(after Pika Peak).
Named By: Charles Walcott - 1911.
Classification: Chordata, Cephalochordata?
Species: P. gracilens (type).
Size: Around 38 millimetres long.
Known locations: Canada, British Columbia - Burgess Shale.
Time period: Middle Cambrian.
Fossil representation: Many individuals.
has been one of the most talked about creatures discovered from the
Cambrian era Burgess Shale, yet there is still controversy over
exactly what it was. In 1979 Simon Conway Morris noted the
presence of a proto-notochord, an anatomical structure that later
creatures would develop into a spine creating the first true
chordates. Chordates are better known as vertebrates, animals that
have a hard backbone that also includes human beings. Morris however
went so far as to suggest that Pikaia was itself a
chordate, which in
turn has led to popular speculation that Pikaia may
have been ‘the’
ancestor to all vertebrates, including humans.
This is the main source of the controversy surrounding Pikaia, because not everyone is convinced that Pikaia are even chordates at all. It has been suggested to have had a segmented exoskeleton as well as the presence of short tentacles, both anatomical features of invertebrates, creatures without a backbone. In fact, when Pikaia was first described by Charles Walcott in 1911, it was as a kind of polychaete worm. Today Pikaia is more commonly envisioned as a cephalochordate, similar to the lancelets that we know today. With this in mind Pikaia might have been related to the true ancestors of the chordates, yet was still separate from them.
The exact lifestyle of Pikaia is still uncertain, due to its similarity to lancelets it was probably a free swimming creature that moved through the water with side to side undulations of its body. As it swam through the water it may have picked up small morsels of organic matter that were then digested in the gut. Although merged with the body, Pikaia is noted for still having a distinct head.
- The Middle Cambrian fossil Pikaia and the evolution of chordate swimming - T. Lacalli - 2012.
- Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale - N. J. Butterfield - 1990.
- Pikaia gracilens Walcott: stem chordate, or already specialized in the Cambrian? - J. Mallatt, J & N. D. Holland - 2013.