Pikaia - Discovery

Discovery

P. gracilens was discovered by Charles Walcott and first described by him in 1911. It was named after Pika Peak, a mountain in Alberta, Canada. 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. However, the status of Pikaia as a chordate is not universally accepted; its preservational mode suggests that it had cuticle, which is uncharacteristic of the vertebrates (although characteristic of other cephalochordates); further, its tentacles are unknown from other vertebrate lineages. The presence of earlier chordates in the Chengjiang, including Haikouichthys and Myllokunmingia, appears to show that cuticle is not necessary for preservation, overruling the taphonomic argument, but the presence of tentacles is still intriguing, and the organism cannot be conclusively assigned even to the vertebrate stem group. Its anatomy closely resembles the modern creature Branchiostoma.

Averaging about 1+1⁄₂ inches (3.8 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 comparable to those in the present-day hagfish, a jawless chordate. Only 60 specimens have been found to date.