Pikaia gracilens Walcott, 1911
Chordata
Cephalochordata
Pikaiidae
Middle Cambrian
Burgess Shale
British Columbia, Canada
Length: 5 cm
This member of the famous Burgess Shale Cambrian fauna was originally described as a polychaete worm, until Conway Morris recognized it as a chordate some 68 years after its discovery. The popular 1989 book "Wonderful Life: The Burgess shale and the Nature of History" by Stephen Jay Gould propelled Pikaia to instant celebrity as the ancestor of all vertebrates. It is not until 2012 however that a comprehensive description of this little animal based on some 114 fossils is published. It turns out to be quite dissimilar from the lancelet (amphioxus) to which it was often compared to and shows specialized features that makes it an offshoot of an early chordate side branch rather than a true vertebrate ancestor.
July 27, 2015
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