Inglorious beginnings: Experts trace humanity's origins to ancient worm

CALGARY — It seems an inglorious beginning, but some scientists are now convinced humanity's origins can be traced to an ancient, flat, fishlike worm.

A team of researchers subjected the 505-million-year-old Burgess shale fossils of Pikaia gracilens to the latest technology and found evidence that could settle a decades-long debate about the primitive species.

Notably, that they had the seeds of a spine.



"We can see and discern the positive location of the notochord and the nerve chord. This was not obvious at all, you needed these techniques to see it," said Jean-Bernard Caron, the curator of invertebrate paleontology at the Royal Ontario Museum.



Caron is the co-author of a study to be published Monday in the British journal, Biological Reviews. The lead author was English paleontologist Simon Conway Morris.



The earliest explorers of the Burgess shale collected specimens of Pikaia in 1911. But the creature was overlooked as an ancestor of the earthworm.



"They had no idea it might be something more important to us then, at first sight," Caron said.



It wasn't until the '70s that Morris first suggested the lancelet-like species could in fact be one of the earliest known members of Phylum Chordata — the class that spawned animals with spines. He noted what looked like a notochord, a primitive spine that forms in the embryos of all vertebrate animals, including humans.



But he was not able to prove the link, and the classification bridge species remained in dispute.



In the '90s, Caron said more Pikaia specimens were collected and, more recently, were subject to the exacting eye of an electron microscope. Using the latest technology, the researchers were able to identify myomeres, which are bands of muscles that are the precursors to skeletal spines. They also found blood vessels and a vascular system.



That puts Pikaia on humanity's family tree, along with every other animal with a spine.



"It's giving us a very clear idea of what the origin of our group, what it looked like. It gives us a clear window into our roots, into our deepest roots, really," Caron said.



The Pikaia would be one of the earliest known chordates, although others may have existed at the time.



The fossil record is sketchy on our ancestors as soft tissue tends to preserve imperfectly in all but ideal conditions, like those of the shale.



In its heyday, the average Pikaia would have grown to the length of a human thumb. It was a flat creature, with a head the size of a period. Two tentacles sprung from the front.



"Those are enigmatic," Caron said. "Perhaps they were used for feeding, but their role is not very clear. Other than that, the body itself had a very discrete dorsal and, perhaps, a ventral fin. But otherwise, it was a very streamlined animal."



The Pikaia would have been like a small, early fish. In fact, its s-shaped movement would have struck modern watchers as being eel-like.



"The electron microscope helped us interpreting tremendously the key features of these animals. We could see details we couldn't see otherwise using normal photographic techniques."
http://www.calgaryherald.com/technology/Inglorious+beginnings+Experts+trace+humanity+origins+ancient+worm/6251165/story.html