Pikaia
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Extinct (fossil)
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Pikaia gracilens is an extinct animal known from the Middle Cambrian fossil found near Mount Pika in the Burgess Shale of British Columbia. It was discovered by Charles Walcott and was first described by him in 1911. Based on the obvious and regular segmentation of the body, Walcott classified it as a Polychaete worm. It resembles a living chordate commonly known as the lancelet and perhaps swam much like an eel.
During his re-examination of the Burgess Shale fauna in 1979, Paleontologist Simon Conway Morris placed P. gracilens in the chordates, making it perhaps the oldest known ancestor of modern vertebrates, because it seemed to have a very primitive, proto-notochord.
Averaging about 1 1/2 inches in length, Pikaia swam above the seafloor using its body and an expanded tail fin. Pikaia may have filtered particles from the water as it swam along. Only 60 specimens have been found to date.
[edit] See Also
[edit] References
Gould, Stephen Jay. 1989. Wonderful Life: The Burgess Shale and the Nature of History. W.W. Norton, New York, NY. Morris, Simon Conway. 1998. The Crucible of Creation: The Burgess Shale and the Rise of Animals. Oxford University Press, New York, New York.
