Let your backbone slide
Scientists draw link between eel-like animal and today’s vertebrates
ROM researchers prove eel-like creature had a spine, making it the oldest ancestor of modern humans,
Humankind’s earliest ancestor was a bottom feeder with a primitive backbone — not unlike some who walk the Earth today — that swam off Canada’s west coast more than 500 million years ago.
Researchers from the Royal Ontario Museum and the University of Cambridge confirmed Pikaia gracilens had a notochord, a flexible rod that becomes part of the backbone found in today’s animal embryos.
The Pikaia is the most primitive animal with a backbone and, therefore, the common ancestor to all vertebrates.
The findings were published in the British journal Biological Reviews on Monday.
Life on land was much different 500 million years ago. Plants wouldn’t appear for another 75 million years and dinosaurs didn’t stalk the earth for another 270 million years.
But life at the bottom of the sea was similar to today’s tropical waters with sponge-like creatures, but without coral and anything with vertebrae.
Our earliest ancestor resembled a tiny eel, just five centimetres long, with two tentacles near its mouth, a dorsal fin and no eyes.
“We can now say with some certainty that Pikaia likely swam because of the presence of the dorsal fin and the muscles, known as myo- meres, along its back,” said Simon Conway Morris, a University of Cambridge professor and the study’s lead author.
The sea creature would have spent its time feeding on sediment near the sea floor while avoiding the top dog at the time, Anomalocaris canadensis, a metre-long beast with a double trunk that was part squid, part Star Wars character. American paleontologist Charles Doolittle Walcott discovered Pikaia in 1911 in British Columbia’s famed Burgess Shale, but he thought it was more like today’s earthworms than an eel. Scientists long suspected the Pikaia had a primitive backbone, but couldn’t prove it, until now. They found the bone using Jean-bernard Caron’s advanced imaging techniques at the ROM. They found the backbone in a location consistent with other early vertebrates. The older imaging techniques revealed what everyone thought was the backbone, even though it was the wrong size and in the wrong place. Now the researchers suspect that may be an organ used for storage. That, of course, requires further study. “The Pikaia now fits into the tree of life even though it’s a weird animal,” Morris said. “But that’s what science is: progressive, surprising and delightful.” Morris began working on the Pikaia in the 1970s while completing his PHD, but never finished. A few years ago, he reached out to the ROM because, with 61 fossils, it is the largest Pikaia collection in the world. That collection, along with another from the Smithsonian Institution, gave the study the power of numbers, which is rare in evolutionary research.
Older fossils with a backbone have been found in China, but those species are much more evolved and therefore considered younger than the Pikaia.
The Burgess Shale is the crown jewel for researchers studying evolution. That’s because ocean mudslides trapped animals off an underwater cliff. Due to complex chemistry, which scientists still don’t really understand, the mud preserved the fleshy parts of an animal.
The Pikaia couldn’t have been described in such detail under normal fossil conditions, where only bone survives. Caron said he plans to study at the Burgess Shale, part of a UNESCO world heritage site in Yoho National Park that is about a two-hour drive west of Calgary.
“The Burgess Shale is iconic,” Morris said. “We are just scratching the surface, to use a geological pun.”