When the ancient worm-like creature Pikaia gracilens was unearthed in the Canadian Burgess Shale in 1911, paleontologists thought it was just as it looked: a very old ancestor of the common earthworm. But Simon Conway Morris of the University of Cambridge and Jean-Bernard Caron from the Royal Ontario Museum have shown that this little squiggler is something much more interesting. P. gracilens was apparently our early ancestor. Morris and Caron analyzed the fossil and found traces of what appears to have been a rudimentary backbone, called a notochord. Their conclusion? Pikaia is the oldest chordate yet discovered, living more than a half-million years ago. A chordate is any animal with a backbone, including all vertebrates (fish, amphibians, reptiles, birds, mammals) and a couple of other, more obscure or extinct groups. Only five centimeters long, P. gracilens had a flat body and swam just above the ocean floor using an undulating side-to-side swimming motion. It sported a tiny head with two tentacles. Morris and Caron found nearly indisputable characteristics of chordates in Pikaia: it had a nerve chord, vascular system, and myomeres, the chordate form of skeletal muscles. Prior to Morris and Conway’s recent analysis, scientists had a couple of contenders in mind for the oldest chordate. Many believed that a fossil found in China, dubbed Cathaymyrus, which was another small, worm-like, ocean-dwelling organism was the oldest chordate. Now the title belongs to Pikaia gracilens.
Read more at CBC News.
Find the original article in the journal Biological Reviews.
For more about Cathaymyrus, see Science News.
For more about the Burgess Shale in British Columbia, Canada, see The Burgess Shale Geoscience Foundation.