A 500-million-year-old fossilized arthropod found in the Burgess Shale, a fossil field in the Canadian Rockies, may provide clues to how heads evolved in early animals. The fossil is a submarine-shaped arthropod, Odaraia alata, of the Middle Cambrian Period. A paper in Current Biology reports that both Odaraia alata, originally found about 100 years ago, and another ancient arthropod have a hard plate, known as the anterior sclerite, and eye-like features that were connected by nerves to their brains. They may have controlled their vision in much the same way that modern insects, crustaceans and spiders do.

The fossil of a submarine-shaped arthropod was found in the Burgess Shale in the Canadian Rockies.                                                       Credit Jean Bernard Caron/Royal Ontario Museum