Worm-like fossil a 'distant cousin' of humans

A finger-sized creature unearthed in the Canadian Rockies is the oldest known member of the group that contains all animals with a backbone, including humans.

A tiny worm-like creature that swam the seas half a billion years ago is not exactly the first thing that comes to mind when you think about who you share your genes with.

But according to a newly released analysis of a fossil unearthed in the Canadian Rockies a century ago, the finger-sized creature — known as Pikaia gracilens — is the oldest known member of the chordates — a group containing all animals with a backbone, including humans.

"It's a very, very distant cousin," Jean-Bernard Caron, an assistant professor of ecology and evolutionary biology at the University of Toronto and the study's co-author, said in an interview. "We share the same genes...we share some of the basic features."

The fossil of Pikaia gracilens was discovered in 1911 in the Burgess Shale fossil beds in Yoho National Park in Western Canada. (University of Toronto/Canadian Press)

However, the chance that humans might have evolved from the five-centemetre-long creature is a "long shot," cautioned Caron.

The research, published Monday in the British scientific journal Biological Reviews, determined Pikaia has a notochord, a flexible rod found in the embryos of all chordates that makes up part of the backbone in vertebrates.

It also found evidence of a nerve cord and vascular system and extensive myomeres, blocks of skeletal muscle tissue that are characteristic of chordates.

Professor Simon Conway Morris of the University of Cambridge, the study's lead author, said the findings of myomeres clearly places Pikaia as the planet's most primitive chordate.

The Burgess Shale

The Burgess Shale is considered one of the most important fossil fields in the world due to age, diversity and the excellent preservation of its fossilized animals, which were mostly soft-bodied invertebrates. It was discovered in 1909 by American paleontologist Charles Doolittle Walcott on the southwest side of a ridge between Mount Field and Wapta Mountain, in Yoho National Park. The fossils date back to the Cambrian Period around 505 million years ago, when North America was rotated 90 degrees relative to its current position and British Columbia was located under a tropical sea near the equator.

The importance of the site was recognized by UNESCO World Heritage Site designation in 1981. Three years later, it was integrated into the Canadian Rocky Mountain Parks UNESCO World Heritage Site which includes Banff, Jasper, Yoho and Kootenay National Parks and Assiniboine, Hamber and Robson Provincial Parks.

"The discovery of myomeres is the smoking gun that we have long been seeking," Morris said in a news release. "Next time we put the family photograph on the mantelpiece, there in the background will be Pikaia."

Pikaia likely swam above the sea floor by moving its body in a series of side-to-side curves.

The fossil was discovered in 1911 in the Burgess Shale fossil beds in Yoho National Park in Western Canada. It was placed in the care of the Smithsonian Institute and stored away in Washington for decades until the early 70s, when Morris referred to it as a likely chordate in a scientific paper.

Members of the Royal Ontario Museum went back to the fossil beds in the 1990s and found more specimens. Caron, who arrived at the ROM in 2006 as curator of invertebrate palaeontology, teamed up with Morris to better describe the Pikaia.

The findings are prompting researchers at the ROM to return to the fossil beds this summer to look for more specimens to help determine if there are chordate cousins of Pikaia, Caron said

"Was Pikaea alone at the time, I don't think so, I think there were more."