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Palaeontologists in British Columbia have found a fossil of the oldest known ancestor of scorpions and spiders.
The thumb-sized Mollisonia plenovenatrix was discovered on the Burgess Shale site, which is in Yoho and Kootenay national parks.
Its discovery places the origin of the chelicerate group of animals – which contains more than 115,000 species – at over 500 million years ago.
Mollisonia plenovenatrix had a “multi-tool head”, long legs and numerous pairs of limbs that could be used to grasp, crunch and chew.
It also had a pair of tiny pincers in front of its mouth called “chelicerae” – from which the chelicerate groups gets its name.
"Before this discovery, we couldn't pinpoint the chelicerae in other Cambrian fossils, although some of them clearly have chelicerate-like characteristics," said lead author Cédric Aria, a member of the Royal Ontario Museum's Burgess Shale expeditions since 2012.
"This key feature, this coat of arms of the chelicerates, was still missing."
Aria added: "Chelicerates have what we call either book gills or book lungs.
"They are respiratory organs are made of many collated thin sheets, like a book. This greatly increases surface area and therefore gas exchange efficiency. Mollisonia had appendages made up with the equivalent of only three of these sheets, which probably evolved from simpler limbs."
Scientists believe the creature would have hunted close to the sea floor.
The discovery of the fossil only enhances the importance of the Burgess Shale in the study of the Cambrian explosion, an event about 541 million years ago in which most major animal groups appeared in the archaeological record.
“This area keeps giving us wonderful treasures year after year,” Jean-Bernard Caron, Richard M Ivey Curator of Invertebrate Palaeontology at the Royal Ontario Museum, said.
"I would not have imagined that we could, in a way, rediscover the Burgess Shale like this, a hundred years later, with all the new species we are finding."
