered the fossil of a spiky-headed worm that they believe would have struck fear in the hearts of other creatures swimming in ancient seas.

"This new species would have been an efficient predator and a terrifying sight to many of the smallest marine creatures that lived during that time," said Jean-Bernard Caron, senior curator of invertebrate paleontology at the ROM.

The 500-million-year-old critter has been dubbed Capinatator praetermissus, which incorporates Latin words for to grasp, swimmer and overlooked.

Capinatator was about 10 centimetres long with 25 spines on each side of its head.

"If you imagine putting your two hands together at the wrist and opening your fingers in a sort of curved manner and bringing them together, you get the idea of what these grasping spines might look like," said Derek Briggs, with the Yale Peabody Museum of Natural History.

"This is quite a good apparatus for grasping prey and bringing it towards the mouth."

Briggs was the lead author of a study published Thursday in the journal Current Biology, which was co-authored by Caron.

Some 50 specimens of the creature were found in the Burgess Shale fossil beds, a UNESCO World Heritage site in British Columbia's Yoho and Kootenay national parks.

The Burgess Shale, discovered more than a century ago, is a rich repository of fossils of some of the Earth's oldest creatures dating back to the Cambrian age.

Sites that are today high up in the Rocky Mountains were under water hundreds of millions of years ago.

The squishy bug-like creatures were encased in sediment, preserving their bodies in striking detail.

Capinatator is believed to be an ancestor of smaller worms that are today abundant in plankton throughout the world's oceans. The current iterations are smaller and have fewer spines around their heads than the fossil specimens.

The discovery offers clues about how the ancient ecosystem evolved, Briggs said.

"Predators tend to be key to developing the structure of marine communities, in that the predators evolved to capture prey and the prey in turn evolves to avoid being predated on," he said.

"So in that sense they indicate that those kinds of predator-prey interactions were important right back in the Cambrian."