I've become comfortably numb.

Pikaia was a primitive chordate that lacked a well-defined head and averaged about 1 1/2 inches (3.8 cm) in length. It had a pair of large, antenna-like tentacles on its head, and a series of short appendages, which may be linked to gill slits, on either side of its head. In these ways, it differs from the living lancelet. The "tentacles" on its head may be comparable to those in the present-day hagfish, a jawless chordate.

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During his re-examination of the Burgess Shale fauna in 1979, paleontologist Simon Conway Morris placed P. gracilens among the chordates, making it perhaps the oldest known ancestor of modern vertebrates. He did this 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.

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The presence of a creature as complex as Pikaia some 530 million years ago reinforces the controversial view that the diversification of life must have extended back well before Cambrian times – perhaps deep into the Precambrian.