PhysOrg greets our oldest known ancestor – a very special worm:
Researchers from the University of Cambridge, University of Toronto and the Royal Ontario Museum (ROM) have confirmed that a 505 million-year-old creature, found only in the Burgess Shale fossil beds in Canada’s Yoho National Park, is the most primitive known vertebrate and therefore the ancestor of all descendant vertebrates, including humans.
The research team’s analysis proves the extinct Pikaia gracilens is the most primitive member of the chordate family, the group of animals that today includes fish, amphibians, birds, reptiles and mammals.
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Averaging about five centimetres in length, Pikaia was a sideways-flattened, somewhat eel-like animal. The flattened body is divided into a series of segmented muscle blocks seen as S-shaped lines that lie on either side of the notochord which runs along most, if not all of the body length. It likely swam above the sea floor by moving its body in a series of side-to-side curves.
When P. gracilens was first discovered in 1911, they thought it was a leech or earthworm. Can you imagine? The nerve of some paleontologists.