Worm is our long-lost relative, say researchers


Michael Platt_op
By , Calgary Sun

First posted: | Updated:

You may have your grandma’s nose but you owe your very existence to this critter — a half-a-billion-year-old fossilized worm that hung out in the ocean and is called Pikaia gracilens. It was found near Field, B.C., and is the ancestor of all vertebrates. Jean-Bernard Caron photos/Royal Ontario Museum

CALGARY -- An exposed slope in the Rockies may offer genealogy buffs the ultimate prize, with people researching their family trees at last certain of where it all began.

The only hitch: getting back to that greatest-of-grandparents will take an estimated 240 million generations, and the family resemblance is fleeting at best.

"I look at myself in the mirror, and I can recognize the elongated body with all these muscle bands, and it's an animal that was certainly very agile," said Dr. Jean-Bernard Caron, curator of Invertebrate Palaeontology at the Royal Ontario Museum.

"Pikaia is something that people can take close to heart, because we are connected."

Maybe. But it's hard to examine a fossilized leech-like worm and make the connection between something that squirmed in the ocean a half-billion years ago and modern humans.

Good thing then scientists like Caron are able to make the connection for you.

The Royal Ontario Museum curator and Professor Simon Conway Morris of Cambridge University are co-authors of a study to be released Monday, confirming a Burgess Shale worm as man's earliest known ancestor.

Found a century ago on the mountain overlooking Field, B.C. -- a site renowned as the world's most important fossil bed -- Pikaia gracilens was long suspected as a pioneer of all modern backbones.

It took Caron and Morris to confirm the link, however, and it's now believed the incredibly rare worm, known for just a few examples, is the ancestor of all modern vertebrae, from mammals to fish.

"There's a lot of excitement, and we think there is going to be a lot of interest," said Caron.

But as rare as the creature is, representing just a tiny faction of the 150,000 fossils found on the protected mountain, the shale where the worms were preserved is almost totally unique.

"Most people are familiar with fossils that represent mineralized parts of animals like bones and shells, but these are animals that never had bones or shells," he said.

"They are not preserved in the fossil record, except in exceptional circumstances like the Burgess Shale -- if we didn't have the Burgess Shale to preserve soft tissue, we'd lose about 95% of the species there."

The discovery answers a mystery long pondered by scientists, who can trace the development of the spine through the fossil record -- only to reach a dead end in the oceans of young Earth.

But no longer.

First discovered in the shale back in 1911 by American palaeontologist Charles Doolittle Walcott, it's been speculated that Pikaia was a chordate because it appeared to have a very primitive notochord.

That's the flexible, rod-shaped body found in the embryos of all chordates, which develops into the spinal column found in most vertebrates, including birds, reptiles and amphibians.

Using scanning electron microscopes to reveal fine details, the authors took a very close look the fossil worms, each just a few centimetres long.

As well as a notochord, the study, published in British scientific journal Biological Reviews, shows extensive myomeres, which are blocks of skeletal muscle tissue characteristic of chordates.

"The discovery of myomeres provides the smoking gun that we have long been seeking," said Morris, a world-renowned Burgess Shale expert.

"With myomeres, a nerve chord, a notochord and a vascular system all identified, this study clearly places Pikaia as one of the planet's first and most primitive chordate animals."

It's another feather in the cap for Yoho National Parks and its palaeontological jewel -- protected as a UNESCO World Heritage Site since 1981.

In January, Burgess Shale researchers announced the discovery of a strange tulip-shaped creature named Siphusauctum, with no known living descendants.

Caron says it couldn't be more different for the little worm with the primitive spine, which is the ancient ancestor of any creature reading this -- and many of the animals around them.



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