"A crucial transformation": Scientists use 500 million-year-old fossilised brain to study evolution of animal heads

By Culture24 Reporter | 13 May 2015

Scientists use most complete fossilised brain from Canadian collection to trace "major transitional step" between worm-like creatures and hard exoskeletons

A black and white photo of a large, long fossilised brain
Odaraia alata, an arthropod resembling a submarine from the middle Cambrian Burgess Shale© Jean Bernard Caron, Royal Ontario Museum, courtesy University of Cambridge
Animal heads once contained a distinct hard plate which connected their eyes to their grey matter, say scientists who have discovered a 500 million-year-old fossilised brain and compared it to a “bizarre” submarine-shaped creature and a soft-bodied marine specimen which was one of the world’s earliest anthropods.

The anterior sclerite – a plate in the heads of early animals – was connected to eye-like features at the front of their bodies through nerve traces from the front of their brains. Photoreceptors were embedded into the sclerite, proving “crucial” in their detection of food and escape from predators.

Prior to the Cambrian Explosion, most animal life on Earth resembled algae or jellyfish. Hard exoskeletons and jointed limbs then began to appear, say a team at the University of Cambridge who found an extremely rare brain fossil in American collections, taken from the famous Burgess Shale rock formations in Canada.

“Heads have become more complex over time,” says Dr Javier Ortega-Hernández, a postdoctoral researcher from Cambridge’s Department of Earth Sciences, who observed the photoreceptors as bright spots at the front of the bodies.

“But what we’re seeing here is an answer to the question of how arthropods changed their bodies from soft to hard.

“It gives us an improved understanding of the origins and complex evolutionary history of this highly successful group.

“The anterior sclerite has been lost in modern arthropods, as it most likely fused with other parts of the head during the evolutionary history of the group.

“What we’re seeing in these fossils is one of the major transitional steps between soft-bodied worm-like creatures and arthropods with hard exoskeletons and jointed limbs – this is a period of crucial transformation.”

The research, supported by Emmanuel College, has been published in Current Biology.

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