Pikaia

Taxobox
name = "Pikaia"
fossil_range = Mid
thumb|right|300px|Pikaia
regnum = Animalia
phylum = Chordata
subphylum = Cephalochordata
genus = "Pikaia"
species = "P. gracilens"

"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 (5 cm) in length, "Pikaia" swam above the sea floor using its body and an expanded tail fin. "Pikaia" may have filtered particles from the water as it swam along. Its "tentacles" may be related to those in present-day hagfish, a jawless chordate.Fact|date=November 2007 Only 60 specimens have been found to date.

ee also

* Haikouichthys
* Myllokunmingia

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.

External links

* [http://www.3d-art.co.uk/3dpages/3ded/edimages/pikaia.jpgAn artist's rendering]
* [http://www.gpc.edu/~pgore/geology/geo102/burgess/burgess.htm Fossils of the Burgess Shale - Middle Cambrian]
* http://www.ucm.es/info/zoo/Vertebrados/JADiaz/evolucion.htm (Spanish)