'This species is very special': Granddaddy of the spider discovered by ROM researchers

It boasts a pair of bulgy egg-shaped eyes, a dorsal skeleton that resembles a shield of sharp armour, and numerous pairs of limbs that could grasp, crush and chew.

And its name is a mouthful:Mollisoniaplenovenatrix.

Fossils uncovered by an expedition team from the Royal Ontario Museum in Toronto have led to the discovery of thisthumb-sized sea-dwelling predator that predates arachnids, the family that includes spiders andscorpions.

It was a pair of fang-like appendages at the front of the creature's mouth that most excited ROM paleontologistJean-BernardCaron, whose findings were published Wednesday in the science journalNature.

The appendages, called chelicerae, meant the species was a member of the family Chelicerate. Not only that, it was that family'soldest knownancestor, at about 506 million years old.

"Chelicerate is a group that is familiar with everybody because it includes spiders, scorpions and horseshoe crabs. Those represent 115,000 species of animals today. And they are part of an even bigger group called arthropods which are defined by a jointed body and limbs," saidCaron.

But while they are one of the largest groups of species, Caron said"their origin has always been puzzling to scientists."

That's why the discovery is so special, he toldCBC Toronto.

"It's important to try to understand the origin of this group. In many ways, these fossils help provide the answer of where they come from. They tell us about the origin of innovations in animal evolution and also about ourselves."

Discovery made atnew Burgess Shale site

The fossils were discovered in the world-renowned Burgess Shale located in the Canadian Rockies of southeastern British Columbia.

It is famous for being one of the earliest fossil beds containing fossil imprints from the Cambrian period, a time when the Earth's biodiversity exploded.

"What's exceptional about the Burgess Shale is the preservation of soft tissue. It is extraordinary, the amount of detail we see. We've discovered some really early fish," saidCaron.

Since 2012, a ROM expedition team has been uncovering fossils in a new site called Marble Canyon.

But it took detailed observations and research, conducted by Caron and his colleague Cdric Aria, to be certain of their discovery of the Mollisonia.

"The animals lived at the bottom of the sea. They were buried very quickly in the mud that became rock, and they were buried at different angles."

Bit-by-bit the two paleontologists were able to make out the characteristics of the prehistoric mini-beast from numerous slabs of rock.

"Before this discovery, we couldn't pinpoint the chelicerae in other Cambrian fossils, although some of them clearly have chelicerate-like characteristics," saidAria.

An even older ancestor waiting to be discovered?

The fossils also showed the creature having back limbs likegills, suggesting it had already adaptedto its watery environment.

"This discovery tells us that at the time of the Cambrian they were already there. They probably evolved earlier than that," Caron said.

"We know this is the oldest fossil showing chelicerae. But it's likely there are fossils before that we haven't found yet."

Caron intends to head back to Burgess Shale next summer to continue exploring.

In the meantime, as curator of invertebrate paleontology at the ROM, he is busy planning for a new gallery entitled Dawn of Life.

The Mollisonia will be just one of many fossils from the Burgess Shale that will be on display in the gallery, scheduled to open in 2021.