Pikaia

Pikaia gracilens is an extinct, primitive chordate that lived approximately 505 million years ago during the Middle Cambrian period. Its exceptionally preserved fossils were first discovered in the Burgess Shale of British Columbia, Canada, by Charles Doolittle Walcott in 1911. Physically, Pikaia was a small, laterally compressed, eel-like creature, typically measuring about 4-5 centimeters in length. Its most significant feature was a stiff, flexible rod running along its back, identified as a notochord—a hallmark characteristic of the phylum Chordata, which includes all vertebrates. It also possessed a series of V-shaped muscle blocks, known as myomeres, along its body, which would have allowed it to swim with an undulating, fish-like motion. Pikaia likely lived near the seafloor, feeding on organic particles in the sediment. Its discovery and subsequent re-examination in the 1970s by Simon Conway Morris were pivotal moments in paleontology. Initially misidentified as a worm, its chordate features established it as one of the earliest known ancestors of the vertebrate lineage, including fish, amphibians, reptiles, birds, and mammals. Pikaia provides crucial fossil evidence for the deep evolutionary origins of our own phylum, demonstrating that the fundamental body plan of vertebrates had already emerged during the Cambrian explosion, a period of rapid animal diversification. Its existence underscores the contingent nature of evolution; had this small, unassuming creature not survived, the history of life on Earth, including the rise of humans, might have been vastly different.