Pikaia

Pikaia was a chordate from the Middle Cambrian of the Burgess Shale.

Description
Pikaia was a long, leaf-shaped creature measuring 5 centimeters or less in length. It had a pair of tentacles on its front end, and possible gill slits on the side of its body. It was similar in morphology to the modern lancelets, and was probably a slow swimmer.

The first signs of heads in animals are seen in Pikaia and similar fossils. It is believed that the front end of animals containing the mouth, being the first part of the body to come into contact with food, needed additional sensory equipment in order to find food more easily. This necessitated larger nerves in that body region to interpret the information gathered by these structures, resulting in the development of the brain.

Classification
Simon Conway Morris classified Pikaia as a primitive chordate, making it possibly one of the earliest ancestors of modern vertebrates. However, not all paleontologists support this view.

Discovery
The first and only species, Pikaia gracilens, was discovered in the Burgess Shale in Canada and described by Charles Walcott in 1911. It was named after Pika Peak, a mountain in Alberta. Walcott first identified the animal as a type of marine worm. Only 16 specimens of Pikaia have been found to date in the Burgess Shale.