Ancient brain fossils hint at body evolution of creepy-crawlies

Odaraia alata

The fossilized brain of Odaraia alata, an arthropod ancestor found in western Canada’s Burgess Shale, had a hard plate that may have had nerves connecting its eyes and brain.

Jean Bernard Caron/Royal Ontario Museum

Fossilized brains of the ancient ancestors of spiders, insects and crustaceans are giving hints about how those creatures evolved from soft- to hard-bodied.

Javier Ortega-Hernández from the University of Cambridge studied 500-million-year-old brain remnants from two types of arthropod ancestors, including the submarine-like Odaraia alata. In these creatures, traces of nerves appear to connect the front of the brain to eyelike features and a hard plate, called the anterior sclerite, Ortega-Hernández reports May 7 in Current Biology.

Modern arthropods don’t have these hard plates. Finding them in arthropod ancestors suggests the plates acted as a transitional element that helped the animals evolve from soft, jellylike organisms to the hard-bodied creatures of today, Ortega-Hernández argues.

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