Temporal range: Mid Cambrian
Pikaia gracilens is regarded as the earliest known primitive chordate from the Middle Cambrian fossil found near Mount Pika in the Burgess Shale of British Columbia. It was discovered by Charles Walcott in 1911. Walcott classified it as a Polychaete worm. It was about 40 mm in length and swam above the sea-floor. Pikaia may have filtered particles from the water as it swam along. Only 60 specimens have been found to date.